Best Heat Pump Water Heater: Tank Size, Yearly Savings and Fit

Start with your busiest hour. The DOE sizing worksheet counts 10 gallons of hot water per shower, 4 for sink use, 6 for a dishwasher load and 7 for a clothes washer. Two showers, the sink and the dishwasher in the same morning hour is 30 gallons. The heater's first-hour rating, printed on its EnergyGuide label, has to be at least that.

Then check the makers' household charts. Rinnai puts 3 to 4 people on a 50-gallon tank, 4 to 5 on 65 gallons and 5 or more on 80. Our calculator uses 50 gallons for up to 4 people, 65 for 5 and 80 for 6 or more, and steps up when the peak hour beats a class's first-hour rating: about 69 to 73 gallons for the 50-gallon tanks, 80 for 65 gallons and 91 for 80 gallons.

Do not undersize to save money. A heat pump heats slowly; when a too-small tank runs low, it switches to its electric element, which costs as much to run as the tank you replaced.

Method: a household of four on the DOE high-use pattern draws 84 gallons of hot water a day, heated 67 F. That is about 4,961 kWh of heat a year. Divide by each heater's UEF to get what it burns. We compare against a new tank at today's federal minimum efficiency, so these savings are a floor; a 10-year-old tank does worse.

Electric tank (UEF 0.93): about 5,334 kWh, $923 a year at the 17.3 cent US average. A 3.75 UEF heat pump uses about 1,323 kWh, $229. You save about $694 a year, and the existing 240V circuit usually carries over. ENERGY STAR's own estimate for a family of four is about $550 a year.

Propane tank (UEF 0.627): about 295 gallons a year, $826 at $2.80 a gallon. The heat pump saves about $597 a year at the US average rate and still saves over $400 in high-rate states like Massachusetts. Propane is expensive heat, which is why this switch pays.

Natural gas tank (UEF 0.627): about 270 therms, $405 a year at $1.50 a therm. The heat pump saves about $176 a year at the US average rate, about $230 to $250 in low-rate states like Idaho (11.8 cents) and Washington (13.1 cents), and close to nothing in Massachusetts (30.5 cents). In California (32.5 cents) and Hawaii (40.6 cents) it costs more to run than gas.

By state, against an electric tank: about $474 a year in Idaho, $526 in Washington, $611 in Florida, $621 in Texas, $774 in Pennsylvania, $1,059 in New York, $1,223 in Massachusetts and $1,305 in California. The higher your rate, the more a heat pump saves over resistance heat.

Air: most makers ask for about 700 cubic feet of air around the heater, a 10 x 10 ft room with a 7 ft ceiling, and ACiQ asks for 700 to 1,000. In a closet, a louvered door or a duct kit borrows air from the next room. The heater cools and dries the space it sits in, a plus in a damp basement and a minus in a small conditioned closet.

Temperature: the Rinnai and ACiQ compressors run down to about 37 F and the Stiebel Eltron down to 42 F. Below that the tank heats with its element at standard-tank cost. A garage that freezes can crack the tank and lines.

Drain: the heat pump drips condensate whenever it runs, so it needs a floor drain, laundry sink or condensate pump, plus the usual pan and relief valve line.

Size and noise: the 80-gallon Rinnai is about 25.7 in. wide and 74.6 in. tall, and the Stiebel Eltron is 27 1/8 in. wide, so measure the door and ceiling. ACiQ rates its 50-gallon at 49.5 dBA and Stiebel Eltron its Accelera at 52 dB(A) at 3.3 ft.

Every heat pump water heater we list runs on 240V. The Rinnai units call for a 30 A circuit, the same circuit a standard electric tank already has, so an electric-to-heat-pump swap usually needs no new wiring. The Stiebel Eltron Accelera 220 E needs only a 15 A, 240V breaker.

Replacing gas or propane is the harder case: there is no 240V circuit at the old tank. You either run a new 240V, 30 A circuit (and may need panel space), or buy one of the newer 120V plug-in heat pump models from Rheem, A.O. Smith or GE that run on a dedicated standard outlet. Those 120V models are sold through plumbing supply houses and home centers rather than Amazon, so we do not list them. Ask the store for the first-hour rating; plug-in models recover more slowly.

The federal 25C credit (30% of cost, up to $2,000) ended for heat pump water heaters placed in service after December 31, 2025, under the One Big Beautiful Bill Act. If you are reading payback numbers from before 2026, they likely subtract $2,000 you will not get.

What is left: state Home Electrification and Appliance Rebates (HEAR) pay up to $1,750 for a heat pump water heater where your state has launched the program. Households under 80% of area median income can get the full cost covered up to that cap, and households between 80% and 150% get half. HEAR also covers electrical wiring (up to $2,500) and panel upgrades (up to $4,000), which matters when you are replacing gas.

Utilities run their own rebates, often as an instant discount at the store or a mail-in check. Search your ZIP code on ENERGY STAR's Rebate Finder and your state energy office's site before you buy, since some programs require ENERGY STAR certification (the Senville and Rinnai units have it) or a pre-approval.

A heat pump water heater installs like a standard tank, plus a condensate line. Most homes with a backflow preventer or pressure-reducing valve on the main need a thermal expansion tank. The Rinnai units have 3/4 in. NPT connections that take standard braided connectors.