Properly size a pellet boiler

Heating with wood pellets: the question to ask before choosing this method of heating?

How to properly size its future wood boiler?

The average power of his boiler must correspond to the average losses of his home when it is coldest. To estimate the losses, that is to say to make a thermal balance, is therefore to find the right power for your boiler.

The best way to properly size is to make or have a study done on the thermal losses of the dwelling. In some regions, this study is subsidized.

a) Make a complete thermal study

Doing a reliable study is not necessarily easy. Some sites on the internet allow you to make approximations with as input data, the place of residence, the general characteristics of the house… See "Find out more" below.

Spending a few hours to test multiple sites and / or method is a pretty good method to have a consistent trend.

b) Use the old power of your boiler

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In the event of a change of boiler, taking an equivalent power can be tempting but it is not necessarily the right solution because:
- old heaters are often oversized
- as we have seen previously: the oversizing of a wood-fired boiler can be catastrophic in performance
- a more powerful boiler costs more
- improvement work (insulation, change of frames, etc.) may have been carried out in the house: the needs are therefore less important than before.
- global warming: in many regions, winters have been milder for a decade. The basic temperatures of heat balance calculations may therefore need to be reviewed ...

3) Approximation by volume

A very simple method but also very imprecise is the first approximation to use the volume of your home.

We can also multiply the volume inhabited by 30W / m3 (very well insulated) to 50W / m3 (poorly isolated) but the margin of error is large and oversizing your boiler is possible with the problems that this entails.

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Note for additional heating

If you have an additional heater in the chimney or woodstove style, and you make a complete calculation from the base temperature of your area, consider raising it a few degrees or to integrate the power provided by the fireplace in the calculation.

If it is -15 ° C once every 10 years, and the boiler is not powerful enough that day, you will build an additional chimney fire.


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Sizing the wood boiler is essential, even more than for fuel oil or gas.

The heating professionals are not necessarily the most competent to make a thermal balance and, commercially, some will tend to offer more powerful equipment because more expensive.

So do not hesitate to call on a thermal study office: the cost of the thermal balance study will be tenfold if it saves you from buying a more powerful boiler, therefore oversized.

You can also use thermal balance tools that we put at your disposal.


- Make a thermal assessment or an energy diagnosis
- Thermal Balance and DPE by ADEME
- Forum wood heating
- Housing, insulation and heating downloads

Read more: Pellet consumption estimate calculation

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