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Generators

Enough fuel for the outage. Far enough from the house.

Put in your generator's tank size and its rated runtime, and see how much gasoline, propane or diesel to store. Then run it at least 20 feet from the house.
Work out my fuelSafety first

Carbon monoxide: the rules that matter

  • Run it outdoors, at least 20 feet from windows, doors and attached garages (Ready.gov, CDC).
  • Never indoors (Ready.gov), and never in an attached garage, even with the door open (NFPA).
  • Put carbon monoxide alarms with battery backup on every level of the home (Ready.gov).
  • Turn it off and let it cool before refueling. Store fuel in labeled containers made for it, outside living areas (NFPA).
  • Generators caused an average of 74 carbon monoxide deaths and about 4,314 medically treated poisonings a year in 2004-2021 (CPSC).
  • CO shutoff features (UL 2201, ANSI/PGMA G300) are voluntary standards, not a legal requirement. They help; they do not replace the 20-foot rule.

Your generator, your outage

1. Fuel

Enter both to see which runtime figure on the spec sheet to use.

Fuel to store

Enter the tank size and the runtime from your generator's spec sheet. Makers list runtime per tank at a stated load, such as 25% or 50%. We do not guess a fuel rate, because it varies a lot from one generator to the next.

Watts you will run

Add the running watts of what you will plug in at once. Make sure the generator also covers the biggest starting load. Typical figures from the Eugene Water & Electric Board's generator sizing sheet; your appliance's label is better.

Typical running and starting watts for common household loads
LoadRunning wattsExtra to start
Well pump (1/3 HP)1,000 W2,000 W
Furnace blower fan (1/3 HP)700 W1,400 W
Refrigerator or freezer700 W2,200 W
Microwave1,000 W—
Laptop60 W—
Phone charger20 W—

To work out a whole outage day, use the power outage backup calculator.

A battery instead?

A portable power station makes no fumes, so it can sit next to the fridge or the CPAP indoors. It holds far less energy than a tank of fuel, but solar panels can top it up. For the fridge and essentials it is often enough; see power stations for a refrigerator and the best portable power stations.

Frequently asked questions

How long will a generator run on a tank of gas?

Check the spec sheet. Makers publish runtime per tank at a stated load, such as 25% or 50% of rated output, and it varies a lot between models. The lighter the load, the longer it runs. Enter that runtime and the tank size in our calculator to get fuel an hour, a day and for the whole outage.

How much fuel should I store for a generator?

Fuel an hour × hours a day you will run it × days. Fuel an hour is the tank size divided by the maker's runtime on that tank at your load. Running it in shifts, for example a few hours morning and evening to cool the fridge and pump water, cuts the fuel you need a lot.

How far from the house should a generator be?

At least 20 feet from windows, doors and attached garages, outdoors (Ready.gov, CDC; the older NFPA tip sheet we cite says 5 feet, and we use the stricter 20), with the exhaust pointed away from the house (NFPA). Never run one indoors (Ready.gov), and never in an attached garage, even with the door open (NFPA). Put battery-backed carbon monoxide alarms on every level.

Do new generators shut off automatically if carbon monoxide builds up?

Some do, but it is not required by law. The UL 2201 and ANSI/PGMA G300 standards include carbon monoxide shutoff or reduced emissions, and both are voluntary. The Consumer Product Safety Commission's rule is still a proposal. Look for those standards on the label, and keep the 20-foot rule either way.

How do I connect a generator to my house?

Only through a properly rated transfer switch installed by a qualified electrician (NFPA). Otherwise, plug appliances straight into the generator, or use heavy-duty outdoor-rated extension cords with all three prongs.

Estimates only. Fuel use depends on your generator, its load and conditions; the maker's spec sheet and manual come first. Follow the manufacturer's instructions and local codes. See our disclaimer.

Sources

  1. Ready.gov, Generator safety — generators and fuel outdoors, at least 20 ft from windows, doors and attached garages; let it cool before refueling
  2. Ready.gov, Power outages — fridge keeps food cold about 4 hours, a full freezer about 48; throw out food at 40°F or higher for 2 hours; generators at least 20 ft from windows, doors and attached garages; CO detectors on every level
  3. CDC, Prevent carbon monoxide poisoning — at least 20 ft from the house, away from doors, windows and vents; install a battery-operated CO detector
  4. CPSC, Portable generators regulatory agenda statement (October 2025) — an average of 74 generator CO deaths and about 4,314 medically attended injuries a year, 2004-2021
  5. CPSC, Portable generators: voluntary standards — UL 2201 and ANSI/PGMA G300 CO shutoff standards are voluntary
  6. NFPA, Generator safety tip sheet (copy hosted by the Village of Penn Yan) — never in an attached garage; CO alarms; cool before refueling; fuel in labeled containers outside living areas; transfer switch by a qualified electrician
  7. Eugene Water & Electric Board, Generator sizing considerations — running and starting watts: well pump 1/3 HP 1,000 W (+2,000 W to start), furnace fan blower 1/3 HP 700 W (+1,400), refrigerator/freezer 700 W (+2,200), microwave 1,000 W, laptop 60 W, phone charger 20 W

Keep going

Photo: Devon MacKay on Unsplash (Unsplash License).