Wood-burning stoves are the ultimate off-grid heating machines, capable of heating large, open spaces without costing a cent in electricity.
The best part is that burning wood does not emit any extra carbon dioxide versus natural biodegradation – you are simply speeding up the process. Trees also absorb carbon dioxide, bringing a stove's carbon footprint close to neutral.
We measure the heat output of wood-burning stoves in Kilowatts (kW), with a higher kW signifying a more powerful stove. However, the heating output is nothing without efficiency – the amount of heat the stove transfers to the space.
Maximizing efficiency is the key to burning less fuel for more heat, saving money, and reducing your carbon footprint.
In this guide, we cover the essential tips and tricks for improving wood stove efficiency in your home.
What is 'Efficient' For a Stove?
While an open fire has an efficiency of around 15%, with 85% of heat lost up the chimney, stoves control the wood burning in an enclosed chamber and radiate heat, giving them an efficiency rating north of 70%.
Some of the newest log burners can reach efficiencies touching 90%, giving you lots more heat from the same fuel.
However, many wood stoves run at less than 60% efficiency in practice due to improper usage, low-quality fuels, and poor maintenance.
The most efficient wood-burning stoves are EPA-certified; they undergo tests to ensure they burn fuels at specific rates.
Note that HHV (higher heating value) is an efficiency rating recognized by the EPA but indicates efficiency in the fuel, not the stove.
It uses all the heat in the wood when calculating efficiency, helping you buy good fuel. This is important when trying to eke out more efficiency from your stove.
How to Improve Wood Stove Efficiency
So you'd like to get your stove working at its efficient best?
Make sure you check off all the boxes with these tricks for boosting wood stove efficiency.
16. Burn seasoned wood
Firstly, the fuel you burn plays a critical role in stove efficiency.
The worst fuel is wet/unseasoned wood, which produces more smoke and emissions than dry wood and burns slowly at a lower temperature.
You should burn seasoned/kiln-dried wood with a maximum moisture content of 20% (15% is even better). You can tell when the wood is seasoned because it weighs less and makes a hollow sound when you thump it.
Ash, Birch, Beech, Oak, and Elm are ideal firewood varieties. The heavier the seasoned wood, the better, because it means a longer burn time and more heat providing it meets the maximum 20% moisture content.
15. Use small logs and work your way up
The second biggest mistake you can make after using unseasoned wood is throwing on enormous logs too early into the fire.
For larger logs to burn, you need lots of coals and embers ripping at the bottom of the chamber, and this requires at least half an hour of steady burning with smaller logs and kindling.
As a rule of thumb, start small and work your way up, letting the embers die down and settle before throwing on a giant log.
14. Keep up with flue cleaning
You can't see inside your flue, but if you could, you would see it laced with soot and maybe even creosote, which is mainly tar.
Keeping your flue/chimney clean increases wood stove efficiency by providing a clear pathway for smoke to escape outside. Cleaning is critical for air flow – air can only enter your stove to fuel the fire when old air escapes.
We recommend having your flue cleaned twice yearly or following every sixty uses to ensure that all that soot doesn't build up.
13. Let logs warm up before chucking them on
If you think a ripping hot wood-burning stove will burn through cold logs quickly, think again. Cold logs catch alight slower and struggle to combust, reducing heat output and your stove's overall efficiency.
It's best to bring logs inside and let them warm up for a day before throwing them on the fire. This simple trick will give you more heat! Many people bring their logs inside a week before burning them, but a day will do.
12. Don't strip away all that ash
Leaving a thin layer of ash at the bottom of your wood stove is a great way to insulate the hot coals that form after your wooden logs have burned.
The coals from your logs will continue providing lots of heat, and the layer of ash from the previous session will help them burn for longer.
A layer of ash won't interrupt combustion or reduce efficiency because air will push through the ash when the bottom vent is open.
So hold off using your ash vacuum of a little longer!
11. Newspaper is your best friend for fire spread
Nothing beats scrunched-up newspaper as a fire spreader. A few bunches of newspaper will help your kindling catch alight quickly and heat up the chamber and flue, priming your stove for the intense heat it's about to generate.
This tip will help you get your stove ripping hot faster. However, don't scrunch the paper up too much; otherwise, it will struggle to burn.
If you don't have any newspaper to hand, you can use non-glossy magazine paper (gloss will produce toxins) or regular printer paper.
10. Control the vents properly
It sounds simple, yet so many people forget to open and close the vents on their wood-burning stoves.
Your stove probably has a bottom and top vent, letting you adjust the oxygen levels in the chamber to aid combustion.
Opening and closing vents adjust the ferocity of the fire and, by extension, how hot it burns. However, increasing airflow burns fuel faster, so you must play with your stove to find the right balance.
Once your stove is ripping hot, you can close the bottom air vent and keep the top one open to maintain a steady temperature. If your fire starts dying down, open the bottom vent.
9. Get yourself a stove thermometer
If your wood-burning stove doesn't have a thermometer, it's worth getting one to see what temperature it’s producing.
This is helpful for several reasons:
Place your thermometer on the top, front, or side of a flat or curved surface. The best place is the flue collar.
8. Don't let your fire smolder
Smoldering fire might tick away, but it won't provide significant heat. It's better to open an air vent until the fire has enough oxygen to produce flames and then keep it open to increase the temperature inside the chamber.
To maximize stove efficiency, we recommend maintaining low flames across the burning session, which usually means adding new logs every few hours.
You want a temperature of at least 350°C (662°F) to stop the wood from smoldering – get a stove thermometer (see above) to keep on top of things.
7. Fuel your stove with just enough wood
A common mistake people make with wood-burning stoves is having a small fire that won't produce anywhere near the kW output of the stove.
The problem is that the stove will never get hot enough to maintain a stable and comfortable temperature, severely reducing its heat effects.
It's best to fuel your stove with lots of wood so it can burn away – you can always reduce the fire intensity by restricting oxygen with vents.
6. Don't over fuel your stove
While using enough wood to maintain a high temperature is critical to heating efficiency, over-fueling your stove is one of the worst things you can do.
Over fueling is when you pack the chamber with too many logs, significantly reducing the amount of oxygen in the chamber. When this happens, the fire might never get going, or the fuel will burn inconsistently at low temperatures.
The same goes for kindling and scrunched paper. Remember – fire needs oxygen to burn, and a compacted chamber will restrict oxygen.
5. Protect your chimney from the wind
Although heat, smoke, and carbon dioxide escaping your chimney will keep the wind out, wind can push these elements back down the flue.
Backdrafts can be dangerous if your stove doors are left open, and they can lower the temperature of your fire by killing flames.
The best way to protect your chimney is with a baffled cap, which redirects the wind away from the chimney so smoke can escape freely.
4. Perfect the art of top-down fire building
Let's not beat around the bush – much of a wood-burning stove's efficiency depends on the quality of the fire you build.
We like the top-down method, which uses a parallel layer of big pieces of wood over the bottom of the chamber and more layers of thin wood in a pyramid type arrangement, one on top of the other. This method burns from top to bottom.
The top-down approach works because it brings the chamber to temperature, and the smaller kindling pieces burn and drop down, creating embers.
3. Get an EPA-certified wood-burning stove
If you haven't purchased a wood-burning stove, consider looking at models with EPA certification for maximum efficiency. These models promise efficiency improvements of up to 50% versus non-certified stoves.
You can find the EPA label on the back of stoves, or you can check with the EPA the current list of stoves certified under the scheme.
The EPA in the United States began regulating wood stove emissions in 1988, and they have adjusted regulations over the last two decades (and quite significantly over the last few years).
2. Get a stove fan to circulate heat
Wood-burning stoves radiate heat, but they don't circulate it. One way to push more heat into your space without boosting the fire intensity is with a stove fan – a bolt-on device that pushes heat away from the stove exterior.
Although they are a recent innovation, stove fans are excellent devices. They are self-powered Peltier devices that generate electricity by having one side hot and the other cooler, producing voltage to drive the fan motor.
Do they work? You bet! A stove fan will push warm air around your room, helping heat the space and improve your stove's heating abilities.
1. Make sure your house (or space) is insulated
An insulated house won't make your wood-burning stove burn hotter for longer, but it will ensure all that heat is put to good use.
The last thing you want is to feed your space with lots of heat, only for it to escape immediately. This is a recipe for burning through more wood than you can afford, and it also increases the risk of overusing your stove.
If your house is a timber frame build, timber stud walls are easily insulated with mineral fiber (glass or rock) or wood fiber/wool. If you have a masonry build, you can usually get cavity wall insulation between the outside wall and plasterboard.
Drafts are another area to focus on – feel for drafts with a wet finger and inspect windows, doors, and floorboards closely. Plug any gaps you find.
The Final Checklist
You can boost your wood-burning stove's efficiency by:
Lastly, remember to take care when using your stove – it is deceptively dangerous and capable of significant indoor air pollution that can affect your health. You should also add a fireguard if you have pets or children.
That's a wrap! Good luck, stove owners.