Electric water heater vs gas: what does it do to my panel?
A standard 4,500 W electric tank adds 7.5 A to this 1,700 ft² house under the NEC 220.82 optional method (from 80.5 A to 88.0 A) and 18.8 A under the standard method, where it moves the minimum service from 100 A to 125 A. A 120 V plug-in heat pump water heater adds only 1.7 A on the optional method and needs no new 240 V circuit. On a 100 A service with gas everything else, either electric option fits; on a house that already has electric heat, the 4,500 W tank is often the load that tips the calculation.
Updated September 23, 2026. Numbers on this page are computed by the same engine as the calculators, under NEC 2023.
Worked example: 1,700 ft² house with a 4,500 W electric tank
Calculated per NEC 2023Optional method (220.82)
Inputs
| NEC edition | NEC 2023 |
|---|---|
| Floor area | 1,700 ft² |
| Small-appliance circuits | 2 |
| Laundry circuits | 1 |
| Cooking | Electric range 10 kW |
| Clothes dryer | 5,000 VA |
| Appliances fastened in place | Dishwasher 1,200 VA; Electric water heater, 4,500 W elements 4,500 VA |
| Heating | Gas or none (no electric heating load) |
| Air conditioning | 3,000 VA |
Result
| With a gas water heater | 80.5 A19,320 VA calculated |
|---|---|
| Calculated load | 21,120 VAfrom 33,300 VA connected |
| Calculated current | 88.0 Aat 240 V |
| Minimum service rating | 100 A240.6(A) standard rating, not less than 100 A |
| The water heater’s share | 7.5 A4,500 VA of nameplate at 40% past the first 10,000 VA = 1,800 VA |
| Line item | NEC | Connected | Demand | Basis |
|---|---|---|---|---|
| General lighting and receptacles | 220.82(B)(1) | 5,100 VA | (in subtotal) | 1,700 ft² × 3 VA/ft² |
| Small-appliance and laundry circuits | 220.82(B)(2) | 4,500 VA | (in subtotal) | 3 circuits × 1500 VA |
| Appliances fastened in place | 220.82(B)(3) | 5,700 VA | (in subtotal) | 2 at nameplate |
| Ranges, ovens and cooking units | 220.82(B)(3) | 10,000 VA | (in subtotal) | 1 at nameplate |
| Clothes dryers | 220.82(B)(3) | 5,000 VA | (in subtotal) | 1 at nameplate |
| Permanently connected motors | 220.82(B)(4) | — | (in subtotal) | None |
| Other fixed loads | 220.82(B)(3) | — | (in subtotal) | None |
| EV supply equipment | 220.82(B)(3)a | — | (in subtotal) | None |
| General load after demand factors | 220.82(B) | 30,300 VA | 18,120 VA | First 10,000 VA at 100%; remaining 20,300 VA at 40% = 8,120 VA |
| Electric space heating | 220.82(C) | — | 0 VA | None |
| Air conditioning and cooling | 220.82(C)(1) | 3,000 VA | 3,000 VA | 100% of 3,000 VA; largest selection |
The tank goes into the general load with the other appliances, where everything past the first 10,000 VA counts at 40%. So 4,500 VA of nameplate becomes 1,800 VA of calculated load, 7.5 A: from 80.5 A to 88.0 A, still inside a 100 A service.
Three water heaters, two methods
Calculated per NEC 2023Optional method (220.82) and standard method (Article 220 Part III)
Inputs
| Gas water heater (no electrical load) | 28,800 VA connected |
|---|---|
| Standard electric tank, 4,500 W | 33,300 VA connected |
| 120 V plug-in heat pump water heater, 1,000 VA | 29,800 VA connected |
Result
| Gas water heater (no electrical load): optional | 80.5 A100 A minimum |
|---|---|
| Gas water heater (no electrical load): standard | 96.9 A100 A minimum |
| Standard electric tank, 4,500 W: optional | 88.0 A100 A minimum |
| Standard electric tank, 4,500 W: standard | 115.7 A125 A minimum |
| 120 V plug-in heat pump water heater, 1,000 VA: optional | 82.2 A100 A minimum |
| 120 V plug-in heat pump water heater, 1,000 VA: standard | 101.1 A110 A minimum |
The standard method feels the tank more (18.8 A) because 220.53 takes fastened-in-place appliances at 100% until there are four or more of them. The heat pump water heater’s 1,000 VA barely registers on either method.
Where a water heater lands in the calculation
A storage water heater is an "appliance fastened in place" under NEC 220.53, not space heating, so it never gets the 100% treatment that electric heat does. In the optional method it joins the general load; in the standard method it is counted at nameplate, or at 75% when the house has four or more such appliances. A 4,500 W tank has two 4,500 W elements that never run together, so 4,500 VA is the nameplate load, on a 30 A, 240 V circuit.
That is why the tank is a modest load in a house full of gas appliances and a decisive one in a house that already carries electric heat, a range and a dryer: it is the same 4,500 VA either way, but in the second house it arrives after the demand factors have been used up.
Heat pump water heaters
A 240 V hybrid heat pump water heater still carries 4,500 W backup elements, so its nameplate and its calculated load are the same as a standard tank even though it uses far less energy. The 120 V plug-in units are different: no backup elements, about 1,000 VA on a shared or dedicated 15 or 20 A circuit, and a much smaller footprint in the calculation. They recover slowly and want a warm space to sit in, but for an older house with no spare 240 V capacity they solve two problems at once.
What to check before switching
Three things decide whether the switch from gas is trivial or a project:
- Headroom. Run the estimator on the house as it is; if it is already above 90 A on a 100 A service, the tank needs the existing-dwelling check an electrician runs (NEC 220.83).
- Panel space. A standard tank needs a 2-pole 30 A breaker; a full panel is a cost item separate from the calculation.
- Circuit route. Water heaters are usually far from the panel; the run may cost more than the heater.
Frequently asked questions
- Does an electric water heater need a 30 A breaker?
- A 4,500 W element at 240 V draws 18.75 A. Water heaters are treated as continuous loads by 422.13, so the circuit is sized at 125%, 23.4 A, which lands on a 30 A breaker with 10 AWG copper.
- Is a tankless electric water heater the same?
- No, and this is the trap. Whole-house tankless units are 18 to 36 kW, three to eight times the load of a tank, on two to four 40 A circuits. On this house a 27 kW tankless would add roughly 45.0 A on the optional method and far more on the standard method; most need a 200 A service.
- Will the switch raise my bill?
- A standard electric tank costs more to run than gas in most markets; a heat pump water heater usually costs less than gas. The appliance calculator can compare them on your rates.
- Does the water heater affect the neutral?
- A 240 V tank does not; it has no neutral. A 120 V heat pump water heater does, at its nameplate, which is one reason the calculator asks for the voltage of each fixed appliance.
Related questions
- Will my panel handle a heat pump, or do I need a service upgrade?A 1,900 ft² house on 150 A swaps its gas furnace and air conditioner for a heat pump. The NEC 220.83(B) existing-dwelling calculation, run with 5, 10 and 15 kW of backup strip heat, shows where the service runs out.
- How many amps does a house use?Calculated service current for four typical houses under the NEC 220.82 optional method, from a 1,200 ft² gas home to a 2,600 ft² all-electric one, and why the appliances matter more than the square footage.
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