What is the balance point?

The outdoor temperature where heat pump output exactly meets the home's heat loss.

Where do I find capacity at 17 °F?

In the AHRI/NEEP cold-climate listing or the maker's extended tables.

What design temperature should I use?

The ASHRAE 99% heating design temperature for your location.

Why does capacity drop in the cold?

There's less heat to extract from colder air.

Is a high balance point bad?

It means more hours on backup and higher bills.

How much does strip heat cost?

1 kW of strip heat uses 1 kW; a heat pump uses 2–4× less per kW of heat.

Heat pump balance point calculator

Design load, design and indoor temperatures, and heat pump capacity at 7 °C and −7 °C (45 °F and 19 °F): you get the balance point and backup heat at design conditions.

Backup heat at design temperature

7301.983 BTU/h

Balance point-0.7 °C
Load at balance point22588.378 BTU/h
Heat pump capacity at design temperature19995.15 BTU/h
Backup heat needed at design temperature7301.983 BTU/h

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How it's calculated (visible formula)

load(T) = design load × (Ti − T) ÷ (Ti − Td); capacity linear between 7 °C and −7 °C; balance where load = capacity

Net geometric measurement, no waste.
Adjustable waste % for cuts and breakage.
Purchase rounded up to sellable units (boxes, bags, buckets, boards).

See methodology and formula versions

How to calculate it, step by step

Work out the heating load at outdoor design temperature.
Set the indoor setpoint.
Look up heat pump capacity at 47 °F and 17 °F (or 7 °C / −7 °C).
Find where load and capacity meet.
Work out backup heat needed on the coldest day.

Worked example: 8 kW load at 23 °F (−5 °C), 68 °F indoors, 8 kW at 45 °F and 5.5 kW at 19 °F

Load: 0.32 kW per °C
Capacity: 5.5 + 0.179 × (T + 7)
Equal at −0.7 °C

→ Balance point ≈ 31 °F; at 23 °F you need 2.1 kW (7,300 BTU/h) of backup.

Common mistakes

Using rated 47 °F capacity all winter.
Ignoring defrost cycles below about 40 °F.
Using another region's design temperature.

Pro tips

In cold climates choose a cold-climate certified model.
Backup can be electric strips or the existing furnace.
Shelter the outdoor unit from wind and allow defrost drainage.
Better insulation lowers the balance point and backup need.

From calculation to quote

Add labor, overhead and your margin, and generate the professional PDF.

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FAQs

What is the balance point?: The outdoor temperature where heat pump output exactly meets the home's heat loss.
Where do I find capacity at 17 °F?: In the AHRI/NEEP cold-climate listing or the maker's extended tables.
What design temperature should I use?: The ASHRAE 99% heating design temperature for your location.
Why does capacity drop in the cold?: There's less heat to extract from colder air.
Is a high balance point bad?: It means more hours on backup and higher bills.
How much does strip heat cost?: 1 kW of strip heat uses 1 kW; a heat pump uses 2–4× less per kW of heat.

Sources and standards

Maintained by Srikanta M · Formula v1.0.0 · Verified 2026-09-10 · Updated 2026-09-10 · Limits: quantity estimation, not structural design or site supervision.