FLUE REQUIREMENTS FOR STOVES IN TINY SPACES
Building regulations state that the flue height should be a minimum of 4.5m (15’) from the top of the stove. However, it is generally accepted that this will not always be practical or aesthetically pleasing for temporary leisure accommodation such as sheds, log cabins and shepherd huts and therefore a compromise, which is both safe and practical, should be sought – but only after complying with the critical BS8303 spillage tests (more about this below). Here’s some important considerations...
If the stove that you’re considering for your tiny space has a 150mm (6”) diameter flue outlet then in our opinion it’s unlikely that it’s going to be appropriate – so please think again. This is because it will probably have an unsuitably high output for such a space. It will probably mean that you won’t be able to burn it with a full fuel load so that it will usually be burning inefficiently, causing nuisance smoke and unwelcome and potentially dangerous tar build-up inside your chimney system. Further, in order to create a safe and sufficient flue updraught with a 150mm flue system you will require a much taller flue which would therefore need additional strong supports anchored to your roof. This will cost significantly more money, create more work and in the end will probably look disproportionate and out of place on your structure. At the end of the day, if you’re slow burning or slumbering the stove because the heat output is too high for your space then no matter what the height of the flue it will probably still be difficult to guarantee sufficient updraught to safely clear the combustion gases and to maintain a clean stove glass.
It is much better therefore to aim for a sub-5kW stove with a 125mm (5”) or specialist 100mm (4”) flue diameter. Either of these flue diameters will have the advantage of letting you get a way with a reduced flue height, again subject to successful spillage tests. Stoves with 100mm (4”) flue diameters, like those from Salamander, will always offer you the best chance of a dependable flue draught especially with a significantly reduced flue height.
Do not use the stoves's rear flue outlet since, however small the horizontal run of connecting flue pipe – even with a swept 90º bend, this will most certainly interfere with the safe flow of combustion gases when flue pressure is compromised with a lower flue height. Always use the connecting flue pipe straight off the top of the stove and avoid introducing any bends you will have a much better chance of a achieving sufficient updraught.
The minimum recommended flue pressure for most stoves is usually 12Pa although many can safely operate at 9 or 10Pa when a good flue is part of the system. Provided the flue pressure reading is within the 9Pa to 18Pa range then most stoves should operate satisfactorily – subject to any spillage test outcomes. Where the flue pressure is significantly less than 12Pa appropriate steps should be taken to improve this. This usually means extending the flue height and ensuring that it is well insulated for the whole of its height and also checking that the stove has an adequate supply of combustion air.
Ideally your connecting flue pipe should include an inspection hatch which will allow you to regularly check the performance of your fuel and flue and provide you with an indication of when the flue will need sweeping. This hatch can also be used to sweep the flue for much simpler cleaning although these days most stoves have been designed with drop down baffles to also allow the flue to be swept through the stove.
A word of warning – under no circumstances should the flue pipe diameter be less than the flue outlet size of the stove and never use flexible flue liner for any part of the flue system as this will offer no protection from the extremely hot flue gases. Flexible flue liner should always be contained within a brick or stone built chimney.
Go Back to Guide to Stove Installation in Huts, Sheds and Cabins Menu Page
