The heat pump backup-heat mistake we catch on other companies’ installs
The most common heat pump problem we find on other companies’ work is not the equipment. It is how the backup heat was sized and programmed.
The backup-heat mistake we catch over and over is a heat pump that was undersized for the home, paired with bad programming that lets the expensive electric backup heat take over too soon. The heat pump should run unrestricted even when the emergency heat kicks on, because moving heat from outside is far cheaper than making it with electric resistance.
On top of that, the electric heater kit is usually undersized, so the home falls behind during defrost. A small electric baseboard in a utility room is cheap insurance against frozen pipes if the system ever fails.
The mistake almost every time: an undersized heat pump
When we get called out behind another company’s heat pump install and the homeowner says it cannot keep up, the problem is usually the same. The heat pump itself was undersized for the home.
Why does that matter so much? Because of how the economics work. Taking energy from outside and transferring it into your home is way more efficient than releasing energy you already paid the utility company for through electric resistance heating. So when the heat pump is too small, the system leans on that expensive backup heat far more than it should, and your bill climbs while you are still not comfortable.
The programming nobody sets up right
Here is the part that gets botched constantly, and it costs you money every cold day. The system has to be programmed so the heat pump keeps running unrestricted even when the emergency heat is running.
Think about it this way. The heat pump is your cheap, efficient heat. The electric backup is your expensive heat. When it gets cold enough that you need a little extra, you want the backup to add to the heat pump, not replace it. Too many installs are set up so the moment backup heat comes on, the heat pump shuts down, which is exactly backwards. You end up paying full electric-resistance prices when your efficient heat pump should still be doing most of the work.
- The heat pump must be sized correctly for the home in the first place.
- The controls must let the heat pump run unrestricted even while the emergency heat is on.
- The electric heater kit (the backup resistance heat) must be sized correctly for the home.
The defrost problem from an undersized heater kit
This one is sneaky. On a straight heat pump system, that electric backup heater kit is also what carries the home during a defrost cycle, when the outdoor unit briefly stops heating to clear ice off itself.
We typically find these heater kits undersized. So when the system goes into defrost on a cold day, the undersized kit cannot keep up, and the house gets cold for a stretch. Sizing that kit correctly is part of doing the job right, and it is exactly the kind of detail that separates a real install from a rushed one. We walk through more of these distinctions in our heat pump buying guide.
Cheap insurance against frozen pipes
I always think it is smart to have a secondary set of backup heat in the home. Electric baseboards in a utility room are cheap insurance to make sure your pipes do not freeze if the system ever fails, and systems can fail.
I do not recommend running electric baseboard all the time. It is expensive to operate. But having it there as a backstop can be life-saving, and in a Pittsburgh winter, frozen pipes are no joke. If you have a hybrid setup with a furnace as backup instead, that changes the picture, and we cover that in our dual fuel hybrid page.
The quick version
- The most common backup-heat problem is an undersized heat pump leaning too hard on expensive electric backup.
- Moving heat from outside is far cheaper than making it with electric resistance, so the heat pump should do the heavy lifting.
- Program the system so the heat pump runs unrestricted even when the emergency heat is on, never shutting it off.
- An undersized electric heater kit struggles during defrost and leaves the house cold.
- A small electric baseboard in a utility room is cheap insurance against frozen pipes if the system fails.
The biggest backup-heat mistake I see is an undersized heat pump with programming that shuts the heat pump off the second the electric backup comes on.
That is backwards. The heat pump is your cheap heat, so it should keep running even when the expensive backup is adding to it. Get that wrong and you are burning money every cold day.
David WahlCEO & Master Plumber, Wahl Family
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Call 1-855-GET-WAHLFrequently asked questions
Why is my heat pump’s electric bill so high in winter?
Usually because the heat pump is undersized or programmed to hand off to electric backup heat too soon. Electric resistance heat is expensive compared to moving heat from outside, so if your backup is doing most of the work, your bill climbs. Correct sizing and programming usually fixes it.
Should the heat pump keep running when the backup heat comes on?
Yes. The system should be programmed so the heat pump runs unrestricted even while the emergency heat is on. The backup should add to the heat pump on the coldest days, not replace it. Shutting the heat pump off the moment backup engages is a common and costly setup error.
Why does my house get cold during the heat pump’s defrost cycle?
During defrost, the outdoor unit pauses heating to melt ice off itself, and the electric heater kit carries the home. If that heater kit is undersized, which we see often, it cannot keep up and the house drops in temperature. Correctly sizing the kit prevents this.
Do I need electric baseboard heat with a heat pump?
Not for everyday heating, but a small electric baseboard in a utility room is cheap insurance against frozen pipes if the system ever fails. We do not recommend running it all the time because it is expensive to operate, but as a backstop in a Pittsburgh winter it can save you from a burst pipe.
How do I know if my heat pump is undersized?
Signs include constant reliance on backup heat, a home that never quite catches up on cold days, and high winter electric bills. The real answer comes from a load calculation that compares your home’s heat loss to the system’s capacity. We can evaluate an existing system and tell you straight.
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