Everything you need to know to get the most out of your wood burning stove
Is there that much to know?
I mean, it’s just fire in a box, right? Well yes and no – lighting a fire is easy but operating a modern efficient stove requires a bit of a knack. But don’t despair, I’ve tried to include everything you’ll need to know in one place; this page!
The Stove
The place in which the magic happens. There’s not much to a firebox, but there are a few bits that can vary; let’s cover the main aspects.
Types
Modern stoves comes in two main types – wood burning and multi-fuel. As the names suggest, you can burn only wood in the former, but also coal and the like in the latter. I have a standard wood burner because I like to gather and process my own firewood, because it’s not our primary heat source, and because I’m not stoked about burning fossil fuels.
Multi-fuel stoves have a grate to accommodate airflow from below but a wood burner generally shouldn’t; wood burns best on a bed of ashes and embers. If you’re using a multi-fuel stove but are only burning wood, consider covering the grate with a piece of sheet metal. The grate may well be removable, so check your stove’s instructions.
Size
They come in all shapes and sizes, with the main difference being the output rating. 5kW is the most common for a single room or well-insulated open plan home, but anything up to 15kW+ are not uncommon for those relying on the heat. It’s tempting to get a huge stove, but big stoves burn a lot of wood, and you have to give serious consideration to air admittance. Back boilers are often connected to larger units so that water can be heated and pumped around the house.
Air source
Many stoves have the option of using an external intake, which means that the stove’s air is fed directly from outside your home. If you can run another pipe to the stove then it’s definitely recommended. It will cut down on a draughts in an older house, and make it useable in a well-sealed home. Why pull cold air in through your windows and floors if it’s not necessary.
Vents
The air intake vents are ultimately the main way to control the fire – more air make fire big, less air make fire small. There are always at least two, but normally three on a modern wood stove.
The primary vent is usually on the front near the bottom; it’s used to start the fire and allow maximum airflow. It’s fully closed once the stove is up to temperature, unless you’re burning coal in a multi-fuel.
The secondary vent is also open fully whilst getting up to temperature. Normally at the top just above the glass, it’s then the only vent used to control a wood fire. This is also often called the airwash vent because it pulls air down and across the glass, helping to keep it clean. If you’ve got a DEFRA approved wood burner then it should have a limiter to stop it being closed completely.
You might not have a tertiary vent, but it controls how much pre-heated air gets into the rear of the stove. If you can see holes along the back plate then you probably have one. It could be located anywhere, but normally it’s on the underside or at the back.
The tertiary aids combustion at the top of the firebox. Generally you set it once and forget it even exists. Mine is as closed as it can be, which still lets some air in.
Exhaust
Normally you will have a flue liner connected to the stove. They’re easy to sweep, less prone to creosote build-up, and you get a better draw. What’s creosote? Black unburnt deposits that can build up within a flue or chimney. It can get so bad that there isn’t enough room for air to leave the fire, but worse still, it can ignite and cause a chimney fire. Maybe the fire will be contained in the chimney, maybe your house will burn down – you don’t want to find out.
You don’t need a liner if you have a chimney in good condition, but they are highly recommended. Much of the benefit of running your fire correctly is keeping the flue in good condition. There are twin and single-walled options. Generally you use a double when it’s not going through a full chimney and would otherwise cool down too quickly. Cold flues are a bad jam for deposits. 902 stainless steel is normally recommended for multi-fuels.
Accessories
First and foremost – a carbon monoxide detector. Everyone should have one in their home, and it’s a legal requirement if you have a stove. You can’t detect carbon monoxide by odour, and it is a legitimate killer. For the minimal cost it’s absolutely worth every penny. Consider this a reminder to press the test button if you already have one in your home.
Magnetic temperature gauges are another low cost bit of kit for a quality of life bump. You can easily see if you’re running the stove within the ideal temperature range. Most are designed to sit about 12 inches above the stove, but for those with less space (or non-magnetic flues) you can get some designed to sit on the flue collar or stove body. They areb’t necessary, but they are cheap and very useful.
Moisture meters can be useful if you doubt the quality of your logs or you’re seasoning your own wood. Remember that you need to split the wood and measure the fresh surface to get an accurate reading!
Lastly, and least important of all – tools to process your own firewood. Mauls, axes and chainsaws are essential if you’re going to be taking delivery of unseasoned tree trunks. Most people don’t do it themselves, but if it takes your fancy, please be careful. Chainsaws take no prisoners – you can lose a limb and bleed out before you even realise what’s happening. I highly recommend buying protective gear and taking a chainsaw course before using one yourself.
Fuel
It will come as no surprise that you will want to burn wood; well-seasoned wood. I’m going to stick to the main options here – please don’t burn any old junk in the stove. MDF, plywood, or anything with paint/varnish produces toxic smoke. It won’t do your liner any good, and it definitely won’t do anyone outside any favours. It’s also illegal and you can be fined.
Stick to plain and simple logs, well-seasoned to below 20% moisture. UK suppliers are legally required to make sure their firewood is under 20% for amounts under two cubic metres, but it can still be hit and miss.
You might wonder why the moisture content matters when it’s going into a roaring fire. Basically wet wood creates more smoke, which causes more air pollution and creosote inside your flue. Damp wood also doesn’t burn as hot, so the flue will be colder – and yup, you guessed it, more creosote. If that wasn’t enough, under-seasoned wood doesn’t kick out as much heat! Half the output will be swallowed up bringing the logs to temperature and driving out the moisture.
A little bit of surface moisture from rain or snow isn’t the end of the world; that is driven out relatively quickly. Some folks like to leave those to dry out near the fire, but don’t have them too close…
Hardwood
The good stuff. Hardwood burns the longest and provides good heat output. Not all hardwoods are equal, and if you’re buying it then you generally want stuff like Ash, Oak, Beech, Cherry, etc. While willow and the like are technically hardwood, they aren’t very good fuel. Quick to burn and not a lot of BTUs in return.
Hardwood needs a good bed of embers to burn properly, so it’s a good idea to buy some softwood too.
Softwood
Often looked down upon as the poor man’s fuel. Fools! It’s the best thing for getting the fire up to temperature, and very useful for mixing with hardwood when you reload. It’s also not bad on its own – you just need to reload the stove more often.
There’s a misconception that softwood will gum up the flue with creosote. Wood such as pine and cypress does contain more resin than hardwoods, but it’s absolutely fine when fully seasoned. I’ve got loads of Leyland Cypress drying in my garden as I type.
Kiln dried
The sort of stuff you’ll find in bags outside a superstore; these logs have been dried within an inch of their life in a kiln. Very dry, easy to light, and very expensive compared to a seasoned load. I do occasionally buy it for when I’m away and the other half will be using the fire; it’s a lot easier to burn if you aren’t used to seasoned hardwood.
Usually birch, which is a very light hardwood – it’s ok in a pinch but a pricey way to run a fire. You need to keep it indoors or it absorbs moisture from the air and will be no dryer than seasoned wood.
Kindling
Baby logs! Small pieces of softwood with a large surface area for a quick start. If you don’t have any handy then you can split a log into pieces and it will do just fine.
Free (unseasoned)
If you’re got more free time than money, you can often grab free logs from tree surgeons or Facebook Marketplace. You’ll normally need to collect it yourself… and then there’s the cutting, chopping, stacking and seasoning. You can register your home as a drop site on ArbTalk, and you might get really lucky when an arborist needs to get rid of a load.
There’s no such thing as a free lunch, and almost all of the price paid for seasoned logs is to cover the effort of processing the wood. I recently grabbed a load of Leyland Cypress and it took me the best part of four days it chop it all up and stack it to season – and I’ll still need to wait at least a year to burn it!
Running the fire
Start-up wood arrangement
The trick to starting a fire is getting it very hot very quickly. The flue needs to be hot to stop smoke condensing and forming creosote, and you want a base of embers to get the first load burning. You also want minimal smoke.
There are two main ways to light a fire – top-down and bottom-up. Bottom up involves building a Jenga tower of kindling, lighting it, and then placing smaller logs on when it’s down to embers. Very simple, can’t go wrong. Top-down is a traditional Scandinavian method; you place a couple of large logs on the bottom, then add smaller and smaller pieces. Top with a bit of kindling and light the apex.
I prefer the top-down method because there’s less smoke and you don’t need to add wood for ages. The downside is that you need small pieces of wood.
Airflow
Open your primary and secondary vents fully, and leave them that way until the stove and flue are really hot (200C on the flue). Close the primary vent and then close the secondary/airwash in stages.
You want to get the flames down to a lazy pace. I normally put it straight down to hallway, then reduce to 3/4 closed – or as low as I can while still having a good amount of flames. It’s entirely dependent on your stove, and it will take a while to find the sweet spot.
Temperature
Heat is a bit subjective, so unless you are very familiar with stoves, how hot is too hot or cold? Thankfully there are temperature gauges available for very little money.
They normally sit 6-12 inches up the flue, but if that isn’t possible (or you have a non-magnetic twin flue), then you can get thermometers designed to go on the stove body. Stove thermometer have a nice easy range for an optimum burn. Why does temperature matter? Mainly for the health of the flue. Smoke will condense less on a hot flue, so you’ll get less creosote build-up. You don’t want it too hot though, it can damage the stove and cause premature failure.
I normally aim for the upper range during the start of the fire, then let it gradually come down to 200C. Remember that the temperature will drop a bit when you reload, so aim to refuel early enough that the temperature stays in the green.
Maintenance
Leave the fire be until it’s down to embers, then throw another couple of pieces on. If you have a good base of embers and the wood is properly dry, it should catch within a few minutes and you need not touch the vent. If it’s been left too long or it’s the first reload, you may need to open the secondary vent a bit until it gets going.
Ultimately you want a bit of flame so that the volatiles/smoke combust into flame, but not so much that you are reloading frequently. A good target is every 1-2 hours for hardwood, and that’s two reasonably large pieces in my 5kW.
The amount of wood you’ll add will vary depending on its surface area – that’s what matters. A greater surface area releases more volatiles, which will need more flames (so more air) to burn completely. Many smaller pieces of wood will burn much quicker than a couple of large pieces. Volatiles which can’t be burnt due to insufficient air will go up the flue as wasted potential energy. Here’s what it should look like after it’s been going a while:
Slumbering
Slumbering is the act of throttling back the intake so greatly that the wood burns at a snail’s pace. It was really common for people to ram the firebox full of wood then turn it right down just before bed.
I don’t like slumbering. It produces way more emissions and wastes a lot of energy. It will black up your stove glass and will massively increase flue deposits. There is also the increased risk of carbon monoxide poisoning. As the flue gets colder and the draw reduces, air could be forced back down the flue by windy weather. That can push smoke into your house.
Don’t slumber your fire, please.
Sweeping
Chimneys and flues need to be swept, it gets rid of the soot and keeps the fire safe. We pay about £55 to have ours done once a year, so not overly pricey. The sweep will probably tell you what sort of stuff he’s removed and give you advice if you need to change your ways. Listen to your chimney sweep, they generally know what they are talking about.
A lot of people will say ‘just run your stove hot and you won’t need it swept’. This might be true if your wood is perfect and your flue is short, but most people will have some level of build-up near the top of the flue.
Common problems
Stove glass turning black
There are four main causes of soot on stove glass; insufficient temperature, wet wood, too much fuel, and logs against the glass. Firstly you want the temperature to be hot enough that smoke combusts and any deposits are burnt away. Don’t fret about a little blackening – it will disappear when the stove gets up to temperature.
Wet wood produces more smoke and less heat, so you’ll get black build-up unless you’re running the stove at full pelt. That’s probably also just pushing the problem further up into the flue. If I’ve not said it enough, don’t burn damp wood. Too much fuel in the stove results in too many volatiles. That means you end up with too much fire and the airflow needs to be turned down to stop the stove overheating. Turning the flow down means much of the volatiles cannot combust and they end up on your glass.
Wood that falls against the glass will normally leave a black outline. It’s not the end of the world – you can either push the wood back or ignore it. The soot will burn off soon enough.
Seasoned hardwood isn’t burning
You might have a bad (damp) load of wood, but it could be your technique. Hardwood produces a lot of heat, but it also needs a lot of heat to burn properly. Start off with either softwood or relatively small pieces of hardwood; get a good bed of embers going and then add your chunkier logs. Don’t feel too bad about not getting the knack immediately, I’m not ashamed to admit that I too considered a couple of wood deliveries to be under-seasoned. When you’ve used a few different suppliers and you get the same result, you start wondering where the fault really lies.
Frequent reloading
If you’re burning hardwood and you’re up every hour adding more wood, then you’re probably either adding too little or have the vent open too much. If those aren’t true, check your rope seals and make sure you have a good snug fit all the way around. You can place pieces of paper between the rope and the stove body and see if they pull out very easily; do that all the way around. If you’re ever checked fridge or freezer seals, it’s basically the same technique.
Strange smells
Is your stove new? If so, it’s going to take a while for the paint to cure fully. Each time your stove is hotter than the last it will likely emit a bit of an odour; air the room out and it should disperse quickly enough. If it’s not new, check that nothing has fallen against the stove body. Our dog is a nightmare for throwing rubber balls next to ours. If it’s nothing so simple, it can’t hurt to have someone come out and give the old girl a once-over. Stoves shouldn’t generally smell of anything.