WaterHeaterCalculator.com
Tune ZIP code, current heater, hot-water demand, fuel setup, venting, location, water quality, and energy assumptions for a more detailed replacement estimate.
Start with defaults, then tune the fuel prices and installation details if you know them.
Transparent assumptions
The calculator separates operating cost from installed cost. Operating cost is physics-driven and easier to source. Installed cost is the messy part, so the current ranges are planning assumptions until we collect contractor-facing and real-quote data.
We estimate gallons per day from household size, bathrooms, peak use, and your usage slider. Efficiency Maine notes that gallons per day is an adjustable driver and that a typical family uses about 50 gallons per day.
Energy depends on the gap between incoming water and the heater setpoint. Efficiency Maine describes a typical rise from 50°F incoming water to 120°F hot water.
The model converts BTUs to kWh, therms, or propane gallons using public calculator conventions: 3,412 BTU/kWh, 100,000 BTU/therm, and 91,500 BTU/gallon of propane.
Current and replacement heaters are adjusted by EF/UEF. ENERGY STAR product data gives real heat pump tank UEFs, Navien helps sanity-check condensing tankless assumptions, and the Rheem sheet gives legacy tank examples.
Install ranges start as rough planning bands, cross-checked against public replacement-cost guides like Arthur Heating & Air, then add likely costs for crawlspace or attic access, gas-line upgrades, venting changes, electrical work, and hard-water treatment.
The next data layer should combine ENERGY STAR product records with contractor price books, supplier catalogs, flat-rate plumbing menus, permit records, rebate databases, and anonymized homeowner quotes by ZIP and job scope.
ENERGY STAR product data
The ENERGY STAR heat pump water heater finder exposes brand, model, UEF, storage volume, first-hour rating, retailers, installers, API access, dataset access, and an Excel export. That means this calculator can eventually compare certified product classes against tankless on lifetime value.
Current ENERGY STAR results also show models around 4.2+ UEF from brands such as Bradford White, LG, and Eco-Logical.
Use this as product-class guidance, not a direct endorsement. The right product still depends on local availability, rebates, warranty, installer familiarity, noise/location constraints, and whether the home needs electrical or condensate work.
A like-for-like tank swap is usually the lowest-cash, lowest-surprise quote. It is the first number to beat when the old unit still works.
The unit can be efficient, but gas line sizing, venting, condensate, electrical, and scale control decide whether the quote stays reasonable.
Hybrid water heaters can slash operating cost, but they need the right location, air volume, drainage, noise tolerance, and rebate math.
Next: paste the quote and check for missing permits, vague exclusions, disposal, venting, gas line work, electrical work, condensate, and scale prevention.