Heat Pump Electrical Requirements: Circuits, Breakers and the 2026 GFCI Change

Homeowners usually find this page after an installer says the words “you may need a panel upgrade,” or after a quote comes back with an electrician’s line item that costs more than expected. Both are normal. Heat pumps are the largest new electrical load most houses have added since the clothes dryer, and the wiring side of the job is where quotes diverge the most.

The good news is that the rules are readable. The equipment manufacturer has already done the hard math and printed the answer on the side of the box. Your job as the homeowner isn’t to do the calculation — it’s to know what the numbers mean, so you can tell whether the person doing the work is reading them correctly.

This guide goes deep on the electrical side alone. For the rest of the project — the load calculation, the refrigerant work, the commissioning — see our step-by-step installation walkthrough. For where the equipment physically goes, see our indoor and outdoor placement guide.

MCA and MOP: the only two numbers that matter

Walk out to your outdoor unit and look at the metal or foil label on the side of the cabinet, usually near the electrical access panel. Among the model number, serial number and refrigerant charge, you’ll find two lines that look something like MCA 22.6 and MOP 35 (some brands write “Max Fuse/HACR Breaker” instead of MOP, and some write MOCP). Those two values are the whole electrical spec.

MCA — Minimum Circuit Ampacity is the smallest conductor ampacity that can safely feed the unit. Wire is chosen so that its rated ampacity is at or above the MCA. The manufacturer has already built in the code multipliers: 125% of the largest motor load plus the remaining loads at 100%. That’s why the MCA is always higher than the amps the unit actually draws while running. You never add another safety factor on top — that’s already in there.

MOP — Maximum Overcurrent Protection is the biggest breaker or fuse allowed on that circuit. It exists because a compressor’s startup surge would trip a breaker sized purely to the running current. So the code lets the overcurrent device be considerably larger than the wire’s ampacity for this specific class of equipment, and the equipment’s own internal protection handles the rest.

That combination trips up people who know general wiring rules. On a normal 15-amp lighting circuit, the breaker and the wire match. On a heat pump circuit, a 35-amp breaker sitting on conductors rated 30 amps can be entirely correct, because the branch-circuit rules for air-conditioning and refrigeration equipment work differently from ordinary circuits. If someone tells you the breaker looks “too big for that wire,” they may simply be applying the wrong article of the code.

The BTU rating tells you how much heat the unit moves. It tells you nothing about how much current it draws. Two 3-ton heat pumps from different brands can want very different circuits.

— Why a tonnage-based wiring chart is always a guess

There’s one more rule that surprises people. When the MOP isn’t a standard breaker size — say the nameplate reads 27.6 — you go down to the next standard size, not up. A 25-amp breaker is legal; a 30-amp breaker exceeds the maximum. It’s the opposite of the habit most people have from sizing other loads.

A worked example, start to finish

Here’s how a real circuit gets sized. Say the nameplate on a mid-size ducted heat pump reads MCA 22.6 and MOP 35, at 208/230V single phase.

1. Start with the MCA for the wire

   The conductors need an ampacity of at least 22.6 amps. In a typical residential installation with 75°C-rated terminations, 12 AWG copper is rated 25 amps and 10 AWG copper is rated 35 amps. Both clear 22.6, so both can be code-compliant on paper.

2. Check the run length before you settle

   If the outdoor unit is 30 feet from the panel, 12 AWG is fine. If it’s 90 feet away around the side of the house, voltage drop pushes most electricians to 10 AWG. Longer runs generally get upsized a gauge.

3. Take the MOP for the breaker

   The largest allowed device is 35 amps, and 35 is a standard size, so a 35-amp two-pole HACR-rated breaker is the normal choice. A 30-amp breaker would also be legal here because it’s still above the MCA — but going smaller narrows the margin against startup surges, so most installers use the MOP value.

4. Confirm the breaker type

   Heat pump circuits generally call for a HACR-rated breaker. Nearly every modern residential breaker carries that marking, but on an older panel it’s worth confirming rather than assuming.

5. Add the disconnect and the whip

   A fused or non-fused disconnect goes on the wall within sight of the unit, with a short flexible whip from the disconnect to the equipment’s electrical box.

6. Do the same for the air handler

   The indoor unit gets its own separate circuit, sized from its own nameplate — and that’s the one that gets big if there are backup heat strips.

Notice what never entered the calculation: the tonnage, the SEER2 rating, the square footage of the house. If you want to understand what those numbers do control, our SEER2 and HSPF2 explainer and sizing guide cover that ground.

115V vs. 230V, and which sizes use which

Residential heat pumps run on one of two supplies. The smaller end of the ductless market offers 115V models — the same voltage as a wall outlet. Everything else, including essentially all central ducted systems, runs on 208/230V, which needs a two-pole breaker and both hot legs from your panel.

As a rough guide, single-zone mini-splits at 9,000 and 12,000 BTU/h are commonly available in a 115V version, and some 18,000 BTU/h units are too. Above that, 208/230V is effectively universal. Multi-zone systems are always 230V. Central heat pumps are always 230V.

The 115V option is genuinely useful in a garage, a workshop or an addition where running a new 240V circuit would mean opening walls. It is not free of trade-offs. A 115V unit draws roughly twice the current of an equivalent 230V unit for the same output, so it’s more sensitive to long wire runs and it eats more of a small panel’s capacity than the wattage suggests. Efficiency ratings on 115V versions of the same model are also often slightly lower. If you’re weighing this for a detached space, our garage mini-split guide goes through the trade-offs in context.

One thing a 115V unit does not get you is permission to plug into an existing outlet. Even the plug-in models are meant to have a dedicated circuit of their own, which we’ll come back to next.

Why every unit needs its own circuit

A dedicated circuit means one breaker feeding one piece of equipment and nothing else. No shared receptacles, no lights tapped off it, no second unit doubled up. Both the equipment’s listed installation instructions and the branch-circuit rules for air-conditioning equipment point the same direction, and installation instructions are themselves enforceable — an inspector can fail work that ignores them.

There are practical reasons behind the rule. A compressor starting up briefly pulls several times its running current. On a shared circuit, that surge shows up as a voltage sag that dims lights and can drop out electronics on the same run. Worse, the combined load can sit right at the breaker’s limit, so the breaker warms up and eventually trips on a hot afternoon for no obvious reason. Repeated thermal cycling shortens a breaker’s life.

Inverter-driven equipment adds another wrinkle. A modern variable-speed heat pump is a big switching power supply with a compressor attached. It’s electrically noisy, and it’s happiest on a clean, dedicated feed with a solid ground. Sharing a circuit with a laser printer or a well pump is a recipe for odd, hard-to-diagnose faults.

In a full system you should expect at least two circuits, sometimes three:

• Outdoor unit — one dedicated 208/230V circuit, sized from the outdoor nameplate.
• Indoor air handler or furnace — its own circuit. Small if there are no heat strips, large if there are.
• Condensate pump, UV light or a service receptacle — sometimes a third small circuit, depending on the install.

Ductless systems are a little different. On most single-zone mini-splits, the power lands at the outdoor unit and the indoor head is fed from it through the interconnecting cable, so one circuit covers both. On multi-zone systems it’s usually still one circuit at the outdoor unit, but check the manual — a few designs power the heads separately.

Reading your panel: slots, amps and headroom

Open the panel door — the outer cover with the breaker handles showing, not the inner cover that exposes live bus bars. You’re looking for three things.

The main breaker rating. It’s the biggest breaker, usually at the top, and it’ll be stamped 100, 125, 150 or 200. That’s your service size. A 100-amp service is the usual sticking point; 200 amps is the modern standard and generally has room for a heat pump.

Free slots. Count the empty spaces where a breaker could go. A 208/230V heat pump circuit needs two adjacent slots for a two-pole breaker. Two circuits — outdoor and air handler — need four. If the panel looks full, look for tandem breakers already installed (two thin switches in one slot) and read the panel’s own label, which states the maximum number of circuits the panel is rated for. A panel can be physically full but electrically fine, which is a much cheaper problem: a subpanel adds slots without touching the utility service.

Whether the load actually fits. This is the part you can’t eyeball. An electrician runs a service load calculation that adds up your existing loads with the code’s demand factors, then adds the new heat pump and any heat strips. The result either fits under your service rating or it doesn’t. Homes with an electric range, an electric water heater and an electric dryer already on a 100-amp service are the ones most likely to come up short — especially if an EV charger is anywhere in the plan.

There is a third path worth asking about. Circuit-sharing devices and smart panel controllers can let a heat pump and, say, an EV charger coexist on a service that couldn’t otherwise carry both, by never letting them run at full tilt at the same time. Availability and code acceptance vary by jurisdiction, and not every electrician stocks them, but in an older home it can be dramatically cheaper than a service upgrade. Costs for both routes are covered in our 2026 installed cost guide, and some utility programs still help with panel work — see current rebates.

Backup heat strips: the load nobody counts

Here’s the single most common reason a heat pump project turns into a panel project. Most ducted heat pumps in a heating climate pair with an air handler containing electric resistance heat strips — the backup that runs during defrost and on the coldest nights. They’re typically sized between 5 kW and 20 kW, and they are enormous electrical loads compared with the heat pump itself.

Run the numbers. A 10 kW heat strip package at 240V draws roughly 42 amps. Because it’s a continuous load, the circuit is sized at 125% of that, which lands near 52 amps and calls for a 60-amp breaker on 6 AWG copper. A 15 kW package pushes past 78 amps. A 20 kW package can exceed 100 amps and is normally split across two circuits.

Put that beside a 3-ton outdoor unit on a 30-amp circuit and you can see the imbalance. The compressor — the thing that does almost all the work, almost all the time — is the small load. The backup that runs a handful of hours a year is the load that forces the panel upgrade.

That’s why it’s worth pushing back on oversized strips. Installers sometimes default to the largest package the air handler accepts, on the theory that it’s cheap insurance. But every extra kW of strip heat is load on your service, and it’s the most expensive heat in the house to actually run. A properly sized cold-climate heat pump with a good Manual J load calculation behind it may need far less backup than the default. In milder climates some homes need none at all beyond what defrost requires.

The disconnect within sight of the unit

Every outdoor unit needs a disconnecting means — a switch, a pull-out block or a breaker in a weatherproof enclosure — mounted so a technician standing at the equipment can see it and reach it. The code’s phrase is “in sight from,” and it has a specific meaning: visible from the equipment and not more than 50 feet away. Both conditions have to be true. A disconnect around the corner of the house, 15 feet away but out of view, doesn’t satisfy it.

The reason is straightforward safety. Someone opening a live cabinet to service a compressor needs to be able to kill power without walking to a basement panel and trusting that nobody flips it back on while they’re working.

Practical points that come up on real installs:

• Mount the disconnect on the wall beside the unit, not on the unit itself, and not behind it where the equipment blocks access.
• Leave the service clearance in front of it clear — that’s the same space the technician needs to pull the electrical panel on the heat pump.
• Fused or non-fused both exist. Which one you need depends on whether the branch circuit’s overcurrent protection is adequate on its own, which is your electrician’s call from the nameplate.
• The whip from the disconnect to the unit should be a listed flexible assembly, properly supported, with the connector torqued down so water doesn’t track in.
• For ductless indoor heads, there’s often no separate indoor disconnect because the head is fed from the outdoor unit — but the outdoor disconnect still has to meet the rule.

When you’re deciding where the outdoor unit goes, remember the disconnect has to go somewhere too. Tucking a condenser into a tight side-yard alcove sometimes leaves nowhere legal to put it. Our placement guide covers the clearance side of that decision in detail.

Wire gauge, long runs and voltage drop

Ampacity gets you a legal wire size. Voltage drop gets you a wire size that works well. They’re not the same thing, and the difference shows up on long runs.

Electricity loses a little voltage over distance. On a short run it’s irrelevant. On a 120-foot run to a detached garage it can be enough that the compressor sees noticeably less than nameplate voltage, which makes it draw more current, run hotter and start harder. The widely used target is to keep branch-circuit voltage drop at or under 3%. In the National Electrical Code that target sits in an informational note rather than a hard requirement, so it’s guidance an electrician applies with judgment — but it’s guidance worth insisting on for equipment you want to last 15 years.

Two caveats on that table. Aluminum conductors carry roughly one gauge less than copper for the same ampacity and drop more voltage over the same distance, so an aluminum feeder gets upsized. And ampacity itself gets reduced when conductors run through hot attics, when several circuits share a conduit, or when the terminations are only rated 60°C — all of which an electrician accounts for and none of which you can read off a chart.

The 115V case deserves a separate warning. Because voltage drop is measured as a percentage of a smaller number, a 115V mini-split tolerates roughly a quarter of the run length a 230V unit does before hitting the same 3%. A 115V unit 60 feet from the panel on 14 AWG is already marginal. If the equipment is far from the panel, 230V is the better answer even when a 115V model exists.

The 2026 GFCI change (NEC 210.8(F))

This is the live issue in 2026, and it’s worth understanding because it may change what your installer has to put on the wall.

The 2020 edition of the National Electrical Code added section 210.8(F), requiring GFCI protection for outdoor outlets on dwelling-unit branch circuits. The word “outlet” in code language doesn’t just mean a receptacle — it means any point where current is taken to supply equipment. That definition swept in hardwired outdoor air conditioners and heat pumps, which had never needed GFCI protection before.

The industry pushed back, and the code added an exception: GFCI protection wasn’t required for listed HVAC equipment. But the exception carried an expiration date written into the text — September 1, 2026. That date has now passed. The 2026 edition of the code keeps the same expiring exception and adds an alternative compliance path using special-purpose GFCI devices.

Why ordinary GFCIs and inverter heat pumps fight

The technical problem is real and it isn’t a defect. Variable-speed, inverter-driven equipment uses power electronics with EMI filtering, and those filters intentionally shunt a small amount of high-frequency current to ground. It’s by design and it’s harmless. But a standard Class A GFCI is built to protect people, so it trips at roughly 4 to 6 milliamps of imbalance. Several inverter units on one system, or one unit with long line runs, can produce enough steady leakage to sit near that threshold — and the device trips for no fault at all.

That’s not a theoretical annoyance. A heat pump on a nuisance-tripping GFCI is a heat pump that’s off when you get home in January, and it’s a service call that finds nothing wrong.

The two devices that actually work

Two compliance paths have emerged for equipment that leaks by design:

The “HF” marking is the one to remember. It signals a device evaluated to handle high-frequency leakage from electronic loads while still giving full personnel protection against a genuine 60 Hz ground fault. The Class C special-purpose device sits at a higher threshold — around 20 mA — which is equipment protection rather than personnel protection, and it’s permitted only where the code specifically allows it.

The practical takeaway for a homeowner: if you’re getting a heat pump installed in the second half of 2026, ask your contractor one direct question — “does my jurisdiction require GFCI protection on this circuit, and if so, what device are you using?” A vague answer is a reason to keep asking. Reports of availability suggest residential-format compliant devices were still filtering into distribution around the deadline, so this is a genuine scheduling risk on some projects, not just paperwork.

Permits, inspection and what gets checked

Almost everywhere in the US, adding a new branch circuit requires an electrical permit, and installing a heat pump requires a mechanical permit. Sometimes they’re pulled together, sometimes by two different trades. The contractor pulls them; you shouldn’t be pulling permits for a licensed contractor’s work.

Skipping the permit is a genuinely bad idea even when it saves a few hundred dollars and a week. Unpermitted electrical work surfaces at the worst moments: when you sell and the buyer’s inspector flags it, when a homeowner’s insurance claim is investigated after a fire, and — very practically — when you apply for a utility rebate. Most rebate and financing programs require proof of a permitted, inspected installation. Our 2026 rebate guide and financing overview both assume permitted work.

What an electrical inspector typically looks at on a heat pump job:

• Conductor size against the nameplate MCA, and the overcurrent device against the MOP.
• A dedicated circuit with no shared loads.
• The disconnect’s location, type and working clearance.
• Proper grounding and bonding, and correct connections at the equipment lugs.
• Weatherproof fittings, correct outdoor-rated enclosure, no water path into the conduit.
• Panel labeling — the new circuit identified on the directory.
• Whatever the local rule currently says about GFCI protection.

The inspection usually happens after the mechanical work is complete but sometimes in two visits, with a rough-in inspection before anything is closed up. Build the schedule into your expectations: a failed inspection and a re-inspection can add a week.

7 expensive electrical mistakes

Frequently asked questions

Your final checklist

Once the circuit design is settled, the next decision is physical: where the outdoor unit sits, how high off the ground, and where the indoor head goes. Those choices affect comfort and noise more than most people expect — our heat pump placement guide covers both ends. And if you’re still choosing equipment, how heat pumps work and our 2026 top picks are the right places to start.