Heat Pumps

Have you considered getting a heat pump to avoid using fossil fuels to heat your house? You may want to wait.

I have just recently had a gas furnace and heat pump installed, thinking that I could reduce my carbon footprint by using the heat pump as much as possible and the furnace only on really cold days. My mistake was …..

But let’s start with how I made my decision. I looked at the different types of heat pumps. First I looked at ground source heating where heat is extracted from the ground which is generally about 4° C year round. Much as I would have liked to go this route, a ground source heat pump was out of the question since I don’t have the yard space or the money to put in a ground source system. This type of system really needs to be put in at the time of building. Water sourced heat pumps also exist but you need a source of water. I had no lake in my backyard so that was out.

That left ducted or ductless air sourced heat pumps. I seriously considered the ductless heat pumps because of their efficiency. There are 2 manufacturers that make heat pumps that they claim work at temperatures to -30° C. What dissuaded me was the thought of water running through my walls and the possibility of leaks. As you may know, a heat pump works by condensing a substance (usually a refrigerant), making it hot and then pumping the substance into the house to the coils of a unit that can attach to part of your room or basement. As the blower in the unit blows air over the coils, the air heats up and is directed to warm your room(s). However, as cold air hits the warm coils, water condenses on the coils and the water has to drain to a location in your house, presumably through a pipe. In hindsight, that might not have been a bad idea. But then there are also refrigerant leaks to consider as the system ages.

Being afraid of leaks (rational or not), I chose a heat pump that would work in tandem with my new gas furnace and any condensate would drain into my already existing sump pump pit. Leaks of refrigerant would be confined to the basement. I needed the furnace because a heat pump becomes less and less efficient as the temperature outside gets colder.

I now have a much more efficient 2-stage gas furnace that works well and is much quieter than the old furnace. Time will tell if I see a decrease in the amount of natural gas I use.

I also have a new 1.5 tonne air source heat pump that the supplier assured me would work down to -15° C. It has a “heating seasonal performance factor” (HSPF) of 9.5. This is the heating efficiency rating. At the time of negotiations, I did ask about the wattage of the heat pump but I never got an answer. That should have been a red flag. My new heat pump keeps the house at my preferred temperature as long as the temperature outside is above about -8° C. At that point, the temperature in the house slowly decreases. The manual tells me that once the temperature gets to about 2° C below the thermostat setting, the furnace will kick in and the heat pump turns off. Ok, I can live with -8° C but it is a bit of a disappointment that I can’t use the heat pump in lower temperatures. Perhaps if my house was not a leaky sieve, the heat pump would perform better.

At the outside temperatures at which I have so far tested the heat pump (4° C to -8° C), the heat pump is on continuously below 0 and is on about half the time when the temperature is between 0 to 4° C. Perhaps at temperatures above 4° C it will be on even less. I hope so, because a test over several hours showed that the electrical usage was about 2kwh per hour. If it were on all day, that would be 48 kWh and for the month, that would cost me about $271 just for the heat pump depending on rates, time of day usage, etc. So, I will wait until the temperature warms up a bit and test it again. Stay tuned!

Moral of this story, unless you are using the heat pump as an air conditioner in the summer or you don’t mind spending a lot of money, or you have a source of really cheap electricity (like solar) or maybe if your house is well insulated and very tight, I would recommend waiting until there is better heating technology before installing an air source heat pump. Perhaps work on making your house more air tight with weather stripping, insulation and high quality windows and doors. If you are still keen on getting an air source heat pump, do your research and don’t be pushed around by any salesmen. Be sure to get a heat pump that has a very high efficiency rating – this means an HSPF rating as close to 14 as you can afford.

Have you experience with a heat pump? Please add your comments to this blog!

2 thoughts on “Heat Pumps”

  1. Lenore and I are going into our 4th year heating a 1920s Glebe rowhouse using a cold-weather heat pump exclusively, no backup gas furnace. This has cut the carbon footprint of our home energy use by 90%. The dollar-cost of heating with the heat pump has worked out better than expected. In 2018, the first full year of using the heat pump, the total amount we paid for natural gas and electricity was the same we were paying previously when heating with a high-efficiency natural gas furnace.

    You can read the story of our conversion here: https://medium.com/@wnuttle/heat-pump-proves-to-be-economical-climate-remedy-even-in-ottawa-fae648d52ae9

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