Performance
What happens to capacity below freezing
How rated capacity, COP, and the balance point change as outdoor temperatures fall, and what the published low-temperature ratings actually mean.
Read article →Cold-climate heating reference
Heat pumps that keep working when the thermometer drops.
How air-source heat pumps perform, get sized, and stay efficient through a Canadian winter — written for homeowners who want the technical detail, not a sales pitch.
The basics
How a heat pump heats a home in winter
A heat pump does not burn fuel to make heat. It moves heat that already exists in the outdoor air indoors, using a refrigerant cycle that reverses the way a refrigerator works. Because it transfers energy rather than generating it, a single unit of electricity can deliver several units of heat.
The efficiency of that transfer falls as the outdoor temperature drops, since there is less ambient heat to capture. Cold-climate models address this with variable-speed compressors, larger heat-exchange surfaces, and refrigerants chosen to keep working at low temperatures.
Two numbers describe the result: the Coefficient of Performance (COP), which compares heat delivered to electricity consumed at a given temperature, and the Heating Seasonal Performance Factor (HSPF), which averages performance across a heating season.
Articles
Practical guides for cold-weather operation
Sizing
Sizing a unit for a Canadian winter
Why a heat-loss calculation matters more than floor area, and how the design temperature for a region shapes the equipment you choose.
Read article →
Operation
Backup heat and the defrost cycle
How auxiliary heat sources, dual-fuel setups, and the defrost cycle keep a home comfortable during the coldest stretches.
Read article →Reading the cold
Why outdoor temperature changes everything
Capacity fades with cold
Heating output is highest in mild weather and lowest on the coldest day. Manufacturers publish capacity at multiple outdoor temperatures so the curve can be matched to local conditions.
Efficiency is a moving target
COP is not a single figure. A unit may exceed 3.0 near 8.3°C and fall closer to 2.0 in deep cold, which is why seasonal measures like HSPF are more useful for planning.
The balance point matters
The balance point is the temperature where heat-pump output equals the home's heat loss. Below it, supplementary heat covers the gap.
Contact
Send a question about cold-climate heating
Reading the ratings on a spec sheet can be confusing. If you have a question about a term used on this site, send a note and it will be reviewed.
Editorial contact
Email: editor@pinewindowhouse.org
PineWindowHouse is an independent informational reference. It is not affiliated with any equipment manufacturer and does not sell, install, or service heating equipment. Content is general in nature and should not replace advice from a licensed HVAC contractor.