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Ecotrust Canada’s Community Energy team partners with Indigenous communities to implement home energy upgrade projects, delivers retrofit support programming in rural coastal BC, and engages in policy research and advocacy. Our work focuses on using clean energy solutions to put an end to energy insecurity, supporting retrofits in people’s homes to improve health, affordability, and climate resilience. We primarily work on individual homes and small residential buildings in the province of British Columbia, Canada.
This backgrounder summarizes information and policy pathways to reduce instances of unsafe indoor temperatures and increase climate resilience, particularly for tenants. This work builds on our 2024 Research Report on Advancing Tenants’ Rights to Retrofits and Energy Efficiency.
Thermal safety
By thermal safety, we mean temperatures that are safe for the occupants of a home to live in – enough but not too much heat, to prevent negative health impacts of both under- and overheating. It can be operationalized by measuring indoor temperatures, where air temperatures below the range of 18-21°C are too cold, and over 26°C being too hot. Related concepts include:
- Thermal comfort: The narrower range of temperatures at which people feel comfortable with the level of heat in a space.
- Thermal resilience: Maintaining comfortable and safe temperatures over the lifetime of a building, especially during challenges such as extreme weather or power outages.
- Passive survivability: How long a building can maintain safe indoor temperatures during a power or water outage.[1]
The safety of temperatures is influenced by humidity, airflow, solar and reflected radiation, and radiant heat variables, as determined by:
- Outdoor conditions, including weather, green space, shade.
- Building variables such as its orientation, insulation, shading, ventilation, heating and cooling.
- Occupants, including how many people, their activity in the space, and what they are able to do to adjust the indoor temperature.
It is well documented that cold housing contributes to excess winter mortality and morbidity (disease).[2] Low indoor temperatures impact cardiovascular and respiratory health, negatively affect mental health, can exacerbate health conditions, and have other wide ranging impacts on wellbeing, including playing a role in social isolation and food insecurity.[3] It also makes moisture and mold issues in the home more likely.[4] The World Health Organization (WHO) recommends 21°C in living rooms and 18°C in bedrooms, and multiple studies suggest 18°C as a minimum to avoid adverse health impacts.[5]
Health risks from extreme heat include cardiovascular illness and collapse, dehydration leading to kidney injury and failure, heat stroke, and lung damage, all of which can be fatal. While these health consequences are noticeable more quickly following exposure than indoor cold-related impacts, “cognitive and organ dysfunction can persist for years,” increasing the affected person’s risk of death by two to three times for decades after the event.[6]
The human body cools itself first by increasing peripheral blood flow, and next, at higher core temperatures, by sweating, the effectiveness of which is reduced if relative humidity is high. Depending on the intensity and duration of exposure, these cooling efforts can overtax the body, resulting in the above health consequences. 26°C is suggested as a maximum, where temperatures below this threshold are generally considered safe for most people, though this is not true for all, including some medically vulnerable people. This is based on a 2015 report by Toronto’s Medical Health Officer and the BC Coroner’s review of the 2021 heat dome deaths.
People can acclimate to heat physiologically, to an extent, within weeks. This allows those in warmer climates and those living in warmer, unconditioned spaces to tolerate higher temperatures. It also results in worse impacts of extreme heat events earlier in summer, when people have not yet acclimatized to warmer weather.[7] Another important variable involves nighttime heat exposure. This can be particularly consequential[8] because:
- Nighttime exposure impedes the ability to recover from heat stress from the day[9] – increasing morbidity and mortality,[10] especially among the elderly.[11]
- The option to avoid the heat by going to cooled public spaces is generally not available overnight.
- It impedes sleep, which has wide-ranging health and well-being consequences.
Health risks and impacts differ between people, including based on what they are adapted to and their vulnerability, which refers to how susceptible a person or community is to a hazard such as unsafe indoor temperatures.[12] It results from the combination of:
- Exposure, e.g., climate, quality of housing, physical location
- Sensitivity, e.g., age, chronic/mental illness, taking certain medications/drugs
- Ability to adapt, e.g., income, control over home (low for tenants), disability
A note on rural communities: While the urban heat island effect is well documented, it should not be assumed that rural areas will be less affected by overheating challenges. Research findings on rural heat impacts are mixed, but multiple studies have found greater vulnerability, higher rates of emergency department visits, and worse health outcomes from heat exposure than in urban areas. [13] Rural communities tend to have less health care and cooling centre access, higher energy costs, and potentially more heat exposure due to outdoor work.[14] They may also have warehouses and large paved areas that can spike surface temperatures as much as urban downtowns.[15]
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[1] Liyanage, D. R. et al. (2024). Thermal resiliency of single-family housing stock under extreme hot and cold conditions, Energy & Buildings, 323, p. 3.
[2] Janssen, H. et al. (2022). Cold Homes and Their Association with Health and Well-Being: A Systematic Literature Review. WHO Collaborating Centre on Investment for Health and Well-being, Public Health Wales NHS Trust.
Green, K. L. (2024). Interventions for cold homes: a rapid review of the health impacts, European Journal of Public Health, 34(4), pp. 682–695.
[3] The Marmot Review Team (2011). The Health Impacts of Cold Homes and Fuel Poverty. Department of Epidemiology & Public Health, University College London.
[4] Howden-Chapman, P. et al. (2023). Review of the Impact of Housing Quality on Inequalities in Health and Well-Being, Annual Review of Public Health, 44, p. 236.
[5] Jevons, R. et al. (2016). Minimum indoor temperature threshold recommendations for English homes in winter – A systematic review. Public Health, 136, pp. 4-12.
[6] Ebi, K. L. et al. (2021). Hot weather and heat extremes: health risks, The Lancet, 398(10301), pp. 698-708.
[7] Laouadi, A. et al. (2022, Feb. 16). Climate resilience buildings: guideline for management of overheating risk in residential buildings. National Research Council Canada, p. 8.
[8] Peacock, A. D. et al (2010). Investigating the potential of overheating in UK dwellings as a consequence of extant climate change. Energy Policy, 38(7), 3277–3288.
[9] Kovats, R. S., & Hajat, S. (2008). Heat stress and public health: A critical review. Annual Review of Public Health, 29(1), 41–55.
[10] Anderson, M. et al. (2013). Defining indoor heat thresholds for health in the UK. Perspectives in Public Health, 133(3), 158–164.
[11] Murage, P. et al (2017). Effect of night-time temperatures on cause and age-specific mortality in London. Environmental Epidemiology, 1.
[12] United States Environmental Protection Agency (Jan. 18, 2025). Understanding the Connections Between Climate Change and Human Health.
[13] Lippmann, S. J., Fuhrmann, C. M., Waller, A. E., and Richardson, D. B. (2013). Ambient temperature and emergency department visits for heat-related illness in North Carolina, 2007–2008, Environmental Research, 124, p. 40.
Hess, J. J., Saha, S., and Luber, G. (2014). Summertime Acute Heat Illness in U.S. Emergency Departments from 2006 through 2010: Analysis of a Nationally Representative Sample, Environmental Health Perspectives, 122(11), pp. 1209-1215.
Mendrinos, A. et al. (2024). Association between summertime emergency department visits and maximum daily heat index in rural and non-rural areas of Virginia (2015-2022). Science of the Total Environment, 948.
Ahn, M., Keith, L., and Brown, H. E. (2025). Rural heat health disparities: Evidence from the U.S. National Emergency Medical Services Information System (NEMSIS). The Journal of Climate Change and Health, 22.
[14] Nicholas Institute for Energy, Environment & Sustainability, Duke University (n.d.). Rural Interventions. Retrieved March 24, 2025.
[15] United States Environmental Protection Agency (Dec. 10, 2024). What Are Heat Islands?