Furnace and heat pump sizing in Newfoundland and Labrador
St. John's runs about 4,690 heating degree-days a year, which puts it in the cold band at roughly 50 BTU per square foot of heating. But Newfoundland and Labrador does not sit in one band — the table below shows the spread.
The island of Newfoundland has a long, damp, wind-driven heating season with a comparatively mild design temperature — the cold is persistent rather than extreme. Labrador, on the mainland, is a different climate entirely and sits far colder than any station on this page.
Heating degree-days and January temperatures in Newfoundland and Labrador
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 |
|---|---|---|---|---|---|
| St. John's | 4,690 | -4.2 °C | -7.8 °C | Cold | ~50 |
| Gander | 4,996 | -6.6 °C | -10.4 °C | Cold | ~50 |
| Happy Valley-Goose Bay | 6,484 | -17.0 °C | -21.7 °C | Very cold | ~60 |
How the province compares to itself
Worked example
Take a 1,500 sq ft home in St. John's. At the cold band of 50 BTU per square foot:
1,500 sq ft × 50 BTU/sq ft = 75,000 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 79,000 BTU/h of input. That falls between the standard 60,000 and 80,000 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.
Heat pumps in Newfoundland and Labrador
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. St. John's averages a January daily minimum around -7.8 °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.