Generator Size Calculator: What Size Generator Do I Need?
Answers: what size generator do I need?
Generators
Portable and standby generator sizing, running vs starting watts, what a furnace needs, and safe placement outdoors.
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- Reviewed Oct 3, 2026
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What Size Generator to Run a Furnace? Watts for Gas, Oil and Electric Heat
A gas or propane furnace needs about 300–875 running and 1,600–2,350 starting watts. What oil furnaces, electric furnaces and heat pumps draw, from generator charts and furnace spec sheets, with the altitude derate for 15 cold-winter cities.
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Portable Generator Safety: The Rules and the CPSC Data Behind Them
Outdoors only, 20 feet from the house, exhaust away, CO alarms on every level. CPSC records of 789 generator CO deaths show why each rule exists.
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