So, autumn is here, and winter is on the way. You’ve been thinking about getting a log burner, but there are hundreds on the market, and miraculously every single installer has exactly the one you want. Choice in the marketplace has stopped being a Good Thing and has started to be a real headache. To help you make a decision, I’ve pulled together some handy hints for choosing a stove.
Specifying the size of a stove is (unfortunately) often more of an art than a science and it can be quite complicated. The two critical things to bear in mind are the physical size of the appliance, and the total amount of heat it can produce (the rated output).
The physical size is important because it determines what size fuel you’ll need. While some log suppliers will offer logs custom cut to a specific size, I’d suggest that you’d have to have a good reason why you wanted to install a stove that needed a log shorter than around 11 inches. This is a fairly average length for suppliers in the UK which will mean that you’ll be able to shop around between suppliers to get the best price.
Most stoves have a quoted output rating. This is measured in kilowatts (kW) and gives an indication of the maximum output. This is a fairly flexible number, as it is basically whatever the stove manufacturer can achieve with optimum refuelling and good quality fuel (similar to a MPG for cars). Don’t automatically get the highest output you can afford (or that will fit in your fireplace), as you could easily end up with a living room like a sauna, and a stove that never gets used to capacity.
There are a number of guides online for estimating how big a stove you’ll need, but most of them seem to be little more than rules of thumb. There really is no substitute for discussing the project with an experienced professional, as the appropriate size of stove will depend on other heat sources, what the building is made of, what part of the country you live in, and the degree of insulation etc.
Primary and Secondary Air
Any stove that you are using to burn wood should have both primary and secondary air controls (primary goes to the fire bed, secondary goes to the flames above it). In my opinion, you really should ensure that any new stove you buy has independently controllable primary and secondary air flows, as this allows a much greater range of fine-tuning. Don’t worry if it is impossible to close the secondary air vent fully, as there are no circumstances when you’d need to do this during proper stove operation anyway.
Most modern stoves are designed to re-circulate air through the system. This allows for a more efficient heat transfer, and more efficient mixing of fuel and air. This process involves passing the flue gas through the combustion zone to ensure that any particulate matter and other vapours have been completely burnt, increasing efficiency and reducing the nasties that can crop up in flue gasses.
Pre-heating / air-wash
Many stoves use a hollow door system. This uses air to insulate the stove door (allowing you add fuel more easily) while increasing the temperature of the air coming into the firebox. This increases efficiency and can be used to keep any glass in the door (relatively) clear of soot.
There are some hybrid stoves on the market, which combine the room-heating function of a stove with the ability to provide domestic hot water and sometimes radiators as well. These can be tricky to operate well, as the water in the heating system can cool the firebox, providing a perfect surface for water in the flue gases to condense on. There are ways of getting round this but you really need to get it installed by an experienced professional to minimise the risks (top tip – have a look at Chris Laughton’s book Home Heating with Wood if you’re interested in this).
Direct air ventilation
All stoves require a good source of air to burn efficiently. It is fairly common to draw this from the air in the room. However, to ensure that there is no reduction of breathable oxygen in the room it is often necessary to add additional ventilation (most installers find that their customers enjoy breathing). This can lead to an obvious drawback, as cold air is drawn into the room from outside to replace hot air going up the chimney. Many newer stoves are designed to overcome this problem by drawing in air directly from outside the building into the firebox. Direct air is obviously only feasible if you are installing the appliance on an exterior wall.
There are a wide range of different stoves on the market that are sold as ‘multi-fuel’ meaning that they can accept a range of different solid fuel types. This is can be a compromise between the requirements of coal and wood (which means that it is optimised for neither) but in many cases this actually means that the stove can be set up to burn coal or logs (though not both simultaneously). To burn wood well on a multi-fuel stove you’ll need to do a little bit of fine tuning. Since the insulating effect of ash is helpful for maintaining a wood fire, you may want to empty the ash less frequently or even blank off the grate completely with a metal plate. If you want to burn wood and coal on the same fire, you will need to try and find a happy medium between the two fuel types, though you do run the risk of getting the worst of both worlds.
If you’re installing in the UK, you need to be aware of the Smoke Control Act. This (slightly archaic) piece of legislation makes it illegal to emit “dark smoke” from a chimney within a smoke control area. The only way you are allowed to burn fuels within a smoke control area is a) if they are “approved smokeless fuel” or b) in an approved appliance. No form of wood is an approved fuel, but there is an extensive list of approved appliances available here. Basically, if you live in a smoke control area, your choice of log stove is restricted to one off the list.
Finding a stove is definitely not a simple as many people think, and while it might not be the definitive guide, I hope that you’ll find this article help to determine what you actually need as well as what would be quite nice. If you’ve got any other questions why not contact me or drop in to the Log Book’s Facebook page for more answers?
Will Rolls is an independent consultant with expertise in forestry, biomass and sustainability, with a strong personal interest in developing sustainable systems and practices. This article is a slightly modified version of one that originally appeared in the Big Issue North in 2012.