Furnace and heat pump sizing in Northwest Territories
Yellowknife runs about 8,009 heating degree-days a year, which puts it in the very cold band at roughly 60 BTU per square foot of heating. It is the only station in the territory with a published annual degree-day normal.
The Northwest Territories are past the point where southern rules of thumb hold. The heating season runs most of the year and the design condition is extreme enough that envelope performance, not equipment size, usually governs whether a house stays comfortable.
Heating degree-days and January temperatures in Northwest Territories
Degree-days below 18 °C and January temperatures from the Environment and Climate Change Canada Canadian Climate Normals 1991–2020. The band column applies the mapping described on the Canada index.
| City | Heating degree-days (18 °C) | January daily mean | January daily min | Band | BTU/sq ft |
|---|---|---|---|---|---|
| Yellowknife | 8,009 | -25.5 °C | -29.4 °C | Very cold | ~60 |
Worked example
Take a 1,500 sq ft home in Yellowknife. At the very cold band of 60 BTU per square foot:
1,500 sq ft × 60 BTU/sq ft = 90,000 BTU/h
A gas furnace is rated by input, so divide the output by the AFUE to get the rating you shop for: at 95% AFUE that is about 95,000 BTU/h of input. That falls between the standard 80,000 and 100,000 BTU/h sizes. Which one you should buy is exactly the question a load calculation answers and a rule of thumb cannot — rounding down leaves the house short on the coldest nights, and rounding up brings the short-cycling problems of an oversized furnace. Run your own numbers in the furnace-size calculator, and use AFUE typical bands if you do not have the nameplate.
At these degree-days the arithmetic above is an illustration of scale, not a usable size. Envelope performance dominates the load long before equipment selection does.
Heat pumps in Northwest Territories
A heat pump loses capacity as the outdoor temperature falls, exactly when the house needs the most heat. The temperature where its output equals the house load is the balance point; below that, backup heat makes up the difference. Yellowknife averages a January daily minimum around -29.4 °C, and the design condition is colder still.
At these degree-days a heat pump needs a genuine cold-climate rating and backup heat sized to carry the house on its own at the design condition, not merely to supplement. Rated capacity at 8.3 °C tells you almost nothing about performance here; ask for the capacity table at low outdoor temperature.
The heat-pump-size calculator works from the same band, the balance-point calculator finds the crossover temperature. Dual fuel and the balance point explains where backup heat takes over.
A note on units
Canadian homes are almost always described in square feet and equipment is rated in BTU/h or tons, but outdoor temperature is in °C and degree-days are on the 18 °C basis rather than the American 65 °F. The two degree-day scales are not interchangeable: an American HDD65 figure is about 1.8× the Canadian HDD18 number for the same place. Every degree-day figure on this page is the Canadian 18 °C basis. If you have a floor area in square metres, multiply by 10.76 to get square feet before using the calculators.