Heat Pump Economic Balance Point
On your electricity and gas rates, there is a heat-pump COP at which running the heat pump and running the furnace cost exactly the same. Above that break-even COP the heat pump is cheaper; below it — on the coldest days, when COP sags — the furnace takes over. This is the economic switchover a dual-fuel system uses.
Calculator
The economic switchover is at about COP 2.78. Above this COP the heat pump is cheaper; the furnace/backup wins once the COP falls below it as temperatures drop. Estimate — real COP varies with outdoor temperature.
A dual-fuel (hybrid) system pairs a heat pump with a gas furnace and switches between them. Engineers talk about the thermal balance point — the outdoor temperature where the heat pump can no longer keep up. But the economic balance point is often what saves money: the point where the heat pump, whose COP is falling as it gets colder, becomes more expensive to run than the furnace. This tool finds the heat-pump COP at which the two cost exactly the same on your rates. Compare it to the COP your heat pump actually delivers at a given temperature (from its capacity table or the COP-at-temperature tool) to decide which system should be running.
Formula
Set the heat pump's delivered $/MMBTU equal to the furnace's and solve for COP:
break-even COP = electricity price × 100,000 × AFUE ÷ (3,412 × gas price)
Here 100,000 is BTU per therm and 3,412 is BTU per kWh. When the heat pump's real COP is above this break-even value it delivers heat more cheaply than the furnace; when its COP drops below it — typically on the coldest nights — the furnace becomes the cheaper source and a hybrid control should switch over.
Worked example
With electricity at $0.15/kWh, gas at $1.50/therm and a 95% AFUE furnace:
break-even COP = 0.15 × 100,000 × 0.95 ÷ (3,412 × 1.50) = 14,250 ÷ 5,118 = 2.78
So the economic switchover is at about COP 2.78. If your heat pump is running at COP 3.0 (a mild day) it is cheaper than the furnace and should stay on. When a cold snap drags its COP down to, say, 2.5, the furnace becomes the cheaper choice and a dual-fuel thermostat should hand over. Raise the gas price and the break-even COP falls (the heat pump wins more of the season); raise the electricity price and it climbs (the furnace wins sooner).
Putting the balance point to work
This is a purely economic switchover based on delivered $/MMBTU. It assumes the furnace can meet the load on its own once it takes over, which is usually true for a properly sized furnace. It does not account for electric backup strips, defrost cycles, cycling losses or demand charges — real behavior varies, so treat the number as a planning estimate. The COP you enter should be the heat pump's COP at the temperature you care about, not the mild-weather nameplate value.
To use it in practice, pull two or three COP-versus-temperature points from the unit's submittal or expanded performance data, compute each delivered cost with the COP-at-temperature tool, and set your hybrid control's switchover near the outdoor temperature where the real COP crosses this break-even value.