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Do You Need a New Electrical Panel for a Heat Pump?

The heat pump fits. The backup heater doesn't.
Adding up what runs at once: the heat pump fits the panel, the 10 kW backup heater does not.

Ask about a heat pump and somebody will tell you that your 100-amp panel has to go first. Usually it does not. If your house already has central air conditioning, the heat pump itself almost always fits the panel you have. What does not always fit is the electric backup heater that gets installed next to it.

The heat pump is the easy part

A heat pump is an air conditioner that can run backwards. In summer it moves heat out of the house, in winter it moves heat in. The outdoor unit draws about the same power as the air conditioner it replaces, and it plugs into the same 240-volt circuit. Newer inverter models often draw less at start-up, because they ramp up gently instead of slamming on.

Your electrical panel is like the main water pipe into your house. It does not care how many faucets you own. It only cares how many are running at the same time.

That is why the backup heater matters. On the coldest nights, and for a few minutes while the outdoor unit melts frost off itself, an electric heating element in the indoor unit switches on. A common 10 kW element draws as much power as about seven hair dryers running at once. That one item, not the heat pump, is what pushes an older panel over the line.

The most common mistake I see is a homeowner who calls three installers and gets three different panel verdicts, because nobody actually ran the numbers. The one who asked for a year of utility data was the one who got it right.

A new 200-amp panel typically runs $1,500 to $4,000 in the US, and more if the utility has to touch the service drop. That is real money, so it is worth finding out whether you need it before anyone assumes you do.

How to check before you sign anything

Open the panel door and read the number on the big main breaker at the top. 100, 150 or 200 is your panel size. If you see round fuses instead of breakers, plan on an upgrade no matter what you install.

Ask your utility for a year of peak demand data. Many smart-meter portals show it in 15-minute steps. This is the figure the electrician needs, and it is what the electrical code lets them use to prove your existing house fits.

Ask the installer how big the backup heater is and whether it can be smaller. A cold-climate heat pump sized for your heating load may need only a small element, or none. If you have a working gas furnace, keeping it as the backup (dual fuel) removes the electric heater from the picture entirely.

Ask for a load calculation for the house, not a like-for-like swap. Today's inverter heat pumps put out more heat per ton than the 20-year-old unit they replace, so the right size is often smaller.

On a two-story house I looked at last winter, the 10 kW heater the installer had quoted out of habit turned into a 5 kW one after we ran the load calculation, and the 100-amp panel stayed. 

Anything inside the panel, and the load calculation that goes with it, is licensed electrician work with a permit. Your job is to bring the demand data and the questions. Theirs is to sign the math.

Go deeper: the load calculation that decides it

The US National Electrical Code gives two shortcuts for adding load to an existing house. NEC 220.87 takes the highest 15-minute demand recorded over the past 12 months (or 30 days of recording that covers the heating or cooling season), multiplies it by 125 percent, and adds the new load at nameplate. Without meter data, NEC 220.83(B) applies demand factors to a nameplate tally instead.

Worked example on a 100 A, 240 V service (24 kVA). Metered peak 9.6 kW, times 1.25, is 12 kVA or 50 A. A 3-ton inverter heat pump with a minimum circuit ampacity (MCA) of 25 A adds 6 kVA (a current Bosch 3-ton unit lists 26.3 A MCA, 45 A maximum breaker). Total 75 A. It fits. A 10 kW resistance heater adds 41.7 A more, total 117 A, and it does not. A 5 kW element lands at 96 A, in with little to spare. Dual fuel with the furnace kept as backup stays at 75 A.

The 2023 NEC added a third route. Section 220.70 lets an energy management system that limits service current per 750.30 count as a single continuous load equal to its ampere setpoint. In practice, a load-management relay that sheds the strip heat when the house nears its limit.

My own preference in a house with a working gas furnace is dual fuel. The panel question disappears, and the furnace only runs on the few coldest days.

Why this is news this week. Midea's David Rames told ACHR News on 16 September that existing panels usually are not the barrier people assume, and that his company's cold-climate heat pump needs the same maximum overcurrent protection as a conventional air conditioner. AHRI's July figures, out 14 September, put heat pumps at 45.1 percent of central air conditioner and heat pump shipments, 413,679 units in the month and up 17.6 percent on a year earlier. California's SB 222, a statewide heat pump permitting standard for roughly 600 local jurisdictions, awaits the governor's decision by September 30, 2026. Gone is the federal 25C credit (up to $2,000 for a heat pump, $600 for a 200 A panel), which covers only equipment placed in service before the end of 2025.

ScenarioTotal loadAmps at 240 VFits a 100 A panel?
House today, 125% of 9.6 kW peak12 kVA50 AYes
Plus heat pump (25 A MCA)18 kVA75 AYes
Plus 5 kW backup element23 kVA96 AYes, barely
Plus 10 kW backup element28 kVA117 ANo
Dual fuel, gas furnace as backup18 kVA75 AYes

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