In March 2020 I made a decision to do without a heater this Winter after cycling in Tasmania and surviving some cold nights in only a tent. Had I known about losing one job in April, an increased time spent at home from August and a lack of warm clothes, I probably would have still decided to continue on this experiment, albeit because of my selectively stubborn nature to persist with an idea.

This is part of a personal journey to understand the reasons behind some things I have become accustomed to and to better understand the outcome of reducing consumption in some of the largest areas of impact. Yes, the best and smartest method is to build housing stock which is energy efficient and cosy, however in Australia this market is yet to affect the majority of habitants and we have a majority of homes which remain comfortable purely because of a space heater in climates which are predominantly cooler.

In many international standards, comfortable temperatures are deemed to lie between 20°C and 25°C and in another definition, you feel cold when your head and/or toes are colder than the rest of your body. In my dwelling, heat pours out of the only windows adjacent to the living area, two south-facing single glazed windows of around an area of 1.2m² each. When the sky is dark, the temperature drops significantly. I chose not to set up a thermometer in the house to measure the temperature, however I guarantee that it frequently dropped below 20°C as I felt this on my feet, head and hands.

The average temperatures during Melbourne’s Winter in 2019, according to the BOM (it really is ‘the bomb’) were warmer than average. The warmest temperature recorded was 20.6°C at Moorabbin Airport and the coldest temperature recorded was -2.0°C, with the coldest daytime temperature being 4.3°C. For 2020, the monthly mean maximum temperature is colder than 2019, though by less than a degree on all months. What does this mean for my home?

From a thermal comfort perspective, when temperature drops below 20°C we are likely to heat space to bring it to a more desirable temperature level. Reaching a low-average of around 14 – 15°C during Winter makes it almost certain that the average inhabitant is going to be turning on the heater, therefore it makes sense to look at average statistics when analysing the outcomes of this action.

In 2014, Energy Rating (Australian Government) found that space heating accounts for 40% of energy use.[1] This number is confirmed by yourhome.gov.au.[2] ‘Compare the market’ did some research on energy usage in 2017, throughout Summer and Winter and in a four-person household. Melbourne had a Winter energy use of 1,738kWh, 40% of this can be attributed to space heating, a value of 695.2kWh, an average of 7.72kWh per day over 90 days.

AusGrid looks at the average usage during Winter being 8 hours per day.[3] With this usage per day, the average heater size would be around 925W without any energy efficiency coefficient or split system efficiencies. My heater is 2.5kW peak, has an energy efficiency coefficient of 4.18 and I’ve estimated the compressor to be on for 60% of the time.

With these numbers, turning my heater off for the whole of Winter saved around 2.87kWh per day and a total of 258kWh over Winter. This equates to a cost saving of $155 and a saving of 280kg of Greenhouse Gas Emissions according to Powershop.[4] 100% Greenpower is used at home, so this is only a theoretical number.

As a bonus, this year I did not catch a cold (or COVID-19) during Winter. I kept warm by still having warm showers (Hot Water accounts for half the energy use of space heating), wearing warm clothes inside and to bed and wearing two pairs of socks to bed. I did not need to wear gloves this year.

I also learnt that using a slow cooker warms a place up pretty well at a peak energy load of 180W (my space is around 35m²) and so does baking bread. The hardest time was being at home during lockdown in August, we had some of the coldest weekends of Winter towards the end of the month and sometimes the Sun did not shine to allow me to warm up.

Most of the time this was a positive experience and worth the experiment. It challenged me to keep pursuing ways to reduce energy consumption in the home and allowed me to be critical about good design.

Author: Alex Slater

[1] https://www.energyrating.gov.au/products/space-heating-and-cooling

[2] https://www.yourhome.gov.au/energy/heating-and-cooling

[3] https://www.ausgrid.com.au/-/media/Documents/energy-use/Winter-heating-guide.pdf

[4] https://www.powershop.com.au/carbon-calculator/