Water Heater — Sizing & Cost
The water-heater math and money: size a storage tank by peak-hour demand and first-hour rating, size a tankless unit from simultaneous GPM and temperature rise (BTU/hr = GPM × 500 × ΔT; electric kW = GPM × ΔT × 0.1465), work out recovery rate, estimate installation / replacement cost from your own line items, compare tank vs tankless lifetime cost, check heat-pump water-heater savings, and size a thermal-expansion tank. No price list is stored; a water-heater swap usually needs a permit and a licensed installer.
Planning estimate: this is a planning estimate from the numbers you enter and standard reference quantities — not a bid or a contract. Get itemized written quotes from licensed plumbers and confirm measurements before you commit.
Illustrative math, not advice: This is illustrative math on the figures you enter — not financial advice. Energy prices, water rates, usage and product performance vary; savings are never guaranteed.
Water Heater SizeFind what size water heater you need from your peak-hour hot-water demand — free calculator with the first-hour-rating method, a worked example and FAQ.Tankless SizingSize a tankless water heater from flow (GPM) and temperature rise: get the required BTU/hr for gas or kW for electric, with formula, example and FAQ.Recovery RateCalculate a water heater's recovery rate in gallons per hour from the fuel input, efficiency and temperature rise, with formula, worked example and FAQ.Installation CostEstimate water-heater installation or replacement cost from your own quotes: unit, labor, permit, fittings and disposal, plus a contingency buffer.Tank vs Tankless CostCompare tank vs tankless water heater lifetime cost on your own figures — upfront plus annual energy over the years you choose, with example and FAQ.Heat-Pump SavingsEstimate the annual energy savings of a heat-pump water heater versus a standard electric tank, on your own kWh use and rate, with formula and FAQ.Expansion Tank SizeSize a thermal expansion tank for your water heater from its gallon capacity, using a labeled planning band, with formula, example and code note.
Every Water Heater — Sizing & Cost tool is calculated server-side — visible immediately — with its formula, a worked example and a reference table, and works on the prices you enter. Background reading is in the guides.