Water heater buying guides

Decision guides written and reviewed by people, with the calculations done from the same dataset that powers the rest of the site. Each guide states its sources and its last-updated date.

• Heat pump vs gas water heater: the running-cost math

  Heat pump water heaters use a quarter of the energy, but electricity costs more per unit than gas. The annual-dollar math across every certified model, and when gas still wins.

• Tank vs tankless water heater: which fits how you use hot water?

  A tank rides out simultaneous use from storage but can run out; a tankless never runs out but caps simultaneous flow. The two mental models, with the sizing numbers for each.

• How to size a water heater by household (first-hour rating and GPM)

  Size from your busiest hour, not the tank sticker: DOE first-hour-rating bands for tanks and simultaneous-fixture flow math for tankless, with worked examples per household size.

• 40 vs 50 gallon water heater: when the smaller tank is enough

  The 10-gallon difference matters less than first-hour rating and recovery. What the certified data shows about each class, and the household profile where 40 gallons genuinely suffices.

• Tankless water heater sizing: real GPM at your groundwater temperature

  Marketing GPM assumes warm groundwater. How to compute the flow you'll actually get from the certified input rating and your local temperature rise, with a climate table.

• 120 V vs 240 V heat pump water heaters: plug-in convenience vs recovery speed

  A 120 V plug-in model can replace a gas heater with no new wiring; a 240 V unit recovers faster with resistance backup. The install-cost and capacity trade-offs, from certified data.

• UEF explained: what the efficiency number actually means in dollars

  A UEF of 3.9 vs 0.93 sounds abstract until it becomes an annual bill. How the rating is measured, why it beats EF comparisons, and the dollar spread across the certified market.

• What a water heater really costs to run per year

  Certified annual energy use converted to dollars at national average rates, across every heat pump, gas storage, and tankless model — and how to adjust the math to your local rates.

• Heat pump water heater installation requirements (space, air, drain, noise)

  Air volume, condensate drains, compressor cutoff temperatures, and clearances — the four requirements that decide whether a heat pump water heater fits your utility room or garage.

• Gas water heater venting: atmospheric, power vent, and direct vent explained

  Matching the existing vent type is usually the cheapest replacement path. What each vent category means, which certified models use which, and when switching categories pays off.