A collaborative project between the City of Vancouver, Vancouver Coastal Health, and the BC Centre for Disease Control.

City of Vancouver and Vancouver Coastal Health conducted a self-reported survey of indoor temperatures during the summer of 2021. This survey was sent out via Twitter and Easy Survey platforms on July 29 asking participants to self-report the highest indoor air temperature that was recalled during the first and very dangerous heat event of the summer (June 25-July 1) often referred to as the “heat dome”. Respondents were also asked to record more detailed information throughout the day on indoor temperatures for the subsequent less severe heat events (July 29-August 2, August 11-15) that summer. This survey also included questions on characteristics of the respondent’s residence and actions taken to reduce heat. A summary of the responses follows:

Distribution of highest reported indoor air temperature during the June 25-July 1 heat event

One hundred and fifty respondents reported the highest indoor air temperature recorded in their home during the heat event from June 25-July 1, referred to as the “heat dome” (Fig. 1). The mean highest indoor air temperature reported was 34.1°C, the median 33°C, while the highest indoor air temperature reported by any participant was 56.2°C (a substantial outlier, with the second-highest reported maximum temperature being 47°C). During this time period, the highest outdoor air temperature recorded at Vancouver Harbour was on June 28 at 33.8°C.

Fig 1. Distribution of reported maximum indoor air temperatures (n=150) during the June 25-July 1 heat event

Fig 1. Distribution of reported maximum indoor air temperatures (n=150) during the June 25-July 1 heat event


Highest reported temperature by time of day, July 29 - August 2, 2021

During the second heat event for this survey between July 29 and August 2 (Fig. 2), the average temperature taken was 25.3°C in the morning, 28.5°C during the afternoon peak, and 26.9°C before bedtime. During this time period, the highest outdoor air temperature recorded at Vancouver Harbour was on June 28 at 29.3°C.

Fig 2. Daily reported indoor air temperatures during the July 29-August 2 heat event

Fig 2. Daily reported indoor air temperatures during the July 29-August 2 heat event

Highest reported temperature by time of day, August 11 - August 15, 2021

Another heat event took place between August 11 and 15 (Fig. 3) and was the third one recorded for this survey. During this time, the average temperature taken was 25.5°C in the morning, 28.7°C during the afternoon peak, and 27.7°C before bedtime. During this time period, the highest outdoor air temperature recorded at Vancouver Harbour was on June 28 at 32.2°C.

Fig 3.Daily reported indoor air temperatures during the August 11-15 heat event

Fig 3.Daily reported indoor air temperatures during the August 11-15 heat event


Locations of survey respondents

There were 139 responses that reported location information, including eight residences outside of the Vancouver Coastal Health Authority. The points on the map display the highest reported indoor temperature during the heat dome (click to display).


Building characteristics associated with highest indoor temperatures during the June 25-July 1 heat event

The following results display the relationship between building characteristics and the highest reported indoor air temperature for the duration of the heat dome between June 25 and July 1.

Indoor air temperature by air conditioning

Only three survey respondents reported central air conditioner (A/C) use in their homes, and among them the median highest reported temperature was 25°C (Fig 4). There were n=39 respondents who used portable A/C, among whom the median highest reported temperature was 32°C. Most (n=108) reported no A/C use; the median highest reported temperature for this group was 34°C.

Fig 4. Highest reported indoor air temperature during the June 25-July 1 heat event by A/C use

Fig 4. Highest reported indoor air temperature during the June 25-July 1 heat event by A/C use


The use of air conditioning, particularly central A/C, was the building factor with the greatest influence on indoor air temperature. However, other building factors play an important role in the modulation of indoor air temperatures as well. To tease apart the effects that other building factors have on indoor air temperature, the analyses that follow only include units that reported no A/C use (n=108).

Indoor air temperature by type of building

The highest reported indoor air temperature during the heat dome was highest in duplexes, townhouses, or multi-unit detached housing (n=18) where the median temperature was 38.2°C (Fig. 5). The median highest indoor temperature in apartments or condos (34, n=63), and single detached houses (n=23) was 34°C.

Fig 5. Highest reported indoor air temperature during the heat dome by housing type for units that reported no A/C use

Fig 5. Highest reported indoor air temperature during the heat dome by housing type for units that reported no A/C use


Indoor air temperature by age of building

A total of 42 buildings were constructed before 1970 (Fig. 6). The highest reported temperature in these buildings was the highest (median temperature = 35°C) compared to newer years of construction (median=33°C).

Fig 6. Highest reported indoor air temperature during the heat dome by year of construction for units that repoted no A/C use

Fig 6. Highest reported indoor air temperature during the heat dome by year of construction for units that repoted no A/C use


Indoor air temperature by renters vs. owners

Median highest reported indoor air temperature was highest in those who lived in co-ops (Fig.7, n=4, 37°C), although data on the measure should be interpreted with caution due to small numbers in this sub-group. Highest reported indoor air temperature was similar between renters (n=62, 35°C) and owners (n=51, 33°C).

Fig 7. Highest reported indoor air temperature during the heat dome for renters vs. owners for units that reported no A/C use

Fig 7. Highest reported indoor air temperature during the heat dome for renters vs. owners for units that reported no A/C use


Indoor air temperature by presence of trees outdoors

There was little difference between those who reported that there was landscaping or trees on their property providing shade (n=20, median=33.6°C) and those that did not (n=88, median=34°C), see Fig. 8 below.

Fig 8. Highest reported indoor air temperature during the heat dome for properties with outdoor shade from landscaping for units that reported no A/C use

Fig 8. Highest reported indoor air temperature during the heat dome for properties with outdoor shade from landscaping for units that reported no A/C use


Indoor air temperature by floor of unit

Ninety-two participants noted the floor of their unit (see Fig. 9). Median highest indoor temperatures were lowest for units that were on floors 1-3 in the building (°C, ) and highest for those who lived on the tenth floor or higher (35°C, n=9). Median highest indoor temperatures were the same among those who lived on the highest floor in their building (34°C, n=7) compared to those who did not live on the highest floor in their building (34°C, n=54). Note that these findings should be interpreted with caution given that some units that were on the top floor may have been classified as not living on the top floor due to categorization of survey response options.

Fig 9. Highest reported indoor air temperature during the heat dome by floor of unit for units that reported no A/C use

Fig 9. Highest reported indoor air temperature during the heat dome by floor of unit for units that reported no A/C use

Fig 10. Highest reported indoor air temperature during the heat dome by highest floor in building vs. other floors in building for units that reported no A/C use

Fig 10. Highest reported indoor air temperature during the heat dome by highest floor in building vs. other floors in building for units that reported no A/C use


Indoor air temperature by direction of windows

Survey respondents reported the direction the windows in their residence faced (Fig. 9). Each response represents a window direction; a participant could have reported more than one window direction. The highest average indoor air temperature was highest in residences with windows facing west (36.3°C) and south-west (35.9°C), with East (35.8°C) and South (35.2°C) facing windows following closely behind.

Fig 11. Average highest indoor air temperature (°C) during the heat dome by window direction for units that reported no A/C use

Fig 11. Average highest indoor air temperature (°C) during the heat dome by window direction for units that reported no A/C use


Indoor air temperature by opening of windows

Participants were asked about if and when they opened their windows during the heat dome (Fig. 12). Those that opened their window all day had the highest indoor air temperatures (median=35°C, n=46), followed by those that opened their window in the morning or evening (median=33.6°C, n=56). Those that did not open their windows had the lowest median indoor air temperatures (33°C, n=6).

Fig 12. Highest reported indoor air temperature during the heat dome by opening of windows for units that reported no A/C use

Fig 12. Highest reported indoor air temperature during the heat dome by opening of windows for units that reported no A/C use


Indoor air temperature by window coverings

Participants reported using a variety of methods to cover the sunlight (Fig. 13): outdoor shades (n=7), curtains and/or foil (n=73), or a combination of both (n=1). A number of participants did not use any means of window covering to block the sunlight (n=27). The median indoor air temperature was similar across groups (33-34°C).