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Originally Posted by Azure
Interesting.
So it seems to be more efficient if you have a REALLY warm climate (middle to southern US), or even perhaps if you need a lot of air conditioning in the summer as it can help with that?
Here in Manitoba we have all electric heating, and use heat pumps for air conditioning in the summer (outside air). Works great. Always wondered if it would help to use a heat pump water heater, as it SHOULD be more efficient than a normal Marathon electric hot water tank. And then in the summer you can route the cool air generated from the heat pump hot water heater into your ducting that is used for cooling to help with that.
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It depends what you're comparing it against. A heat pump water heater will always be more efficient than an electric water heater. So even in a cold climate, a HPWH will save energy vs. a resistance electric water heater simply due to the savings in non-heating months. So even in colder climates, they can be a great idea where electricity is relatively cheap and produced cleanly (i.e. Quebec, Manitoba, BC, etc.) or if you have solar panels.
Where it's not necessarily advantageous is when you're comparing to heating water with gas, and even more so in places where electricity is generated by burning gas. Gas-fired plants are pretty inefficient (~50% I believe) and then you have transmission losses in the electric grid, so it might take twice as much gas to produce a given number of BTUs with electric water heating compared to just heating with gas. So even with the efficiencies gained by a HPWH in non-heating months, there isn't necessarily a benefit environmentally and it's likely significantly more expensive based on the rates timun posted above where per kW (or GJ), electricity is about 5x more expensive than gas in Alberta.
So basically, if the electricity generation is largely non-fossil fuel and relatively inexpensive, then HPWHs definitely make sense. And the warmer the climate (fewer heating days) the more efficient they are.