Thursday, October 15, 2009

Is it true that for every degree you decrease your thermostat you can save up to 15% off your heating bill?

I was recently asked "is it true that for every degree you decrease your thermostat you can save up to 15% off your heating bill?"

I'm not an energy expert, but I do tend to think things through since I have science training in my background. What concerns me about the statement is it doesn't ever seem to be backed by a link to appropriate research. In addition I've heard a figure of 10% mentioned a number of times.

I actually think there is a bit of trick to the figure. If you think things through you'll see it is probably a true statement, but it does require certain assumptions.

As an outright statement of fact, I'd guess it is probably misleading, unless put in context.

Why context?

In Melbourne let's check the average temperature for the past week. The average temperature has been 12C. The maximum 21C and the minimum 2C. I've seen a figure of 18-20C degrees as the suggested temperature to set the thermostat for Winter.

If the average temperature has been 12C and you set your thermostat at 18C then the difference is 6C. Each one degree is roughly 16.66%. Drop the thermostat by one degree to 17C and you'll save the suggested 15%. If you originally had the thermostat set to 20C then the difference is 8C and one degree change to 19C will be 12.5%.

So really a figure of 10-15% saving is probably realistic.

The assumption here I suspect is you leave your heating on 24 hours, 7 days a week. This approach means once your home is heated to a certain level your heating will cut in and out to maintain the temperature. The average then should tend to work out.

My question then is, is it better to leave your heating on 24 hours a day, or to only use your heating as required?

For example when we get up we often turn the heating on. Once everyone goes off to school or work we turn it off. Later at night we'll turn the heating on again for a few hours. The heating is thus running 4-5 hours a day and not 24 hours a day.

Is turning your heating off when not required a better approach?

I don't know the answer to that question and perhaps I should do a study for a couple of days using the two approaches. Whilst it won't be exact as the weather will change from week to week, it might give a good indication.

The reality however for us is if the heating was left on 24/7 the heater would turn on and off regularly during the night. We find the noise of the heating if we leave it on, to disturb our sleep. So from a practical point of view it wouldn't work for us.

In my case I recently determined that parts of my home were not used, but the heating vents were open. I decided to close unused vents and to only heat the parts of the home as required. Parts of our home often don't get used for days. For example sometimes we don't use the lounge dining area because the family is busy doing other things. I see this part of the house not being used for 2-3 days at a time. During the day the sun warms the area, so at times there is little reason to heat the area. The immediate effect of closing off vents was the areas with open vents heated up much more quickly.

My thought about the statement you can save 10-15% of your heating costs by reducing your thermostat by one degree is it is probably true, if it is based on your running your heating 24/7. I also think it is one of those shock figures marketers use because for most people it just seems unbelievable.

I could be completely wrong, but my gut feeling is using only what you need, when you need it, and in the areas you need it, possibly uses less energy than reducing the thermostat. Reducing the thermostat to a comfortable level and wearing appropriate clothes is also a good way to reduce energy usage.

I'd really like to see what my gas bill would be if I did run heating 24/7 compared with how I currently run my heating.

My yearly gas bill for the past two years (which includes heating and hot water) has averaged $616 a year. I've started closing off areas of my home that don't require heating and I'm interested in seeing how that affects the gas bill.

I know the pilot light on the gas heating uses perhaps 10% of the gas each year. I could turn off the pilot light during winter, but I've found relighting the pilot light to be an experience that is very frustrating. They've hopefully improved that in more modern heaters.

I often wonder how my bill compares with other people's gas bills and I wonder how others reduce their gas costs. I've been able to find some great ways to save money on electricity using the Energy Cost Calculator, so perhaps it is time to check out what can be done with saving gas.

If you have any tips or thoughts please feel free to share.

- Kelvin Eldridge

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