What does a waterbed heater cost to run?

Run the numbers on your own use

Change any of these and the figures update. The defaults are the typical case described above; your rate is the input that moves the answer most.

Why this is lower than the number you will see elsewhere

Almost every published answer to this question multiplies the rating on the label by the hours the appliance is switched on. For a waterbed heater that gives 2,628 kWh a year, or $482.

Thermostatic, holding several hundred litres of water at body temperature against a cooler room, every hour of the year.

The arithmetic, step by step

Nothing here is hidden, so you can check it or change it. Working in the order the formula runs:

1. 300 W — what it draws while it is actually drawing. This is the rating on the plate.
2. × 35% — the share of its in-service time it is really pulling that. Thermostatic, holding several hundred litres of water at body temperature against a cooler room, every hour of the year.
   That gives 105 W averaged across the hours it is on.
3. × 24 hours a day × 365 days — A queen waterbed in a normally heated bedroom.
   105 × 24 × 365 ÷ 1,000 = 920 kWh a year.
4. × 18.34¢ — the US average residential rate for June 2026.
   920 kWh × 18.34¢ = $169 a year.

Change any assumption in the calculator above and every figure on this page moves with it. The two that matter most are your rate, which varies 4× across the country, and the hours — the duty cycle is a property of the appliance, but the hours are a property of you.

How sensitive is that number?

A single figure invites more confidence than it deserves. Here is the same appliance under assumptions either side of the default, so you can see how much of the answer is the appliance and how much is the guess about how you use it.

Everything else held at the default. The spread here is the honest error bar on the headline figure.

What it costs per hour, day and month

At 18.34¢ per kWh, the US residential average for June 2026.

The thing worth knowing

Holding 300 litres of water at 30°C in a 19°C room never stops, and the losses scale with that difference. This is why waterbeds have a reputation for surprising bills — the mattress is a large, poorly insulated hot water tank you sleep on, and unlike a real tank nobody insulates it.

What it costs in your state

The appliance is the same everywhere; the rate is not. Running this waterbed heater costs $485 a year in Hawaii and $121 in Nevada — a difference of 4×.

Cost of running one waterbed heater for a year, by state. Residential average price, EIA June 2026.

Other heating and cooling costs

• Electric furnace

  $1,653 a year

  Whole-home resistance heating in a cold climate.

• Heat pump (heating)

  $423 a year

  Whole-home heating in a mixed climate.

• Central air conditioner

  $421 a year

  A 3-ton system in a hot-summer climate.

• Dehumidifier

  $228 a year

  A 50-pint unit holding a basement at 50% relative humidity.

• Electric baseboard heater

  $218 a year

  One 1,000 W baseboard unit in one room. Most homes have several.

• Heated towel rail

  $193 a year

  Left permanently on, which is how most of them are used.

Questions

Source: U.S. Energy Information Administration, Electric Power Monthly, Table 5.6.A, June 2026. U.S. Government work, public domain.

How every figure on this page is computed · Where the data comes from