Biomass

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Domestic biomass heating systems come in two basic flavours: wood-burning stoves and automatically fed boilers burning wood pellets. Both work most cleanly and efficiently at full throttle, so do not install a larger system than you need.

The wood-burning stoves usually sit in a fireplace and need to be fed manually with logs or briquettes (see below about briquettes). Many stoves can also burn coal, but this is a fossil fuel so not at all eco-friendly. There are a vast range of stoves on the market, including many secondhand ones, and they are much more efficient at heating a room than an open fire. A simple stove can be bought for as little as £100 secondhand, but you will need to fit it yourself. There is also the problem of fitting a flue. Traditional chimneys work well with open fires because a lot of heat goes up them with the smoke. With stoves less heat goes up the chimney, although the older the stove the more heat is likely to rise. If the smoke cools too much on the way up, the stove will not draw properly and large amounts of soot and tar may be deposited on the chimney sides. This can lead to trouble, so it is recommended that the chimney is lined (can be done DIY, but beware building regulations). A new stove is likely to cost from £350 to £3,000, depending on size and styling. Having a flue installed to line a chimney or instead of a chimney is likely to cost about the same again.  

The step up from simple space heating is to have a stove with back boiler, which will heat the room, the hot water and central heating system. These are not that much more expensive than their simple cousins, starting at around £500 for something that will just manage to heat the hot water, not run the central heating. Stoves with back boilers tend to produce less heat into the room than without the boiler, but still have that real-fire look and kick out a reasonable heat compared to an open fire. Stove boilers are rated in BTUs (British Thermal Units), with a standard hot water tank needing around 10,000 BTUs to work well and each radiator needing an additional 4,000 BTUs. Remember that when the fire is lit, you won’t need the radiators so much. 1kW roughly equals 3,000 BTUs.

Logs cost an arm and a leg if you buy them in small quantities from a national delivery service, so try and find a local supplier (local papers often have ads for this). I would think that a 2 cubic meter load should cost around £100 – that’s quite a lot of logs, probably enough for an autumn to spring burning season.You cab find local suppliers of logs (as well as pellets etc) via the Logpile search utility.

Briquettes are a good alternative and you can either buy them or make them yourself. The bought variety are usually made out of waste wood (especially dust and chippings) which is compressed into a briquette. They tend to give out more heat than logs. You can make them yourself using waste paper, leaves etc: mulch everything down in a bucket, then squeeze all the water out to make a kind of papier-mâché log. There are dedicated briquette makers out there to do the squeezing, or you could make you own (go on - use some string and sticky-backed plastic).

Automatic feed boilers have a hopper to hold the compressed wood pellets, which are then automatically fed to the wood-burning boiler via a vacuum feed or conveyer belt (Archimedes screw or similar). They are usually not decorative items, acting very much like a traditional boiler in that they are kept out of the way and burn a fuel to heat water. However, it is possible to get some that fit into the living room and look like a normal wood-burning stove. Some of these you can fill manually with around 10kg of pellets (about half a day’s burn), or the hopper and feed system will have to be incorporated somewhere and be connected to the stove/boiler by the pellet feed line.

The pellet boilers can be pretty funky, including the decorative stove ones. They usually need to burn continuously, using a small amount of fuel to act as a pilot light when not in use, but can be programmed to ignite fully at various times, just like a normal boiler. Some can be controlled remotely too. Some have automatic ash collection and cleaning systems to reduce manual input and most are fairly robust and low maintenance, but do remember to sweep the chimney.

Pellet boilers start at around £4,000 with hopper and autofeed, but installation will bump that up to around £5,000 if you need a new flue or chimney lining. Even the bigger and fancier outfits with tricky installation are unlikely to cost more than £12,000 ready to go.

Wood pellets are usually made out of waste from the woodworking industry.  As a rule of thumb, 1kg of pellets gives as much heat as 1 litre of heating oil. They can either be bought by the bag or truck load, depending on how much storage room you have.

Pellets cost between 14p and 20p per kilo. Although it is ridiculous to generalise about consumption, I will: budget for using around 25kg of pellets a day. This will produce around 25g to 50g of ash, which can be used as a fertilizer once collected.

If you burn any coal in a multi-fuel stove, DO NOT put the ash on your garden as fertilizer. It will contain traces of tar and other nasties that will kill your plants.

If you do not have a chimney and need to raise a flue, you may need planning consent, especially in conservation areas or in a listed building. It is probably worth checking anyway, as councils can get a bit shirty if they catch people doing things on the sly. If you live in a smokeless zone, you can only use exempt kit (see the last sentence). Makers of such exempt boilers include Clearview, Vermont Castings, Dovre Castings Ltd, Dunsley Yorkshire Stoves, Morso, Osier and Jotul.

Stoves Are Us have a highly unoriginal name, but a good range of stand-alone wood-burning stoves and stoves with back boilers. Something for everyone, pretty much. Prices are keen, but you will have to sort out your own installation.

Treco offer wood pellet boilers (as well as other related products) that you can install yourself (they have DIY guides), part install yourself with help from your local plumber, or Treco can design and install a complete system for you. The site survey and cost estimates are done free of charge and with no obligation.

Alternatively, you can do a regional search for certified microgeneration installers at greenbook. They also have lists of certified microgeneration products.

Biomass heating is not eligible for the new Feed In Tariff grant system, so there will be no official financial help until the Renewable Heat Incentive gets here.

The Logpile search utility is great for finding suppliers of all types of biomass fuel. The Log Pile website from the National Energy Foundation is well worth visiting if you are thinking of going down the biomass route.

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