Heat Pump Electrical Load Calculator

A heat pump electrical load calculation converts the heat pump’s minimum circuit ampacity basis and auxiliary electric heat rating into a common VA load, then expresses that combined load as current at the selected system voltage and phase arrangement.

The primary result is Panel load current. It provides an early planning value for reviewing available panel or feeder capacity, comparing connected HVAC demand with an existing load schedule, and identifying whether a larger feeder, panelboard, raceway, or service-load review may be required.

This calculation is particularly useful when the outdoor or indoor equipment nameplate provides Heat pump MCA and the auxiliary heat package is identified in kW. It is not a replacement for the manufacturer’s required branch-circuit conductor and overcurrent-protection instructions.

Equipment and Auxiliary Heat Inputs

The calculator uses these inputs:

Input	Electrical purpose
Heat pump MCA	The minimum circuit ampacity or verified nameplate current basis for the heat pump equipment
Auxiliary heat	The electric heat load in kW
System voltage	The voltage used to convert between current and apparent power
Phase	Selects single-phase or balanced three-phase current math

Heat pump MCA is entered in amperes and converted to volt-amperes using the selected System voltage. This creates a common load basis that can be added to the auxiliary electric heat.

Auxiliary heat is entered in kilowatts. Electric resistance heat is converted directly from kW to VA for this worksheet’s load arithmetic:

\(\displaystyle \text{Auxiliary heat load (VA)} = \text{Auxiliary heat (kW)} \times 1{,}000\)

The combined VA is then converted into the estimated current shown as Panel load current.

Load Calculation Formula

For the heat pump equipment portion:

\(\displaystyle \text{Heat pump equipment load (VA)} = \text{Heat pump MCA (A)} \times \text{System voltage (V)} \times k_{\phi}\)

For auxiliary electric heat:

\(\displaystyle \text{Auxiliary heat load (VA)} = \text{Auxiliary heat (kW)} \times 1{,}000\)

The calculator combines both loads:

\(\displaystyle \text{Total heat pump load (VA)} = \text{Heat pump equipment load (VA)} + \text{Auxiliary heat load (VA)}\)

With Single-phase selected, panel current is:

\(\displaystyle \text{Panel load current (A)} = \frac{\text{Total heat pump load (VA)}}{\text{System voltage (V)}}\)

With balanced three-phase selected, current is calculated using three-phase apparent-power math:

\(\displaystyle \text{Panel load current (A)} = \frac{\text{Total heat pump load (VA)}}{\sqrt{3} \times \text{System voltage (V)}}\)

The phase selection changes the equipment VA conversion and the panel-current conversion method. It does not change the entered heat pump MCA or the auxiliary heat kW.

Calculation Example

Use the following values:

Field	Value
Heat pump MCA	24 A
Auxiliary heat	10 kW
System voltage	240 V
Phase	Single-phase

First, convert the heat pump MCA basis to volt-amperes:

\(\displaystyle 24\text{ A} \times 240\text{ V} = 5{,}760\text{ VA}\)

Then convert the auxiliary heat rating:

\(\displaystyle 10\text{ kW} \times 1{,}000 = 10{,}000\text{ VA}\)

Add the two loads:

\(\displaystyle 5{,}760\text{ VA} + 10{,}000\text{ VA} = 15{,}760\text{ VA}\)

Finally, calculate the single-phase current:

\(\displaystyle \frac{15{,}760\text{ VA}}{240\text{ V}} = 65.6667\text{ A}\)

The calculator result is:

Result	Value
Heat pump equipment load	5,760 VA
Auxiliary heat load	10,000 VA
Total heat pump load	15,760 VA
Panel load current	65.6667 A

For an early panel-load review, the heating system contributes approximately 65.67 A at 240 V single-phase on the calculator’s combined-load basis.

Panel, Feeder, and Raceway Planning

Panel load current is useful when reviewing the electrical path serving the HVAC equipment:

• Compare the calculated current with available panelboard or feeder capacity during an upgrade, replacement, or load-addition review.
• Convert the HVAC heating load into a VA value that can be placed alongside other connected loads on a panel schedule.
• Identify when feeder conductor ampacity, conductor size in AWG or kcmil, raceway fill, and conduit routing may need further design review.
• Establish a current basis for preliminary voltage-drop calculations on long branch-circuit or feeder runs.
• Compare the electrical effect of different auxiliary heat kW packages before equipment selection is finalized.

The result does not itself select a conductor, breaker, disconnect, or raceway size. Those decisions depend on the complete installation and the equipment manufacturer’s listing and instructions.

Field Verification

Verify Heat pump MCA from the applicable equipment nameplate or verified manufacturer documentation. MCA is an equipment-specific value used for minimum branch-circuit conductor ampacity; it should not be substituted with a guessed running current, compressor FLA, or a generic heat-pump amperage estimate.

Verify that Auxiliary heat represents the electric heat load actually installed. Air handlers may accept multiple heater-kit sizes, and the installed kW package can differ from a base air-handler rating.

Confirm the actual system voltage and whether the equipment load is properly represented by the selected Phase. A nominal 240 V single-phase system and a balanced three-phase system use different current calculations even when the total VA is the same.

For final design and inspection, separately evaluate the manufacturer’s minimum circuit ampacity, maximum overcurrent protection, terminal rating, insulation temperature rating, conductor ampacity, adjustment factor, correction factor, current-carrying conductors, voltage drop, disconnecting means, and applicable AHJ requirements. The calculator performs the stated VA and current arithmetic; it does not determine code compliance or equipment-specific branch-circuit protection.

Related calculations: Electrical Panel Load Calculator, Service Upgrade Calculator, Electrical Load Calculator.