Generators

At least 20 feet, with the exhaust pointed away from doors, windows and vents. Never in a garage, on a porch, in a basement or in any partly enclosed space, even with the door open. Carbon monoxide from a portable generator kills people in the United States every storm season, and a CO alarm in the house is a reasonable second line of defence.

If you are running laptops, modern TVs, variable-speed appliances or anything with a circuit board, yes. Inverter models produce a clean sine wave, typically under 3% total harmonic distortion; conventional models can exceed 20%, which sensitive electronics tolerate badly. Inverter units are also markedly quieter and throttle down under light load. For a pump or power tools, a conventional unit is fine and cheaper per watt.

No. That is backfeeding, it is illegal in most jurisdictions, and it energises the utility line outside your home — which can kill a lineworker restoring your power. The legal routes are a transfer switch or an interlock kit, both installed by an electrician. This is the one item on this page where the wrong answer hurts somebody else.

Gasoline is easiest to find and gives slightly more power, but it degrades in months and is hard to buy when the power is out because the pumps are down too. Propane keeps essentially forever in a sealed tank and starts cleanly in cold weather, at roughly 10% less output. Dual fuel gives you both and is why it is worth the premium for standby use.

A mid-size portable at half load burns roughly 0.5 gallons an hour, so about 12 gallons a day if you run it continuously. Most people do not — running it in blocks to cool the fridge and charge devices stretches the same fuel across several days and is far quieter for the neighbours.

Add the running watts of what you want on at once, then add the single largest surge on top of that number, not all the surges combined. Well pumps and air conditioners are usually the constraint. The calculator works this out from an appliance list.