Heat Pumps Explained
This guide is for homeowners considering a heat pump for heating and cooling. You will learn what COP means, how sizing and climate affect performance, when backup heat is useful, and how heat pumps behave in cold weather—so you can evaluate options and talk clearly with contractors.
Key concepts
- Heat pump: A device that moves heat from one place to another. In heating mode it takes heat from outside (air or ground) and delivers it indoors; in cooling mode it works like an AC, moving heat from inside to outside. The same equipment can provide both heating and cooling.
- COP (Coefficient of Performance): The ratio of heat delivered to electrical energy used. A COP of 3 means you get 3 units of heat for every 1 unit of electricity. Higher COP means better efficiency. COP drops as outdoor temperature falls, so cold-climate performance is a key consideration.
- Sizing: Heat pumps are sized to match the heating and cooling load of the home. Undersizing leads to poor comfort and excess backup heat use; oversizing can cause short cycling and reduced efficiency. A load calculation (Manual J or equivalent) is the right basis.
- Backup heat: In cold climates, heat pump capacity drops. Many systems include electric resistance strips or a gas furnace as backup. The backup kicks in when the heat pump can’t meet the load or during defrost. Sizing and control strategy affect comfort and operating cost.
Sizing and performance considerations
Sizing should be based on a proper load calculation, not rule of thumb. The calculation accounts for insulation, windows, climate, and desired indoor temperature. In heating-dominated climates, the heating load usually dictates size; in cooling-dominated climates, cooling load may. Oversizing in cooling can leave the system short on heating capacity in cold weather if not chosen with that in mind.
| Factor | What to consider |
|---|---|
| Climate | Cold-climate units are rated for lower outdoor temps; standard units may need backup earlier |
| Existing ducts | Ducted systems use existing or new ducts; ductless (mini-split) avoids ducts but may need multiple heads |
| Backup heat | Electric strip vs gas furnace; strategy (lockout temp, setpoints) affects cost and comfort |
| Winter performance | Efficiency and capacity drop in cold weather; check specs at your design temperature |
Common mistakes
- Sizing by square footage alone instead of a load calculation.
- Ignoring cold-weather performance and assuming the heat pump will handle the worst winter day without backup.
- Setting backup heat to come on too early, which increases electric or gas use and cost.
- Not sealing and insulating the building first; a smaller, efficient heat pump can do the job in a tight, well-insulated home.
Cost drivers (general)
Cost depends on system type (ducted vs ductless, single vs multi-zone), capacity, and whether ductwork or electrical upgrades are needed. Incentives can reduce net cost in many areas. Operating cost depends on local electricity and gas rates, climate, and how much backup heat is used. Compare full installation quotes and ask for estimated annual operating costs.
Safety and permitting
Heat pump installation involves electrical and refrigerant work and may require permits and inspections. Proper sizing, refrigerant handling, and electrical connections are important for safety and performance. Use a qualified HVAC contractor and confirm local requirements.
FAQ
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