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Getting the most out of a wood-burning stove.

Posted by Andrew McGowan on 31 October 2017 at 9:20 am

Andrew McGowan has 15 years of wood-burning experience and experimentation with Morso and Stovax stoves. As our guest blogger this week, Andrew shares with us his tips on efficient wood burning techniques in the home. 

 
  • Use well-seasoned (dry) wood with moisture content 20% or below.  Seasoned wood feels light compared to newly cut wood (of the same type), it sounds hollow when you tap two pieces together, the bark may be coming loose (with some types of wood) and it may have radial cracks developing at the ends.  Generally wood needs to be seasoned (covered from the rain, raised off the ground, well ventilated - not wrapped up - and preferably in sunshine rather than shade) for two summers.  Ideally check with a moisture gauge.  Hard wood is preferable - soft wood burns more quickly so the fire needs re-filling frequently (but I wouldn’t throw it away!
     
  • Use plenty of paper to get your kindling sticks going.  Crumple the paper LIGHTLY, to get a fast, hot burn.  Don’t fold, twist or roll the paper because this excludes air and will result in a slow, smoky burn, which won’t get your kindling burning.  I almost fill the firebox with paper - we generally have a surplus of paper from non-glossy junk mail and office/school waste so I don’t need to be sparing.  However be careful not to block your flue with paper!Add your kindling sticks on top and stand some on end at the front of the fire. A large amount of paper not only lights the kindling quickly but also rapidly warms the flue, creating an up-draught which powers the fire.If you have greasy/oily pans after cooking wipe them with kitchen towel and save them for the fire - they work as excellent fire-lighters.  Better for your drains too!
 
  • Light the paper at the base and push the door to straight away, without fastening it closed, to create a turbulent flow of air into the fire which helps the fire spread to all the paper quickly.
  • Once the paper is burning strongly (usually after just a few seconds) fasten the door closed, ensuring the top and bottom vents are fully open first (the fire will die down almost instantly if you have left the vents closed).

  • In a short time (a minute or two) the kindling will be burning strongly. This is the time to add a few small logs (preferably pre-warmed under the fire).  Don’t add too many at one time, or you may quench the fire.  Continue adding a few (warmed) logs at intervals, using larger logs as the fire becomes stronger.  While doing this minimise the time the door is open.  Keeping the door open allows too much cool air into the fire and will quickly dampen down the fire.  Have logs in your hand, ready to toss in before you open the door then close the door immediately once the logs are in. Wood-burners gain their efficiency from regulating the air-flow, as opposed to open fires which allow uncontrolled, excess air flow, meaning heat is wasted going up the flue.  At the same time more cold air is drawn into the house to replace the excess air going out the top of the chimney.
  • Try to position the logs with about 1-2 cm between them to allow a good air-flow, while being close enough so that they help each other burn.  
 
  • The vents in most wood-burners are positioned to encourage an air-flow from top front, down the inside surface of the door (helping keep the glass clean), then along the floor of the fire, front to back, then up the back wall of the fire, then along the top of the firebox towards the front of the fire and up the flue.  This air flow helps the fire to burn efficiently by making the air take a long path through the fire so giving time for more of the oxygen to be utilised.  Avoid positioning your wood width-ways across this flow, especially if you’re using LARGE logs, because this impedes the flow. 
     
  • This is rarely a problem when using a lot of small logs, (as opposed to a few large logs) because there are plenty of air spaces, in which case you don’t need to be so careful about how you position your logs.  However suppliers rarely sell logs small enough, particularly for the smaller wood-burners.  My stove is small (Morso Squirrel 5kw) so I always cut my logs short (about 10cm).
  • If you’re burning square-section/ flat-faced (waste) wood, rather than logs, it is especially important to leave gaps.  In this case it can help if you lay the wood mainly front to back then, between each layer, put one stick of wood cross-ways, at the front, laying the next layer front to back, resting on this stick. 

  • Once the fire is well-established (probably in about 10 minutes) and giving out substantial heat (you feel the warmth on your face from arms length) start to close the bottom vent a little at a time.  If you do this too quickly you may start to quench the fire.  In time you will be able to fully close the bottom vent.  This slows the burn, your wood last longer, while not wasting too much heat up the flue or drawing too much cold (replacement) air into your house, so you get the best heat output from your wood.  You may be surprised to find this actually increases the heat from your fire despite the reduced air flow and a less fierce burn.
     
  • Start to close your top vent too if your fire continues to burn well, further improving the efficiency of your fire.  If you find that this starts to cause your fire to die down then re-open the vent sufficient to sustain the burn.  While you still have flames from your wood (as opposed to just hot glowing ‘coals’) leave the top vent partly open to avoid sooting up the glass. As you gain experience with your own fire you will learn to judge the best times to turn down the vents.  

Signs of an efficient burn are:

  1. there is no hissing noise when you open the door of the stove (this is the noise of moisture being boiled off showing that your wood is not sufficiently seasoned).
  2. Blue tinges to the flames (like a gas ring/ bunsen burner) rather than purely yellow/orange flames.
  3. Flames seem to ‘float’ gently in the air, as opposed to a fierce burn.
  4. Sooty blackness on the fire bricks on the walls of your fire burns off to give a clean, light-brown colour.
  5. The air-flow into the fire is not noisy (air vents only open small amount).
  6. Go outside and look - no smoke from your chimney!
   
  • If necessary re-position your logs in the fire to maintain 1-2cm distance between them. Continue to add logs at intervals while you still have a substantial amount of hot glowing ‘coals’ , and while the fire can be easily revived.
     
  • When you won’t need the fire to keep burning much longer (you’re going to bed / going out) - let the fire burn down till you just have glowing ‘coals’ (no flames) then shut down the vents almost completely (if you have a DEFRA-approved stove the vents can be fully closed because there will be some small vents that are constantly open).  Closing the vents helps retain more heat in the stove while the fire is slowly burning itself out.  To get the most out of your wood gather the glowing coals together from time-to-time.
     
  • Don’t worry about cleaning out ash too thoroughly - the ash provides some insulation at the base of the fire and helps establish a strong burn.  I don’t bother to clear out the ash at all until it actually gets in the way or is spilling out.  Rescue the bits of charcoal from your ash - it’s great kindling.  If your fire is burning efficiently you will rarely need to clean your door glass with anything other than a quick rub with the paper that you light your kindling with.  If you have stubborn deposits a cream bathroom cleaner (e.g. Ecover) works well, but NOT while the glass is hot - risk of fracturing the glass.
 
  • Review your user-guide instructions from time-to-time especially with regard to maintenance (cleaning, inspecting for gaps/cracks, renewing seals, having the flue swept annually).

 

About the author:

Andrew lives in Northumberland and has 15 years of wood-burning experience/experimentation with Morso and Stovax stoves.  

His stove is used whenever possible as a supplement to his gas central heating. When the fire heats the room beyond 18C the boiler control turns off his central heating. 

Andrew is keen to minimise his carbon footprint, run an battery electric car (Leaf), grow some of his own food, make his own compost, and have 2.45MWp solar panels on his small roof, an ongoing ‘super-insulation’ project in his home ('Rockwool’ in cavity walls, 100mm extruded polystyrene in loft, draught-proofing, plans to insulate window reveals, eventually Argon-filled double-glazing replacements, possibly heat-recovery-ventilation).

If you have a question about anything in the above blog, please ask it in the comments section below.

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Comments

5 comments - read them below or add one

Eco Andrew

Eco AndrewComment left on: 13 November 2017 at 4:09 pm

Thanks for your comment Emilly9291 - it's encouraging that you feel inspired to start using your woodburner now the cold weather is here.

After so long without use it's important that you have your chimney swept particularly to ensure it is not blocked (by birds nest, fall of soot or other debris) before you light your stove.

My experience with wood suppliers is that you need to try a few and compare how their wood burns (preferably check how dry it is with a moisture meter - see chainsawjournal.com link: HOME / BLOG / FIREWOOD MOISTURE METER | BUYING GUIDE)  Hope that helps.

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Emilly9291

Emilly9291Comment left on: 13 November 2017 at 2:40 pm

I'm a proud owner of an old stove, which has been sitting in the front room for decades. I have never even thought of getting any use of it, but this winter this might change thanks to your post. The biggest issue is getting a good amount of at least decent wood - it's not an easy task when you're living in a centre of a big city. 

Have a nice day,
Emma


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Eco Andrew

Eco AndrewComment left on: 4 November 2017 at 11:58 am

Thanks for the comment, Ian, it's great for others to share their experiences.  I have also found proprietory cleaners to be ineffective and a waste of money.  Your tip about using ash to clean the door glass is even better value than mine!

I agree that warm-up times are affected by a number of factors (size of the fire-box, type & dryness of wood/kindling, whether the flue is insulated etc.) so my timings can only be an approximate guide for others, even if they have the same model of stove.

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Ian Smith

Ian SmithComment left on: 1 November 2017 at 4:20 pm

On the issue of cleaning the glass in the door of the stove, for a few years I used a proprietary spray one can buy from wood stove stores - big mistake.  On just a few occasions I used it to clean the front of the glass but, where it dripped down the pane to the cast iron surround, it immediately removed the black finish that Morso use on their stoves.  This now rusts.  The rest of the stove is nearly as prisine as when I got it twenty years ago.  I find the best. and greenest, way is to dampen a cloth or kitchen towel, dab it into the ash in the fire and use the resulting paste to clean the glass.  Works a treat.  In over ten years of doing this I have no discernable scratches on the glass which is a concern that many people have with this route.

On the issue of how long to keep the door open when lighting the stove, this does depend on a number of factors.  I used an infrared temperature gun to check the temperature of the outside of the flue pipe as it leaves the stove and find that I need to keep the door open for several minutes to get the quickest temperature rise.  Normally with combustion appliances, one uses more excess air during start up than when the appliance is at its normal operating temperature as this tends to give the cleanest combustion.  If the primary air controls can provide all this air, then one close the door early.  My stove does not have this capability.

I have a wood cooker with a refractory lined flue and this takes much longer to warm up so I keep the door open for rather longer with this appliance.

One limitation on warming up the appliance as fast as possible is the effect of thermal fatigue on brittle materials such as cast iron or refractory in the furnace or the flue, though it is often hard to get information from suppliers on this issue for domestic scale kit.

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Ian Smith

Ian SmithComment left on: 1 November 2017 at 4:20 pm

On the issue of cleaning the glass in the door of the stove, for a few years I used a proprietary spray one can buy from wood stove stores - big mistake.  On just a few occasions I used it to clean the front of the glass but, where it dripped down the pane to the cast iron surround, it immediately removed the black finish that Morso use on their stoves.  This now rusts.  The rest of the stove is nearly as prisine as when I got it twenty years ago.  I find the best. and greenest, way is to dampen a cloth or kitchen towel, dab it into the ash in the fire and use the resulting paste to clean the glass.  Works a treat.  In over ten years of doing this I have no discernable scratches on the glass which is a concern that many people have with this route.

On the issue of how long to keep the door open when lighting the stove, this does depend on a number of factors.  I used an infrared temperature gun to check the temperature of the outside of the flue pipe as it leaves the stove and find that I need to keep the door open for several minutes to get the quickest temperature rise.  Normally with combustion appliances, one uses more excess air during start up than when the appliance is at its normal operating temperature as this tends to give the cleanest combustion.  If the primary air controls can provide all this air, then one close the door early.  My stove does not have this capability.

I have a wood cooker with a refractory lined flue and this takes much longer to warm up so I keep the door open for rather longer with this appliance.

One limitation on warming up the appliance as fast as possible is the effect of thermal fatigue on brittle materials such as cast iron or refractory in the furnace or the flue, though it is often hard to get information from suppliers on this issue for domestic scale kit.

report abuse

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