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Article

The Impact of Heating Methods on Respiratory and Allergic Diseases in Preschool Children: A Repeated Cross-Sectional Survey Across Northern and Southern China

by
Chenyang Wang
1,2,
Shaohua Li
3,*,
Yan Zhang
1,2,
Haixia Zhou
1,2,
Peiwen Zhang
1,2 and
Wei Yu
1,2,*
1
Joint International Research Laboratory of Green Buildings and Built Environments (Ministry of Education), Chongqing University, Chongqing 400045, China
2
National Centre for International Research of Low-Carbon and Green Buildings (Ministry of Science and Technology), Chongqing University, Chongqing 400045, China
3
Institute of Defense Engineering, Academy of Military Sciences, Beijing 100036, China
*
Authors to whom correspondence should be addressed.
Buildings 2025, 15(2), 234; https://doi.org/10.3390/buildings15020234
Submission received: 4 December 2024 / Revised: 1 January 2025 / Accepted: 5 January 2025 / Published: 15 January 2025
(This article belongs to the Section Building Energy, Physics, Environment, and Systems)
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Abstract

:
Indoor heating methods may influence the prevalence of respiratory and allergic diseases among preschool children. However, limited research has explored the relationship between indoor heating methods and childhood illnesses over time or on a large urban scale, and particularly the relationship between heating methods and asthma or allergic rhinitis among preschoolers from 2010 to 2019. This study conducted cross-sectional investigations in two northern cities (Taiyuan and Urumqi) and two southern cities (Chongqing and Changsha) in China during two periods: Period I (2010) and Period II (2019). Using Pearson’s chi-squared tests, we analyzed the associations between four indoor heating methods—convective heating (CH), convective and radiant heating (CH&RH), radiant heating (RH), and polluting heating (PH)—and nine respiratory and allergic diseases. Logistic regression models were employed to explore the relationships between heating methods and disease prevalence. The results revealed substantial differences in heating method choices between northern and southern Chinese cities (p < 0.001). These differences were significantly associated with the prevalence of respiratory and allergic diseases in preschoolers. Heating behaviors may have contributed to a decrease in the lifetime prevalence of asthma, pneumonia, rhinitis, and the 12-month prevalence of eczema in preschool children. In southern households, CH was linked to a lower risk of lifetime asthma (AOR: 0.63) and 12-month wheezing (AOR: 0.53). However, RH in southern households increased disease risks (AOR: 0.53). This study provides insights into the associations between heating methods and the prevalence of diseases among preschoolers across two periods in China. The findings offer new perspectives and guidance for families in selecting appropriate heating methods.

1. Introduction

The prevalence of asthma and allergic rhinitis among children has been increasing, attracting significant attention from researchers [1,2,3]. Since genetic factors affect only specific populations, they are unlikely to explain this rising prevalence. Instead, gradual changes in environmental factors are considered potential contributors to this phenomenon [4]. Compared to adults, children are more susceptible to the indoor environment due to their higher breathing rate and immaturity. Identifying risk and protective factors in the living environment is essential to mitigating the rising prevalence of respiratory diseases in preschoolers.
Extensive prior research has examined the association between environmental risk factors and the prevalence of diseases in preschoolers. They spend more time indoors than outdoors, and the health risks associated with indoor environments are more complex and variable. The interactions between various environmental elements and their effects on children’s health require further investigation [5]. High relative indoor humidity is a common issue for preschoolers, often caused by HVAC system deficiencies (e.g., poor ventilation, inadequate heating) and building defects (e.g., insufficient insulation, improper materials) [6]. Additionally, high air tightness and low ventilation rates in building envelopes create favorable conditions for mold germination and growth [7,8]. A review of recent studies on school indoor air quality highlighted the impacts of ventilation, thermal comfort, productivity, and exposure risks on health [9]. A study, funded by the framework of the European Commission and the Greek government, carried out passive and active system renovations in 10 schools in Greece to enhance their energy efficiency [10]. In one of them, located on the island of Crete, a solar-thermal combined heat and power system was installed, with an effective introduction algorithm and overall system layout provided [11]. The first green sustainable schools in Israel conducted a study to identify and separate the “green premium” in schools, which was able to provide better product quality for students and teachers [12]. A disaster risk survey conducted in Gilgit city in northern Pakistan found gender differences in how environmental risks were addressed. Although both boys and girls exhibited low risk awareness, boys seemed better prepared for emergencies [13]. Similarly, a sociological survey conducted in Pakistan indicated that age and industry experience could be the root causes of people’s responses to environmental stress [14]. This suggests that extreme environmental changes may cause more harm to sensitive populations such as children and the elderly. Another study summarized the health effects of pollutants from solid fuel combustion on children, demonstrating that indoor pollutants can increase the prevalence of low birth weight, acute lower respiratory infections, anemia, and premature mortality through mechanisms such as oxidative stress, DNA methylation, and gene activation [15]. Research on building dampness exposure over time found a significant association between children’s lifetime doctor-diagnosed diseases and dampness in buildings (adjusted odds ratio, AOR > 1) [16]. A review of 141 studies from 29 countries identified strong links between indoor exposure to high concentrations of particulate matter, NO2, and VOCs and respiratory symptoms, especially asthma in children [17]. In Chongqing, China, a comparative study conducted over the years found that by 2019, the proportion of homes with dampness indicators and the prevalence of diseases had significantly declined compared to 2010 [18]. These findings suggest that poor ventilation and dampness exposure are key factors affecting preschoolers’ health.
Research has also explored potential protective factors in the environment. A review of portable air purifiers (PAPs) found that they effectively reduce indoor PM2.5 concentrations, and long-term reductions in PM2.5 levels may positively impact children’s health [19]. A study utilizing U.S. commercial insurance data for children aged 0–17 years from 2016 to 2019 estimated the association between extreme heat and emergency department visits, revealing an inverse relationship between high temperatures and respiratory diseases (Odds Ratio, OR: 0.93, 95%CI: 0.90, 0.96) and asthma (OR: 0.89, 95%CI: 0.81, 0.98) [20]. Another study in Singapore linked climate data with five common pediatric respiratory diseases (2003–2008), finding a negative correlation between respiratory infections (upper and lower) and both relative humidity and maximum temperature [21]. These studies generally suggest that higher temperatures may serve as a protective factor for preschoolers. However, few studies have investigated whether indoor heating methods might act as a protective factor for preschoolers.
With rapid urbanization, an increasing number of Chinese households tend to adopt indoor heating systems to maintain comfortable temperatures. Over the past two decades, significant changes have occurred in northern and southern China [22]. A cross-sectional survey on preschoolers in China revealed that heating methods had a protective effect on visible damp/mold (D/M) and humid bedding [23]. A significant decline was observed in allergic and respiratory diseases among preschoolers, except for lifetime allergic rhinitis [24]. Additionally, studies have shown that using electric cooking fuel indoors (OR: 0.87, 95%CI: 0.80–0.94) and air conditioning for cooling (OR: 0.85, 95%CI: 0.80–0.90) were associated with a reduced risk of pneumonia [25]. Cold environments were significantly associated with asthma, dry cough, and pneumonia in children (adjusted odds ratio, AOR: 1.34; 95%CI: 1.11–1.23) [26]. Furthermore, air conditioning for heating (AOR: 1.84; 95%CI: 1.41–2.40) was significantly linked to an increased incidence of common cold events among preschoolers [27]. These studies collectively suggest that heating methods may serve as protective factors for the health of preschoolers. However, no comprehensive research has compared the relationship between different winter heating methods and the prevalence of allergic and respiratory diseases in preschoolers in China.
Preschoolers are particularly vulnerable to the indoor environment. Previous studies have identified risk factors in their living environments and highlighted that increased temperatures may serve as a protective factor. However, research on the relationship between different indoor heating methods and disease prevalence in preschoolers remains limited. To address this gap, this study selected cities in both northern and southern China (two cities from each region) and conducted cross-sectional questionnaire surveys in 2010 and 2019. Four common household heating methods in China were evaluated: convective heating, convective and radiant heating, radiant heating, and polluting heating. The study examined their associations with nine different allergic and respiratory diseases in preschoolers. The findings aim to guide the parents of preschoolers in choosing heating methods that minimize disease risk, ensure the physical health of preschoolers, and support informed decision-making about winter heating.

2. Materials and Methods

2.1. Study Design and Subjects

This study employed a repeated nationwide cross-sectional research design to investigate the relationship between heating methods in northern and southern households and the incidence of diseases among preschoolers in China. The data were derived from two national surveys conducted in China in 2010 (hereafter referred to as Period I) and 2019 (hereafter referred to as Period II) as part of the CCHH project (China, Children, Homes, and Health). The CCHH project aimed to comprehensively investigate the indoor environment of Chinese households and the health status of children. It adopted the ISAAC protocol [28] for questionnaires on childhood allergic diseases and used a multi-stage cluster sampling method to select preschools for the survey. Initially, all districts in each city were coded, and the required sample size was calculated based on the basic population of children under eight years old. Subsequently, districts and preschools were randomly selected. Questionnaires were distributed to the selected preschools and completed by parents or other guardians of the children. Finally, the research teams in each city collected the completed questionnaires, digitized them, and applied standardized data coding and processing protocols. Both Period I and Period II surveys were approved by the Ethics Committee of the School of Public Health at Fudan University. Written informed consent was obtained from parents or guardians before the surveys commenced.
It is worth noting that the Period I survey covered 10 major cities across China, including northern cities (Harbin, Beijing, Taiyuan, Xi’an, Urumqi) and southern cities (Nanjing, Shanghai, Wuhan, Changsha, Chongqing). The Period II survey conducted follow-up investigations in seven of these cities, excluding Harbin, Beijing, and Xi’an. After data entry, processing, and integration, 48,219 valid questionnaires were collected in Period I and 45,891 in Period II. These samples demonstrated consistent socioeconomic backgrounds, minimal confounding factors, and enhanced comparability between the two periods. The sampling process for both periods has been detailed in previously published studies [18,23,29,30].
To ensure consistency in cross-sectional comparisons, this study focused on preschoolers aged 3–6 years who had not changed residences since birth. A total of 9849 preschoolers from Period I and 17,949 from Period II were included in the analysis. Data from four cities—Taiyuan, Urumqi, Changsha, and Chongqing—were selected for this study. In China, the boundary between northern and southern regions is defined by the Qinling Mountains–Huai River line. Due to differing climatic characteristics and regional energy policies [31], the Chinese government generally discourages the use of regional heating systems in residential buildings in southern regions (except for in some high-altitude areas), whereas centralized district heating systems are widely adopted in most northern areas. As a result, significant differences exist in heating methods between northern and southern households. In this study, Taiyuan and Urumqi were classified as northern cities, while Changsha and Chongqing were classified as southern cities.

2.2. Study Process

According to the Köppen–Geiger climate classification system [32], most regions in China fall within the BWk, Cwa, Cfa, and Dwa climate zones. The primary types of heating devices used by ordinary Chinese households during winter include air conditioners, electric heaters, floor heating systems, etc. Specifically, air conditioners distribute heated air indoors through forced convection, electric heaters rely on natural air convection and radiation from enclosing surfaces and indoor furniture to provide heat, and floor heating systems primarily use radiant heat to warm indoor spaces. The category of “other heating methods” (PH) refers mainly to traditional household systems that burn solid fuels, such as coal stoves, kang beds, firewalls, or braziers. These methods may generate particulate matter such as PM2.5 and PM10, posing significant health risks. In response to increasing demands for cleaner heating solutions and improved health standards, most Chinese households have shifted away from these polluting heating methods. Based on the primary heat transfer mechanisms and the distinct characteristics of these heating methods, this study classifies air conditioners as convection heating (CH), electric heaters as convection and radiant heating (CH&RH), floor heating systems as radiant heating (RH), and other polluted heating methods as polluting heating (PH).
To ensure clarity and consistency during the survey process, the questionnaire used in the CCHH project referenced similar studies conducted in Sweden [33], Bulgaria [34], Singapore [35], and the United States [36]. The questionnaire covered residential characteristics and indoor environmental factors and was later revised to include questions specifically related to heating methods. Questions regarding the heating systems in the residences initially asked, “What specific heating method is currently used in the preschoolers’ residence? (Air conditioner/Floor heating/Electric heater/Oil heater/Firewall heater/Stove heater/Brazier)”. Based on the observed changes in actual usage frequencies, these questions were refined to: “Does the child’s current residence use air conditioning for heating (CH)?” (Yes/No), “Does the child’s current residence use floor heating (RH)?” (Yes/No), “Does the child’s current residence use electric heaters (CH&RH)?” (Yes/No), and “Does the child’s current residence use polluted heaters (PH)?” (Yes/No). The ‘polluted heating methods’ category includes oil heaters, firewall heaters, stove heaters, or braziers.
Health outcomes related to preschoolers’ allergic and respiratory diseases were assessed using questions adapted from the ISAAC study [37]. During both Period I and Period II, nine diseases were recorded, including allergic rhinitis, pneumonia, asthma, wheezing, eczema, and rhinitis, as well as symptoms of wheezing, eczema, and rhinitis in the 12 months preceding the survey (‘current’). Specifically, allergic rhinitis, pneumonia, and asthma were classified as physician-diagnosed conditions, while wheezing, eczema, and rhinitis were identified as self-reported symptoms. A preschooler was considered to have a particular condition if the answer to the corresponding question was “Yes”. Additionally, personal information such as age, gender, duration of breastfeeding, exposure to passive smoking, and family history of atopy was collected. Family environmental factors, including home renovations, homeownership, and the construction period of the residence, were also recorded.

2.3. Statistical Analysis

This study conducted separate analyses for the survey samples from Period I and Period II. Pearson’s chi-squared test was used to compare the baseline information of preschoolers, the choice of heating methods, and the occurrence of illnesses among preschoolers in southern and northern China during the two periods. The Pearson correlation coefficient was used to measure the magnitude of these differences. To account for the multi-stage sampling method, binary logistic regression models were applied to explore the association between the heating method and the occurrence of illnesses in preschoolers.
Significant changes were observed in population survey characteristics, except for gender, between Period I and II in southern and northern cities. Notably, at least one family member (siblings, parents, or grandparents) in these households had one or more illnesses (e.g., asthma, eczema, allergic rhinitis), suggesting a genetic predisposition. This indicates that genetic factors are significantly associated with the incidence of diseases in preschoolers [38]. Furthermore, residential ownership and family location serve as indicators of socioeconomic status, which can greatly influence the risk of illness in preschoolers [39]. To account for these factors in the binary logistic regression analysis, the following were included as adjustment variables: age [40], gender [41], family history [42], residential ownership [18], breastfeeding duration [18], family location [43], and exposure to environmental tobacco smoke in the household [44]. These variables are suspected to be significantly associated with respiratory and allergic symptoms in preschoolers. The results are presented as AORs and 95%CI. All statistical tests were two-tailed, with a significance threshold set at p < 0.05. Statistical analyses were performed using SPSS software (Version 25, SPSS Inc., Chicago, IL, USA).

3. Results

3.1. Demographics and Covariates in Southern and Northern Cities

According to Table 1, in northern cities during Period I, there were 4567 preschoolers surveyed, with approximately 51.9% being boys. About one-third of the preschoolers were aged 4 or 5 years, and 59.2% had been exposed to environmental tobacco smoke (ETS). Among these families, 15.9% reported a family history of hereditary conditions. Furthermore, 70.6% of the households were homeowners. In terms of residential locations, the majority (87.1%) were in rural areas, with 9.9% in suburban regions. Residential construction periods showed that 46.7% of the families’ houses were built before 2000, while 50.5% were constructed between 2001 and 2010.
During Period II, the sample size in northern cities expanded to 9460 preschoolers, of whom 49.5% were girls. Preschoolers aged 4 and 5 years accounted for 23.2% and 38.7% of the total, respectively. The percentage of children breastfed for ≤6 months dropped to 31.9%. Families reporting ETS exposure for their preschoolers decreased to 33.4%, while the proportion of families with a history of hereditary conditions rose to 30.0%. Additionally, the percentage of homes built before 2000 dropped to 20.0%. Urban households constituted 86.5% of the surveyed residences. When comparing the information between Period I and II for northern cities, significant changes were observed in factors such as breastfeeding duration, ETS exposure, hereditary history, residential ownership, location, and construction periods. Gender distribution remained statistically unchanged. In southern cities, during Period I, 5282 preschoolers were surveyed, of which 51.9% were boys and 48.1% girls. In Period II, the sample size increased to 8489 preschoolers, with boys accounting for 52.9% and girls for 47.1%. Similarly to northern cities, there were declining trends in the proportion of families reporting breastfeeding for ≤6 months, ETS exposure, and homes built before 2000. However, the percentage of families with a hereditary history of conditions decreased from 13.0% in Period I to 10.6% in Period II.

3.2. Changes in Heating Methods in Southern and Northern Cities

The statistical analysis of the heating methods used is presented in Table 2, showing significant differences in the proportions of the heating methods chosen by households in southern and northern cities during Period I and Period II. In northern cities, the majority of preschooler households used CH as their primary heating method (11.3% in Period I, increasing to 50.9% in Period II). Fewer households used CH&RH, RH, or PH. In Period I, the proportion of preschooler households using RH in northern cities was 11.3%. Due to the superior thermal comfort, uniform temperature distribution, and low-temperature heating advantages of floor heating, RH became increasingly popular in newly constructed residential buildings in both southern and northern cities over the 10 years between the two periods [45]. Specifically, in northern cities during Period I, 2.4%, 11.3%, and 2% of preschooler households reported using CH, CH&RH, and RH, respectively. By Period II, these proportions increased to 8.7%, 50.9%, and 5.2%, representing statistically significant differences (p < 0.001). In southern cities, the proportion of households using CH&RH decreased significantly, from 41.4% in Period I to 21.2% in Period II (p < 0.001). In contrast, the use of CH (17.8% in Period I to 58.2% in Period II, p < 0.001) and RH (2.0% in Period I to 10.8% in Period II, p < 0.001) increased significantly. The rise in CH and the decline in CH&RH in southern cities are attributed to the widespread adoption of heat pumps [46]. Additionally, the increased proportion of RH suggests that more southern preschooler households prefer RH for winter heating [47].
PH in both southern and northern cities remained relatively low, with no significant changes between the two periods. However, in southern cities, the proportion of PH increased nearly threefold, from 1.5% in Period I to 4.4% in Period II, although the number of households remained small. In conclusion, there remain differences in heating methods between southern and northern cities. During winter, most northern households tend to choose RH as their primary heating method, while southern households are more likely to choose CH or CH&RH for heating, rather than RH.

3.3. Variation in Preschoolers’ Health Outcomes

Comparing southern and northern cities, the trends in the prevalence of certain diseases among preschoolers showed significant differences between Periods I and II, except for lifetime eczema and rhinitis in the past 12 months. From Table 3, the prevalence of lifetime eczema increased from 12.6% to 15.5% in northern cities, while it decreased from 24.6% to 19.2% in southern cities. Similarly, the prevalence of rhinitis in the past 12 months rose in northern cities (4.2% to 5.4%) but declined in southern cities (7.9% to 4.4%), with both exhibiting significant differences. For other health outcomes, including asthma, pneumonia, wheezing, rhinitis (lifetime), and eczema or wheezing in the past 12 months, there was a downward trend across both northern and southern cities from Period I to Period II. For instance, in northern cities, the lifetime asthma among preschoolers decreased from 2.6% to 1.7% (p = 0.001). In southern cities, the lifetime rhinitis dropped dramatically from 43.0% to 23.8% (p < 0.001).
Notably, the trends in lifetime allergic rhinitis were different. In northern cities, it slightly increased from 6.4% to 7.0% (p = 0.211), and in southern cities, it also rose marginally from 7.5% to 7.9% (p = 0.397), but neither trend was statistically significant. Additionally, during Period I, there was no significant difference in wheezing in the past 12 months between preschoolers in southern and northern cities (p = 0.302). However, by Period II, this difference became statistically significant (p < 0.001). Excluding lifetime and recent wheezing, the changes in other health outcomes during both periods consistently exhibited significant differences.

3.4. Associations of Heating Methods with Preschoolers’ Respiratory and Allergic Diseases

In northern cities, the impact of heating methods on the prevalence of diseases among preschoolers showed variations over time. As illustrated in Figure 1, during Period I, RH was identified as a significant risk factor for lifetime allergic rhinitis (AOR: 1.60, 95%CI: 1.12–2.29, p = 0.010) and eczema in the past 12 months (AOR: 1.64, 95%CI: 1.15–2.34, p = 0.007). Similarly, CH&RH was associated with an increased risk of wheezing in the past 12 months (AOR: 1.64, 95%CI: 1.15–2.34, p = 0.007). For preschoolers with rhinitis in the past 12 months, CH (AOR: 2.62, 95%CI: 1.29–5.34, p = 0.008), RH&CH (AOR: 4.46, 95%CI: 2.28–8.70, p < 0.001), and PH (AOR: 2.53, 95%CI: 1.14–5.62, p = 0.023) emerged as significant risk factors. In Period II, however, these associations shifted. RH was found to reduce the risk of lifetime asthma among preschoolers (AOR: 0.37, 95%CI: 0.16–0.82, p = 0.014). Furthermore, CH&RH, which was previously a risk factor for wheezing and rhinitis in Period I, became a protective factor against lifetime pneumonia (AOR: 1.35, 95%CI: 1.02–1.77, p = 0.035) and rhinitis in the past 12 months (AOR: 0.36, 95%CI: 0.15–0.90, p = 0.029).
In southern cities, as shown in Figure 2, CH was significantly associated with an increased incidence of eczema in the past 12 months during Period I (AOR: 1.37, 95%CI: 1.11–1.69, p = 0.003). CH&RH was linked to a higher prevalence of lifetime allergic rhinitis (AOR: 1.37, 95%CI: 1.10–1.71, p = 0.005), lifetime rhinitis (AOR: 1.15, 95%CI: 1.02–1.27, p = 0.024), and rhinitis in the past 12 months (AOR: 1.33, 95%CI: 1.08–1.64, p = 0.007). These findings diverged from a study conducted in New Zealand [48], where children diagnosed with asthma predominantly lived in homes using smoke-free or plug-in heating systems, resembling the PH in this study. Such heating systems may release particles or chemicals that could trigger asthma in children. In Period II, CH&RH was associated with a reduced risk of lifetime rhinitis (AOR: 0.80, 95%CI: 0.67–0.95, p = 0.010). During this period, CH was linked to a lower risk of lifetime asthma (AOR: 0.63, 95%CI: 0.43–0.92, p = 0.018), allergic rhinitis (AOR: 0.70, 95%CI: 0.52–0.94, p = 0.015), lifetime rhinitis (AOR: 0.73, 95%CI: 0.60–0.88, p = 0.001), and wheezing in the past 12 months (AOR: 0.53, 95%CI: 0.36–0.81, p = 0.003). Conversely, RH was significantly associated with an increased prevalence of lifetime rhinitis (AOR: 1.60, 95%CI: 1.31–1.97, p < 0.001), eczema (AOR: 1.39, 95%CI: 1.12–1.73, p = 0.003), and rhinitis in the past 12 months (AOR: 1.60, 95%CI: 1.06–2.41, p = 0.026). Additionally, PH was found to reduce the risk of lifetime rhinitis (AOR: 0.73, 95%CI: 0.60–0.88, p = 0.001). Notably, CH, initially a risk factor for eczema in the past 12 months during Period I, transitioned to a protective factor against lifetime asthma, allergic rhinitis, and rhinitis in Period II.

4. Discussion

This study reveals significant differences in the heating methods used between southern and northern cities in China. During winter, most households in northern cities tend to use RH as their primary heating mode, whereas households in southern cities often opt for CH or CH&RH rather than RH. Consequently, this study differentiates between northern and southern cities to examine the impacts of heating methods. By conducting repeated cross-sectional surveys across multiple cities, this study identifies significant associations between heating methods and allergies and respiratory diseases. These methods may act as protective or risk factors. From the perspective of safeguarding preschoolers’ health, this study proposes tailored guidelines for household heating methods for parents.

4.1. Association Between Heating Methods and Allergies and Respiratory Diseases in Preschoolers

In northern cities, RH was a risk factor for lifetime allergic rhinitis and eczema in the past 12 months during Period I, consistent with findings from a 2013 survey conducted in Urumqi (AOR:1.24, 95%CI:1.05–1.47, p < 0.05) [49]. However, RH became a protective factor against lifetime asthma in preschoolers during Period II (AOR: 0.37, 95%CI: 0.16–0.82, p = 0.014). A field study in Japan also noted lower absenteeism rates due to common colds among students in schools using RH (adjusted incidence rate ratio [aIRR] = 0.39; 95%CI: 0.23–0.67) [27]. In New Zealand, using RH or PH demonstrated greater health benefits than insulation improvements. These findings suggest that improvements in heating methods can yield significant health gains [48].
In both southern and northern cities, using a combination of central heating and radiator heating was a risk factor for rhinitis in preschoolers during Period I but became protective in Period II. A study in Adelaide, Australia, observed a significant reduction in daytime asthma incidence among schoolchildren when switching to CH&RH during early winter (OR: 0.39; 95%CI: 0.17–0.93) [50]. Similarly, this study found that in southern cities, CH was a risk factor for eczema in preschoolers during Period I but consistently became a protective factor for asthma, allergic rhinitis, and rhinitis in Period II. In contrast, a Japanese investigation linked CH to fever caused by the common cold in children (aIRR = 1.84; 95%CI: 1.41–2.40) [27], which diverges from this study’s findings. Differences between CH and RH likely arise from their respective heating characteristics: CH provides short-term, effective heating, whereas RH delivers sustained, comprehensive heating. Cross-sectional studies in China have highlighted significant correlations between allergic rhinitis and indoor dampness or visible mold [18,24,29]. A Swedish longitudinal study suggested potential reporting biases regarding dampness or mold due to heightened awareness of their link to asthma risk [51]. The findings underscore the importance of comprehensive assessments in identifying health-related heating methods.

4.2. The Causes of the Associations Between Heating Methods and Allergies and Respiratory Diseases in Preschoolers

4.2.1. Local Climate Differences

Among the four cities studied, Urumqi and Taiyuan are classified into the BWk and BSk climate zones while Chongqing and Changsha fall into the Cfa and Cwa climate zones. A survey conducted in Australia revealed a complex relationship between latitude and asthma prevalence, with a higher prevalence of current asthma observed among individuals living closer to the equator [52]. Consequently, this study compared its findings to previous research conducted in regions with similar climatic conditions.
This study compared cities with climate types resembling those of the northern cities. A study investigated the relationship between thermal comfort conditions and respiratory system diseases in Amasya, Turkey (BSk). The results indicated that for every 1 °C increase in the temperature of thermal comfort conditions, the number of patients presenting with respiratory diseases decreased by 64 to 67 individuals [53]. Turkey, situated in the transitional zone of mid-latitude air masses, experiences frequent changes in thermal comfort conditions due to sudden weather fluctuations. Another study involving 326 cities across Latin America—spanning the Aw, BSh, BWk, and Cfa climate zones—examined the relationship between temperature and mortality. It found that during extreme cold periods, a 1 °C decrease in temperature was associated with a relative risk of death of 1.03 (95%CI: 1.03–1.04) [54]. These findings are inconsistent with the conclusions drawn for Period I in the northern cities but align with those of Period II. In Period II in northern cities, RH was associated with a reduced lifetime risk of asthma in preschoolers (AOR: 0.37, 95%CI: 0.16–0.82, p = 0.014). Furthermore, CH&RH shifted from a risk factor for preschoolers in Period I to having protective effects against lifetime pneumonia (AOR: 1.35, 95%CI: 1.02–1.77, p = 0.035) and rhinitis in the past 12 months (AOR: 0.36, 95%CI: 0.15–0.90, p = 0.029) in Period II.
This study also compared cities with climate types similar to those of the southern cities studied. A survey conducted in four universities in the Netherlands (Cfb) found that indoor heating was not a risk factor for rhinitis in university students (AOR: 1.64, 95%CI: 1.15–2.34, p = 0.007) [55]. In Period II, the relationship between heating methods and preschoolers’ health outcomes changed. RH was associated with a reduced lifetime risk of asthma in preschoolers (AOR: 0.37, 95%CI: 0.16–0.82, p = 0.014). These findings are consistent with a study conducted in England (Cfb), which found that heating methods effectively alleviated respiratory symptoms in school-age children [56]. Additionally, a survey conducted in Japan (Cfa) evaluated the association between heating methods and the incidence of common colds in children. The results revealed a significant association between the use of convection heating (CH) and febrile episodes in children (aIRR: 1.84, 95%CI: 1.41–2.40), consistent with the climatic conditions and widespread use of air conditioning for heating in southern cities observed in Period I.

4.2.2. Local Heating Policy

In this study, the northern cities of Taiyuan and Urumqi were classified as heating zones, while the southern cities of Chongqing and Changsha were not covered by heating policies. In the northern cities, most households in Period I utilized traditional heating methods such as radiators. As radiator technology originated in Russia, the water supply temperature is relatively high; a supply temperature of 95 °C and a return temperature of 70 °C are used [57]. The questionnaire in this study did not include questions specifically about radiators because it was based on a survey conducted in Sweden [33], and the surveys revealed that radiator heating is rarely used in households in southern cities [58]. In the northern cities, RH was identified as a risk factor in Period I for lifetime allergic rhinitis and eczema in the past 12 months among preschoolers. This phenomenon is hypothesized to be due to the tendency of families to use centralized heating to keep windows closed during winter, leading to visible mold, damp stains, or watermarks, which increase disease risks for preschoolers. However, in Period II, RH transitioned into a protective factor against lifetime asthma in preschoolers (AOR: 0.37, 95%CI: 0.16–0.82, p = 0.014). This shift is hypothesized to result from an increased awareness of the importance of ventilation.
In the southern cities, CH&RH was a risk factor in Period I for rhinitis in the past 12 months but became a protective factor in Period II. During the heating season in southern Chinese cities, residents rely heavily on natural ventilation through windows [59], which reduces indoor relative humidity. It is speculated that differences in the heating characteristics of CH&RH and RH influence ventilation preferences in southern China. Due to the lack of regional energy policies in southern areas [31], residents tend to close windows or reduce the frequency of window openings, which makes RH a risk factor for disease in preschoolers. The reasons why RH and CH&RH are becoming protective factors might be the improvements in indoor air quality during Period II.

4.2.3. Local Economic Level

China’s economic growth has brought significant changes to heating methods in recent years [22,60]. As shown in Table 2, the proportion of heating methods chosen by preschooler households has changed significantly. For instance, RH in northern cities increased from 11.3% in Period I to 50.9% in Period II, while in southern cities, CH rose from 17.8% to 58.2%, and CH&RH decreased from 41.4% to 21.2%. The economic development levels differ between southern and northern cities in China, and wheezing is more prevalent in cities with a lower GDP per capita and lower urbanization levels [61]. In European cities, strict energy policies and traditional heating systems have led more households to use PH for heating, which has introduced indoor pollution issues. A study of air pollution and health across 36 Polish cities found that residents of more polluted areas were more aware of air pollution, highlighting the urgent need to reduce pollution levels and raise public awareness. A survey in Germany revealed a significant negative correlation between wood stove heating and allergic rhinitis in children (OR: 0.61, 95%CI: 0.61–0.91, p = 0.001), while no association was found with other diseases [62]. In Belarus’s Grodno Region, reduced coal heating was significantly associated with a lower incidence of spastic bronchitis in children (OR: 0.64, 95%CI: 0.44–0.93) [63]. An Iranian study reported that open fireplaces might cause symptoms such as throat dryness (33%) and fatigue (33%) among users [64]. Although this study found that PH became a protective factor in Period II for lifetime asthma, allergic rhinitis, and rhinitis among preschoolers in southern cities, the limited number of households using PH in the sample suggests that the relationship between PH and preschooler health outcomes requires further investigation.

4.3. Differences in the Protective and Hazardous Factors of Heating Methods

From Table 1, it is evident that all the demographic characteristics of preschoolers underwent significant changes except for gender. Variables such as age distribution, breastfeeding duration, tobacco exposure, homeownership, housing location, and heating methods all showed notable differences. A report from New Zealand highlighted that children diagnosed with asthma often lived in homes with smokeless heating, similar to PH in this study, which could produce particulates and chemicals that may trigger asthma [48]. A 2021 survey conducted in Chongqing, China, indicated that natural ventilation through windows was heavily relied upon during summer and winter [59]. Numerous studies have established significant associations between indoor pollutants and health effects, showing that household dampness indicators, PM2.5 levels, NO2, and VOC concentrations in indoor environments are often significantly linked to respiratory symptoms in preschoolers [16,18,23,24,29,30,43]. Poor ventilation, dampness, and mold exposure are identified as key factors affecting health. The changes observed between the two periods in this study might be attributed to the differing heating methods used by families in southern and northern cities, potentially leading to varying disease incidences among preschoolers.
In northern cities, most families (50.9%) still chose RH as their primary heating method, while in southern cities, the majority (58.2%) used CH. In northern cities, RH was found to have transformed into a protective factor against asthma in preschoolers. This shift highlights the importance of ensuring proper ventilation and maintaining indoor air quality when using heating systems at home, especially for CH&RH users. Given the higher relative humidity in southern regions, dampness and mold control have always been major concerns [23,43,61]. To reduce the risk of rhinitis-related symptoms in preschoolers during winter, it is advisable to periodically open windows at fixed times. Although it could lead to heat loss, window-opening schedules should be regulated. In summary, appropriate ventilation and indoor air quality management during heating should become common sense in both southern and northern cities. These measures can help maintain good indoor air quality and reduce the risk of respiratory and allergic diseases in preschoolers. Striking a balance between minimizing heat loss and maintaining healthy indoor air quality remains a challenge. For southern and northern cities, differences in household heating methods and preschooler health outcomes suggest the need for distinct research approaches, which need further exploration.

4.4. Strengths and Limitations

This study focused on the choice of different heating methods in southern and northern Chinese cities and compared their impacts on respiratory and allergic diseases in children over the past decade. The sample included nearly 30,000 participants from four cities in southern and northern China, providing a large sample size that enhances the validity of the results. From a temporal perspective, the nearly 10-year span of the repeated investigations facilitated the exploration of trends in preschoolers’ diseases. Additionally, the use of the ISAAC questionnaire to reflect children’s health status, which has been demonstrated to align closely with clinical diagnoses [65], further strengthened the reliability of the findings. Furthermore, binary logistic regression models were applied to examine the relationship between heating method choices and the occurrence of diseases in preschoolers. By calculating adjusted odds ratios (AORs), this study accounted for potential confounding factors such as family medical history, homeownership, and breastfeeding duration, reducing their influence on the evaluation of disease risk.
This study also has certain limitations. First, it relied on questionnaire surveys to assess heating methods and children’s health conditions, which may introduce response and recall biases [23]. However, the large sample size ensures that the results are unlikely to be significantly affected by individual respondent bias. Second, the survey did not investigate radiators, a common heating method used in northern Chinese households. This omission may be due to the significant differences in heating systems between the southern and northern regions, highlighting the need to address this heating method in future studies. Finally, this study was limited to two cross-sectional investigations in Periods I and II, which restricts its ability to capture more detailed trends and changes over time. To further verify causal relationships, cohort studies or clinical observations and diagnoses would provide more persuasive evidence.

5. Conclusions

This study conducted cross-sectional investigations in two northern cities (Taiyuan and Urumqi) and two southern cities (Chongqing and Changsha) in China during Period I and Period II. The study analyzed the potential reasons behind the impact of heating methods on preschoolers’ illnesses and reached the following conclusions:
(1) From Period I to Period II, there were significant differences in heating methods among southern and northern cities. The occurrence of most respiratory and allergic diseases in preschoolers may be significantly associated with the choice of household heating methods.
(2) In northern cities, RH emerged as a potential protective factor for preschoolers against respiratory and allergic diseases. However, during Period I, RH was identified as a risk factor for lifetime allergic rhinitis (AOR: 1.60) and eczema in the last 12 months (AOR: 1.64). This shift may have been due to increased awareness of ventilation during winter.
(3) In southern cities, CH remained the primary heating method for preschooler households. CH was associated with a lower risk of lifetime asthma (AOR: 0.63) and wheezing in the last 12 months (AOR: 0.53). However, RH increased the risk of these diseases, likely due to regional heating policies and different heating methods.
This study clarifies the potential impacts of various heating methods on respiratory and allergic diseases in preschoolers. It provides new insights and perspectives on heating method selection for families with preschoolers, contributing positively to safeguarding preschoolers’ health. Future studies should conduct more comprehensive field intervention surveys and precise laboratory experiments. Additionally, animal studies based on molecular biology could further enhance our understanding of how heating methods influence the prevalence of diseases in preschoolers.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/buildings15020234/s1. Table S1: Questions about building envelope dampness exposure. Table S2: Questions about health outcomes. Table S3: Comparison of the heating and cooling methods for preschoolers in northern China and their allergies and respiratory diseases. AOR, adjusted odds ratio; CI, confidence interval. Table S4: Comparison of the heating and cooling methods for preschoolers in southern China and their allergies and respiratory diseases. AOR, adjusted odds ratio; CI, confidence interval.

Author Contributions

Conceptualization: S.L. and W.Y., Data curation: C.W., Y.Z., H.Z. and P.Z. Formal analysis: W.Y., C.W. and Y.Z. Investigation: S.L., Y.Z., H.Z. and P.Z. Methodology: C.W., S.L., Y.Z. and P.Z. Supervision: W.Y. and Y.Z. Visualization: S.L., C.W. and Y.Z. Writing—original draft: C.W. and S.L. Writing—review and editing: W.Y., Y.Z. and H.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by a grant from the National Natural Science Foundation of China (Grant No. 52078076).

Institutional Review Board Statement

The surveys were approved by the Ethics Committee of the College of Life Sciences at Huazhong Normal University (protocol code CCNU-IRB-2019-002 and date of approval: 8 October 2019).

Informed Consent Statement

Informed consent was obtained from all subjects involved in the study.

Data Availability Statement

Data available on request.

Acknowledgments

The authors are grateful to all the teachers and students at the National Centre for International Research of Low-carbon and Green Buildings, who provided suggestions and guidance for this experiment and its modeling. We also thank the three reviewers for their constructive comments.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Comparison of the correlation between heating methods and allergies and respiratory diseases in preschoolers in northern China. Columns represent AORs, rows represent 95% CIs, and red lines indicate that an AOR is statistically significant (p < 0.05). Age, gender, family genetic history, residential ownership, breastfeeding duration, family location, and tobacco smoke exposure in the family environment were used as adjustment factors. AOR is the adjusted odds ratio, and CI is the 95% confidence interval. Detailed information on the AORs and 95% CIs in the figure is shown in Table S3.
Figure 1. Comparison of the correlation between heating methods and allergies and respiratory diseases in preschoolers in northern China. Columns represent AORs, rows represent 95% CIs, and red lines indicate that an AOR is statistically significant (p < 0.05). Age, gender, family genetic history, residential ownership, breastfeeding duration, family location, and tobacco smoke exposure in the family environment were used as adjustment factors. AOR is the adjusted odds ratio, and CI is the 95% confidence interval. Detailed information on the AORs and 95% CIs in the figure is shown in Table S3.
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Figure 2. Comparison of the correlation between heating methods and allergies and respiratory diseases in preschool children in southern China. Columns represent AORs, rows represent 95% CIs, and red lines indicate that an AOR is statistically significant (p < 0.05). Age, gender, family genetic history, residential ownership, breastfeeding duration, family location, and tobacco smoke exposure in the family environment were used as adjustment factors. AOR is the adjusted odds ratio, and CI is the 95% confidence interval. Detailed information on the AORs and 95% CIs in the figure is shown in Table S4.
Figure 2. Comparison of the correlation between heating methods and allergies and respiratory diseases in preschool children in southern China. Columns represent AORs, rows represent 95% CIs, and red lines indicate that an AOR is statistically significant (p < 0.05). Age, gender, family genetic history, residential ownership, breastfeeding duration, family location, and tobacco smoke exposure in the family environment were used as adjustment factors. AOR is the adjusted odds ratio, and CI is the 95% confidence interval. Detailed information on the AORs and 95% CIs in the figure is shown in Table S4.
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Table 1. Summary of population information of preschoolers in two surveys.
Table 1. Summary of population information of preschoolers in two surveys.
ItemsSample Size, n (%)
North (N = 14,027) South (N = 13,771)
Period I (N = 4567)Period II (N = 9460)p-ValuePeriod I (N = 5282)Period II (N = 8489)p-Value
Gender 0.123 0.271
Boy2372 (51.9)4782 (50.5) 2741 (51.9)4487 (52.9)
Girl2195 (48.1)4678 (49.5) 2541 (48.1)4002 (47.1)
Age 0.000 *** 0.000 ***
3817 (17.9)1592 (16.8) 1265 (23.9)1580 (18.6)
41706 (37.4)2198 (23.2) 1844 (34.9)2705 (31.9)
51412 (30.9)3664 (38.7) 1579 (29.9)2674 (31.5)
6632 (13.8)2006 (21.2) 594 (11.2)1530 (18.0)
Breastfeeding duration 0.000 *** 0.000 ***
≤6 months1853 (40.6)3018 (31.9) 2412 (45.7)3242 (38.2)
>6 months2572 (56.3)6427 (67.9) 2757 (52.2)5217 (61.5)
Household environmental tobacco smoke 0.000 *** 0.000 ***
Yes2705 (59.2)3165 (33.4) 3704 (70.1)5498 (64.8)
No1862 (40.8)6298 (66.6) 1578 (29.9)2991 (35.2)
Family genetic history 0.000 *** 0.000 ***
Yes726 (15.9)2836 (30.0) 686 (13.0)896 (10.6)
No3841 (84.1)6624 (70.0) 4477 (84.8)4574 (83.6)
Residential ownership 0.000 *** 0.000 ***
Owner3226 (70.6)7837 (82.8) 3408 (64.5)7138 (84.1)
Renter1251 (27.4)1033 (10.9) 1759 (33.3)866 (10.2)
Residence locations 0.000 *** 0.000 ***
Urban69 (1.5)8180 (86.5) 277 (5.2)5986 (70.5)
Suburban453 (9.9)994 (10.5) 641 (12.1)1876 (22.1)
Rural3976 (87.1)208 (2.2) 4268 (80.8)553 (6.5)
Construction age 0.000 *** 0.000 ***
≤20002133 (46.7)1893 (20.0) 2232 (42.2)1328 (15.6)
2001–20102304 (50.5)4166 (44.0) 2926 (55.4)3297 (38.9)
>2010/3223 (34.1) /3285 (38.7)
In the p-value column, *** represents p < 0.001.
Table 2. Proportion of four heating methods used by preschoolers’ families in Periods I and II in the South and North.
Table 2. Proportion of four heating methods used by preschoolers’ families in Periods I and II in the South and North.
ItemsNorthSouthPeriod IPeriod II
Period I Period II Period I Period II North vs. SouthNorth vs. South
Case (Proportion), n (%)p-ValueCase (Proportion), n (%)p-Valuep-Valuep-Value
CH0.000 *** 0.000 ***0.000 ***0.000 ***
Yes110 (2.4)689 (8.7) 921 (17.8)3440 (58.2)
No4418 (97.5)7236 (91.3) 4261 (82.2)2475 (41.8)
RH 0.000 *** 0.000 ***0.000 ***0.000 ***
Yes514 (11.3)4081 (50.9) 105 (2.0)641 (10.8)
No4019 (88.7)3943 (49.1) 5078 (98.0)5274 (89.2)
CH& RH0.000 *** 0.002 **0.000 ***0.000 ***
Yes89 (2.0)408 (5.2) 2145 (41.4)1087 (21.2)
No4439 (98.0)7512 (94.8) 3037 (58.6)4045 (78.8)
PH0.771 0.4850.0230.001 **
Yes95 (2.1)171 (2.2) 78 (1.5)261 (4.4)
No4472 (97.9)7752 (97.8) 5204 (98.5)5654 (95.6)
In the p-value column, ** represents p < 0.01 and *** represents p < 0.001. Polluting heating (PH) includes brazier heating, firewall heating, boiler heating, brick bed heating, etc.
Table 3. Incidence of respiratory and allergic diseases in preschoolers in Periods I and II in the South and North.
Table 3. Incidence of respiratory and allergic diseases in preschoolers in Periods I and II in the South and North.
ItemsNorthSouth Period I
North vs. South		Period II
North vs. South
DiseasesPrevalence, n (%)p-ValuePrevalence, n (%)p-Valuep-Valuep-Value
Period I Period II Period I Period II
Lifetime (From birth to now)
Asthma 117 (2.6)153 (1.7)0.001 **418 (8.0)400 (4.9)0.000 ***0.000 ***0.000 ***
Allergic rhinitis 277 (6.4)648 (7.0)0.211386 (7.5)656 (7.9)0.3970.0210.025
Pneumonia 1677 (37.4)2567 (27.4)0.000 ***1828 (35.1)2541 (30.2)0.000 ***0.0190.000 ***
Eczema 530 (12.6)1438 (15.5)0.000 ***1274 (24.6)1602 (19.2)0.000 ***0.000 ***0.000 ***
Wheeze 909 (20.6)370 (3.9)0.000 ***895 (17.4)575 (6.8)0.000 ***0.7430.743
Rhinitis 1887 (42.7)2401 (25.7)0.000 ***2205 (43.0)1995 (23.8)0.000 ***0.000 ***0.004 **
In the past 12 months
Eczema 264 (6.1)246 (2.6)0.000 ***624 (12.2)321 (3.8)0.000 ***0.000 ***0.000 ***
Wheeze 911 (20.7)343 (3.7)0.000 ***1026 (19.8)409 (4.9)0.000 ***0.3020.000 ***
Rhinitis 194 (4.2)505 (5.4)0.004 **417 (7.9)374 (4.4)0.000 ***0.000 ***0.003 **
In the p-value column, ** represents p < 0.01 and *** represents p < 0.001.
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Wang, C.; Li, S.; Zhang, Y.; Zhou, H.; Zhang, P.; Yu, W. The Impact of Heating Methods on Respiratory and Allergic Diseases in Preschool Children: A Repeated Cross-Sectional Survey Across Northern and Southern China. Buildings 2025, 15, 234. https://doi.org/10.3390/buildings15020234

AMA Style

Wang C, Li S, Zhang Y, Zhou H, Zhang P, Yu W. The Impact of Heating Methods on Respiratory and Allergic Diseases in Preschool Children: A Repeated Cross-Sectional Survey Across Northern and Southern China. Buildings. 2025; 15(2):234. https://doi.org/10.3390/buildings15020234

Chicago/Turabian Style

Wang, Chenyang, Shaohua Li, Yan Zhang, Haixia Zhou, Peiwen Zhang, and Wei Yu. 2025. "The Impact of Heating Methods on Respiratory and Allergic Diseases in Preschool Children: A Repeated Cross-Sectional Survey Across Northern and Southern China" Buildings 15, no. 2: 234. https://doi.org/10.3390/buildings15020234

APA Style

Wang, C., Li, S., Zhang, Y., Zhou, H., Zhang, P., & Yu, W. (2025). The Impact of Heating Methods on Respiratory and Allergic Diseases in Preschool Children: A Repeated Cross-Sectional Survey Across Northern and Southern China. Buildings, 15(2), 234. https://doi.org/10.3390/buildings15020234

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