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Calculate heat strip size in kW from heating load and heat pump output. Use our Heat Strip Size Calculator for fast, simple HVAC sizing.
| Term | Meaning | Notes |
|---|---|---|
| Q_load | Design heating load (BTU/hr) | From a proper Manual J load calculation |
| Q_HP | Heat pump output at design temp (BTU/hr) | Use manufacturer's data at the actual design temperature, not the nominal 47°F rating |
| Q_deficit | Q_load − Q_HP (clamped at 0) | Shortfall the strip must cover |
| 1 kW | 3,412.14 BTU/hr | Electric resistance heat conversion |
| 1 BTU/hr | 0.000293071 kW | Inverse conversion |
A Heat Strip Size calculator helps you find the electric heat strip capacity needed when a heat pump cannot meet the full heating load. It gives the required heat strip size in kW.
The calculator uses two main values. You enter the design heating load and the heat pump output at the design temperature. It then finds the heating gap and converts that gap into kW.
This makes heat strip sizing quick and easy for HVAC planning.
The core Heat Strip Size formula used by our calculator is:
Heat Strip Size (kW) = max(0, Design Heating Load − Heat Pump Output) ÷ 3412.14
The load and heat pump output must first be converted to BTU/hr.
The calculator uses:
1 kW = 3412.14 BTU/hr
So, if the heat pump already meets the heating load, the required heat strip size is 0 kW.
For example, if the heating load is 45,000 BTU/hr and the heat pump supplies 16,200 BTU/hr:
Heating Deficit = 45,000 − 16,200
Heating Deficit = 28,800 BTU/hr
Heat Strip Size = 28,800 ÷ 3412.14
Heat Strip Size = 8.44 kW
The next available standard size in the calculator is 8.5 kW.
Using our online Heat Strip Size in kW calculator is simple.
The calculator shows the heating deficit, required heat strip size in kW, and the next standard heat-strip size when available.
Suppose a home has a design heating load of 45,000 BTU/hr. The heat pump provides 16,200 BTU/hr at the design temperature.
First, find the heating deficit:
45,000 − 16,200 = 28,800 BTU/hr
Now convert the deficit to kW:
28,800 ÷ 3412.14 = 8.44 kW
Therefore:
Required heat strip size = 8.44 kW
The calculator checks its standard heat strip size chart. Since 8 kW is too small, the next listed size is:
Standard heat strip size = 8.5 kW
The Heat Strip Size calculator finds the supplemental electric heat capacity needed after the heat pump's output is considered. Its core formula is simple:
Heat Strip Size = max(0, Heating Load − Heat Pump Output) ÷ 3412.14
The result is given in kW. The calculator also checks the result against its built-in standard heat strip sizes.
Keep in mind that heat strip size is different from heat strip wire size and heat strip breaker size. Electrical wiring and breaker selection need to follow the equipment data and applicable electrical requirements. Likewise, a heat tape calculator chart or heat trace sizing calculator uses different calculations and should not be substituted for heat-strip sizing.
A Heat Strip Size calculator finds the required electric heat-strip capacity in kW based on the heating load and heat pump output.
Heat Strip Size (kW) = max(0, Heating Load − Heat Pump Output) ÷ 3412.14, after converting both values to BTU/hr.
The calculator uses 3,412.14 BTU/hr per kW.
If the heat pump output equals or exceeds the design heating load, the calculator returns 0 kW of required heat-strip capacity.
No. Heat strip size measures heating capacity. Wire size depends on electrical load, voltage, installation conditions, and applicable electrical requirements.
Yes. The calculator subtracts heat pump output from the design heating load. A lower heat pump output creates a larger supplemental heat requirement.
A heat pump sizing chart can help with equipment selection, but it doesn't replace the specific heat-strip calculation. The heat pump's actual output at the design temperature is important.