Water & Pumps generator calculators
Pump loads are the classic generator-sizing trap: a motor that runs at 1,000W can demand two to four times that to start, and many of them — deep-well pumps especially — run on 240V, which most small generators simply do not supply. These calculators size well pumps, sump pumps and pool pumps by horsepower, flag the 240V cases prominently, and cover the electric water heater with an honest answer about why it rarely belongs on a portable generator.
Pick your calculator
Well Pump Generator Size Calculator (by HP)
Well pump generator sizing by horsepower: sourced running and starting watts (1/2, 3/4, 1 HP), why 240V capability decides your generator before wattage does.
Open calculator →Sump Pump Generator Size Calculator (by HP)
Sump pump generator sizing by horsepower: sourced watts (1/3 HP ~800W running, ~1,300W starting), storm duty-cycle math, and battery backup comparisons.
Open calculator →Pool Pump Generator Size Calculator
Pool pump generator sizing by horsepower: sourced running and starting watts (1 HP ~1,600W/~3,600W), 120V vs 240V variants, and when a pool can just wait it out.
Open calculator →Electric Water Heater on a Generator: Honest Math
Can a generator run an electric water heater? Honest answer: a 4,500W 240V element needs ~5,625W of 240V generator — usually impractical on portables. Full math inside.
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Which calculator should I use?
If you are on well water, the well pump calculator is the one to get right — without it an outage means no running water, and the 240V requirement decides your generator choice before wattage does. The sump pump page matters most where storms and power cuts arrive together; pair it with the dehumidifier page for basement cleanup. Pool pumps can wait out an outage, but the calculator is useful for sizing job-site or off-grid power. The electric water heater page exists mostly to tell you the honest math of why hot water is usually the load to shed.
Running several of these at once? Themulti-appliance builder adds them up with the staggered-start surge math, and the outage scenarios cover the common combinations pre-built.