Appropriate Chimney Height (Above the Roof) in the UK
The minimum chimney height on the roof recommended for the minimum performance of wood-burning and multi-fuel appliances is 4.5m from the top of the appliance to the top of the chimney.
The distance between the cowl of the flue and the adjacent roof/wall/structure should be higher than 2.3 metres.
It is best to position the chimney, so that it goes straight up as near to the roof ridge as possible. The diagram below, taken from Document J (building regulations), shows the minimum flue discharge heights and positions for all wood burning and multi-fuel applications.
What does this mean for the height of the flue on the roof, though? Here’s the correlation between roof pitch and flue height on the roof:
|Pitch of the roof
|Height on the roof
In some cases, particularly when chimneys are towards the bottom of a sloping roof or at the eaves, it may be necessary to increase the chimney height above these minimum mandatory requirements. The reason for this is to clear pressure zones created by wind hitting the roof and nearby structures, like trees, which may interfere with the updraught required by the appliance or fire.
Why Is Chimney Height Important?
There are many different reasons why chimney height is important. Some of these include the following:
- Draft Efficiency - Having the right chimney height is essential when it comes to draft efficiency. A chimney that’s too short will have an inefficient draft, but one that’s too tall will lose far too much heat.
- Combustion Efficiency - If the chimney isn’t at the correct height, it can quickly lead to inefficient combustion. With a draft that isn’t working properly, the fuel won’t burn as well as it should, leading to higher fuel bills and inefficient heating.
- Prevention of Downdrafts - An appropriately sized chimney will help to prevent downdrafts resulting from inefficient drafts and other similar problems.
- Prevention of Creosote Buildup - An appropriate chimney height helps to prevent the buildup of creosote and other combustion residues.
- Compliance with Building Codes - UK building codes specify particular chimney height requirements. Having a chimney that’s too short can result in fines and other problems.
- Prevention of Smoke and Odour Issues - An appropriately sized chimney helps to prevent gases from filtering back into the room, thereby avoiding odour issues.
- Optimal Heating System Performance - The height of the chimney has a significant impact on the overall performance of the system. To ensure that it keeps working properly, it’s vital to have the correct chimney height.
Chimney Height Considerations
When trying to discern how much the chimney height above the roof should be, there are several factors you need to consider. Some of these include the following:
- Appliance Type - Different types of appliances have different requirements in terms of chimney height. For example, a wood stove may not require the same chimney height as a pellet stove would.
- Environmental Conditions - Wind patterns, topography, and other environmental conditions may have an impact on the chimney height you will require.
- Chimney Temperature - Cold chimneys may not work as well as warm chimneys, which is why it’s sometimes necessary to pre-heat the flue. The exception being insulated pipes, which work well either way.
Freestanding chimney height on the roof
The maximum freestanding stack height above the roof for a traditional masonry chimney is 4.5 times the narrowest horizontal part of the chimney.
In the case of stainless steel system chimneys, the manufacturer’s installation instructions should be consulted; however in most cases it will be around 3 metres. This measurement is taken from the last point where the chimney stack passes the through or past the edge of the roof up to the chimney capping or termination. Tall chimneys may need bracing so, always consult the manufacturer for advice.
For buildings with combustible roofs e.g. felted roofs, the flue must terminate a minimum of 1.8m above the combustible surface.
Knowing the appropriate height for the chimney on your appliance is essential. However, if you’re not well-versed in this kind of situation, deciphering the appropriate height can seem complex. If you require assistance with this kind of project, feel free to contact us.
We stock a wide range of different chimney flues, flue pipes, flue liners, and other products required for these setups. We also have a lot of knowledge and experience and can help you determine what the best setup will be for your appliance chimney.