Gas vs Electric Water Heater Recovery
Updated July 2026
A 40,000 BTU gas burner reheats about 43 gallons an hour; a 4,500 W element about 20. That one gap decides why electric tanks must be bigger. The arithmetic, shown.
Every gas-versus-electric sizing question reduces to one line of arithmetic. Water takes 8.33 BTU to lift a gallon one degree. A standard residential gas burner is 40,000 BTU per hour and puts about 80% of that into the water through the flue design, so through the standard 90°F test rise it recovers 40,000 × 0.80 ÷ (8.33 × 90) = 43 gallons an hour. A 4,500-watt element is 15,354 BTU per hour, and although nearly all of it reaches the water (98%, the element being immersed), that recovers just 20 gallons an hour. The gas tank refills more than twice as fast, forever, by design.
What the gap does to sizing
During a busy hour, hot water comes from two places: gallons already stored, and gallons recovered while the hour runs. Gas recovery is large enough to carry a whole extra shower (43 gallons is two 20-gallon showers with change), so gas tanks stay small. Electric recovery is not, so electric tanks carry the hour in storage: where a 40-gallon gas covers a 66-gallon morning, the same morning needs an 80-gallon electric. Our calculator shows both answers side by side for any hour you enter.
The gap also sets the recovery wait after the hour is lost. Drain a 50-gallon tank and the gas version is fully back in about 55 min; the electric takes 1 h 56 min. That is why the second cold shower of the morning is so much more common in all-electric houses.
Where electric still wins the sizing argument
Households with calm, spread-out usage barely touch recovery; they run on storage, and storage is fuel-agnostic. One or two people, staggered showers, warm-wash laundry: a 40 or 50-gallon electric handles that pattern for a decade without complaint. And a heat pump water heater changes the ledger again, trading even slower recovery for much cheaper heat; it sizes one step up, which is its own guide. The recovery gap is a guide to sizing electric by the label FHR rather than by habit. It argues for precision, not against electric.