System sizing

System size for an all-electric home

Enter your home size, heating type, and electric appliances. Get a system size built for a home with no gas backup, where heating and water heating carry a much bigger share of the load.

Your numbers

1 Project details Optional
Shown on your exported report. Leave blank to skip.
2 Your home
Your conditioned floor area, not including garage or unfinished space.
All-electric heating load is far more climate-sensitive than gas backup homes.
A home that's occupied all day runs heating and devices longer.
3 Space and water heating
A heat pump typically uses 2.5 to 3 times less electricity for the same heat.
A heat pump water heater uses roughly a third the electricity for the same hot water.
4 Other electric loads

How it works

Sizing for a home with no gas backup

Step 1

Start with home size, climate, and occupancy

These three set your baseline load the same way they would for any home. If you're not sure your home is fully electric or want a simpler sqft-only estimate, the fixed-size home tools are a good starting point instead.

Step 2

Be honest about your heating and water heater type

Heat pump versus resistance heating is the single biggest factor in this estimate, often larger than climate or home size. Check your equipment nameplate or ask your installer if you're not sure which you have.

Step 3

Add other electric loads and confirm with a real bill

Dryer, cooking, and planned EV charging all add real, countable load on top of heating. Once you have a bill from an all-electric period, the monthly usage tool or annual usage tool work from your real numbers instead.

Why all-electric homes need their own sizing tool

Heating type is the single biggest lever

A 2,000 sq ft all-electric home with a heat pump and heat pump water heater in a moderate climate needs roughly 12.0 kW. The same home with resistance heat, a resistance water heater, and EV charging in a cold climate, occupied most days, needs closer to 24.4 kW, more than double.

A heat pump moves heat instead of generating it

A heat pump typically produces 2.5 to 3 times more heat per kWh than resistance heating, consistent with the roughly 65% reduction in heating electricity the Department of Energy attributes to modern heat pumps, since it transfers existing heat rather than converting electricity directly into it. Isolating just the heating type on an otherwise identical 2,000 sq ft home, this tool estimates 10.8 kW with a heat pump versus 14.8 kW with resistance heat, holding everything else constant.

Water heating follows the same logic, at a smaller scale

A heat pump water heater uses roughly a third the electricity of a resistance water heater for the same hot water output, adding about 1,200 kWh a year in this estimate versus 3,600 kWh for a standard resistance unit, consistent with the Department of Energy's own figure of 60 to 70% less energy use for ENERGY STAR qualified heat pump water heaters. Smaller than the heating difference, but still a real, countable input worth getting right.

Why a gas-backup home tool would undersize you here

A tool built for a typical gas-backup home assumes space and water heating stay off the electric bill entirely. An all-electric home carries that full load on solar instead, which is why this tool exists separately rather than folding heating type into the standard sqft-based tools.

What to do with this number next

An all-electric home has no gas bill to fall back on, so take your estimated system size to the payback period calculator to see what it might save you over time, or to the federal ITC calculator to check what programs apply to a system of this size.

Questions

Frequently asked

A 2,000 sq ft all-electric home with a heat pump and heat pump water heater in a moderate climate needs roughly 12.0 kW. The same home with resistance heat, a resistance water heater, and EV charging in a cold climate, occupied most days, needs closer to 24.4 kW, more than double.

A heat pump typically produces 2.5 to 3 times more heat per kWh than resistance heating, since it moves heat rather than generating it directly. Isolating just the heating type on an otherwise identical 2,000 sq ft home, this tool estimates 10.8 kW with a heat pump versus 14.8 kW with resistance heat.

Less in absolute terms but still real. A heat pump water heater uses roughly a third the electricity of a resistance water heater for the same hot water output, adding about 1,200 kWh a year in this estimate versus 3,600 kWh for a standard resistance unit.

If you're planning one, yes. Adding EV charging to an otherwise identical all-electric home raises the estimate by roughly 3,000 kWh a year, which is usually cheaper to build into the original system than to add as a second array later.

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