Have you gotten a heat pump quote back with a second, separate number attached to it for electrical work? If you own a home built before roughly 1990 and you are pricing a cold-climate system with electric backup heat, that second number is frequently the one that decides whether the project happens at all.
The equipment itself is rarely the constraint. A 3-ton cold-climate ducted heat pump commonly lists a minimum circuit ampacity between 25 and 35 amps, which is roughly what an existing electric dryer already draws.
What moves the math is the backup heat strip kit sitting inside the air handler above it. A 10 kW kit pulls 41.7 amps at 240 volts on its own, and a 20 kW kit pulls 83.3 amps — more than four-fifths of a 100-amp service before the range, the water heater, or a single light is counted.
A heat pump compressor rarely overloads a panel. Electric backup heat strips do — a 10 kW kit adds 41.7 amps at 240 volts, roughly what a range and a dryer draw together.
Panel Capacity And Service Capacity Are Two Different Numbers
Contractors and salespeople use "panel upgrade" as a catch-all, which hides the fact that four separate things can fail independently. Sorting out which one applies to your house is the difference between an $800 fix and a $5,000 one.
Your service is what the utility delivers — the overhead drop or underground lateral, the meter, and the service-entrance conductors feeding the main disconnect. Your panel is the enclosure on the other side of that disconnect, defined by its busbar rating and the number of breaker spaces inside it.
Only one of the four failure modes requires the utility to get involved, and that distinction drives most of the cost spread. Here is what an electrician is actually evaluating when they pull the deadfront off:
- No free breaker spaces. The service is adequate but the enclosure is physically full. Some panels are listed for tandem breakers in designated slots, and where they are not, a subpanel fed from the existing main solves it without touching the meter.
- Busbar rating too low. A panel can carry a 100-amp bus behind a 200-amp service, or the reverse. The bus rating is stamped on the label inside the door and it caps what the enclosure may carry regardless of what the utility delivers.
- Calculated load exceeds the service. This is the code-driven failure, and it is the one the load calculation is designed to catch. It is also the one most often solved with paperwork and controls rather than copper.
- Obsolete or hazardous equipment. Federal Pacific Stab-Lok and Zinsco panels have documented breaker-trip failures and are typically replaced on sight. Challenger and Pushmatic panels are usually a parts-availability problem instead of a safety one, though the practical outcome is often the same.
Note that a heat pump project can trigger any of these four, and a quote line that reads "panel upgrade — $4,800" tells you nothing about which. Asking your electrician to name the specific constraint is the fastest way to find out whether a cheaper path exists.
What An NEC Load Calculation Actually Measures
A load calculation is not a measurement of how much electricity you use. It is a code-defined estimate of worst-case demand, and it deliberately assumes you will never run everything simultaneously.
For an existing dwelling adding air conditioning or space heating, the governing method is NEC 220.83(B). It counts 100% of the first 8 kVA of general load and 40% of everything above that, then adds the new heating or cooling equipment at 100%.
The most consequential rule inside that method is that heating and cooling are never added together. NEC 220.60 treats them as noncoincident loads, so the calculation takes the larger of the two and discards the smaller entirely.
NEC 220.83(B) counts the first 8 kVA of existing load at 100% and the remainder at 40%, then adds the larger of heating or cooling at 100%. The two are never summed.
NEC 220.82(C) applies parallel logic to the optional method, with one clause that matters enormously for heat pumps specifically. It counts the compressor and the supplemental heat together — unless the controller prevents them from operating at the same time.
That single conditional is the most valuable sentence in the article for anyone sitting on a 100-amp service. It converts a control decision into a code-recognized reduction in calculated load.
NEC 220.82(C) lets you drop supplemental heat from the calculation when a controller prevents the compressor and strips from running together. That interlock can save a service upgrade.
There is also a third path most homeowners never hear about. NEC 220.87 permits sizing an existing service from 125% of the actual maximum demand recorded over the previous 12 months, which for a house with a smart meter means the utility is already holding the data.
This method routinely clears services that the standard calculation fails, because the standard calculation assumes an electric range and dryer running flat out on the coldest evening of the year. Availability varies — some jurisdictions accept a 30-day recording, others require the full 12 months of interval data.
NEC 220.87 lets an electrician size an existing service from 125% of metered peak demand over 12 months. Real interval data often clears a 100-amp service that the standard calculation rejects.
How Backup Heat Strips Drive The Ampacity Math
Electric resistance heat is one of the few household loads the code treats as continuous. Under NEC 424.3(B), fixed electric space heating is assumed to run at full nameplate for three hours or more, so conductors and overcurrent protection are sized at 125% of the connected load.
That 25% adder is why strip kits consume service capacity so aggressively relative to their cost. A 15 kW kit draws 62.5 amps but requires an 80-amp circuit, and a 20 kW kit usually has to be split across two separate circuits.
| Strip kit | Draw at 240 V | Continuous sizing (×1.25) | Typical circuit |
|---|---|---|---|
| 5 kW | 20.8 A | 26.0 A | 30 A |
| 10 kW | 41.7 A | 52.1 A | 60 A |
| 15 kW | 62.5 A | 78.1 A | 80 A |
| 20 kW | 83.3 A | 104.2 A | Two circuits, commonly 60 A + 60 A |
Electric resistance heat is a continuous load under NEC 424.3(B), so circuits are sized at 125% of nameplate. A 15 kW kit drawing 62.5 amps needs an 80-amp circuit.
Keep in mind that delivered output falls with the square of voltage. A kit nameplated at 10 kW on 240 volts produces closer to 7.5 kW on a 208-volt service, which is a frequent and under-diagnosed source of complaints that backup heat "does not keep up."
The number that governs the wiring is the minimum circuit ampacity on the equipment nameplate, not the tonnage on the model number. Minimum circuit ampacity sets the smallest conductor permitted, and maximum overcurrent protection sets the largest breaker permitted — an installer sizes wire to the first and the breaker at or below the second.
A Worked Example: 1,800 Square Feet, Two Different Baselines
Abstract percentages are hard to argue with a contractor about. Running the arithmetic on a representative house makes the strip-kit decision visible in a way a rule of thumb never does.
Take an 1,800-square-foot home. General lighting and receptacles come to 5,400 VA at 3 VA per square foot, two small-appliance circuits add 3,000 VA, and the laundry circuit adds 1,500 VA.
In an all-electric version of that house, add a 12,000 VA range, a 4,500 VA water heater, a 5,000 VA dryer, and a 1,200 VA dishwasher. That totals 32,600 VA, which under NEC 220.83(B) becomes 8,000 VA at 100% plus 9,840 VA at 40%, for a general-load subtotal of 17,840 VA.
In a mixed-fuel version with gas cooking and gas water heating, the same house totals 16,100 VA. The demand math yields a subtotal of 11,240 VA — roughly 6,600 VA of headroom that exists purely because two appliances burn gas.
Now layer a 3-ton cold-climate heat pump with a 28-amp minimum circuit ampacity onto each baseline, with strip kits of increasing size. The calculated service demand looks like this:
| Configuration | All-electric baseline | Mixed-fuel baseline |
|---|---|---|
| Compressor only, no strips | 102 A | 75 A |
| Compressor + 5 kW strips | 123 A | 96 A |
| Compressor + 10 kW strips | 144 A | 117 A |
| Compressor + 15 kW strips | 165 A | 137 A |
| Compressor + 20 kW strips | 186 A | 158 A |
The mixed-fuel column is where the decision lives. A 5 kW kit lands at 96 amps and fits a 100-amp service; a 10 kW kit lands at 117 amps and does not, and nothing about the heat pump itself changed between those two rows.
The all-electric column tells a harder story. That house is already at 102 calculated amps with no backup heat at all, which means the conversation is not about avoiding an upgrade so much as about whether NEC 220.87 metered demand or a load-management device can defer one.
Both baselines assume a correctly sized system. An oversized heat pump paired with an oversized default strip kit is the most common way a project ends up needing 200 amps it did not actually require — start with cold-climate heat pump sizing and a real Manual J before anyone prices electrical work.
Load Management Options That Avoid A Service Upgrade
A service upgrade is one solution among several, and it is usually the last one worth pricing rather than the first. The options below are ordered roughly by cost, and several of them can be combined.
Cost figures here are estimated ranges drawn from typical residential quotes, and regional variance is large — utility labor rates, permit fees, and lateral type move these numbers substantially. Verify anything you plan to budget against a local quote.
| Option | What it changes | Estimated installed cost | Catch |
|---|---|---|---|
| Right-size the strip kit | Removes amps from the calculation permanently | $0–$400 delta at install | Requires a real load calculation and a design-temperature capacity check |
| Dual-fuel with existing furnace | Eliminates strips entirely | $0–$600 for controls | Retains a combustion appliance and its venting |
| Compressor / strip interlock | Lets NEC 220.82(C) count only the larger load | Often native to the air handler board | The inspector must accept it; trims capacity at design temperature |
| Listed energy management system | Caps total service draw under NEC Article 750 | $1,500–$4,500 | Depends on which NEC edition your jurisdiction has adopted |
| NEC 220.87 metered demand | Replaces assumptions with 12 months of meter data | $0–$300 for the analysis | Requires utility interval data and an AHJ that accepts the method |
| Subpanel | Adds breaker spaces only | $800–$1,800 | Does nothing for service ampacity |
| 100 A → 200 A service upgrade | Raises the ceiling outright | $2,000–$6,000+ | Utility scheduling; underground laterals and mast relocation push higher |
One distinction is worth flagging because it trips up homeowners and installers alike. Setting an outdoor lockout so the strips only energize below a chosen temperature reduces your energy use meaningfully, but it does not by itself reduce the calculated load unless the control scheme genuinely prevents simultaneous operation in a manner the inspector accepts.
Those two things get conflated constantly. The energy argument for balance point controls and the code argument for an interlock are related but separate, and only the second one changes what goes on the load calculation worksheet.
Dual-fuel deserves its own mention because it sidesteps the entire problem. Keeping an existing gas or propane furnace as the backup stage removes the strip kit from the equation, and the trade-offs are covered in more depth in the breakdown of heat pump backup heat strategies.
What Rebates Cover, And What They Do Not
Electrical work is treated as a first-class measure under the federal Home Electrification and Appliance Rebates program, which is a meaningful change from earlier incentive design. HEEHRA sets a $4,000 cap for an electrical panel or service upgrade and $2,500 for wiring, inside a $14,000 per-household maximum.
Those caps interact with income tiers rather than applying universally. Households under 80% of area median income can have 100% of project cost covered up to the caps, and households between 80% and 150% of area median income can have 50% covered — the mechanics are detailed in the walkthrough of HEEHRA income tiers.
HEEHRA caps electrical panel rebates at $4,000 and wiring at $2,500, inside a $14,000 household maximum. Under 80% of area median income, 100% of cost can be covered up to those caps.
HEEHRA is state-administered, so eligibility rules, contractor networks, and launch timing differ by state. The current status by state is tracked in the HEEHRA state program guide.
Utility rebates behave differently and are usually narrower. Programs such as Mass Save, NYSERDA, ConnectedSolutions, ComEd, Eversource, and BGE generally scope their heat pump incentives to the equipment and its installation, so panel and service work often falls outside the eligible-measure list — the program's own measure sheet is the only reliable answer.
Federal tax credit treatment of panelboards, subpanels, and feeders has changed materially in recent years, and the terms that applied to a 2024 installation are not a safe guide to a 2026 one. Confirm current federal tax credit status before assuming any portion of electrical work is creditable.
How To Get A Real Answer Before You Sign
The sequence matters more than any single step, because each stage removes assumptions that the next stage would otherwise have to price defensively. Working it in the wrong order is how a project acquires a service upgrade it never needed.
If you are pre-purchase and still comparing systems, the first task is a Manual J on the actual house rather than a square-footage rule of thumb. The output determines the strip kit size, and the strip kit size determines everything downstream — the heat pump load calculator is a reasonable place to sanity-check a contractor's number before the site visit.
If you already have quotes in hand, ask each contractor to state which of the four panel failure modes applies and to show the load calculation worksheet. A quote that names "200-amp service upgrade" without a completed 220.83(B) or 220.87 worksheet attached is an assumption with a price tag on it.
If the calculation genuinely fails, the order of cheaper alternatives is strip-kit reduction, then interlock, then metered-demand recalculation, then an energy management system, and only then the service upgrade. Equipment selection also shifts the math, since cold-climate models with strong low-ambient capacity need smaller backup kits — the cold-climate heat pump brand comparison covers which platforms hold capacity at design temperature.
All of this adds up to a fairly narrow question. Given your existing loads, your design temperature, and the equipment you have selected, how many kilowatts of backup heat do you actually need — and what is the smallest electrical change that supports that number?
Frequently Asked Questions
How many amps does a heat pump use?
A 3-ton cold-climate ducted heat pump typically lists a minimum circuit ampacity of 25 to 35 amps at 240 volts. Ductless mini-splits often run 15 to 25 amps. Read the minimum circuit ampacity on the nameplate, not the tonnage.
Can I install a heat pump on a 100-amp service?
Often yes, if backup heat is limited or eliminated. A compressor-only cold-climate system with dual-fuel furnace backup, or a small 5 kW strip kit on a mixed-fuel home, frequently fits inside 100 amps under NEC 220.83(B).
Does HEEHRA cover an electrical panel upgrade?
Yes. HEEHRA sets a $4,000 cap for an electrical panel or service upgrade and $2,500 for wiring, within a $14,000 household maximum. Rollout, eligibility, and contractor requirements are set by each state energy office.
What is the difference between MCA and MOCP on a nameplate?
Minimum circuit ampacity sets the smallest conductor allowed. Maximum overcurrent protection sets the largest breaker allowed. An electrician sizes the wire to the minimum circuit ampacity and the breaker at or below the maximum overcurrent protection.
Can a smart panel replace a service upgrade?
Sometimes. A listed energy management system under NEC Article 750 can cap total draw so calculated load stays under the service rating, but acceptance varies by local inspector and by which NEC edition the jurisdiction has adopted.
This article is for informational purposes and is not financial, tax, legal, or medical advice. Consult a licensed professional — a CPA, an elder-law attorney, a licensed electrician, an HVAC contractor, or your state energy office — before acting.