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Hot air ducting from a woodburner

 
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mr brightside



Joined: 01 Apr 2011
Posts: 228
Location: On the fells

PostPosted: Sun Oct 07, 2018 5:47 pm    Post subject: Hot air ducting from a woodburner Reply with quote

Anyone ever done this before? It's a freestanding 4.5kW with nothing to facilitate any kind of hotbox arrangement, so i'm looking at simply moving warm air from one room to another over a distance of about 8m in a straight line. I need a duct fan and the ducting needs to be insulated as it'll be running in the loftspace of a bungalow.

Early research is suggesting warm air is problematic to move effeciently.
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fuzzy



Joined: 29 Nov 2013
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Location: The Marches, UK

PostPosted: Sun Oct 07, 2018 6:09 pm    Post subject: Reply with quote

If you are going to blow cold air into an airtight burner and use the exhaust, can't you feed it underfloor, then out the house, so that the heat works best?
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kenneal - lagger
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PostPosted: Sun Oct 07, 2018 7:00 pm    Post subject: Reply with quote

Get some 100Ø flexible ducting, a 100mm computer fan and a 12V battery with a small trickle charger. Lay the ducting under your loft insulation and Bob's yer uncle!! Works in our house. As long as there is a return path for the air it will work so you might also have to take 5 or 10mm off the bottom of the doors.
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adam2
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PostPosted: Sun Oct 07, 2018 7:34 pm    Post subject: Reply with quote

Yes, no need for any connection to the stove itself, simply extract hot air from ceiling height near the stove and blow this hot air into another room that would otherwise be cold.
Since heated air rises the outlet into the second room needs to be at floor level.
A refinement would be to control the fan with a thermostat in one room.

Remember that the duct and the fan will spread fire and smoke from one room to another, or into the loft space.
It would be prudent to fit an intumescent grille at each end.
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kenneal - lagger
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PostPosted: Sun Oct 07, 2018 7:40 pm    Post subject: Reply with quote

The hot air introduced at ground level would rise, Adam, so you would end up building the heat down from the ceiling anyway. Might as well just blow it in from there and let it build down from there. It's one of the problems of hot air heating.
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mr brightside



Joined: 01 Apr 2011
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Location: On the fells

PostPosted: Thu Oct 11, 2018 8:31 pm    Post subject: Reply with quote

kenneal - lagger wrote:
Get some 100Ø flexible ducting, a 100mm computer fan and a 12V battery with a small trickle charger. Lay the ducting under your loft insulation and Bob's yer uncle!! Works in our house. As long as there is a return path for the air it will work so you might also have to take 5 or 10mm off the bottom of the doors.


The internet says 150mm is what you need, and yes i'm just extracting from over the stove with a vent in the ceiling. Really i need insulated ducting, but where do you get it from? Even better i need a company who specialise in warm air heating systems, but who the hell bothers!
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vtsnowedin



Joined: 07 Jan 2011
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Location: New England ,Chelsea Vermont

PostPosted: Fri Oct 12, 2018 1:27 am    Post subject: Reply with quote

mr brightside wrote:
kenneal - lagger wrote:
Get some 100Ø flexible ducting, a 100mm computer fan and a 12V battery with a small trickle charger. Lay the ducting under your loft insulation and Bob's yer uncle!! Works in our house. As long as there is a return path for the air it will work so you might also have to take 5 or 10mm off the bottom of the doors.


The internet says 150mm is what you need, and yes i'm just extracting from over the stove with a vent in the ceiling. Really i need insulated ducting, but where do you get it from? Even better i need a company who specialise in warm air heating systems, but who the hell bothers!
People in the profession will of course have precise guidance they know you should follow. I the layman with a few decades of heating with wood look at it a bit differently. Any duct that moves hot air from above the wood stove (a space no human could or would want to occupy) and into a room or space where people want to spend time , working or otherwise, to blend with the air that would otherwise be there unheated is a good thing. Gathering it at the ceiling above the stove makes sense as that is where the hottest air is. Discharging it low in the desired room lets it rise through and mix with the air already in the room creating a circulation that blends the two together without creating uncomfortable drafts. Ceiling to ceiling ducts will work but slower and leaving bare feet and ankles on the floor uncomfortable for more time then you want to hear the nagging from the female creatures you are in charge of making comfortable.
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You can ignore this advise if you wish but I for one like sleeping indoors. Rolling Eyes
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Mr. Fox



Joined: 24 Nov 2005
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PostPosted: Fri Oct 12, 2018 11:18 am    Post subject: Reply with quote

We did this... I used one of these '12v marine bilge blowers', with one of these PWM speed controllers to set the speed (& to keep noise down) and a mechanical thermostat (in the room with the burner) to automate it.

As Ken suggests, just run the ducting under the loft insulation (or wrap it in any spare that you have). Maybe consider suspending the fan by a bungee to further minimise noise.

It worked OK, 100mm seemed to be enough, but I still had to move the sodding GCH thermostat out of the room with the woodburner in, though. Wink
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Mr. Fox



Joined: 24 Nov 2005
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Location: In the Dark - looking for my socks

PostPosted: Fri Oct 12, 2018 11:22 am    Post subject: Reply with quote

mr brightside wrote:
Really i need insulated ducting, but where do you get it from?


Here - but be careful when you open the package... It leaps out like a jack-in-the-box and smacks you in the face!
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kenneal - lagger
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PostPosted: Fri Oct 12, 2018 12:01 pm    Post subject: Reply with quote

If you put the ducting under the insulation but ensure there's 100mm of Rockwool under it as well that will sound insulate as well as anything.
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vtsnowedin



Joined: 07 Jan 2011
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Location: New England ,Chelsea Vermont

PostPosted: Fri Oct 12, 2018 5:20 pm    Post subject: Reply with quote

Mr. Fox wrote:
mr brightside wrote:
Really i need insulated ducting, but where do you get it from?


Here - but be careful when you open the package... It leaps out like a jack-in-the-box and smacks you in the face!
Been there done that!!! Shocked Inside a big walk in closet that suddenly wasn't big enough. Wink
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mr brightside



Joined: 01 Apr 2011
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Location: On the fells

PostPosted: Wed Oct 17, 2018 8:38 pm    Post subject: Reply with quote

That's really great that, cheers. The ceiling vents should be the easy bits to get hold of.
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