Guidance on upper indoor temperature limits: Protecting the health of older adults

June 2026

Table of contents

• 1.0 Executive summary
• 2.0 Introduction
  • 2.1 Purpose
  • 2.2 Intended audience
• 3.0 Background
• 4.0 Evidence review
  • 4.1 Limitations of current evidence
  • 4.2 Summary
• 5.0 Recommendation: Indoor temperature limit based on evidence and health risk for older adults
• 6.0 Resources
• 7.0 Acknowledgements
• 8.0 References
• Appendix A: Summary of evidence
  • A1.0 Overview of rapid literature review methodology
  • A2.0 Thermal safety versus thermal comfort
  • A3.0 Descriptions of supporting evidence
  • A4.0 Moving forward
• Appendix B: Policies, regulations, standards and guidance

1.0 Executive summary

Climate change is reshaping Canada's health landscape. Rising temperatures and more frequent heat events pose serious health risks, particularly for especially susceptible populations such as older adults.

Health Canada recommends an upper indoor temperature limit of 26°C to protect older adults, defined in this document as those aged 60 and over, from heat-related illness and death. This threshold is based on a rapid evidence review of available epidemiological studies and controlled exposure research, and aligns with World Health Organization guidance and policies in several Canadian jurisdictions. Research indicates that indoor temperatures above 26°C increase physiological strain and risk of heat-related illnesses; sustained exposure to indoor temperatures between 26°C and 31°C, especially overnight, should be avoided whenever possible. While focused on older adults, these measures may also support broader population health during heat events.

This guidance is intended for public health officials and stakeholders to inform policies and interventions. It emphasizes health protection rather than comfort and acknowledges that 26°C may not fully safeguard individuals with severe frailty or multiple health conditions. Examples of possible actions that could be considered when implementing this guidance include proactive heat safety planning, discussion of personal cooling strategies, and flexible accommodations for those needing cooler conditions. This list of actions is for illustrative purposes and is not intended to be exhaustive or prescriptive.

As climate change accelerates and Canada's aging population grows, implementing indoor temperature limits is critical to reducing preventable heat-related health risks. Health Canada will continue to encourage research and policy development to protect susceptible populations.

2.0 Introduction

Recent evidence from Environment and Climate Change Canada shows that Canada is warming at over twice the global average, with northern regions warming at nearly three times the global mean^{Footnote 1Footnote 2}. With the rapid increases in global temperatures, and with Canada warming at a higher rate compared with the rest of the world, actions aimed at protecting people living in Canada from the health impacts of climate change are becoming increasingly important.

In recent years, Canada has experienced extreme heat events, most notably in Quebec in 2018^{Footnote 3} and in British Columbia in 2009^{Footnote 4} and 2021^{Footnote 5}, resulting in the deaths of hundreds of people, the majority of whom died indoors. For instance, during the 2021 British Columbia heat event, 98% of heat-related deaths occurred indoors, and most victims were over 60. More specifically, 67% of decedents were 70 years and older and 90% were 60 and older, closely mirroring provincial mortality rates of 70% and 85% for these age groups^{Footnote 6}. Globally, heat attributable excess mortality in this demographic has increased 81% from the 2000 to 2005 average, reaching a record 345,000 deaths in 2019^{Footnote 7}.

Currently, provincial and national building codes, except in British Columbia^{Footnote 8}, do not require maintaining upper indoor temperature limits. Active cooling systems are also not universally available. In 2023, Statistics Canada reported that on average, 77% of Canadian households had at least one type of air conditioner; of these (with significant variation by province), 41% of Canadian homes had central air conditioning, and 20% had stand-alone units (for example, window-mounted air conditioner)^{Footnote 9}. In Canada, extreme heat events have increased^{Footnote 10} and are projected to become more frequent, more intense and of longer duration^{Footnote 11}. Protecting populations at greater risk, such as older adults, from heat stress is critical for reducing the growing health burden.

Since 1998, Health Canada has worked with provincial and territorial partners to address the health impacts of climate change, including extreme heat^{Footnote 2Footnote 12}. Following the 2003 European heatwave, where 72,000 deaths were recorded^{Footnote 13}, Canada prioritized understanding and reducing heat-related health risks. Health Canada supports provinces, territories and other partners to develop and implement protective measures nationwide through capacity building, standards and guidance, public messaging and tools like Heat Alert and Response Systems^{Footnote 14}, developed in collaboration with Environment and Climate Change Canada and local health authorities. To fill knowledge gaps, Health Canada funded physiological studies to better understand how elevated temperatures affect people living in Canada^{Footnote 15Footnote 16Footnote 17Footnote 18Footnote 19Footnote 20Footnote 21Footnote 22Footnote 23Footnote 24Footnote 25Footnote 26Footnote 27Footnote 28Footnote 29Footnote 30}.

Recognizing elevated indoor temperatures as a growing health risk, Health Canada partnered with the Global Heat Health Information Network to develop a globally relevant toolkit to help public health agencies protect susceptible populations in a warming climate^{Footnote 31}. Indoor overheating is an increasingly urgent policy issue, with data from North American and European cities showing that 54% to 98% of heat-related deaths occur at home^{Footnote 5Footnote 32Footnote 33Footnote 34}. To advance this work and support provincial and territorial partners, Health Canada is releasing this guidance on upper indoor temperature limits, specifically dry-bulb air temperature^{Footnote i} (hereafter referred to as "temperature"), with a focus on older adults. Although other factors, such as humidity, could influence health outcomes and an individual's perception of temperature, this guidance does not consider these other factors in its recommendation due to limited scientific evidence.

The development of this guidance was informed by Health Canada's work since 1998 and a recent rapid review of the evidence base (see Appendix A).The rapid literature review focuses on research findings for protecting heat-susceptible older adults and includes a parallel review of existing policies and regulations on elevated indoor temperatures (see Appendix B). Based on existing epidemiological research and controlled exposure studies, this guidance recommends an upper indoor temperature limit of 26°C. This aligns with recommendations from the World Health Organization (WHO)^{Footnote 35Footnote 36} and from other jurisdictions across Canada^{Footnote 8Footnote 37Footnote 38Footnote 39Footnote 40Footnote 41} (see Appendix B).

2.1 Purpose

This document provides a recommendation for an upper indoor temperature limit of 26°C for older adults, defined for this purpose as individuals aged 60 and over (which aligns with the WHO's definition^{Footnote 42}), along with the research that supports this recommendation.

This recommendation is framed as a health-protective threshold and proposed action level for intervention rather than a comfort target. It also acknowledges that 26°C may not be protective of all older adults (for example, those with multiple health conditions or severe frailty).

2.2 Intended audience

This guidance is intended to provide a reference to assist public health officials and other stakeholders in developing their own policies and interventions to ensure the safety and well-being of susceptible individuals exposed to excessive elevated indoor temperatures within the built environment.

3.0 Background

Canada has experienced an increase in average temperatures of 1.7°C between 1948 and 2016, about twice the average warming observed globally^{Footnote 2}. Canada's Northern regions are particularly affected, with an average increase of 2.3°C, about three times the global rate of warming^{Footnote 2}. The number of days above 30°C is expected to double or triple in some parts of Canada in the near term (2021 to 2050) as a result of climate change^{Footnote 43Footnote 44}. A recently published study showed that for Canada, rising temperatures could lead to more heat-related deaths through to 2059 under high greenhouse gas emission scenarios, especially among older adults^{Footnote 11}.

During the same period, the number of older adults in Canada will continue to grow^{Footnote 42Footnote 45}, increasing the potential number of heat-related deaths. Currently, 18.9% of Canadians are 65 or older (the definition of older adult used in Canada), and projections suggest this could reach 21.6% to 31.7% by 2074^{Footnote 45}, highlighting the importance of addressing heat-related health risks for this large and expanding demographic.

Climate change is increasing the frequency, intensity, and durations of heat waves, which is having significant impacts on the health of people living in Canada^{Footnote 11Footnote 46}. While reporting of heat-related health impacts is uneven across jurisdictions, available data illustrate the seriousness of the issue. During a severe extreme heat event in western Canada in the summer of 2021, at least 619 people died in British Columbia, with 98% of deaths caused by heat injuries occurring in dwellings^{Footnote 5}. Similarly, a 2018 heat event in Quebec, between June 30 and July 5, resulted in 86 possible heat-related excess deaths across the nine regions affected by the heat wave^{Footnote 3}. Sixty-six of the reported deaths were in the city of Montreal, of which 83% occurred in private dwellings^{Footnote 3}. In Quebec, during the period of 1996 to 2019, heat exposure resulted in an average of roughly 470 deaths, 225 hospital admissions, 36,000 emergency department visits, 7,200 ambulance transports and 15,000 calls to the 811-health hotline every summer^{Footnote 47}.

The effects of exposure to extreme heat extend beyond physical health (for example, sleep disturbances, heatstroke, worsening of existing health conditions, pregnancy complications, higher rates of non-accidental and injury-related deaths) and mental health (for example, aggressive behaviour, worsening depression or anxiety)^{Footnote 48}; they can also diminish quality of life and livelihoods (for example, limiting workers' ability to safely perform their jobs both indoors and outdoors, reducing social interactions)^{Footnote 2}. Heat-related illnesses also add pressure to an already strained healthcare system, marked by limited primary care access and record-long emergency department wait times. Many of Canada's existing health facilities, among the oldest public infrastructure in use, with about half built more than 50 years ago, were not designed to withstand extreme climate events^{Footnote 49Footnote 50}.

The risk of overheating and its health impacts result from a complex interaction of external and internal factors within the built environment^{Footnote 51}. Externally, climate conditions (for example, elevated outdoor temperatures, solar radiation, wind direction) and surrounding features (for example, the amount of green space, building density) can influence the amount of heat arriving at the building envelope. Internally, building design (for example, building envelope design, availability of cooling measures such as operable windows, shading, and air conditioning), occupant behavior (for example, activities, location, operation of cooling measures), and individual susceptibility to heat affects heat exposure and therefore the risk to the health of occupants. Additional constraints, such as strata or condominium by-laws that limit the installation of specific cooling devices^{Footnote 52}, can further increase risk and underscore the complexity of managing heat exposure in the built environment.

Interest in elevated indoor temperatures is rising, driven by evidence that housing conditions play a key role in protecting health in the context of climate change^{Footnote 48}. Positive housing conditions include air conditioning, ventilation and filtration to improve indoor air quality, and increased incorporation of shading measures such as window shutters or blinds in building design. Multifaceted changes to housing conditions were also found to be better than single upgrades^{Footnote 48}.

Canadian homes were traditionally designed with a focus on winter comfort, but increasingly warm summers have made this an unbalanced approach. During heat events, indoor temperatures can differ significantly from outdoor readings. For example, while outdoor temperatures at nighttime typically decrease from peak daytime levels during hot weather, indoor temperatures tend to remain elevated. Without active or passive cooling, indoor temperatures can rise progressively over consecutive days of extreme outdoor heat, exposing occupants to sustained heat stress^{Footnote 15Footnote 16Footnote 17Footnote 18Footnote 20Footnote 21Footnote 22Footnote 24Footnote 25Footnote 30}. Excess heat retention by buildings can therefore threaten the health and safety of the residents, leading to serious health risks including death^{Footnote 53}.

Exposure to extreme heat can lead to a range of heat-related illnesses, including swelling, rash, cramps, fainting, and heat exhaustion, in addition to dehydration and worsening of pre-existing health conditions. Heat-related illnesses can rapidly become a life-threatening emergency such as heat stroke. From a physiological standpoint, heat exposure can compromise older adults' ability to regulate body temperature, blood flow, and hydration, increasing their risk of heat-related illnesses^{Footnote 16Footnote 30}. Furthermore, older adults often fail to report heat-related symptoms and mood disturbances, even when experiencing greater heat strain^{Footnote 20}; this susceptibility is further compounded if they are using medications that alter physiological responses to heat, elevating their risk^{Footnote 51}. Importantly, severe heat-related illnesses are usually the end stage of a progression that begins with smaller physiological changes. Cardiovascular events and acute kidney injuries can occur before symptoms of severe heat-related illnesses are detected, highlighting the importance of minimizing even modest heat stress^{Footnote 54}.

In response to the increasing frequency of extreme heat and its serious health risks, including death, especially among older adults, Health Canada developed this guidance to consolidate research and recommend indoor temperature limits to support decision-makers.

4.0 Evidence review

The evidence review informing this guidance (see Appendix A) focused on older adults living in Canada (defined in this document as those aged 60 and over^{Footnote 42}), a population that was significantly impacted by recent heat events in the provinces of British Columbia^{Footnote 5} and Quebec^{Footnote 3}. While data for other population groups is limited, available studies show that risk of heat-related illnesses increases progressively for everyone as indoor temperatures rise above 26°C (see Tham et al. 2020 systematic review)^{Footnote 55}. Health Canada encourages stakeholders and public health organizations to further assess the applicability of this guidance to other demographics within their respective jurisdictions.

This guidance draws on existing data about older adults, who can be more susceptible to extreme heat and its associated health impacts, including death^{Footnote 15Footnote 51}. Establishing indoor temperature limits to protect older adults may also benefit other at-risk groups. Health Canada acknowledges that other susceptible populations, such as children and individuals living with chronic illnesses, are also affected by heat^{Footnote 56} and is continuing to encourage research to address the impacts on these populations.

The current guidance has been developed for residential housing units. Ongoing and planned research in occupational health and educational settings, including studies on the built environment, will help establish the scientific base for developing upper indoor temperature limits that are tailored to the unique needs and challenges of these environments. The Government of Canada has published additional information to help health care workers identify heat stress in acute care patients^{Footnote 57}, guidance to help individuals reduce or eliminate their risk of injury and manage heat stress while working in the heat^{Footnote 58}, and guidance to support facility managers for retirement and long-term care during an extreme heat event^{Footnote 59}.

Due to limited scientific evidence related to the impacts of humidity, air circulation, radiant heat, and duration of exposure in combination with indoor temperatures, this guidance does not include a recommendation that incorporates these factors. It recommends an upper indoor temperature limit that is relevant for both daytime and nighttime exposure.

4.1 Limitations of current evidence

There are a limited number of high-quality studies that directly assess the health effects of indoor temperature, and data on household indoor temperatures is limited. Unlike controlled exposure studies conducted in regulated environments, observational studies in natural settings rarely eliminate the influence of outdoor temperatures due to their impacts on indoor conditions and the movement of subjects throughout their environment (for example, changing between outdoor and indoor environments throughout the course of the day).

Three publications cited in this guidance document^{Footnote 25Footnote 26Footnote 30} were based on a single exposure study. The exposure study examined physiological responses to specific temperatures (for example, 22°C, 26°C, 31°C, 36°C) on 16 participants in experimental settings that may have not reflected real-life conditions. The study involved participants from the same geographic region, Ottawa-Gatineau, Canada. Participants were habitually active, nonsmoking, and were not diagnosed with clinical health conditions (for example, type 2 diabetes, heart disease) or taking medications known to impair body temperature or cardiovascular regulation (for example, anticholinergics, beta-blockers)^{Footnote 25Footnote 26Footnote 30}. As pointed out by the researchers, the results of this study are most applicable to public health agencies in Ontario and surrounding areas (for example, Quebec, Canada, and the Midwest and Northeast regions of the United States)^{Footnote 25Footnote 26Footnote 30}. However, there is indirect evidence that these findings may be generalizable to other geographic locations with continental and/or temperate climates^{Footnote 25Footnote 26Footnote 30}.

Epidemiological studies typically evaluated heat-related health impacts across temperature ranges. For this guidance, six epidemiological studies highlighted in Appendix A, Section A3.0, were included because they provided recommendations for maximum indoor temperature ranges, which were then considered alongside the results of the controlled exposure research^{Footnote 60Footnote 61Footnote 62Footnote 63Footnote 64Footnote 65}. Due to limited data, one of the included epidemiological studies used outdoor air temperature as a proxy for indoor conditions when assessing health effects^{Footnote 62}.

The recommendation for an upper indoor temperature limit outlined in this guidance is 26°C. Evaluating whether this limit remains protective over multiple days of exposure to elevated temperatures is important and requires future research, as indoor temperatures often rise above outdoor levels when cooling is insufficient^{Footnote 25Footnote 26Footnote 30}. Maintaining a maximum indoor temperature of 26°C under these conditions, however, would be more protective compared to uncontrolled temperature increases over the course of these heat events.

4.2 Summary

For additional reading, Appendix A provides a summary of the scientific evidence informing this guidance, including its limitations. Appendix B also includes a brief overview of selected domestic and international indoor temperature policies. Both appendices are provided to offer additional context and to encourage further exploration of the topic.

Moving forward, further research is needed to understand factors that may increase health risks from elevated indoor temperatures for older adults (for example, chronic illnesses, medication use, sex, gender, socioeconomic status, acclimatization). Future guidance strategies should be tailored to high-risk groups, including infants, children, pregnant individuals, those with chronic or cognitive conditions, and underhoused populations, to ensure equitable health protection. As new findings emerge, they could help refine this guidance and its applicability to other population groups.

5.0 Recommendation: Indoor temperature limit based on evidence and health risk for older adults

Recommendation: Maintain indoor temperatures no higher than 26°C to reduce adverse health effects, particularly for older adults.

Based on Health Canada-funded research examining the impacts of elevated temperatures on older adults^{Footnote 25Footnote 26Footnote 30}, and on the recent evidence review described in Appendix A^{Footnote 60Footnote 61Footnote 62Footnote 63Footnote 64Footnote 65}, an upper indoor temperature limit of 26°C is being recommended. This aligns with WHO guidance^{Footnote 35Footnote 36} and with standards adopted in Canadian cities like Vancouver^{Footnote 37}, Toronto^{Footnote 38}, and Mississauga^{Footnote 39}. This recommendation is framed as a health-protective threshold and proposed action level for intervention rather than a comfort target.

Available scientific evidence shows that indoor temperatures above 26°C are associated with an increased risk of heat-related illnesses, such as respiratory distress, headache, dizziness and fatigue, and death in healthy adults aged 60 and older^{Footnote 25Footnote 26Footnote 30Footnote 60Footnote 61Footnote 62Footnote 63Footnote 64Footnote 65Footnote 66}. Recent research found that healthy older adults experience greater strain on their heart and on body temperature regulation when the indoor temperature is above 26°C, and this increases their risk of adverse health outcomes during sustained exposure^{Footnote 25Footnote 26Footnote 30}. The recommended 26°C limit, however, may not be protective of all older adults (for example, those with multiple health conditions or severe frailty); actively monitoring and controlling indoor temperatures is a vital strategy to reduce heat-related health risks, including death.

Based on available evidence, older adults are at risk of heat-related death from elevated indoor temperatures^{Footnote 15Footnote 51}. While there is limited data linking elevated indoor temperatures to death in other heat-susceptible groups, such as children, individuals living with chronic illnesses, and those who are socially isolated, available studies show that the risk of heat-related illnesses increases progressively for all populations as indoor temperatures rise above 26°C (see Tham et al. 2020 systematic review)^{Footnote 55}.

To reduce health risks:

• The recommendation for an upper indoor temperature limit outlined in this guidance is 26°C to reduce adverse health effects, especially for older adults.
• Additionally, available evidence reviewed while developing this guidance has shown that indoor temperatures above 31°C represent a critical threshold where health impacts escalate dramatically.
• While the health impacts of indoor temperatures between 26°C and 31°C remains less well-defined, exposure to indoor temperatures within this range, especially overnight and over multiple consecutive days, should be avoided whenever possible.

The following are possible actions jurisdictions could consider when implementing this guidance; the list is not exhaustive or prescriptive and is provided for illustrative purposes.

• Consider highlighting personal protective measures that individuals can take, such as using fans, staying hydrated, visiting cooling centres and other cool places, avoiding strenuous activity, taking cool showers or baths, and wearing loose-fitting, light-coloured clothing made of breathable fabric^{Footnote 67}.
• Consider highlighting the importance of using air-cooling systems in residential facilities for susceptible individuals, such as long-term care homes and seniors' residences, as relocation to cooling centres during heat events may be less feasible for older adults.
• Consider promoting proactive heat safety planning, such as encouraging early season preparation and proactive messaging regarding the risks of elevated indoor temperatures.
• Consider ways to support people who need cooler environments by reducing barriers and providing flexibility to strengthen the inclusiveness of strategies or policies.

This guidance is based on the best available research evidence at the time of its development. Health Canada will continue to encourage ongoing research in this area.

6.0 Resources

For more information on extreme heat related health risks and actions to protect health see Extreme heat events.

7.0 Acknowledgements

Health Canada gratefully acknowledges the following individuals for the development of this document: Dr. Shayna Deecker-Simon and Victor Gallant.

Health Canada gratefully acknowledges the contribution of individuals within the Climate Change and Health Office in supporting the development of this document: Paddy Enright, Graydon Paitich, Dr. Michelle Deveau, Dr. Jessie Hamon, Dr. Marion Doull, Dr. Peter Berry, Melissa Gorman, Gregory Richardson, Maria Derks-Normandin, Jaclyn Paterson, and Carolyn Tateishi.

The Climate Change and Health Office at Health Canada gratefully acknowledges the contribution of individuals within the following internal organizations in providing a review of this document:

• Healthy Environments and Consumer Safety Branch, Health Canada
• Health Products and Food Branch, Health Canada

The Climate Change and Health Office at Health Canada gratefully acknowledges the contribution of individuals within the following external organizations in providing a review of this document:

• Employment and Social Development Canada
• Housing, Infrastructure and Communities Canada
• Indigenous Services Canada
• National Research Council of Canada
• Natural Resources Canada
• Standards Council of Canada
• Statistics Canada
• British Columbia Centre for Disease Control
• Island Health
• Ontario Ministry of Health
• Public Health Ontario
• Direction régionale de santé publique de Montréal
• Toronto Public Health
• Research Centre of the Montreal Heat Institute
• The Human and Environmental Physiology Research Unit, University of Ottawa

Appendix A: Summary of evidence

This appendix summarizes the scientific evidence used to develop Health Canada's indoor temperature guidance for older adults. It presents findings from a rapid review informed by two decades of research, including Health Canada supported physiological studies.^{Footnote 15Footnote 16Footnote 17Footnote 18Footnote 19Footnote 20Footnote 21Footnote 22Footnote 23Footnote 24Footnote 25Footnote 26Footnote 27Footnote 28Footnote 29Footnote 30} The appendix details the rapid literature review methodology and provides evidence summaries from controlled heat exposure and epidemiological studies.

A1.0 Overview of rapid literature review methodology

Standard methodologies for rapid literature review were followed to ensure a rigorous search strategy and evidence assessment. A Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRIMSA) flow chart^{Footnote 68} (Figure 1), illustrates the evidence collection and appraisal process. To ensure completeness, the evidence base includes both peer-reviewed and grey literature, and the term "records" is used throughout this methods section to encompass all evidence types.

Figure 1: Text description

This flow diagram shows the process used to identify, screen and include records for developing guidance to protect the health of older adults from elevated indoor temperatures.

Identification of records

Identification phase:

• A total of 328 records were identified from multiple sources, including:
  • 60 from the WHO 2018 systematic review (Annex D)
  • 60 from the Tham 2020 systematic review
  • 19 records associated with Health Canada
  • 182 from a Health Canada rapid literature search
  • 7 from other sources
• Before screening, 36 records were removed:
  • 12 duplicates
  • 6 unrelated to heat based on citation information
  • 18 removed for other reasons such as broken links

Screening phase:

• After removal, 292 records were screened. Of these, 277 were excluded.
• 15 records were sought for retrieval, and all were retrieved.

Eligibility phase:

• 15 records were assessed for eligibility.
• During this stage, 5 records were excluded, including:
  • 4 review articles
  • 1 record excluded after discussion with additional Health Canada peer reviewers.

Included:

• A total of 10 records were included in the development of guidance.

Health Canada involvement was identified in 19 records via funding or staff authorship. Six records referencing software tools or non-heat-related disease reviews were excluded based solely on their citation information, as they were included in the source literature reviews for contextual purposes.

Evidence collection began with references from two systematic reviews on indoor temperature limits^{Footnote 36Footnote 55}, which discussed available research up until 2020. Additional records linked to Health Canada, identified through funding or authorship, were included. To address gaps and incorporate more recent research that extends the systematic reviews mentioned above, the Health Canada Library conducted a rapid literature search of Medline, Embase, Global Health, CAB Abstracts, and Scopus for studies published from January 2020 to March 2025. The search strategy used keywords related to indoor temperatures, heat-related morbidity and mortality, heat stress, and extreme heat events (Table 1). Other relevant records, identified by reviewers based on their expertise, were also added to the evidence base.

Of the 328 records identified, 292 proceeded to screening. Two independent Health Canada reviewers screened records. Each reviewer initially assessed records based on titles, abstracts, and the potential relevance of key findings. Records were included if indoor or outdoor temperatures or temperature ranges (to avoid inadvertently excluding studies on the indoor environment that used outdoor temperatures as a proxy for indoor conditions) linked to the observed health effects were explicitly reported, subjects included older adults (males and/or females, 60 years of age and over), and the subjects were in their place of residence (for example, private home, apartment buildings, or nursing homes). Records that did not meet these criteria were excluded. Ultimately, 277 records were excluded, and 15 were assessed for eligibility.

During this screening process and throughout the development of this guidance (March 19 to August 8, 2025), reviewers added indoor temperature policies, regulations, and guidance to Table 2 in Appendix B as they were identified. These documents align with Health Canada's recommended 26°C indoor temperature limit, though it is important to note that this policy search was not exhaustive.

Two reviewers independently assessed each record's eligibility using the Critical Appraisal Skills Programme (CASP) checklists^{Footnote 69Footnote 70}. These checklists were developed and assessed by expert working groups to support the structured assessments of published studies. These checklists were used to evaluate potential biases and assess the quality of the included records.

Following the CASP evidence review, the two reviewers discussed their findings. Four records were excluded because they were review articles rather than primary studies and did not introduce any new information beyond the existing primary studies subsequently used for this guidance. One further study was excluded after discussions with additional Health Canada peer reviewers because, although it collected both indoor and outdoor ambient temperature measurements, it did not clarify which were used to form its conclusions. The report addressed ambient temperature impacts only in general terms^{Footnote 71}. In total, 10 records were included in the evidence review^{Footnote 25Footnote 26Footnote 30Footnote 60Footnote 61Footnote 62Footnote 63Footnote 64Footnote 65Footnote 66}.

A2.0 Thermal safety versus thermal comfort

This guidance has been designed to inform public health officials and protect the physical health of older adults. Thermal safety focuses on preventing physical thermal stress and injury by ensuring an individual's core body temperature remains within the optimal range of 36 to 37°C^{Footnote 72}. Inadequate thermal safety can pose serious health risks, including temperature-related illnesses and death^{Footnote 72}. This contrasts with thermal comfort, not the focus of this guidance, which is defined as an individual's subjective perception of their thermal environment and influences satisfaction and productivity^{Footnote 72}. The 26°C recommendation, as presented in the document is health-protective, not comfort-focused.

A3.0 Descriptions of supporting evidence

The supporting research used to inform this guidance consisted of two controlled heat exposure studies and six epidemiological field studies.

Controlled heat exposure studies take place in laboratories where consenting participants are deliberately exposed to specific, carefully regulated, environmental conditions. These studies allow researchers to assess short-term and reversible health effects, such as body temperature increases and cardiovascular responses, in a controlled setting. Despite limitations (see below), controlled exposure studies provide a valuable method for assessing health risks and complement findings from observational research.

Epidemiological studies address factors affecting the health and illness of populations, such as exposure to extreme weather events, and they can serve as the basis for public health and preventive measures^{Footnote 73}. Epidemiology is based on observation, which differs from the controlled exposure studies, defined above. As climate change impacts larger populations, these observational studies are important to understand the wider impacts and implications on people and the locations where they live. Recent systematic reviews^{Footnote 35Footnote 65} identified a small number of studies that evaluated the effects of indoor temperature specifically rather than relying on outdoor temperature as a proxy. Six records provided support for this current guidance.

These six records were considered in the development of this guidance as they focused on older adults (males and females) over 60 years of age. All were field studies published between 2012 and 2022: three were conducted in nursing homes^{Footnote 60Footnote 62Footnote 64}; two in houses or apartment buildings^{Footnote 61Footnote 65}; and one in supportive housing^{Footnote 63}. The studies were international in scope, including Canada^{Footnote 65}, Australia^{Footnote 64},Germany^{Footnote 62Footnote 63}, South Korea,^{Footnote 61} and Slovenia^{Footnote 60}. Five of the records mentioned a temperature limit where negative health impacts were observed. The major limitations of all six studies will be discussed later in this section.

A3.1 Mortality

In 2010, Klenk and colleagues^{Footnote 62} conducted a time-series analysis on the effects of moderate and high temperatures on all-cause mortality in a large cohort of 74,753 nursing home residents aged 65 and older in Baden-Württemberg, Germany. Using comprehensive data from the country's largest statutory health insurer, the study ensured broad and inclusive coverage to minimize selection bias. The results showed that above 26°C, increasing ambient temperatures were associated with increasing mortality rates in nursing homes. The relationship between maximum ambient temperature and mortality was independent of gender, age, or care needs. While susceptibility was similar across age groups, residents requiring less care were less sensitive to heat than those with higher care needs, consistent with previous studies. Three months after a known heat event, excess mortality remained, with 356 additional deaths attributed to the event. These findings underscore the need for robust preventive measures in nursing homes.

A3.2 Morbidity

A 2010 study by Schellen and colleagues^{Footnote 66} examined thermal comfort, physiological responses, and office task performance in eight young (ages 22 to 25) and eight elderly (ages 67 to 73) men under two conditions: a constant temperature of 21.5°C and temperature drift conditions, both over a period of eight-hours. The study found that temperature changes of ±2 K/hr within a 17°C to 25°C range did not cause thermal discomfort in either age group. It also found that thermal comfort for both conditions was associated with skin temperature. Although this study focused on thermal comfort rather than thermal safety, it identified specific temperature ranges related to the observed effects, which justified its inclusion in developing this guidance.

In 2012, Kim and colleagues^{Footnote 61} studied the short-term effects of heat stress on body temperature and blood pressure in adults 65 years of age and older, living in dosshouses. These are small, windowless units in urban slums, often occupied by individuals living in vulnerable situations and lacking air conditioning or ventilation. Twenty elderly participants were recruited through convenience sampling at a dosshouse in Seoul, South Korea. Over two weeks, researchers measured outdoor and indoor temperatures, humidity, and participants' body temperatures and blood pressures. The findings showed that residents experienced indoor temperatures between 4°C and 5°C higher than the recommended summer limit of 26°C to 28°C set by the South Korean government^{Footnote 61}. Room temperatures consistently exceeded 30°C throughout the day. Body temperature increased by 0.21°C for every 1°C rise in ambient temperatures, and participants' blood pressure tended to decrease as indoor and outdoor temperatures rose^{Footnote 61}. Due to impaired thermoregulation, participants evidenced significant body temperature increases on hot days, with some developing mild fevers. Many also reported symptoms such as muscle pain, headaches, movement disorders, and difficulty breathing^{Footnote 61}.

In 2017, Fink and colleagues^{Footnote 60} developed indices to track symptomatic responses to indoor thermal conditions, including temperature and humidity, and air quality, with the goal to aid healthcare workers in detecting early signs of heat-related illnesses in Slovenia. Monitored symptoms included chest pain, reduced heart rate, nausea, fatigue, shortness of breath, cold extremities, ankle swelling, tinnitus, exhaustion from minimal exertion and general malaise. The study recruited two cohorts: 50 individuals aged 65+ with cardiovascular disease (CVD; 54% female), and 27 individuals without a CVD diagnosis (52% female)^{Footnote 60}. Symptom frequency and severity were notably higher in the CVD group, with significant differences in sensitivity to heat and poor air quality. Findings suggested that maintaining a Humidex below 29 and CO₂ levels under 600 ppm is crucial for preventing heat-related symptoms indoors.^{Footnote ii} Referencing the most recent Environment and Climate Change Canada conversion table^{Footnote 74} to assess its alignment with the proposed 26°C upper temperature limit in this guidance, an air temperature of 26°C at 45% relative humidity corresponds to a Humidex value of 29. On the Humidex scale, the value of 29 would represent the upper limit for "little discomfort"^{Footnote 74}.

In 2017, Lindemann and colleagues^{Footnote 63} examined the impact of indoor temperature on the physical performance in older adults. They recruited a convenience sample of 81 independent living older adults (mean age of 80.9 years, 84% women) from ten sheltered living facilities in Stuttgart, one of Germany's warmest regions. Assessments were conducted every four weeks between May 2015 and October 2015. This period included two heatwaves, allowing comparisons between heatwave and non-heatwave conditions. Physical performance was measured using three common tests: 1) modified static balance test to prevent floor and ceiling effects, whereby results cluster at the very bottom or very top of the measurement scale; 2) a five-chair-rise test, where participants stood up and sat down five times as quickly as possible without using armrests; and 3) a habitual gait speed, measured over 4 meters, which was also used as a surrogate for frailty based on previous studies. Participants were categorized based on initial gait speed into a "more frail" group (35 adults) and a "less frail" group (46 adults). In both heatwave and non-heatwave conditions, as temperatures increased, habitual gait speed and chair-rise performance declined in both groups, but balance remained unaffected. The decline in gait speed was most pronounced in the less frail group, decreasing at temperatures below 22°C and above 27.9°C. The study suggested that high indoor temperatures negatively impact older adults' physical capacity and was among the first to explore this relationship.

In 2017, Tartarini and colleagues^{Footnote 64} studied how indoor air temperature affects agitation in dementia patients aged 65+ who lived in a nursing home. Using standardized assessment tools, they found that agitation increased with prolonged exposure to temperatures above 26°C or below 20°C.

A 2022 longitudinal study by Teyton and colleagues^{Footnote 65} examined the effects of chronic and acute elevated indoor temperatures on immediate heat-related health impacts in adults aged 60 years and over who lived in non-air-conditioned buildings in Montérégie, Quebec, during the 2017 to 2018 summer months. Data was collected over three three-day periods: one during cooler temperatures (T1 = 18 to 22°C), and two in warmer ranges (T2 = 28 to 30°C and T3 = 30 to 33°C). Researchers tracked 13 possible heat-related symptoms, including anxiety, dry mouth, cramps, depressive symptoms, light-headedness, fatigue, nausea, headache, loss of consciousness, increased thirst (as a proxy for dehydration), decreased urination, trouble sleeping, and dark urine. The risk of these symptoms emerging increased with increasing temperatures. T3 did show a higher relative risk than T2 compared to the cooler T1 reference period, suggesting an exposure-response relationship. Findings from this study indicate that rising indoor temperatures were associated with the development of many of the symptoms. This study was one of the first to examine the link between indoor temperatures and multiple heat-related symptoms across several summer seasons in older adults without access to air conditioning^{Footnote 65}.

Finally, a recent series of published reports on a cohort of 16 participants in a controlled exposure environmental study^{Footnote 25Footnote 26Footnote 30} examined the effects of indoor temperatures on older adults. Ten males and six females (ages 66 to 78) participated in four randomized eight-hour exposure simulations to various indoor temperatures. These participants were nonsmoking, and were not diagnosed with clinical health conditions (for example, type 2 diabetes, heart disease) or taking medications known to impair body temperature or cardiovascular regulation (for example, anticholinergics, beta-blockers)^{Footnote 25Footnote 26Footnote 30}. For the study, the temperature conditions mimicked an air-conditioned room (22°C), the upper limit recommended by the World Health Organization (26°C)^{Footnote 35Footnote 36}, typical indoor temperatures on a hot summer day (31°C), and peak indoor temperatures during extreme heat waves without cooling (36°C). In all cases, the relative humidity was maintained at 45%.

Together these studies found that in older adults, there were minimal changes in core temperature and cardiovascular strain at 22°C and 26°C, but progressive increases in both parameters at higher temperatures (31°C and 36°C)^{Footnote 25Footnote 26Footnote 30}; there were increases in markers of cellular stress during prolonged exposure above 26°C, which, could be indicative of increasing physiological strain in the elderly participants^{Footnote 25}; and there was disruption to the gastrointestinal tract's protective lining at temperatures above 26°C by analyzing markers of intestinal damage, immune activation, and inflammation from blood samples^{Footnote 26} which can a trigger inflammation and eventually a sepsis-like response and organ damage^{Footnote 75Footnote 76}.

A3.3 Limitations

The controlled studies reported here have limitations, including small sample sizes and the assessment of exclusively healthy participants, which may not represent the broader older aged population. Although the University of Ottawa study^{Footnote 25Footnote 26Footnote 30} had more balanced gender representation than the Schellen study^{Footnote 66}, which included only men, males were still overrepresented overall, potentially limiting the applicability of the findings to older females. Additionally, key thermal stress factors, such as air flow, humidity, and radiant heat, were not examined, restricting insights into how multiple factors interact to influence thermal comfort, safety, and performance. As a result, these findings may not fully reflect real-world conditions, where multiple factors interact to influence human responses to the thermal environment.

Additionally, in the Schellen study^{Footnote 66}, although physiological data was collected, conclusions were largely based on participants' subjective assessments of thermal comfort, potentially limiting their relevance to thermal safety.

All records reported limitations in participant selection, temperature measurement, or other variables of interest, such as blood pressure monitoring^{Footnote 61}. Many reports identified sample size and subject selection methods as constraints, with several using convenience sampling for recruitment. Additionally, demographic distribution varied across records, often skewed by gender and sex, limiting generalizability. Other potential confounding factors in interpreting the results included unknown medication use, overall physical and mobility functioning, and cognitive functioning of the study participants.

While few studies specifically identify 26°C as an indoor temperature upper limit, especially in combination with an older adult population, the reviewed evidence shows health impacts increase above this threshold. This guidance draws from studies involving older adults that recommend indoor temperature ranges based on their findings. Due to limited research, one study using outdoor temperatures to assess indoor health outcomes was also included^{Footnote 62}. Despite limitations, the evidence shows that health risks increase at or above 26°C, a threshold that is also reflected in policies across multiple jurisdictions (see Appendix B).

A3.4 Concluding Remarks

Despite their limitations, the controlled exposure studies in this summary provide scientific support for a 26°C maximum indoor temperature limit to protect the health of older adults. The six epidemiological records described above show an association between excess heat exposure, and physical and mental health stress. Five studies specifically associated temperatures above 26°C with poorer health outcomes^{Footnote 61Footnote 62Footnote 63Footnote 64Footnote 65}. Outdoor temperatures are rising each year, and growing evidence shows that this heat increasingly affects indoor conditions, especially in homes without mechanical cooling, posing health risks to residents.

The research cited in this guidance demonstrates that heat related health risks increase with temperature, especially at temperatures above 26°C. The body of evidence, including controlled exposure studies, observational research, and existing policies and regulations (see Appendix B), linking extreme heat to an increased risk of death and illness in healthy older adults, supports Health Canada's proposal of a 26°C indoor temperature limit to protect the health of older adults living in Canada.

A4.0 Moving forward

The following is a non-exhaustive list of future research considerations with respect to indoor thermal conditions. It draws on limitations found in the peer-reviewed literature and feedback from this guidance document's reviewers.

Future research on indoor thermal conditions should explore how factors like health, medication, fitness, socioeconomic status, and acclimatization influence risk, especially among older adults. It should clarify the relationship between indoor and outdoor heat, and assess how air circulation, radiant heat, humidity, and air quality impact health outcomes and the effectiveness of this guidance. Studies are also needed on single- and multi-day heat events, limited nighttime cooling, and the effects of activity, clothing, and sleep disruption. Research should also define optimal combined indoor temperature and humidity levels and investigate the combined impact of heat and pollution in susceptible urban areas.

Appendix B: Policies, regulations, standards and guidance

Table 2 outlines policies, regulations, and other guidance that define 26°C as a reasonable maximum indoor temperature. This list is provided for additional context and to encourage further exploration in this area. It is not exhaustive and represents the information reviewers encountered while developing this guidance document (March 19 to August 8, 2025) and information that was provided by peer-reviewers.