Heat Pumps 101
A heat pump is an air conditioner that can run in both directions. In summer it moves heat out of your house; in winter it reverses and moves heat from the outside air — even cold air contains heat energy — into your house. Because it moves heat rather than burning fuel to make it, it can deliver several times more energy as heat than it consumes as electricity. That is the whole reason it saves money.
COP and SCOP
- COP (Coefficient of Performance) — heat delivered ÷ electricity consumed, at a given moment. A COP of 3 means 3 kWh of heat for every 1 kWh of electricity drawn.
- SCOP (Seasonal COP) — the average COP across a whole heating season, including the cold days when COP falls. Modern air-source heat pumps achieve a SCOP of roughly 2.5–3.5 in most US climates.
Compare that with electric resistance heat (baseboard heaters, electric furnace strips), which is always exactly COP 1.0 — every unit of electricity becomes one unit of heat, no more.
Running-cost comparison
| Replacing… | Typical outcome with a heat pump |
|---|---|
| Electric resistance heat | Uses roughly one-third the electricity for the same warmth — large savings |
| Cheap natural gas | Closer to a wash; where gas is inexpensive and electricity pricey, a heat pump may cost about the same or slightly more to run |
| Heating oil or propane | Heat pump usually wins on running cost, often substantially |
Where a heat pump does not clearly beat cheap gas on cost, the case rests on the other benefits: you get cooling from the same unit (no separate AC), better humidity control and air filtration, no combustion or carbon-monoxide risk indoors, and lower emissions — especially as the grid gets cleaner.
Cold climates
This is the historical objection, and it is largely outdated. Older heat pumps lost efficiency badly below freezing and fell back on resistance “emergency heat,” which erased the savings. Cold-climate heat pumps (often labelled ccASHP or “hyper-heat”) now maintain useful capacity and a COP above ~1.5–2 down to about −15 °C / 5 °F, and specialised models operate far colder. Many cold-climate installs still keep a backup heat source (the existing furnace, or resistance strips) for the handful of extreme days each winter, sized so it rarely runs.
Practical notes
- Sizing matters more than brand. An oversized heat pump short-cycles, dehumidifies poorly, and wears out sooner; an undersized one leans on backup heat and struggles on design-cold days. Insist on a proper room-by-room load calculation (Manual J), not a “one ton per 500 square feet” rule of thumb.
- Ductless (mini-split) systems suit homes without ductwork, additions, or rooms that need independent control. One outdoor unit can serve several indoor heads. Ducted systems replace a central furnace and AC and use the existing vents.
- Backup and controls. If you keep a gas furnace as backup, a “dual-fuel” or “hybrid” control switches to gas below a set outdoor temperature where gas becomes cheaper than the heat pump at that day’s COP.
- Incentives are significant. Federal and state incentives, utility rebates, and in some areas low-income programs can cover a large share of the install cost. Check what applies before you buy — it can change which system is cheapest overall.
- Electrical capacity. A whole-home heat pump may need a service-panel upgrade; factor that into quotes.
A running-cost example
A home that needs 30 million BTU of heat over a winter (a modest amount, for illustration), with electricity at $0.16/kWh and natural gas at $1.30 per therm:
| Heat source | Efficiency | Energy needed | Winter cost |
|---|---|---|---|
| Electric resistance | COP 1.0 | 8,790 kWh | $1,406 |
| Heat pump (cold-climate) | SCOP 3.0 | 2,930 kWh | $469 |
| Natural gas furnace | 95% AFUE | 316 therms | $411 |
| Heating oil | 85%, $4.20/gal | 249 gal | $1,046 |
| Propane | 90%, $3.10/gal | 366 gal | $1,135 |
The heat pump crushes resistance, oil, and propane, and lands within a few dollars of cheap gas — while also providing summer cooling from the same box. Where electricity is expensive relative to gas, the gap widens in gas’s favour; where it is cheap (or you have solar), the heat pump pulls further ahead. Plug your own rates and SCOP into the heat pump savings calculator.
Common misconceptions
- “Heat pumps don’t work when it’s cold.” Modern cold-climate units do; the old ones did not.
- “The air from the vents feels cool.” Heat-pump supply air is warm but cooler than a gas furnace’s blast, delivered over a longer, gentler cycle. It heats the room to the same temperature.
- “It’s just an electric heater.” No — resistance heat is COP 1.0; a heat pump is COP 2.5–3.5, which is the entire point.
When to install one
The cheapest time to switch to a heat pump is when your existing system needs replacing anyway — a failed AC, a furnace near the end of its life, or an oil or propane system you want out of. At that point you are comparing the heat pump’s cost against a new furnace-plus-AC, not against your paid-off old equipment, and the gap is small or favourable once incentives are counted.
Replacing a working system early, purely to save on running costs, has a longer payback — do the arithmetic with your actual fuel prices and the heat pump savings calculator. It can still make sense if your current fuel is oil or propane, or if you have solar and cheap daytime electricity.
What to ask a contractor
- Insist on a Manual J load calculation (room by room), not a rule of thumb.
- Ask for a cold-climate (ccASHP / hyper-heat) model if you get real winter, and what the rated capacity and COP are at your design-cold temperature.
- Decide ducted vs ductless based on whether you have usable ductwork and whether you want per-room control.
- If keeping a gas furnace as backup, ask for a dual-fuel / hybrid control and the crossover temperature it switches at.
- Get the electrical assessment up front — a service-panel upgrade is a common $1,500–4,000 add.
- Confirm which federal, state, and utility incentives apply and whether the contractor handles the paperwork.
The bottom line
A heat pump heats and cools with one system and delivers 2.5–3.5 units of heat per unit of electricity, so it slashes costs versus electric resistance, oil, or propane, and roughly ties cheap natural gas while adding cooling and cleaner operation. Cold climates are no longer a barrier with a properly sized cold-climate unit and a modest backup. Get a Manual J load calculation, check your incentives, and estimate the running-cost difference for your home with the heat pump savings calculator.