Every heat pump has a temperature where it runs out of steam. Not off, just not enough. Above that point it carries your house alone. Below it, something else has to make up the difference: electric strips, the old furnace, or propane.
That temperature is the balance point, and in Ontario it decides how big the backup has to be and what your winter bills look like. Here is how to find it before you buy.
Picture two lines on a graph. One is your house’s heat loss. It goes up as the outside temperature goes down. The other is the heat pump’s output. It goes down as the outside temperature goes down.
Where they cross is the balance point. Warmer than that, the heat pump has more than enough. Colder, the house is losing heat faster than the heat pump can make it, and the backup has to cover the gap.
The CSA F280 heat loss gives you the house line. The manufacturer’s extended data gives you the heat pump line. Put them together and you know where the crossing is.
The big number on the box is measured at a mild temperature. At -20 C a cold-climate unit might put out a lot less. Size from the cold-weather numbers, not the box.
Take a house near Barrie with a design temperature of -24 C and a calculated heat loss of 40,000 BTU per hour at that temperature. Say the heat pump you are looking at puts out 26,000 BTU per hour at -24 C, from the manufacturer’s data.
At design temperature you are short 14,000 BTU per hour. That is what the backup has to cover on the coldest night. With typical numbers the two lines cross somewhere around -12 C, and above that the heat pump carries the house alone.
These numbers are an example only. Your house and your heat pump will be different. That is the point: you need both real numbers to know.
The heat pump does it all. Most of an Ontario heating season is spent up here, which is why heat pumps save money even with backup.
The backup kicks in for the gap. The colder it gets, the more it does. In most of Southern Ontario that is the coldest stretches of January and February, not the whole winter.
The worst case the code sizes for. Heat pump output plus backup must at least equal the heat loss here.
Simple and cheap to install. Expensive to run on the coldest nights, and they add load to your electrical panel. Size them to the gap, not bigger.
A hybrid or dual-fuel system. The heat pump runs most of the year, the furnace takes over below a set temperature. See hybrid heat pump design.
Common off the gas line. Works the same way as a gas hybrid, at propane prices. See propane heating design.
Great comfort and real backup in a power failure. Needs its own permit and clearances, and someone home to feed it.
The thermal balance point is where the heat pump runs out of capacity. The economic balance point is where it becomes cheaper to burn gas or propane than to run the heat pump, given your prices.
With a hybrid system, the switchover is usually set somewhere near the economic point. Utility rates change, so the right setting can change too. Your installer can adjust it.
Insulation moves both points. Lower the heat loss and the heat pump carries more of the winter alone. That is why we often run the heat loss twice: as the house is, and with the upgrades you are considering.
Shopping for a heat pump? Get the heat loss first. Then you can check any quote against the real cold-weather numbers.
Get Free Quote →It is the outdoor temperature where the heat pump’s output exactly matches the heat the house is losing. Above it, the heat pump carries the house alone. Below it, something else has to help.
Most do, at least for the coldest nights. Cold-climate units keep working well below freezing, but their output drops as it gets colder. At your design temperature, many will not cover the full heat loss on their own.
The thermal balance point is where the heat pump runs out of capacity. The economic one is where it becomes cheaper to burn gas or propane than to run the heat pump. With a hybrid system you set the switchover around the economic one.
Big enough to cover the gap between the heat pump’s output and the house’s heat loss at your design temperature. Some owners size backup to carry the whole house in case the heat pump fails. That is a cost and comfort decision.
In the manufacturer’s extended performance data, and for many cold-climate models in the NEEP product list. Look for output at -15 C and lower, not the nameplate number.
Yes. A lower heat loss moves the balance point colder, so the heat pump carries more of the winter alone. That is one reason envelope upgrades and heat pumps go well together.
Send us your plans or a sketch. We calculate the heat loss at your design temperature so you and your installer can find the balance point and size the backup right.