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Wood burning stoves as secondary heat sources

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Majordennisbloodnok
(@majordennisbloodnok)
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Just wondering, given how many of us have wood burning stoves as secondary heat sources, if there’s any mileage in gathering together practical knowledge here on best ways of running them effectively and efficiently. We, for example, have been surprised at how much benefit we’ve got from heat-powered fans for circulating the warm air, so I’m sure there must be lots of other tips and ideas. 

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and inverter
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; suus solum profundum variat"


   
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Mars
 Mars
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Wood burning stoves, in my opinion, are very underrated. We have two Chesneys (5kW and 8kW) – https://myhomefarm.co.uk/chesneys-beaumont-5-and-8-series-wood-burning-stove-review – that are extremely good at what they do, and when we burn kiln dried hardwood, it probably takes about 50-60 minutes to get through one splintered log (as seen in the picture above), which means we get through 5-6 logs in an evening.

The heat they chuck out, is massive, and the heat-powered fans are extremely good at spreading the heat. Because it's been so mild, we've not really had the fires on this winter, but when we do, one stove will heat our dining/kitchen area (about 60sqm) and it heats the first floor passage way to the master bedroom. 

Our three tips are:

1. Get the most efficient wood burner you can afford
2. Use kiln dried wood
3. Use a heat-powered fan
4. Get the chimneys swept annually

I look forward to getting other tips and ideas from homeowners on the wood burning side of things.

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Majordennisbloodnok
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Totally agree with the fan, the regular chimney sweeping and installing the most efficient stove you can afford. Not quite so sure about the kiln dried logs.

I do, of course, agree that burning properly dry wood is far more efficient and environmentally friendly. However, after a few weeks the moisture content of the logs will be whatever their log store’s environment allows; if they’re left in a leaky damp shed, they’ll suck up the moisture again.

My preference is toinvest in a simple handheld moisture meter and test each container of logs as you bring them into the house. If they’re a bit less dry than is ideal, you can leave them inside to dry out again and go get some others from a drier part of the stack.

I was also recommended a flue thermometer, and it’s been a brilliant investment. For under a tenner, I can see if I’m burning the stove hot enough and when it’s the best time to put more logs on. Come chimney sweep time, about a cupful of soot is taken away and the liner remains pristine.

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and inverter
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; suus solum profundum variat"


   
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Mars
 Mars
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@majordennisbloodnok, I wasn’t aware of flue thermometers - will look into that this week.

You’ve reminded me about our wood moisture metre: https://myhomefarm.co.uk/stihl-wood-moisture-gauge-review

Our logs this year are a bit “wetter” so we will put it to use as the temperatures are set to drop.

Buy Bodge Buster – Homeowner Air Source Heat Pump Installation Guide: https://amzn.to/3NVndlU
From Zero to Heat Pump Hero: https://amzn.to/4bWkPFb

Follow our sustainability journey at My Home Farm: https://myhomefarm.co.uk


   
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(@peterr)
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We're fairly new to log burners.  Ours was only installed about 6 weeks ago and we've only really had about 3 or 4 evenings that have warranted lighting it.

We're definitely going to invest in a heat powered fan to try and distribute the heat around the house a bit more.

Any thoughts on heat logs versus seasoned logs?  Some friends of ours swear by Lekto Woodfuels heat logs, which come with a low moisture content and have quite a high calorific value (about 10kWh per log).


   
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Mars
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@peterr, we get kiln dried oak logs - they’ve shot up in price recently, but a 3m2 pallet used to cost us around £280 and that I saw us comfortably through the winter. We get about 45 mins burn time from each log.

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Majordennisbloodnok
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Posted by: @peterr

We're fairly new to log burners.  Ours was only installed about 6 weeks ago and we've only really had about 3 or 4 evenings that have warranted lighting it.

We're definitely going to invest in a heat powered fan to try and distribute the heat around the house a bit more.

Any thoughts on heat logs versus seasoned logs?  Some friends of ours swear by Lekto Woodfuels heat logs, which come with a low moisture content and have quite a high calorific value (about 10kWh per log).

We've made use of hotmax "logs" in the past (compressed chopped hemp waste) and found they give fantastic calorific value. However, that then means they can produce a fire that's burning too hot for the log burner. We usually get seasoned logs and then supplement with hotmax if we have it; one hotmax log for every 2-3 proper logs works about right and keeps the heat balance within bounds for us.

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and inverter
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; suus solum profundum variat"


   
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Mars
 Mars
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@majordennisbloodnok, I’m going to check them out. Thank you. We may have to supplement our heating with fires this winter.

Buy Bodge Buster – Homeowner Air Source Heat Pump Installation Guide: https://amzn.to/3NVndlU
From Zero to Heat Pump Hero: https://amzn.to/4bWkPFb

Follow our sustainability journey at My Home Farm: https://myhomefarm.co.uk


   
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Majordennisbloodnok
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@editor, no problem. Here's the link.

https://www.hotmax.co.uk/

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and inverter
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; suus solum profundum variat"


   
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(@prjohn)
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I would agree with Mars's tips however I disagree with Kiln dried logs. Kiln-dried are not environmentally friendly, they also have a lower calorific value due to the drying process. You should also store them inside as opposed to a wood shed to avoid reabsorption. I love using birch logs they burn easily and give a good long steady heat. Oak can be harder to burn especially if the stove is not hot enough. Like Mars, I get a 40-minute burn from each log. For a hot house, I use briquettes, the logs by themselves give a cooler burn.

My experience with a fan is mixed, yes it's great at circulating the air in a room and evens out the temperature in that room. But  as my stove heats the whole house it realises in hot air flow across the ceiling into the hall and through the house, a heat fan reduces this process.

Prior to using logs, they should be stored indoors at least overnight to remove excess moisture. A moisture meter is essential, my logs are usually about 16%. Above 20% they will not burn great and you will have a lot of soot and creosote build-up. 

Get a good book, I have found them invaluable to understanding wood burning. 

Recommendations;

The Log Book, Will Rolls

The wood fire handbook, Vincent Thurkettle

Norwegian Wood Chopping, stacking and drying wood, Lars Mytting

Finally, get a good log-splitting axe, this is essential to get the logs the right size for the type of burn you want, helping you control the heat output. i.e big logs more heat, small logs less heat.  Fiskars splitting axe is fantastic. 

 

 


   
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Majordennisbloodnok
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@prjohn, in essence I agree with your points but there are couple of qualifiers I'd make.

Firstly, the stove fan. I can understand that if your house is shaped in such a way that hot air circulation is efficient by design or happy accident, a fan will be both redundant and perhaps detrimental. However, many log burning stoves - mine included - are situated in a chimney breast cavity where an open fire previously was, and in that case the issue is getting cold air to circulate into and warm out of what is essentially a box with just one side missing. If one doesn't do that, a much larger proportion of the heat generated will be used to heat up the surrounding brickwork and the chimney plate, and therefore still end up being channelled up the chimney and out. I see a fan as a great solution to one of the potential problems with running a wood burning stove, but one that should only be used if it provides a real benefit. Try it out and if it works, great. If not, don't use it.

As for kiln dried logs, however, I'd love to know more about your assertion that the drying process can reduce the calorific content of the wood. Certainly, I can agree the log will get lighter, but my understanding is that, since water is being driven out, you're also increasing the calorific density (less mass overall but more of it will burn), not sacrificing some of those calories to the drying process. What I certainly agree with, and made the point earlier as well, is that if a kiln dried log is left for a significant time it'll still reabsorb moisture to regain an equilibrium. Couldn't agree more with you, therefore, about the moisture meter.

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and inverter
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; suus solum profundum variat"


   
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(@prjohn)
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@majordennisbloodnok Unfortunately I can't find the source of that information. My understanding is that wood contains more than just "wood" oil and resin being just two elements within the wood, both of these have a calorific value. Oil is lost when kiln-dried thereby losing calorific value. Granted these components will create more smoke/gasses and this is where secondary burn comes into its own by recirculating these gasses for a second burn thereby creating more heat and higher efficiencies. Burning gasses is a feature of modern stoves to create high efficiency and to eliminate/reduce co2 emissions.

 


   
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