Guides

The background behind the calculators — what the numbers mean, and what actually changes them.

• What a home sauna really costs to run

  Why the common "kilowatts times hours" estimate is too high, what a session actually costs, and how to cut it.

• Where a hot tub's electricity goes

  Standby heat loss, not bathing, is most of a hot tub's bill. Here's the split, and the three changes that measurably reduce it.

• How sauna heater sizing actually works

  The 1 kW per cubic metre rule, why glass and stone break it, and how to read a manufacturer's chart without getting caught out.

• Sauna or hot tub — which costs more to run?

  A side-by-side of what each actually costs per month, why the answer surprises people, and which one suits how you would really use it.

• Your hot tub cover is the whole bill

  How to tell if a cover has failed, what a waterlogged one costs you each month, and what to look for when replacing it.

• How long a hot tub takes to heat

  Why a fresh fill takes most of a day, what changes the answer, and how to tell when your tub simply will not reach the temperature you want.

• How long a sauna takes to heat

  Typical heat-up times by heater size, why insulation matters more than kilowatts, and whether a hotter sauna is worth the wait.