Wood Burning Stoves FAQ

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This set of Frequently Asked Questions (FAQ) discusses what you need to consider when choosing a log burner or multi-fuel stove – i.e. a stove typically used in place of an open fire to burn wood, coal or other appropriate solid fuels used to heat your home. It does not discuss gas, oil or wood pellet burners used for heating.

Should I worry about air pollution with a stove?

Wood stoves are inherently more polluting that gas boilers or electricity. Even the most efficient stove generates some air pollution, both inside and outside the home. The main problem is fine particulates, (PM2.5) which get into our lungs. High levels in London have been blamed partly on the increasing use of wood stoves (see also Worst London air pollution in six years as home fires burn (Guardian)). We would not recommend using a wood stove as your main form of heat in a city, and even occasional use can have health impacts on your neighbours. However some stoves are a great deal better than others. Biomass boilers are not so bad, though they are not perfect either.

To minimise air pollution from your stove, make sure your fuel is well seasoned and you run the fire hot enough to consume the wood thoroughly. Avoid burning wood that has been treated with paint or preservative as this causes extra pollution.

See also Wood burning - the Inconvenient Truth from CCF, Will air pollution from biomass heating damage our health? from Nicola's blog and this article Wood Burners Triple Harmful Indoor Air Pollution in the Guardian.

Why might I want to buy a stove?

There are numerous reasons you might want a stove including:

  • Saving money - particularly if you use oil heating and have a cheap or free source of wood.
  • Increased Efficiency – if you already use an open fire then a stove would be far more efficient, up to around 80% efficient compared to 20-30% for an open fire. You can hence burn the same amount of fuel and benefit from more heat or burn far less fuel for the same amount of heat.
  • Aesthetics – a stove can be an excellent centrepiece for a room, it’s not unusual for owners to find themselves watching the flames in the stove and talking to each other rather than watching TV in silence!
  • Cutting your carbon foot print - burning wood from renewable resources and replacing other fuels like coal, gas or oil will help cut your carbon footprint

What do I need to consider when buying a stove?

Heat Output

The first decision is how much heat you want to generate. Whilst it’s tempting to purchase the largest that will fit in your room or burns the largest logs possible, you need to be realistic. Too small and it won’t heat your room enough, too large and you’ll overheat or need to limit the flow of air into the stove – burning fuel inefficiently.

Heat output is measured in kilo watts (kW). 1 kW is the equivalent of a one bar electric heater. A normal double radiator (e.g. 600mm x 900 mm) gives out about 1.5kW. An online calculator, e.g. this one: StovesAndFires.com will give you a rough idea of what you may want given the size of the room you’ll be heating. An estimate in kW is (volume of the room in meters cubed) / 14.

Stoves are available ranging from roughly 3kW to 15kW.

Fuel Type

If you are in the one Smoke Control Area in Cambridge this will narrow down your options of fuel and stoves you can use (more details below). If you want to be able to burn both wood and coal, you need a multi-fuel stove. If it’s just wood, a wood burning stove should meet your needs.

Once you’ve worked out the heat output required and fuel type, you can then decide on factors such as style (contemporary or modern?), do you want to also heat hot water (i.e. a boiler stove), do you want a stand alone or inset stove (one built into a fireplace). As with most products, manufacturers also aim to differentiate their models with features such as ‘airwash’ and ‘clean burn’ stoves (these terms are defined below).

Supplier

It’s strongly recommended that you talk in detail with at least 3 stove suppliers, preferably more. Explain your requirements, understand what they think is best for you and why – these discussions will help you considerably. There are a couple of stove suppliers and installers in/around Cambridge city, but do look further afield as well – many in East Anglia will provide what you need. For an up to date list look in your Yellow Pages / Thompson Local under ‘Fireplaces’. See also links below.

How much do I need to budget for a stove?

At a minimum, small stoves start around £500, but you probably also need to budget for a flue to line your chimney. Expect to spend around £2500 upwards on a decent stove and full installation.

Be sure to use a professional when getting your stove installed – an accredited HETAS engineer (www.hetas.co.uk). Poor installation can lead to a multitude of problems including the leakage of carbon monoxide which is poisonous.

At the time of writing, there are no known financial incentives or Government grants for installing and using a solid fuel stove.

Do I need to buy a chimney liner?

At the time of writing (early 2012), it’s not a legal requirement to have your existing chimney lined with a liner (e.g. flexible stainless steel or pumice concrete), but it is recommended – it’ll ensure good draw, the airwash functions properly, increase the efficiency of your stove, stop smoke leaking out through cracks in your chimney and reduce the risk of a chimney fire if tar and soot deposits build up.

If you do not have it lined then you must have a smoke pressure test undertaken to ensure your chimney does not leak. This maybe ok today, but deterioration is ongoing. It is not recommended having a stove where the chimney is more than 10" sq (25.4cm sq) internal dimensions - bigger than this and your chimney will struggle with draw.

Chimney liners are usually installed from the top of the chimney – i.e. from the roof of your house. The majority of installations can be carried out using roof ladders, but where it is dangerous a cherry picker is the next cheapest if you have access, and finally scaffold the most expensive. Check this when talking to your stove supplier.

What about insulating my chimney?

You are likely to get conflicting advice on whether to then insulate your liner, usually by pouring vermiculite insulation down the chimney between the liner and the main chimney. Some argue this keeps the gasses in the liner hot, improving efficiency and the draw of air through the stove etc, others argue that insulation is unnecessary – you may want some heat to spread into the chimney above the fire, e.g. warming the rooms above. Again, best to discuss the options with 3 or more different suppliers/installers and come to your own decision.

What else?

You may also need to budget for alterations to the room in which you plan to install the stove. Building Regulations specify you need to have an area of non-flammable hearth greater than a specific thickness, as well as fireproof finish to any walls within range of the stove. If your stove has a heat output above 5kW you must also have permanently open air vents to allow air in from the outside. (see Building Regulations Approved Document J)

Worth also considering whether you want to use your stove to produce domestic hot water and/or to heat radiator(s) - either by adding a backboiler or in some cases a flue boiler.

Can I use my stove in a smokeless zone?

Cambridge has one ‘Smoke Control Area’ which covers the city centre, west and south west areas - details on the local Council website here.

The Department for Environment, Food and Rural Affairs (DEFRA) set the rules about what can and can’t be burnt in this area – when looking on stove suppliers websites you may see reference to ‘DEFRA exempt stoves’.

If you live in the Smoke Control Area, you have two options, either:

1) You must burn an authorised smokeless fuel (see list here ) – these include anthracite, semi-anthracite and low volatile steam coals. Note that wood is not authorised!

Or:

2) Any coal, wood or other fuel, which is not an authorised smokeless fuel, must be burnt on an heating appliance that is certified exempt for your chosen fuel – a exhaustive list of these appliances is here: http://smokecontrol.defra.gov.uk/appliances.php?country=e ). These include some stoves from manufacturers such as Clearview, Dovre, Dunsley, Esse,Euroheat and Morso amongst others.

If you don’t want to follow the law, there’s the potential of a £1000 fine to persuade you otherwise!

What can I burn - can I put in garden waste, plus household newspapers and paper waste, and cardboard as well as logs?

Assuming you are outside the city of Cambridge’s Smoke Control Area, if you have a log burning stove you’re best to burn dry, untreated logs. If you have a multi-fuel stove you can also burn coal – though best not to burn both wood and coal at the same time (wood burns best on a bed of ash and with air from above, coal best with air from below). Leave the garden waste in the garden – strangely enough it is permissible to burn ‘green’ garden waste on a bonfire in a smoke control area.

Dry newspaper, waste paper, cardboard etc are ideal for starting the fire and will burn well, but if burnt in any great quantity they produce a lot of ash.

The author’s log burner specifically states ‘do not burn kitchen waste, plastic, flammable fluids such as petrol, naptha or engine oil’ due to build up of deposits in the flue.

If you are in the city of Cambridge’s Smoke Control Area then you are legally obliged to only use the fuel for which your stove was certified as ‘smoke free’ (see above).

Where can I get firewood, and what is the best way to store it?

Wherever you source your wood, you’ll want to make sure it’s dry – stack firewood under cover in an open sided store where natural ventilation can dry it for one or preferably two summers. A reasonable estimate is that wood under cover dries at an inch a year. Freshly harvested wood can have a moisture content of > 60%. You may want a moisture meter to test your wood (e.g. see here for moisture meters on Amazon.co.uk ), ideally you want <20% moisture content, greater than this and the wood will burn poorly and produce tar.

There are a number of options when it comes to obtaining fuel to burn:

Buy firewood & smokeless fuels

The following websites maintain a list of suppliers, enter your postcode to carry out a search:

These include a wide range of suppliers, including the likes of Cambridge Woodworks , who reuse waste wood for community benefit, and Newman Farms of Bottisham. There are a number of alternative fuels becoming available that claim low or zero environmental impact - e.g. logs made of Straw waste

Neighbours, Friends, Colleagues & Skips

Do you have any friends & neighbours who are clearing out old or dead trees? Keep an eye open and generally let it be known that you’re looking for wood. It’s likely you’ll have to do some work - sawing, splitting and stacking. Similarly, whilst in theory it’s an offence under the 1968 Theft Act to remove wood from a skip without asking, most skip users will be delighted if you take out wood – provided you ask first!

Tree surgeons, furniture makers, woodworkers etc

If tree surgeons are working near by, it’s worth asking what they’ll be doing with the wood – often they’ll be happy to stack it for you and let you take it away. Off cuts from wood workers etc may also be worth seeking out.

Make ‘logs’ from newspapers & magazines

If you’re time rich but cash poor, you can make logs from newspapers and magazines, with instructions available from the following locations:

Note that these will need to dry for quite a while and, compared to logs, paper tends to produce quite a bit of ash when it burns.

The quality of fuel you use has a big impact on the level of pollution you generate: see Should I worry about air pollution with a stove? above.

What are the best ways to chop/split wood?

If you are handling waste wood you will need to chop it to a suitable length before you can use it and even if you have cut logs delivered they may need splitting. Here are some options requiring different levels of skill and effort.

Cutting to length:

  • A chain saw will handle anything but is potentially very dangerous, also heavy to handle. Do follow the safety instructions!
  • A reciprocating saw will handle small logs and waste palettes, floor boards etc. It takes longer but is lighter to handle. It can still do you a lot of damage if handled incorrectly and the vibrations may make your hand go numb if you use it for too long in one go.
  • A hand saw is less likely to chop your foot off but it is hard work.

Splitting

What sort of precautions should I take if I have waste timber to burn - are there coatings on wood which create noxious fumes when burnt?

You may want to use your stove like an industrial incinerator but it’s not recommended and is certainly illegal in the city’s Smoke Control Area! Burning painted wood, creosoted fence posts etc leads to both noxious fumes and a build up of deposits in your chimney liner, reducing its life and making it harder to sweep.

How should I run my stove to be most efficient?

When wood is heated it gives off tarry gases which are a good fuel but they are also sticky and corrosive. If you don't run the fire hot enough to burn these gases you are not only wasting fuel but they will also stick to your chimney liner. The chimney sweep will need to brush hard to remove these deposits and this will wear out the liner; if they remain they will cause corrosion and are a fire risk. It is very important therefore that you always run the fire hot. You should see lively flames, though not going up the chimney, and no smoke.

This means you should not bed the fire down overnight - to do this you have to slow down the burn which lowers the temperature. You will end up with charcoal in your grate and tar in your chimney.

It is also very important to make sure your wood is dry before you burn it. Otherwise you will be wasting energy driving off the water in the wood, which also cools the burn and encourages tar (see Where can I get firewood and how should I store it?).

There is some very good advice about how to run your stove efficiently here from an experienced chimney sweep

What about 'airwash' and 'clean burn'? How much extra do these cost, and is this worth paying?

Two common stove features are ‘airwash’ and ‘clean burn’, also referred to as a secondary and tertiary air supply. Airwash involves an additional flow of air entering the stove and coming down over the window at the front, reducing tar build up on the window which makes the glass black so you don't have to clean it so often.

‘Clean burn’ is a feature whereby the air entering the firebox passes through hot channels so it is heated up before it gets to the wood. This raises the temperature of the fire, which improves the efficiency of the stove (see above). You get a more complete burn with less ash and very little smoke.

There can be an additional cost associated with stoves that include these features. As an example, the Morso Squirrel 1410 and 1412 are very similar, one with cleanburn, the other without and a difference in price of roughly £100 at the time of writing. However, any good quality stove will have these features. Cleanburn is achieved by other manufacturers simply with a baffle plate in the top of the stove which is shaped so that the gases are burnt off anyway without having a tertiary air supply.

My house is/I want to make my house air-tight following Passiv Haus principles. How can I have a woodburning stove which needs to draw air from the room?

You will need a stove with a direct air intake: a sealed pipe which draws air in either through an outside wall, or from the void under a suspended floor (though this may affect the insulation value of the floor as it will cool the void in winter). There are a number of stoves which have this - for example, the Hase Luno stove - but be certain this will be available when you come to order the most recent model of the stove of your choice, and also that the chosen position is within the maximum distance necessary from an outside air source.

How much maintenance is involved in using a stove?

You’ll need to regularly empty the ash from the cold stove, clean the glass occasionally (newspaper dampened in vinegar cleans the glass well or apply a wet cloth dipped into cold wood ash to the glass) and you’ll need to get the flue swept once a year.

Fireboard / firebricks and bird / rain cowls will need to be replaced occasionally. Depending on the initial materials and frequency of use, they should last 3-8 years.

The lifetime of your chimney liner depends on how efficiently you run your stove: if you get a lot of soot and tar in your chimney it could corrode in 3-5 years but ordinarily it should last at least 10 years. Insulating the chimney reduces deposits and prolongs the life of the chimney liner.

Where can I buy a stove?

Suppliers who will install stoves in Cambridge include:

HETAS have a search page where you can find registered retailers, installers and chimney sweeps. Make sure you talk to at least 3 different suppliers – you may get different (and contradictory) advice!

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