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wombosi 12-13-2009 07:52 PM

adding wood stove to boiler flu?
hi all.

i have a brick chimney in the center of my house currently venting the boiler.

in doing some remodeling work, i discovered three old ducts coming out of the chimney presumably used for wood stoves (there were pipe inserts).

anyway, when i repaired one of these, i essentially had a huge gaping hole in the chimney, and the boiler was running, and there was still a huge draft going up and out the chimney - nothing whatsoever coming into the room.
i stuck a piece of paper over the hole and t he draft held it in place easily.

what i'm wondering is:

1) i know it's illegal for me to stick a stove pipe into this thing and use the single flu for both wood stove and boiler, however:

is there really any danger in doing this?

i feel like 'who's to tell me i'm not allowed to have a wood stove on my own chimney?' somehow i believe it's not at all dangerous.

it would certainly be a wonderful thing to have and help cut down my heating costs.

wondering what you all think.


Scuba_Dave 12-13-2009 08:23 PM

I'm not sure of the exact codes, but pretty sure you can't use one chimney flue for multiple devices
My chimney has 3 seperate flues, one is used by the fireplace, one is used by the boiler
The 3rd is not in use...possible old fireplace on the 2nd floor?

I do know that when I moved in there was an oil fired HW heater that shared the same flue with the boiler
I never knew you could not do never worried about it
The oil fired HW is gone

Usually they point to drafting issues & possible CO leaking in from the 2nd access point
So all 3 just went into the same flue ?
Are both the ones you want to use located in the basement ?

wombosi 12-13-2009 08:27 PM

hey scuba,
all three prior tap-outs are on the 1st floor, boiler is in the basement below.
looks like three stove pipe fittings sitting there and covered over with plaster, literally. i had to rip out a bump-=out wiht one of these and patch it back flat to make room for pipes i was putting inside the wall.

i realize of course if this were a new build and permits were involved, i could never ever do this. but i'm willing to bet that people do it on their own all the time and risk just about zero health or safety hazards.
i don't really know this for sure, though.

edit: when i had it opened up, it appears that there is only one flu, i couldn't see brick inside, just ceramic, i think.

i just would want to use one of the old holes to stick a stove pipe into.

yuri 12-13-2009 08:39 PM

You are tampering with the draft/overfire draft over the oil burner fire. This will affect the combustion and could mess up your oil burner flame and produce CO as well as burn a LOT more oil. A good oil tech sets the barometric damper and overfire draft for proper combustion. Same problem could happen with a gas boiler. When you open up other holes etc you mess up the chimney draft and could create problems. Also, wood can produce creosote if not burned cleanly and if that catches on fire, goodbye house!! If there is ever a fire, goodbye house insurance. Ignorance of the law/ or codes is no excuse in court.

wombosi 12-13-2009 08:43 PM

thanks yuri.
well, any way i could split the existing flu in half, or would that not be sufficient draft for either device?

Scuba_Dave 12-13-2009 08:49 PM

Wrong time of the year to climb up & look at (down) the chimney on the roof
Do you know how big the flue measures ?

wombosi 12-13-2009 08:51 PM


Originally Posted by Scuba_Dave (Post 366318)
Wrong time of the year to climb up & look at (down) the chimney on the roof
Do you know how big the flue measures ?

yeah, i know what you mean. but i did have a good look at it through the hole the other day. i would guess 8-10".
seems the chimney measures about 16" square.

beenthere 12-14-2009 05:27 AM

Fire hazzard.

call your insurance company. Ask them if they will cover you if your house burns down because you ran a solid fuel heater and and oil furnace/boiler into the same chimney flue.

If they say no. Are you still willing to ignore fire codes.

The fire marshall and insurance inspector will know what caused teh fire.

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