# Flue sharing for an oil furnace and a wood stove



## Michael Morgan (Oct 7, 2013)

Hi,

I'm in the process of renovating a 100 year old house in New England and I'm looking to add a wood stove to keep heating costs down in the winter. The chimney was Supaflued by the previous owners and it is now a single 6" flue to which the oil furnace is attached. The furnace is only used to heat the home, the water heater is electric. From what I understand it would not be up to code to have both appliances connected to the same flue. My question has less to do with the code and more to do with the actual safety in this situation. If the wood stove were installed I have _no_ intention of running the oil furnace - in fact I'd disconnect it so that there is no chance it fires up at the same time that I'm burning wood, though it would still be plugged into the flue. Is there any safety risk in a situation like this?

Thanks!


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## jharkin (Oct 7, 2013)

Yes, having the furnace piped in will allow a lot of excess cold air into the flue, like leaving a clean out open. It will kill draft at best, lead to massive creosote at worst.

Its against code for good reasons. Be safe, don't do it.


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## Michael Morgan (Oct 7, 2013)

Thanks for the reply. My biggest concern was carbon monoxide leaks into the house - is this only an issue if the furnace is running?

I would _really_ like to get a stove in, would you have any other suggestions? What if I were to pull the furnace pipe and seal that thimble?

Any help is greatly appreciated!


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## begreen (Oct 8, 2013)

If the furnace flue is disconnected and the thimble hole is plugged, then the wood stove would be the only appliance on the flue. That is acceptable, but are you sure you are ready for wood as a sole source of heat? How will the basement stay warm during very cold weather? Is the stove intended to be located there or upstairs where the heat is needed? Do you have an adequate supply of fully seasoned wood?


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## firefighterjake (Oct 8, 2013)

Which New England state are you living in?


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## fraxinus (Oct 8, 2013)

Maine code permits a woodstove and furnace to share a single flue if four conditions are met: 1) the installation has been in existence since prior to1998. (Although it's possible that this first condition is no longer part of the code). 2) There is sufficient draft as determined by a draft test. 3) the chimney is lined. 4) The building has carbon monoxide detectors.


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## Swedishchef (Oct 8, 2013)

Wow. I didn't know it was allowed in Maine.

My FIL has his stove and furnace on the same chimney. A big no-no around here but he doesn't care and won't listen to me.


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## Michael Morgan (Oct 8, 2013)

Thanks for the replies!

The home is in Maine, however the wood stove installation would be new so it would not pre-date 1998, unfortunately. All of the other conditions would apply - the chimney has a Supaflu and we have smoke / Co detectors throughout the home. I'm not sure about the draft since the stove is not installed yet, but it seems to draft very well in it's current state (furnace only).

Plugging the thimble for the furnace probably isn't the best idea, we realistically need a backup heat source. But if I shut the furnace down while the wood stove is running so that there is no chance of it firing up, is there any physical danger present to my family and I if we run a wood stove on the same flue? At this point that's my biggest concern. What problems are caused if it isn't drafting well enough?

Thanks again!


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## Sprinter (Oct 8, 2013)

Michael Morgan said:


> But if I shut the furnace down while the wood stove is running so that there is no chance of it firing up, is there any physical danger present to my family and I if we run a wood stove on the same flue?


It's just a really bad idea.


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## SteveKG (Oct 8, 2013)

In the long run, the best idea, if you are going to keep the oil burner, is simply to install a stovepipe for the stove, a pipe completely separate from the current oil burner chimney. It will be over, done, and safe.


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## Ashful (Oct 8, 2013)

A few people here have questioned why I hate the whole Supaflu idea so much, and this is exhibit no.1.  You are screwed.  Judging by the age of your house, the flue was likely large enough to install TWO flex liners, but the previous owner has relegated you to one, and there's really no going back, now.  That's not to say Supaflu, and it's equivalents, are never a good option.  It can really help in situations where there is masonry coming loose inside the flue, for example.

Exhausting an oil burner into a chimney used for a wood stove, aside from the other reasons already mentioned, seems like a recipe for potential chimney fires.  Particularly for a novice burner, who may have access only to less than optimally seasoned wood.

Is the existing chimney on the interior of the home, or built into an exterior wall?  I'd be looking to build another masonry chimney exterior to the house, possibly coupled with the existing chimney, for installing a second flue.  We had one built in 1990, roughly 45 feet up, at a cost of only $5k.  Inflation calculator tells me that translates to roughly $9k today... and I'm guessing your chimney is much shorter than ours.


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## Michael Morgan (Oct 8, 2013)

Thanks again for the replies!

SteveKG - I'm starting to like this idea more and more. I would not want to run the pipe on the outside of the house for aesthetic reasons, but is it possible to run the stove pipe straight up through the second floor and attic and out the roof? Would I have to box in the pipe on the second floor and attic? How much should I expect to pay for an installation like this?

Joful - Unfortunately you are correct. It appears from talking to a few people there was plenty of room for two flues, and the previous owners decided to only install one. Not much I can do about it now. The current chimney is on the interior, essentially right in the middle of the house. Does this change the course of action you'd recommend? What do you think of running a stove pipe straight up through the house?

Thanks!


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## Ashful (Oct 8, 2013)

If you can find a clear path to do it, running a stove pipe up thru the house is a great option.  I was going on my own assumption that it's usually tough to find a clear path thru two or three floors.  I did recently post photos of a mill we almost bought in 2007 (and again in 2011, oddly enough), in which they ran a double- or triple-walled polished stove pipe all the way up from the first floor thru the second, third, and roof.  It seemed to work very well!  If you can't find a clear path, then the masonry stack with liner (or even framed and stucco'd stack with liner) on the outside is usually the next best (cosmetically and performance) option for a wood stove.  Your chosen location for the stove inside the house also plays a big role.


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## Michael Morgan (Oct 9, 2013)

Would anyone be able to give me an idea of what this should cost? Best guess I think we're looking at 6 feet of double walled stove pipe, passing through to an 8 foot second story, about 5 feet in the attic, and another 5 on the roof to meet clearances. Thanks so much!


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## begreen (Oct 9, 2013)

Are you asking the cost for self-install or pro-install? Parts alone will likely be around $1.2K, pro-install could be as high as $2K.


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## Batman (Oct 9, 2013)

Perhaps you can powervent the furnace. This would free up the chimney for the wood burner, and should be much cheaper than an additional chimney.


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## Michael Morgan (Oct 9, 2013)

begreen said:


> Are you asking the cost for self-install or pro-install? Parts alone will likely be around $1.2K, pro-install could be as high as $2K.



Thanks for the estimates! I think I could do the installation myself, would you have any recommendations for chimney pipe brands and where I might buy something like this online? I only ask because there aren't any stove shops particularly close by.


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## begreen (Oct 9, 2013)

I have had good luck with www.dynamitebuys.com. There are others for sure though.


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## Dave A. (Oct 10, 2013)

They look like hard prices to beat.  I really shopped around and ended up on ebay thinking I got a good price, but dynamitebuys, even two years later, looks better.

Edit: Maybe not.  Seems liner prices have come down from when I bought.  Ebay still has better deals on flex kits.


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## Ashful (Oct 10, 2013)

dynamitebuys.com seems a decent way to go for someone with experience, doing this for the fourth time.  I'd recommend Rockford, one of our advertisers, for a first-timer.  They have the support you'll need, when you have questions about pipes and connectors.  Their prices seem to be pretty good, versus local.


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## velvetfoot (Oct 10, 2013)

How about converting to propane?


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## Timnus (Oct 10, 2013)

If you go with triple wall pipe, the Duraplus kit at Home Depot (basic kit for through the roof) is $200 (LINK) and then each 3 foot section of Stainless Steel pipe is $85 (LINK).  Pretty good prices.  But, you have to get the rest of your items (elbows, support brackets) etc. from another source though - like dynamitebuys.com or ventingdirect.com  (of course all the components have to be the Duravent brand - triple wall for the chimney pipe and then either double or single wall for the stove pipe sections below the ceiling support box in your stove room)


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## Michael Morgan (Oct 10, 2013)

I've sort of taken this down a whole new path and have questions about stove and chimney pipe brands, so I'm just going to start a new thread. Thanks for all of the help so far everyone!


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## Dave A. (Oct 10, 2013)

I used Rockford (but bought from their ebay site and got better prices) and they were helpful with the phone support before and during the install.   But now looking at dynamite buys videos, I see that some of my mistakes (particularly not using a "terracotta top plate", which I ended up needing) wouldn't have been made if I'd seen their videos.


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