Jenny’s house the day after the heat wave ended. The 1.5 year old ornamental grapevines are making great progress and will keep the house even cooler next summer.

Canberra and much of south eastern Australia experienced a very unusual, extended heat wave over the Christmas New Year period. How did my house (which uses only ceiling fans, passive management strategies and cross ventilation for cooling) and its inhabitants go?

NB. We are very big on sharing data and being transparent about how our houses perform. Be sure to ask other architects and homeowners for their temperature and energy use data if wanting to make comparisons.

Do you know what temperatures your house was at during the heat wave?

Temperatures in four rooms at Jenny’s house during the Christmas Day to January 5 heatwave of 2018-19. See below for an annotated version of the graph for an explanation of the variation in temperature fluctuations.

The first peak on the graph is Christmas day 2018. Me, my partner David, Zac-the-dog and two adult kids were home (hanging out, taking refuge from the heat, cooking, washing, showering) until the 29th when we packed up the cars and headed off in different directions. Me, David and Zac went to David’s mum’s house at Lake Macquarie, which by then was also experiencing a heat wave!

The dramatic drop in temperature on the 5th of January corresponds with the big cool change and storm that rolled into Canberra at the same time as we arrived home.

See the annotated version of the graph at the bottom of this post for an explanation of what is going on. The main take away message is that ceiling fans and night-time venting can keep humans (and dogs) very comfortable in a well-designed house during an extended heat wave in Canberra. Remember, a ceiling fan will make you feel between 2 and 4 degrees cooler depending on the speed you run it at.

We had a contrasting experience at David’s mum’s house, a fairly typical 1980s, single glazed, poorly insulated brick veneer and tile home. Despite its gorgeous location on the edge of Lake Macquarie, good orientation and shaded northern deck overlooking the water (and outside temperatures lower than those in Canberra) we were completely dependent on two split-system air conditioner/heat pumps to stay comfortable and civil to each other for much of the week away! Without the heat pumps running temperatures rapidly increased to uncomfortable levels on most of the days we were there.

While our house stayed at comfortable temperatures during the heatwave in Canberra the same strategies just weren’t enough at the Lake Macquarie house due to its poor design and construction. We have experienced the same thing in former Canberra homes. Upstairs at my previous house, prior to its energy efficiency focused renovation, regularly reached 37 degrees and the kids had to be moved downstairs to have any chance of sleeping.

Sadly summer heatwaves are likely to become the norm. Next Christmas/New Year we will be ready for anything on the heat wave front as we’re having a highly energy efficient split system air conditioner/heat pump installed this autumn as the home’s main form of heating. While the climate in Canberra means we use much more energy for heating than we do for cooling, it will be nice to have this option. A heat pump and ceiling fans work beautifully and very efficiently together - for example, instead of setting the heat pump thermostat to 25 you can put the fans on low and turn the thermostat up to 27 for the same cooling effect.

The rapidly growing deciduous vines will provide significantly more shade next year so we will have even less requirement for cooling… but it means we could cook a roast, and bake lots of cakes, during an extreme heatwave if we felt like it!

You can see a floor plan of the house and read a blog about how the house went in a much ‘friendlier’ heat wave last summer (by friendlier I mean shorter and with cooler overnight temperatures) and another blog about how the house fares in the extremes of winter.

The heatwave low down