Calculators

[The running cost calculator](/tools/running-cost-calculator) takes four numbers — rated watts, your electricity rate, hours a night, nights in the season — and gives you cost per hour, per month and for the whole winter. It exists because published guidance in this category still assumes a rate of roughly 12 cents per kWh, which is years out of date. At the actual June 2026 US average of 18.34 cents, the same fireplace costs about 53% more than those figures suggest.

[The room size calculator](/tools/room-size-calculator) takes your room dimensions and a wattage, and tells you the BTU the unit produces, the BTU the room wants, and the shortfall if there is one. It reports the gap as plainly as the fit, which is the part most sizing tools leave out — a calculator that only ever says yes is an advertisement.

Both calculators use the same functions that produce every static figure elsewhere on this site, so a page and a calculator cannot disagree with each other. The formulas are simple enough to check by hand: cost per hour = (watts ÷ 1,000) × your rate, and BTU per hour = watts × 3.412.

That second conversion is exact rather than approximate. Resistive heating converts essentially all its electrical input into heat, so there is no efficiency factor to estimate and nothing to fudge. It is one of the few places in consumer products where the arithmetic is genuinely clean, which is exactly why it is strange that so little of this category publishes it.