KiloWatt Calculator

Calculate the kiloWatt power needed to heat your room. Simply enter the height, width and length of your room and choose an insulation level, then click submit. The form only accepts numbers.

Calculator Explained

Though only a rough estimate, the formula of our kilowatt number cruncher works as follows: we multiply the width, length and height of your space, and divide by a number between 15-25. That exact final number depends on the insulation of your home:

  • Poorly insulated: mainly refers to homes built before 1950, or a space with multiple draughts present and very little insulation
  • Moderately insulated: usually a home build in the 1990s and fitted with double glazing
  • Well insulated: signifies new, airtight homes built after 2008, after which compulsory heating standards were introduced


If you have a big room, the temptation is to purchase a large, magisterial stove – likewise with cosier living spaces, a more compact stove might appear the best choice. However, this isn’t the best approach. If too small you’ll have to constantly be topping up the fuel load on those chillier days, which risks overheating and can eventually damage the stove. Similarly, bigger stoves need to follow their manufacturing guidelines: starving them of their expected fuel load or firebox temperature will distort the overall efficiency.

Heat Output

All the stoves sold by Choice Stoves are measured in kilowatts (kW). The higher the kilowatt output, the greater the heat generated. You should also note the terms ‘nominal heat output’ and ‘maximum heat output’ – nominal marks the point where fuel supply is efficiently producing a healthy output, and maximum being the highest kW limit a stove should reach.

Another thing to notice is our efficiency ratings, always measured in % terms. This figure compares the amount of heat that’s radiating across your room with the amount that inevitably escapes through a chimney or flue e.g. a 75% efficiency simply means 25% of the overall output is lost elsewhere.

Other Factors

There are a host of other factors that will feed into the decision process, such as how well insulated your rooms are, how old your house is, and the spatial layout of your downstairs. For example, if you have an open plan design with an archway connecting two rooms, this should be treated as one room. Or if there’s an open staircase, meaning heat will inevitably travel upstairs, this will impact on your kW requirements. Even window size and aspect of your house can affect your choice – so overall, ensure you clearly define the confines of your space beforehand.


Wood burning stoves warm the room by convection, heating the air around it which rises and fills the room with heat. To work effectively your stove must have a reasonable amount of space around it. If your stove is fitted into an opening just a few millimetres larger than itself it’s efficiency and the amount of heat put out will be greatly reduced.

You should also take care that there are no combustible materials near your stove, curtains, wallpaper, soft furnishings etc..

We would recommend the following minimum clearances as a guide for safety and best performance:

  • Distance at the back of the stove 50mm – 75mm (as a minimum)
  • Distance at the sides of the stove 100mm – 125mm (as a minimum)
  • Top of the stove 100mm – 150mm (as a minimum)

Of course every situation is unique so please feel free to check any stove related issues with our helpful and friendly staff.