Why square footage is the wrong question
It is the question everybody asks, and it correlates only loosely with the answer. Electrical load is set by what is in the house, not by how much floor it sits on.
Consider two 2,000 square foot houses.
| House A | House B |
|---|
| Heating | Gas furnace, electric blower | Electric heat pump with resistance backup |
|---|
| Water heating | Gas | Electric, 4,500 W element |
|---|
| Cooking | Gas range | Electric range |
|---|
| Water supply | Municipal | 1 HP well pump |
|---|
| Sensible generator | 5,000-7,500 W portable | A standby unit, and a quoted installation |
|---|
Same floor area, completely different answers. Anyone quoting a watts-per-square-foot rule is guessing at which house you have.
The right question, in four steps
1. List what must run. Not what could run — what you would genuinely miss. For most households that is the refrigerator, the freezer, the furnace blower, a sump or well pump, some lighting and the internet.
2. Add the running watts. Use the appliance wattage chart or the plates on your own equipment.
3. Add the single largest starting surge, not all of them. Two motors almost never start in the same instant, and sizing for that coincidence buys a machine twice as big as you need.
4. Add 20% margin. Nameplates are optimistic and older appliances draw more than new ones.
A worked example
A 2,000 square foot house with gas heat, municipal water, and a normal appliance list.
| Load | Running watts | Starting watts |
|---|
| Refrigerator | 150 W average | 500-1,000 W |
|---|
| Chest freezer | 150 W average | 500-1,000 W |
|---|
| Furnace blower | Up to 1,600 W | Higher on start — the largest surge here |
|---|
| Sump pump | About 1,050 W | Up to 2,150 W |
|---|
| Lighting, LED throughout | 100-200 W | None |
|---|
| Router, modem, devices | About 100 W | None |
|---|
| Running total | About 3,250 W | Plus about 2,150 W for the worst single start |
|---|
Figures are the ranges used across this site; see the appliance wattage chart for sources. Refrigerator and freezer figures are cycling averages, not continuous draw.
So the requirement is roughly 3,250 running watts plus headroom for a 2,150W start, and then 20% margin on the running figure. That lands at about 4,000 running watts with real surge capability — comfortably inside a 5,000W machine and very comfortably inside 7,500W.
Note how far that is from the "you need 20 kilowatts for a 2,000 square foot house" answer people are often given. That number is for running the entire panel including central air and electric heat, which is a standby generator's job.
The four things that change the answer
- Electric heat. Resistance heating is thousands of watts continuously and defeats every portable machine. The furnace page covers the difference between a gas furnace's blower and actual electric heat.
- A well pump. Adds a large, unpredictable surge — the well pump page has the figures.
- Central air conditioning. 3,000-5,000W of starting surge, and usually the reason people move up to standby.
- An electric water heater or range. 4,500W and up, sustained. Possible on a big portable, alone.
When the answer stops being a portable
If two or more of the items above apply, the arithmetic stops pointing at a portable generator. Running central air, electric heat and a well pump together is a standby installation sized by a dealer, not a machine you wheel out.
The standby sizing page covers that exercise, which is genuinely different — it works from the service panel rather than from a load list.
The short version
- Ignore square footage. It does not predict load.
- A typical gas-heated 2,000 sq ft house needs about 4,000 running watts for a real critical-load list.
- Add only the largest single surge, not all of them.
- Electric heat, central air or a well pump are what move you up a class — or to standby.
