Answers to the most common domestic wood burning questions

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As the popularity of domestic wood burning continues to rise, the number of questions asked by home owners and installers is also on the up, says David Ebbs, Technical Sales Support at Specflue.

Most people are aware that burning wood is a ‘green’ method of heating their home. The CO given off by burning a log is no greater than simply allowing it to rot and decompose in the garden. However, to be truly ‘green’, we should also be thinking about other aspects before the wood is burnt, such as how the forests are being replenished and how the wood is being transported.

Scandinavian timber has many road and ferry miles on its clock before arriving on your customers driveway, and kiln dried wood has required a large hot ‘oven’ to help force dry the fuel.

With over 25 years of experience in the flue, chimney and wood burning stove industry, we are often asked questions around their installation and use. Here are a few of the most common:

“Can I burn coal as well as wood?”

This depends on the appliance; some are pure wood burners, some are multi-fuel. Most wood burners do offer a multi-fuel kit, so they can be converted to burn coals as well. In essence, wood burns best on a solid base, with a small covering of ash. Coals need to be lifted off this base, to allow air to pass below the fuel.

“How often should the flue be swept?”

The flue manufacturer should specify this in their literature, but as a rule it is twice a year; once after the winter burning season, late spring and again before the burning season starts in October. Spring cleaning removes corrosive deposits, so they don’t attack the flue during the summer. The autumn clean ensures any blockages are removed.

“Who can sweep my flue?”

A qualified chimney sweep who is a member of a chimney sweep association must do this job. The sweeping certificate must be kept, as this will be requested if the liner fails or the property has a fire. (Tip: keep a copy of all certificates within an email account, so they can be accessed remotely).

“What is ‘seasoned’ wood?”

This is wood which has been cut down and left for several weather ‘seasons’ to dry out. Different wood types take longer than others to season; most pine woods take around a year, whilst hardwood elm and oak can take three years. How it is stored also influences how it dries and the only accurate way to know if it is ready to use is by using a moisture meter and looking for figures under 20%. (Tip: It’s often possible to tell that wood is near to the 20%, as cracks start to develop across the grain, the bark falls off, and it feels lighter than expected).

“How is it best to store logs?”

Outside, under cover, lifted off the ground on a pallet, so the air can circulate. The logs should be on their side, not upright.

“How is it best to store coal?”

In a coal bunker; weather will not hurt the fuel, but to attain maximum efficiency, you need to ensure its dry when taking indoors to burn. (Tip: If bought in plastic bags and stored in a garage or shed, open the bags to allow any moisture to evaporate and avoid the fuel sweating).

“Do I need a flue terminal?”

If it’s a twin wall system, it needs a termination fitting. This could be a rain cap style, or be an open stub. If its flexible liner within a chimney stack, it can have a rain cap fitted, or could be left open. Naturally the hot flue gases want to rise and escape, so any type of rain lid obstruction isn’t great for the system. Any type of approved meshed terminal, on wood and solid fuel, must be regularly removed and cleaned to prevent blockages, so access is required.

“Is an air vent needed?”

If the appliance is rated at 5kW or above, then regulations require an air vent into the room. If less than 5kW, then regulations do not call for a vent, but may be needed for the appliance to work efficiently.

“Who can fit the wood/multi fuel appliance?”

A HETAS Approved Installer, who can provide a signed certificate of installation. The local building control officer may also approve the installation, but would not be able to test and provide appliance demonstration and instructions.

“Can I burn any wood?”

No, only seasoned firewood should be used. You shouldn’t use timber offcuts from building sites as this wood is treated. Painted or stained wood should also be avoided as the paint and preservatives can give off aggressive chemicals which attack both the flue and appliance.

“Is a CO alarm required?”

Yes, it is mandatory to install Carbon Monoxide (CO) alarms in every room with a wood or multi fuel appliance. Special CO alarms with flashing lights and pillow vibration pads can now be installed for the deaf or hard of hearing.

“How is it best to use my appliance?”

You should follow the manufacturers’ instructions. Learn how the air wash vents work to keep the glass clean, etc. Never attempt long periods of slumber, (such as overnight burning), as the low flue gas temperature can damage the flue and will invalidate warranties. Always start each period of use with a roaring fire for 15 to 20 minutes. Keep the flue gas temperature at the suggested levels, (Tip: A stove pipe thermometer can advise temperatures).

“I live in a thatched property, can I use my chimney?”

Different regulations exist for thatched properties, so check the HETAS thatch regulations literature. Heat transfer from the stack to the thatch is a concern, so a distance of at least 200mm must be allowed between the thatch and flue outer. The termination height must also be 1.8m above the thatch.

“Will a twin wall flue get hot to touch?”

Yes, obviously different manufacturers products will vary, but for a ‘standard’ 25mm insulated twin wall flue, on a wood burning stove, you could expect the twin wall outer to heat to temperatures in excess on 90o Celsius.

“Can I burn the appliance with the stove door open?”

Generally no. Only a few appliances on the market allow this; the vast majority are ‘closed’ appliances, so whilst alight, the door should be kept shut, apart for refuelling.

“What diameter flue can I use?”

Refer to the manufacturers’ literature. Usually a standard small to medium sized wood stove will need 125mm or 150mm diameter flue. (125mm is only to be used if the appliance has Defra approval). You should not reduce the flue diameter, so a 150mm flue can not reduce down to an existing 125mm flue. Increases can occur, so long as it isn’t too much.

“My proposed flue route does not meet regulations, do I have any other options?”

Possibly as flue top fans can help and most flue suppliers can calculate flue resistances. However, it might be worth thinking about another position for the appliance and flue.

“Can I use chemical cleaners in the flue?”

Some chemical cleaners are approved by the flue manufacturers, but always check before using them. Chemical cleaners are not a substitute for chimney sweeping.

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