Wood stove idea

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Jacob

Pint of bass, porkpie, and packet of crisps please
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Existing wood stove has long length uninsulated flue nearly up to ceiling, then insulated through room above and gives out loads of heat in both rooms.
New house has normal masonry flue/chimney with gas fire, probably lined, probably was an open fire originally.
Another wood stove proposed - wondering about opening front of the whole flue top to bottom 3 floors, to extract max heat from steel flue therein, probably just insulated where it goes through two floors.
Seems an obvious idea - has anybody done this?
 
I’m not 100% as I only ever worked with natural gas flues/ appliances and as such if you release all the heat from around the flue by opening it all up you could inadvertently cool the flue gasses within the flue to a point where the flue stops pulling . The flue products including carbon monoxide can then reverse and you definitely don’t want that . A warm flue is a happy flue . The principal is the same for all fossil fuel burning appliances so tread carefully ..
 
I’m not 100% as I only ever worked with natural gas flues/ appliances and as such if you release all the heat from around the flue by opening it all up you could inadvertently cool the flue gasses within the flue to a point where the flue stops pulling . The flue products including carbon monoxide can then reverse and you definitely don’t want that . A warm flue is a happy flue . The principal is the same for all fossil fuel burning appliances so tread carefully ..
Much more draught through a wood stove once it's warmed up, so I don't think it would be a problem as long as its fairly straight up and down with outlet above the ridge.
Just when starting from cold, sometimes helps to light up a handful of newspaper to get it drawing but only takes a minute or less.
 
So let me get this straight, Jacob. You ask if anyone has done this and you get a reply from someone who works in this area, clearly knows what they are talking about and who advises you that it's not a good idea. But, hey, why am I surprised ? You know best. So why did you bother to ask if you're going to ignore good advice ?
 
As Bingy Man points out, there needs to be a minimum updraft of the flue gases. The cooler they are the slower they will rise, reducing the pull. On the other hand, if they are still very hot when escaping, you are wasting heat. It's a balance, if your stove produces enough heat to still produce a good pull without insulating the pipes all the way up, fine. But that's a judgement call that a qualified heating engineer is better placed to make!
You also have to take in to account variable weather conditions as well. If the wind is blowing hard, it could blow smoke back down the flue if the pull is not very strong! Best get an expert to advise you!
 
Your best bet is a hetas approved engineer but the one thing I remember about wood burners / stoves etc is natural gas has a fairly constant cv but your average wood burner can vary between different types of wood / moisture content and even how it’s been stored so they can be unpredictable so if you alter the dynamics of the flue in any way it would have to be tested under the new conditions for safety . It might not be a good comparison but most of us know what can happen if a charcoal b b q is used indoors . The above comments regarding variable weather conditions are critical , also nearby buildings and trees can also play there part . If you have ever seen a stainless steel terminal on a chimney that spins round - it been fitted because the flue does not pull or is problematic . The spinning effect helps create flue pull to assist removal of the flue products . Most likely is nearby taller buildings or trees etc have created a negative air pressure zone ( these can be deadly if not identified ) they often only show up when the old radiant gas fire is removed and a more powerful fire is installed - so imo and in the interest of your safety contact an approved solid fuel hetas installer before you alter anything to do with a flue and discuss what you are thinking about doing .. stay safe ..
 
Wood stoves have a greater draft/pull as the average flue temperature is higher, normally due to an insulated flue. However the volume of gas in a wood stove flue is much less than an open fire and the risk of condensation of combustion products and creosote is much greater. When wood stoves first became popular there was a rise in chimney fires as a result. Twin wall flues with smaller diameter than existing chimneys were introduced and solved most of these issues. Taking heat out the flue is be concerned about greater levels of condensation as per above.
 
A masonry flue will take longer to heat up than twin wall but will also then radiate the heat for longer . Once established the draught will depend on air intake on an enclosed stove . Overall I don't think worth doing.
 
There must be something in that whenever I’ve seen an extended flue through a building from a wood burner it has always been insulated.
If it was such a good idea surely it would have been done lots of times by now.
 
Someone once had an idea with similarities to this involving the flue to the oil power station on the embankment. the big idea was to ‘scrub’ the exhaust gasses by spring them with mist. The cooler exaust didn’t rise properly (albeit not helped by a shorter chimney than designed being fitted for aesthetic reasons. The gasses didn’t rise much above the building and on a cold day were at street level and were poisoning London. it’s now known as Tate gallery. on days where you need to burn a few sheets of newspaper to get it to draw you can most probably smell your own fire at ground level outside.
 
I watch a lot of the american shows about alaska etc and from what I've seen the flue is normally non-insulated in the cabins.

Whether it's a good idea or not I can't say but they do it and it doesn't seem to cause them a problem.

It's the same with the way the pipes are put together. From my limited understanding we have to put the pipes so the next pipe up has to sit inside the pipe below so any condensate cannot run out of the joint. I don't think they have that rule in the US either.

You are probably better off though heating the chimney bricks though so the heat is released slowly after the fire is out. Rather than having your house at 30degrees for the limited time the fire is on and then dropping rapidly when it goes out. I've seen some stoves that sit in a huge block of concrete so it heats that up and creates a thermal store. i've toyed with putting a big steel block that came out of a night storage heater on top of my woodstove to do the same.
 
You should check what the building regulations say about it too. Just because something was done before does not mean it complies with current standards whereas any new or modified installation will need to comply.
 
My uncle had a 2 storey cottage and log burner with an extractor fan at the top of the flue to help the draw. It’s still working to this day.
 
Jacob, I doubt building regulations would allow what you are proposing, and you now have to get everything signed off. Document J is what you need to read and best of luck with that one. It was a minefield when I had to interpret it for installation at our last house.

Colin
 

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  • Document J - combustion appliances building regs.pdf
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Jacob, I doubt building regulations would allow what you are proposing, and you now have to get everything signed off. Document J is what you need to read and best of luck with that one. It was a minefield when I had to interpret it for installation at our last house.

Colin
Yes I know - bin there dunnit. There'd have to be shielding enclosures etc.
 
Yes I know - bin there dunnit. There'd have to be shielding enclosures etc.
There would also need to be a Structural Engineers report to say that it was appropriate to remove part of the chimney, which is quite likely to be a significant load bearing structure, particularly if it's an older dwelling.
 
There are many fan assisted gas fires in use today but they are interlocked so should the fan fail or the flue becomes blocked the appliance will shut down . I’ve also seen many programs of off grid living in Alaska and seen people installing flues for wood burners but I’ve never seen them test and commission the flue prior to lighting the fire or installing any type of c/o alarm . But they do have huge cabins probably with huge amounts of adventitious ventilation but not sure I’d want to sleep there . They don’t call it the silent killer for no reason .. one of the most common excuses when I told a customer their appliance was dangerous and needed to be disconnected was” it’s been like that for years and it’s never done us any harm “ 🫣😤😫
 
There would also need to be a Structural Engineers report to say that it was appropriate to remove part of the chimney, which is quite likely to be a significant load bearing structure, particularly if it's an older dwelling.
Yes could be a prob. Beginning to think that it woud be better to not use the chimney at all and just re-position the stove so that the flue pipe can go straight up through three floors away from the outside wall with no heat loss through back of chimney. Which is what I've got now but just through 2 rooms. Fair amount of heat comes off the upstairs insulated length - maybe have it black anodised rather than shiny stainless for better radiation.
 
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There are many fan assisted gas fires in use today but they are interlocked so should the fan fail or the flue becomes blocked the appliance will shut down . I’ve also seen many programs of off grid living in Alaska and seen people installing flues for wood burners but I’ve never seen them test and commission the flue prior to lighting the fire or installing any type of c/o alarm . But they do have huge cabins probably with huge amounts of adventitious ventilation but not sure I’d want to sleep there . They don’t call it the silent killer for no reason .. one of the most common excuses when I told a customer their appliance was dangerous and needed to be disconnected was” it’s been like that for years and it’s never done us any harm “ 🫣😤😫
Carbon monoxide detectors are cheap. But I go in for fast intermittent burn rather than slow continuous, hence CO not likely an issue - less of it from a hot burn and it's definitely going up the flue until the fire goes out.
 

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