Build the list before you look at machines
Generator sizing has one rule that eliminates most of the confusion: add every appliance's running watts, then add only the single largest starting surge. Motors almost never start at the same instant, and sizing for simultaneous startup buys a machine two or three times larger than the house needs.
A typical critical-load list, on Champion's published figures:
| Appliance | Running watts | Starting watts |
|---|
| Refrigerator | 150–400 | 800–1,200 |
|---|
| Furnace fan (½ HP) | 300–800 | 800–1,600 |
|---|
| Sump pump (⅓ HP) | 500–800 | 1,000–1,600 |
|---|
| Well pump (½ HP) | 750–1,000 | 1,500–2,000 |
|---|
| Window AC (10,000 BTU) | 900–1,200 | 1,800–2,400 |
|---|
| Microwave | 600–1,200 | — |
|---|
| LED lighting, per bulb | 8–15 | — |
|---|
Source: Champion Power Equipment's published generator wattage chart. Ranges are the manufacturer's — size against the upper end, because a system that only works with the efficient appliance is not a backup system. The full chart, with more appliances.
Add the upper ends of the first four and you get 3,000W running. The largest single surge is the well pump at 2,000W, so the peak requirement is roughly 3,000 − 1,000 + 2,000 = 4,000W. A 5,300W machine covers that comfortably; a 3,500W one does not.
Match the purchase to the outage
Capacity is not a preference. It falls out of two numbers: how long your power is usually off, and what you refuse to lose while it is.
| Your outage lasts | What has to keep running | Realistic product class |
|---|
| Under 8 hours | Fridge, phones, lights | A battery — silent, indoor-safe, no fuel to fetch in the dark
See power stations |
|---|
| 8–24 hours | Fridge, furnace fan, sump pump, lights | 3,500–5,500 running watts
See generators under $1,000 |
|---|
| 1–3 days | Above, plus a well pump and intermittent cooking | 5,300–9,500 running watts, dual fuel
See the hurricane-season picks |
|---|
| 3+ days, whole house | Everything, including central air conditioning | 13,000 running watts, or a standby installation
See whole-house options |
|---|
What an hour of generator costs
Nobody in this category publishes this, and it is computable from published figures. A mid-sized generator burns roughly 0.75 gallons an hour at half load. At the EIA's reported U.S. average of $4.071 a gallon for regular gasoline in the week ending 31 August 2026:
What it costs to actually run
The sticker price of a dual-fuel generator is a fraction of what it costs you. The sticker price of a battery is nearly all of it. Here is the arithmetic, with the inputs stated so you can redo it with your own fuel price.
| Unit | Published consumption | Cost per hour | Cost per 24 h |
|---|
| Mid-size, half load, gasoline | 0.75 gal/hr | $3.05 | $73.28 |
|---|
| Small inverter, half load, gasoline | ~0.35 gal/hr | $1.42 | $34.20 |
|---|
| Mid-size, half load, propane | ~1.0 gal/hr | $2.67 | $64.18 |
|---|
| Block running: 6 h a day, gasoline | 0.75 gal/hr × 6 h | $3.05 | $18.32 |
|---|
The last row is the useful one. Running six hours a day rather than continuously costs a quarter as much, needs a quarter of the fuel, and keeps a fridge and freezer perfectly safe — because a sealed fridge holds temperature for about four hours and a full freezer for around 48. Run it in blocks, and use a battery to carry the quiet hours.
What a generator does that a battery cannot
It does not run out. That is the entire argument, and on day three of an outage it is the only argument that matters. A battery holds a fixed amount of energy; a generator with a fuel can beside it is limited only by how much fuel you can get.
The costs are real and worth stating: it is loud, it must live outdoors at least twenty feet from the house, it needs fuel you have to store and rotate, it needs oil changes, and it produces carbon monoxide that kills people after every major storm. The full comparison works through when each one wins, and the honest answer for many households is one of each.
Before you buy anything else
Two purchases matter more than which generator you choose. A transfer switch or interlock kit, because without one the generator cannot reach the furnace or the sump pump. And a working carbon monoxide alarm on every level of the house, because that is the failure that is not recoverable.
