The rule, in short
Replacing electric resistance heating or oil: a heat pump has a strong, officially documented cost case, and you should be asking why not rather than why. Replacing cheap natural gas: the case is genuinely close and turns on your local electricity and gas prices, so get it modelled on your own rates. Replacing an air conditioner that is failing anyway: switch, because this is the cheapest moment you will ever get.
Step 1: what are you replacing?
Identifying the fuel you are replacing does most of the work in this decision, and skipping it is why so much heat pump advice feels like advocacy. A heat pump does not make heat, it moves heat - which is why ENERGY STAR can say it delivers up to three times more heat energy than the electrical energy it consumes. That advantage is enormous compared with burning electricity directly in a resistance element, and it shrinks as the fuel you are comparing against gets cheaper.
- Electric resistance heating. The clearest case. ENERGY STAR puts heat pump heating at approximately one third the cost of traditional electric heating. If you have baseboard heaters or an electric furnace, this is close to a straightforward win.
- Oil. Also strong - approximately half the cost, per the same source - with the added benefit of removing a delivery schedule and a tank from your life.
- Propane. Usually favourable, though it varies with local propane pricing more than most people expect.
- Natural gas. The honest answer is that it depends, and the next section explains why we are not going to pretend otherwise.
What the official numbers do and do not say
ENERGY STAR publishes two cost comparisons for heat pump heating: about one third the cost of traditional electric heating, and about half the cost of oil heat. It also states that replacing an older central air conditioner with an ENERGY STAR certified heat pump could save nearly $600 over the life of the product on cooling costs alone.
What it does not publish is an equivalent figure against natural gas. That absence is worth more than most of the arguments made in either direction. It is not evidence that heat pumps lose against gas - the comparison genuinely depends on the ratio between local electricity and gas prices, which varies enormously across the country and cannot be reduced to one national number. But it does mean that anyone quoting you a confident national savings figure for switching away from gas is not getting it from ENERGY STAR.
The practical consequence: if you heat with natural gas, ask the installer to run the comparison using the rates on your own utility bills. That is a reasonable request, it takes them very little time, and an installer unwilling to do it has told you something useful.
Cold climates
The old objection - that heat pumps stop working when it gets properly cold - is substantially out of date, and ENERGY STAR states the technology has advanced to the point where an all-in-one heat pump will keep you comfortable from the hottest summers through the coldest winters.
That said, it publishes no specific cold-climate performance data, so treat the category claim as a starting point rather than a specification. The useful question is about the individual model: what is its rated heating capacity at your local design temperature, not at 47°F where headline efficiency figures are measured? Cold-climate heat pumps are a distinct class of product and they behave differently from standard ones in genuinely cold weather. If you live somewhere with hard winters, that distinction matters more than the brand.
Step 2: timing beats technology
The largest single lever on this decision is not which unit you choose, it is when you choose it. A heat pump occupies the same place in the system as a central air conditioner and, as ENERGY STAR notes, can use your existing ductwork without additional renovations. So replacing a dying air conditioner with a heat pump means paying the difference in equipment - while replacing a working one means paying for a whole installation you did not otherwise need.
ENERGY STAR suggests considering replacement once a heat pump or air conditioner passes ten years. If yours is past that and something significant has just failed, this is the decision point, and it is worth getting a heat pump quote alongside the like-for-like one rather than after it.
One more option that rarely gets offered unprompted: a dual-fuel setup, where a heat pump does most of the year and an existing gas furnace takes over in the coldest weather. If you already own a serviceable furnace, it can capture most of the benefit without discarding equipment that still works.
What to ask before you agree
- Run the running-cost comparison on my actual utility rates, not a national average.
- What is this model's rated heating capacity at our local design temperature?
- Is this a cold-climate model, and does that matter where I live?
- Will my existing ductwork and electrical service support it as-is?
- What would a dual-fuel setup with my current furnace cost instead?
- What are the current incentives, and are they included in this quote or applied later?
- If I replaced like-for-like instead, what is the price difference?
The first question is the one that separates a considered recommendation from a sales position, and it is worth asking of every quote you get.