Balance point
The outdoor temperature at which a heat pump's output exactly matches the building's heat loss. Below it, the system needs auxiliary heat or longer run times, so a complaint that appears during a cold snap can describe correct operation rather than a fault.
Also called thermal balance point
What is a heat pump balance point?
The balance point is the outdoor temperature at which a heat pump's output exactly equals the building's heat loss. Below it, the system needs help; above it, it has capacity to spare.
Balance point: how it works
Two lines cross. A building loses more heat as it gets colder outside, while a heat pump delivers less. Plot both against outdoor temperature and the crossing point is the balance point. Above it the heat pump has spare capacity; below it there is a shortfall, and something has to make it up.
Where you meet the term
- In a design calculation, where equipment is selected so the balance point sits at an acceptable temperature for the climate.
- In a cold snap complaint, where reduced comfort below the balance point is expected rather than faulty.
- In an auxiliary heat lockout setting, where the configured temperature should relate to the actual balance point.
How to check it
- Note the outdoor temperature when comfort slips. A consistent temperature at which the house stops keeping up is an observation of the balance point, and it is exactly what a designer needs. Owner check
- Compare the heat loss calculation with the capacity table. The manufacturer publishes output at several outdoor temperatures. Plotting that against the building heat loss gives the crossing point. Technician
Balance point: what it is not
- A balance point is not a fixed property of the equipment. It belongs to the pairing of that equipment with that building at that set point.
- Reaching the balance point is not a fault. It is the temperature the design accepted when the equipment was selected.
Balance point questions
Why does my heat pump keep up until a certain temperature and then stop?
That temperature is the balance point. Above it the equipment has spare capacity, below it the building loses more than the heat pump can deliver, and the difference has to come from auxiliary heat or from longer run times.
Can the balance point be lowered?
Either by reducing the building's heat loss through insulation and air tightness, or by installing equipment with more output at low temperatures. Improving the fabric moves the whole loss line rather than just the crossing point.
Should the auxiliary lockout be set at the balance point?
It is the sensible reference. A lockout set well above the balance point brings expensive backup heat in while the heat pump still had capacity to spare.
Where this definition comes from
Written from government guidance, manufacturer support article material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
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