HSPF rating: what the number tells you
HSPF, or heating seasonal performance factor, measures how much heat a heat pump delivers over a heating season for each unit of electricity it uses, in BTU per watt hour. A higher HSPF means lower electricity use for the same heat, but the number comes from a standard test and does not guarantee results in a very cold climate.
What does HSPF stand for and how is it calculated?
The rating is the total heat the unit supplies over a typical heating season, in BTU, divided by the total electricity it consumes in watt hours. It is determined in laboratory tests at several outdoor temperatures and then weighted to represent a standard season, so it reflects both the efficiency of the unit and how often it would run at each temperature. The cooling counterpart is SEER. Our guide to the cold-climate heat pump guide explains where the heat pump category fits in Canada.
A related and simpler measure is the coefficient of performance, covered in heat pump COP explained. HSPF is, in effect, a seasonal version of it expressed in different units.
How do you convert HSPF to something intuitive?
Divide HSPF by 3.412, the number of BTU in one watt hour. That gives a seasonal COP, which is the heat delivered per unit of electricity. An HSPF of 10, for example, works out to about 2.9, so the unit delivers roughly 2.9 units of heat for every unit of electricity. Electric baseboard heat delivers 1.0.
Here is a worked example with stated assumptions. A house needs 100 gigajoules of heat over the winter, about 94.8 million BTU. At an HSPF of 10, the heat pump uses 94.8 million divided by 10, or about 9,500 kWh of electricity. The same heat from electric baseboards would take roughly 27,800 kWh. Your own heat demand and electricity rate change the result, and the point of the example is only the proportion.
What is a good HSPF, and what is HSPF2?
Higher is better, and the available range spans from basic to premium units. Entry-level models sit well below the top of the range, and premium inverter units reach much higher. HSPF2 is a newer rating based on a revised test procedure that mimics real installations more closely, which generally produces lower numbers than HSPF for the same equipment. Do not compare an HSPF figure with an HSPF2 figure directly. Compare units rated on the same scale.
The label figure is only one input. Capacity, noise and warranty also matter, and how to compare heat pump quotes shows how to line them up.
Why is HSPF not enough in a cold climate?
The seasonal figure is calculated for a standard climate. Much of Canada is colder, so the heat pump spends more hours at low temperatures where its efficiency and capacity drop. Two units with the same HSPF can perform differently at minus 25 degrees. Look for manufacturer data at low outdoor temperatures, and for cold-climate performance listings, not only the headline number. The guide on heat pump sizing in a cold climate shows how capacity at design temperature drives the choice, and heat pump load calculation explains the sizing step.
How does HSPF affect running costs?
A higher HSPF lowers electricity use, but the savings also depend on your electricity rate, the fuel you are replacing and how well the house is insulated. A more efficient unit usually costs more up front, so weigh the extra price against the yearly electricity it saves. If you are comparing against a gas furnace, read heat pump versus furnace, and for price drivers see heat pump cost in Canada.
At Drake Landing Solar Community, the homes ran on very low-temperature heat from a shared loop, which is a different approach described on the how it works page.
Quick answers
What is a good HSPF rating?
Higher is better, and there is no single threshold for every home. Compare units on the same scale, and in Canada also check performance data at low outdoor temperatures.
What is the difference between HSPF and HSPF2?
HSPF2 uses a revised test procedure and usually gives lower numbers for the same unit. The two should not be compared directly.
How do I convert HSPF to COP?
Divide the HSPF by 3.412. An HSPF of 10 equals a seasonal COP of about 2.9.
Does a high HSPF guarantee savings in a cold climate?
No. The rating assumes a standard climate. Check the unit's capacity and efficiency at your coldest outdoor design temperature as well.