| Parameter | Value | Notes |
|---|
Cold-Climate Heat Pump Sizing for Canadian Homes
Sizing a heat pump for a Canadian climate is different from sizing one for Georgia or Texas. The heating load in January in Edmonton is 8-10x higher than the cooling load in July. The heat pump has to carry that load, and it has to do it at -30°C when it's least efficient. Get the sizing wrong and you end up with an undersized system that runs backup heat constantly, or an oversized system that short-cycles and doesn't dehumidify in summer.
Why the 47°F rating is useless for Canadian sizing
AHRI rates heat pump capacity at 47°F (8°C) outdoor air. That's a mild fall day in Vancouver. It's 38°C warmer than Edmonton's design temperature. A heat pump that makes 60,000 BTU/hr at 47°F might only make 35,000 BTU/hr at -22°F (-30°C). Always use the manufacturer's low-temperature performance data — the -13°F (-25°C) or 5°F (-15°C) rating — when sizing for Canadian winters.
Balance point and backup heat
The balance point is where HP output equals building load. Below it, backup kicks in. A cold-climate heat pump sized at 100% of design load has a balance point near or below the design temperature, meaning backup only runs a few dozen hours per year. An undersized heat pump has a balance point of -5°C and runs backup for hundreds of hours — erasing the operating cost advantage.
Standard sizing rules for heat pumps
Standard equipment sizing practice allows heat pump selection at 100-125% of the heating design load at design conditions. Don't exceed 125% or you risk summer overcooling and humidity problems. Use the heat load calculator to get an accurate design load before sizing.
Frequently Asked Questions
A cold-climate heat pump is an air-source heat pump designed to maintain heating capacity at very low outdoor temperatures. Standard heat pumps lose most of their capacity below -5°C and typically shut off at -15°C. Cold-climate units (ENERGY STAR Cold Climate certified) maintain rated capacity at -15°C and produce usable heat at -25°C or lower. Examples include the Mitsubishi Hyper-Heat, Bosch IDS Ultra, Daikin Fit, and Carrier Greenspeed. These are the only heat pumps suitable as primary heating systems in most Canadian climates.
For most Canadian climates except coastal BC, yes — you want backup heat. Even the best cold-climate heat pumps lose efficiency below -20°C to -25°C. A small electric resistance heater (10-15 kW) provides backup for the handful of hours per year when temperatures drop below the heat pump's effective range. In a dual-fuel system, a gas furnace provides backup. In milder cities like Vancouver and Victoria, a well-sized cold-climate heat pump can often serve as the sole heating system.
The calculator uses linear interpolation between your 2 rated capacity data points (47°F and low-temp rating) to estimate HP capacity at any outdoor temperature. It also calculates building heat loss at any outdoor temperature using the ratio: Load(T) = Design Load × (Indoor Setpoint - T) / (Indoor Setpoint - Design Outdoor Temp). The balance point is the temperature where these 2 lines intersect. Below that point, backup heat covers the gap.