Free tool
Sauna heater size calculator
Enter your cabin dimensions to get the effective volume, the heater or stove power you need, an estimated heat-up time to 80 °C and the daily running cost. Works for both electric heaters and wood-fired stoves. Log walls, glass doors and uninsulated stone or brick all increase the load.
Want the full picture? Read the commercial sauna running costs guide.
Heat source
Electric heaters hold temperature on a thermostat, so duty cycle drops once the cabin is up to heat.
Sauna room size
Construction
Running pattern
Calculatory volume
9.9m³
Actual cabin volume 8.4 m³.
Heater power
9.0kW
Calculated requirement 8.9 kW, rounded to the next standard heater.
Heat-up to 80 °C
~50min
From cold, door closed, with the recommended heater.
Cost per day
€10.25
About 29.3 kWh at €0.35/kWh.
These are modelled estimates using standard volume-factor sizing. Real behaviour depends on ventilation, ambient temperature and how often the door opens — which is exactly what SenseStack measures on site.
How the numbers are worked out
Effective volume
Width × height × depth, plus 1.2 m³ for every m² of uninsulated heat-storing surface, plus 1.5 m³ for a glass door. A log cabin multiplies the total by 1.5.
Heater or stove power
Roughly 1 kW per m³ of effective volume up to 6 m³, then 0.75 kW per m³ above that, rounded up to the next standard heater. A wood-fired stove is sized at about 1.4× that figure and rounded to the nearest common stove rating.
Heat-up time
A matched electric heater takes about 45 minutes from cold. Thermal mass adds to it: log walls roughly 18 minutes, a glass door 4, and 3 minutes per m² of uninsulated surface. Wood-fired adds a further 25 minutes for lighting and charging the stove.
Daily energy and fuel
Electric: full power for 90% of the heat-up period, then 35% while holding, times your tariff. Wood: 80% during heat-up and 45% while holding, converted to kilos at 2.45 kWh of useful heat per kg of dry hardwood, times your firewood price.
A model tells you what should happen. SenseStack tells you what did.
Every estimate on this page assumes a closed door, stable ambient temperature and a heater in good condition. In a working venue none of those hold. SenseStack puts a probe at bench head height and a sensor on the door frame, so you see the real heat-up curve, the real recovery time after each guest, and the hours you are paying to hold an empty cabin.
Common questions
How do you size a sauna heater?
Start with the cabin volume in cubic metres (width x height x depth). Add roughly 1.2 m3 of effective volume for every square metre of uninsulated, heat-storing surface such as brick, concrete or stone. Add about 1.5 m3 for a full glass door, and increase the total by around 50% for a solid log cabin. Roughly 1 kW of heater power per cubic metre of effective volume is the working rule for domestic and small commercial cabins.
How do you size a wood-fired sauna stove?
Wood stoves are rated for a cabin volume range rather than a precise kW figure, and they are deliberately oversized compared with electric. Take the same effective volume, then allow roughly 1.4 times the equivalent electric power to account for flue losses and the fact that output rises and falls with each load of wood. A stove rated below the cabin volume will never hold temperature on a cold day, no matter how much wood you burn.
How long does a sauna take to heat up?
A correctly sized electric cabin typically reaches 80 C in 35 to 60 minutes from cold. A wood-fired cabin usually takes 60 to 90 minutes because the fire has to establish before useful output begins, and the stove body and stones must charge. Log walls, glass doors and uninsulated surfaces all add time because they store heat before the air stabilises.
How much does it cost to run a sauna per day?
For electric, multiply heater power by the hours it actually draws current: expect roughly 90% duty during heat-up and 30 to 40% while holding. At Irish commercial rates of about EUR 0.35 per kWh, a 9 kW cabin held for eight hours typically costs EUR 12 to EUR 20 per day. For wood, count kilos instead: dry hardwood delivers about 2.45 kWh of useful heat per kg once stove efficiency is accounted for, so a busy session day commonly burns 15 to 35 kg.
Is this calculator accurate?
It is an estimate based on standard volume-factor sizing. Real heat-up time and energy use depend on ambient temperature, ventilation, door discipline, wood moisture content and how often the cabin is opened. SenseStack measures the actual figures on your site with a probe at bench head height.