What is a heat pump balance point? A simple guide
The heat pump balance point is the outdoor temperature at which the heat pump's output exactly matches the heat the house is losing. Above it the pump keeps up alone, and below it the house needs backup heat or the indoor temperature slowly drifts down.
How does the balance point work?
Two things change with the weather. A house loses heat faster as it gets colder outside, so the heating load rises in a nearly straight line. An air-source heat pump moves heat from outdoor air, and the colder that air is, the less capacity the pump has, so its output slopes the other way.
Plot both on one graph and the lines cross. The outdoor temperature at the crossing is the balance point. Left of it, the house loses more than the pump supplies. Right of it, the pump has spare capacity and cycles or slows down.
What does a worked example look like?
The numbers below are made up for illustration only. Say a house loses 12 kW of heat at an outdoor design temperature of minus 30 and loses nothing at 18 degrees, which is the temperature where internal gains and sun cover the heating. The heat loss is then zero at 18 and 12 kW at minus 30, so it rises by 0.25 kW for every degree of cooling.
Now say the heat pump's rated output at minus 30 is 6 kW and at minus 10 is 9 kW. At minus 10 the house loses 7 kW, which is less than the pump supplies. At minus 30 the house loses 12 kW against 6 kW from the pump. The lines cross somewhere between, at roughly minus 15 in this example, where the house loses about 8 kW and the pump gives about the same. Below that temperature, the missing heat must come from backup heat.
Real work uses manufacturer capacity tables at several temperatures and a proper load calculation, which is explained in the guide to heat pump load calculation.
Why does the balance point matter?
It shows how often you will use backup heat and what it will cost. A balance point of minus 15 in a city where it seldom gets that cold means a few hours of backup each winter. The same point in a place with weeks at minus 25 means a lot more. Local climate data for your area gives the number of hours below each temperature, and your installer or an energy advisor can use it.
It also shapes comfort and equipment choice. Cold-climate heat pumps keep more output at low temperatures, which pushes the balance point lower, as the cold-climate heat pump guide describes. Prairie homes feel this most, which is the focus of heat pumps in an Alberta winter.
How can you lower the balance point?
There are two ways: raise the heat pump's output at low temperatures, or cut the house's heat loss. The cheaper lever is usually the second one. Air sealing, attic insulation and better windows shift the heat-loss line down, so it crosses the pump's line at a colder temperature. Our guide on insulation upgrade priorities ranks where to start, and an air tightness test shows how leaky the house is.
On the equipment side, a larger unit or a cold-climate model lifts the output line. Oversizing has costs of its own in mild weather, so sizing needs a calculation, not a guess; heat pump sizing for cold climates explains the trade-off.
What should you do once you know the number?
Use it to choose the backup type and to set the controls. A dual-fuel system can be told to switch to the furnace near the balance point, as described in the hybrid heat pump guide. An all-electric system can set the lockout temperature for resistance elements so they only run when needed.
Ask the installer to state the balance point in the quote and show the data behind it. A vague answer is a sign the sizing was done by rule of thumb.
Quick answers
What is a good balance point for a heat pump?
A lower one means less backup heat, so a number well below your typical winter low is better. What counts as good depends on local climate and on what your installer calculated for your house.
Is the balance point the same as the lowest temperature a heat pump works at?
No. A heat pump can still run below the balance point, but it no longer covers the whole load there. The lowest operating temperature is a separate limit on the spec sheet.
Does a ground-source heat pump have a balance point?
Usually not in the same way. Ground temperature stays more stable than air temperature, so output does not fall off with the weather, and these systems are often sized to the full load.
Can better insulation lower the balance point?
Yes. Cutting heat loss moves the load line down, so the crossing point shifts to a colder outdoor temperature and backup heat runs less.