this post was submitted on 24 Sep 2023
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Direct electric heat is very efficient. Practically 100%.
My understanding is that you would only need the aux source during extreme cold. So very rarely.
Right - in fact, from my knowledge, heat pumps only see use over direct electrical heating because they are effectively more than 100% efficient. They move more heat energy from outside to inside than they use in the transmission.
The breakdown between gas and electric heating isn’t necessarily a matter of how efficiently the energy is used once it gets to the home, it’s how expensive it is to get it there in the first place. In a lot, if not a majority, of places, it’s much cheaper to get gas piped in than it would be to pay for the same amount of heating via direct electric resistance. Heat pumps change the equation because they can make electric heating in places that don’t get outrageously cold economically competitive with gas.
Yep PGE makes it so that gas is tremendously less expensive than electrical in California. So a lot of people who would normally be upgrading right now will not be doing so.
My heat pump is around 300% efficient. It adds 3X the energy into the house than it spends by stealing that energy from outside.
Except when it's very cold outside, which is what was discussed here. Heat pumps are great (have one in my home), but it might not be ideal in very cold areas, especially if electricity prices are high compared to other energy sources.
You need to be in a very, VERY cold area for that to matter. While these places exists, I'm sure it's not the case for a lot of the states I've seen marked in that article. Heat pump can heat the inside of your house even when it's freezing outside.
...and it will never go below 100% because most have resistive heating as backup.
That's a misleading number. In most other cases where we are using electricity--motors, CPUs, lighting, etc--we consider the heat generated to be inefficiency. It might be more accurate to say that electric resistance heating is 100% inefficient.
If you're using resistance heating to heat your home, using electricity that's originally produced by natural gas, then you're using more natural gas compared to burning that gas for heat directly in a home furnace. Now, electric resistance heating can be a choice when it's fed by clean electrical sources otherwise. Even then, though, you would prefer a heat pump if possible.
And a heat pump powered by a natural gas power plant will bring more heat into the house for the same amount of gas, including losses in transmission. It will likely be more expensive to install and run, though.
But the heat is the goal.
What do you consider "extreme" cold?
I don't know. It's a curve though, not a cutoff.
Icing conditions can also be a factor; freezing rain in the high 20's F (~-4C for those who can't F) will build up a layer of ice on the outside unit especially since it's already the coldest thing around. That ice prevents air from circulating through, so it loses effectiveness. Running the strips for about a half hour or so, then running the air conditioner for about a half hour will defrost it quite effectively and restore it to efficient operation. It is my understanding some systems even do this automatically.