Why Your Heat Pump’s Efficiency Doesn’t Always Mean a Lower Electric Bill in Winter

If you’ve ever looked at a heat pump’s spec sheet and seen numbers like 300% efficiency — or a COP of 3.0 — your brain probably did the math: I’m getting three times the heat for every unit of electricity I use. That sounds incredible. So why does your electric bill sometimes go up after switching to a heat pump?

It’s a question we get a lot, and the answer isn’t what most people expect. Efficiency and cost savings are related, but they’re not the same thing. And in a Massachusetts winter, the gap between those two things can be pretty significant.

The Efficiency Number You’re Seeing Isn’t the Whole Story

When manufacturers rate heat pump efficiency, they typically do it at a specific outdoor temperature — often 47°F. That’s when a heat pump really shines. At 47 degrees, a good cold-climate heat pump might deliver a COP of 3 or even higher, meaning it produces three units of heat for every one unit of electricity.

But in January in MetroWest Massachusetts, we’re not dealing with 47-degree days. We’re dealing with mornings in the teens, windchills below zero, and stretches of days where the temperature barely climbs into the 20s. At those temperatures, even the best cold-climate heat pumps see their efficiency drop. A unit rated at COP 3.0 at 47°F might drop to COP 1.5 or lower when it’s 10°F outside. It’s still heating your home more efficiently than electric resistance heat, but it’s not the powerhouse it is in milder weather.

Heating Cost Comparison Table

Electric Rates Make a Bigger Difference Than You’d Think

Here’s where it gets a little counterintuitive. Even a highly efficient heat pump can produce a higher electric bill than you’d expect if your utility rate is high — and in Massachusetts, it is. We consistently pay some of the highest electricity rates in the country, often in the range of 20–30 cents per kilowatt-hour depending on your utility and the time of year.

Compare that to natural gas. Even with recent price swings, natural gas is often still cheaper per unit of heat delivered when you factor in the cost of electricity. So if you replaced a gas furnace with a heat pump, you might be running a system that’s technically more “efficient” in the engineering sense, but paying more per unit of energy to run it. The math doesn’t always work in your favor — especially if you’re heating a large older home with a lot of heat loss.

This is one of the reasons we spend time talking to homeowners before we recommend a heat pump as a primary heating source. It depends heavily on what fuel you’re replacing, how well-insulated your home is, and what your utility rate looks like. In towns we serve like Marlborough, Framingham, Natick, Newton, Lexington, Concord, and Reading, electric rates can vary significantly depending on your provider. That’s why two homeowners with identical heat pumps can see very different winter bills.

Backup Heat Is Often Running More Than You Realize

Most heat pump systems installed in colder climates have a backup heat source — either electric resistance strips built into an air handler, or a legacy oil or gas system that kicks in as a supplemental backup. When temperatures drop really low, the backup heat often takes over entirely.

Electric resistance backup is essentially 100% efficient — one unit of electricity becomes one unit of heat — which sounds fine until you realize a heat pump at moderate temperatures was giving you three units of heat for that same unit of electricity. If your backup strips are running for hours every night during a cold snap, your bill is going to reflect that, and it can be jarring.

A lot of homeowners don’t know when their backup heat is running. There’s usually no alarm, no notification, nothing visible. It just happens quietly in the background while the electric meter spins faster.

Your Home’s Efficiency Matters More Than the Equipment’s Efficiency

This is probably the most important point we make to anyone considering a heat pump. A heat pump is a delivery system. If your home is losing heat as fast as the system can produce it — through leaky windows, uninsulated attic bypasses, drafty band joists, old single-pane glass — you’re going to be running that equipment harder and longer to stay comfortable.

Weatherization and air sealing do more for your monthly bill than any equipment upgrade. If we put a top-of-the-line Mitsubishi heat pump into a leaky 1960s colonial without addressing the building envelope first, we’re doing you a disservice. The system will work harder, efficiency will drop, and your electric bill won’t look the way you hoped.

That’s actually why Mass Save offers weatherization services alongside the heat pump rebates. It’s not accidental — the program is designed around the idea that you should tighten up the house first, then electrify.

So When Does a Heat Pump Actually Save You Money?

The honest answer: it depends on your specific situation. Heat pumps tend to deliver the clearest savings for homeowners who are replacing electric baseboard heat or oil heat, have a reasonably well-insulated home, use the system heavily for cooling in summer (because that’s where the efficiency advantage is most dramatic), and live in a part of Massachusetts where their electric utility’s rates aren’t at the very top of the range.

If you’re replacing gas and you have a leaky old house, the economics are murkier. You might still come out ahead — especially once you factor in rebates, the eventual cost of a new boiler, and the benefits of not having combustion appliances in your living space — but we’d rather walk through that math with you honestly than just tell you you’ll definitely save money.

Heat pumps are genuinely excellent technology. We install a lot of them, and we believe in them. But “efficient” and “cheap to run” aren’t the same thing, and anyone who tells you otherwise isn’t giving you the full picture.

If you want to understand what a heat pump would actually mean for your electric bill before you commit, we’re happy to have that conversation. No pressure, no sales pitch — just an honest look at your home, your usage, and your options.