How do I know what output I need from my boiler?

stockton 8HB boiler stove

Working out your output requirements for a new boiler can be tricky. When it comes to working out what kind of output you need from a normal stove it is relatively simple in comparison. This is because you only need a normal stove to warm the room in which the stove resides.

(In case you’re wondering, the stove output formula for this is (in metres) (Length x Width x Height)÷14. You’re welcome to use our output calculator tool.)

However many people are looking to use their stove to heat their whole home, which is where a boiler stove comes in to play. The problem is, to the average person on the street, knowing what output you need without a simple formula like the one above can seem quite daunting.

To begin with you need to realistically look at your household’s heating needs. When it comes to talking about central heating systems and heating water we use British Thermal Units (BTUs). To convert BTUs into Kilowatts (kW), which is how we measure the output of a stove, we know that 3,400 BTUs are approximately equal to 1kW.

The average person requires 3kW per day. That is about 10,000 BTUs for domestic hot water. So the first thing you need to do is add up how many people are in your home and the total BTUs.


Next you need to work out the BTU requirement of your home’s radiators. The average 1.2m (4ft) radiator needs 1.5kW, which is 5,000 BTUs. Times this by the number of radiators in your home.

Add together the total BTU of everyone in the home and total BTU of all the radiators in the house and that gives you the figure you need to look out for when buying a boiler for your stove. This figure indicates how many BTUs you will need to run everything – heating, hot water, etc. This figure can be lowered if it is supplemented with the likes of solar panels or a gas boiler.

For ease all of our boiler products are listed with kW to room, kW to water, BTU to water, and number of average radiators that can run on the appliance.

There are many different ways to install a boiler stove and many different factors to consider. It is always best to consult a HETAS qualified engineer when considering an undertaking of this size. They will be able to advise on direct circuit heating vs storage systems, hot water tanks vs thermal heat stoves, and the differences between gravity and pump fed systems.

A boiler stove is a considered purchase but there are a lot more options today than there have ever been before. Whatever your heating situation and requirements, there is a solution for you.

Got a question? Leave it in the comments below or get in touch!

2 thoughts on “How do I know what output I need from my boiler?

  1. Hello,
    We arecommend in a smokeless zone and have been looking at defra approved boiler stoves but this is a very small market. Is it possible to fit a defra approved smoke kit to a boiler stove such as the Stovax View 8HB or the Yeoman CL8HB?

  2. Hi Diana,

    Thanks for the comment, its a very good question. DEFRA Kits restrict the movement of the top air slider, meaning that you can’t fully shut the air supply to the stove down, as such the fire burns hotter and more cleanly and therefore conforms with the DEFRA regulations. As such, unless the stove has been tested and approved for use with the kit on that model, you can’t simply buy the kit and fit it to any stove, even if the manufacture make a DEFRA kit to fit a non-boiler version of the same stove, there is no guarantee that the kit would even fit the boiler version, so this is not an option i am afraid.

    You are quite right there are only a handful of boiler stoves that are available and have been approved by DEFRA for burning wood in a smoke control zone. Here are some links to six of those products:

    If you have any further questions, please let us know or you can contact us directly on

    Fireplace Products

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