Why Your Stove Needs Ventilation
All fires need oxygen rich air to burn fuel and a stove is no exception. A poor air supply is a common cause for a sluggish or slow burning stove. Stoves have air vents through which air is pulled into the stove from the room and onto the fire. If the vents are closed then the stove can’t pull air in and the fire will die down. Likewise if the room is airtight, the stove will pull in what it can but will eventually slow down as there is just not enough air in the room to keep the fire going for long. As the air supply into the stove grows weaker, the possibility that smoke and emissions like carbon monoxide could be pushed back through the air vents into the room increases, so this is a significant issue that needs to be dealt with.
A simple test to see if the air supply in a room is causing poor performance is to open a window in the room. If the fire immediately improves as air is pulled into the room through the open window and onwards into the stove, then you know air supply is the problem and you need to increase the rooms ventilation. Keeping a window open is not solving the problem and it kind of defeats the object of heating the room.
In 1965 building regulations were introduced to limit the amount of energy that could be lost from new homes due to some of the materials used in their construction. These regulations have been updated a few times since then in particular in 2006 when the regulations were significantly tightened up, again to further reduce energy loss. These improvements included fitting insulation in various parts of the building, fitting windows that are practically air tight etc. These changes are great for ensuring homes remain warm without wasting too much energy but they can impact how a stove performs.
Homes built after 2006 all require a permanently open air vent in the room with the stove, venting from the outside, regardless of the size of the stove.
Homes built before 2006 do not require ventilation for a stove that produces up to 5 kilowatts of heat, unless significant improvements have been made to the room, e.g. new windows / door / flooring etc that make the room practically air tight.
In homes built before 2006 with a stove that is greater than 5kW, a permanently open air vent is required. The size of the vent required is proportionate to the size of the heat output of the stove and it is calculated as 550 square millimetres of vent hole per kW of stove, over 5kW.
The table below details the size of a vent hole that is required for stoves of 6kW and up. These dimensions have been rounded up and can be altered as long as the result is the same, i.e. 8cm x 4.2cm = 3300mm2 or 6cm x 5.5cm = 3300mm2. The vent size required can be split across multiple vents, as long as they are in the same room and lead to the outside.
Remember, it is a building regulation to have ventilation in a room with a stove of 6kW output and above which means this will need to be signed off by your HETAS installer or the councils building regs team.
Vent Size, Rounded Up
|kW Output||Vent Size Required mm2||length (cm)||height (cm)|
Position Of Additional Ventilation
Where additional ventilation is required, the vent must be permanently open to the outside and it should not be possible to block or close it. Many older homes have air bricks in the outside wall that enter a room below floorboard level. If the room has exposed floorboards and they are not fitted together tightly it is possible for air to be pulled from the outside through the air brick and up through the floorboards into the room. This may provide sufficient ventilation for the stoves needs.
If the floorboards are tight together or they are covered by a carpet or other flooring, air will not be able to enter the room through the floorboards but a vent could be added in the floor (often just in front of the hearth) i.e. a small rectangle could be cut in the carpet, flooring or floorboards and covered by a smart vent cover, allowing air to flow into the room just in front of the stove. If there is no air brick or any other opening that would allow permanent ventilation, then one will need to be added.
Be aware when you position any new air vent that when the fire is burning well and drawing air in, you may be able to feel air as it travels from the vent to the stove. So don’t position it where you will feel a draught as you sit in the room.