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Comment by francisofascii | Hacker News Reader

Using COP is a easy way to compare heat pump efficiency to conventional heating methods. It is a multiple of the amount of heat energy output given the electricity energy used. A fossil fuel boiler is always less than 1 (usually 0.6-0.8) since it is never 100% efficient at converting the fuel energy to heat energy. Your electric space heater has a COP of exactly 1. So when you see the COPs in the 4-6 range, you get a good sense of how much more efficient heat pumps are.

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> A fossil fuel boiler is always less than 1 (usually 0.6-0.8) since it is never 100%

DOE mandates 80% efficiency for new furnaces, and high efficiency units are in the 90-95% range.

So, this is based on the assumption that electricity coming into the home is 100% efficient and none of the systems inefficiencies in power generation or delivery need to be accounted for, the way they are in fossil fuels?

That doesn't seem particularly useful.

Right, this measure is more for consumers and does not take into account generation or delivery. It is especially useful when comparing heat pumps to electric resistance heat, which is often the backup heat source. If the COP falls below one, you switch to resistance heat. But this article is saying heat pumps built today can operate well over 1 at very low temps.

The COP for a heat pump drops as the temperature decreases. The climate should have a large impact on the choice of technology. Here in Florida it is a no brainer, everyone has a heat pump for the cool winter days. In Minnesota, it is a non starter.

The article is pointing out that heat pumps today can still be more efficient down to -20 C (-4F).

It depends on what else you have available. If you have natural gas available at your house then a heat pump is probably not the most economical choice. Here in New Hampshire though NG is not available at many homes and a cold weather heat pump ends up being the cheapest option versus heating oil or propane.

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