Oil Furnace and Wood Stove on Same Flue

[jpmako]

Wow,

Great responses. It is encouraging to see some others with the same basic set-up that don't have any problems. I am very vigilant with cleaning the chimney as well as inspecting for problems. I am assuming that the previous homeowner used this set-up without having any issues, but am unsure if he used both appliances at the same time or used the wood stove only as a back-up source of heat. Anyway I am going to get a digital CO detector and place it in the basement to compliment the two upstairs that I installed by the bedrooms. I also have two fire extinguishers in the basement as well as two upstairs. I don't anticipate having any problems but would like to be prepared to deal with anything should the need arise. Should a problem occur I will put the skills that I have acquired in the last 10 years as a firefighter to good use.
Thank you all for sharing your knowledge and hopefully I can use this set-up without issue for the remainder of this year.


Jason

 

[NSMaple1]

My old oil/wood boiler had two flue pipe outlets on it. They went into the same flue. The only condition was that the oil had to T into the chimney above the wood.

Looks like that's what you've got going on there, so I think you're good to go.

Would definitely keep an eye on things though, and keep your detectors in good order. Both my flue pipes had barometric dampers in them - so I would get some creosote buildup where the oil pipe T'd in from the fresh air being sucked in through the oil baro. Not major, and I swept 3-4 times a year so it was a non-issue. That was installed, to code, by pros, 18 years ago. Your jurisdiction may be different though.

I had a 30' stainless chimney though, so had lots of draft. How tall is your chimney?

 

[DavidBrown1212]

OK I have to ask. WHY should you not use the same chimney?? I have seen this comment a zillion times on here but never knew the why.
Don't just cite me codes. I could care less about the codes. I want to know the science behind the so called dangerous setup and why you shouldn't do it..

The smaller the the chiminey the faster it warms up, the easier it is to mmaintain a hot fast upward draft.

If you have multiple units on one flue the draft of one appliance may require a draft of one velocity, and the others require different velocities

 

[CTYank]

Two important factors:
1) Some code officers require flue to handle rating of all appliances connected. I.E. 180 KBTU/h furnace & 50 KBTU/h for flue specs. Always seemed pretty fuzzy to me. More relevant to me: simultaneous startup of all appliances should not have discharge into house. All exhaust should be drawn out.
2) Each connected appliance should have throttled connection. IOW none have an open inlet; consider a fireplace sharing a chimney with a furnace- draft could be insufficient for furnace. Gas furnace likely will need damper in flue connection- has worked for me- they generally have way excessive draft.

Certainly not the end of it. Just looking at sharing.

 

[Oliver1655]

The barometric damper is a specialized "tee" normally found in the 6" stove pipe between the stove & flue. It is recommended to be at least 18" from the stove. It has an adjustable weighted door which will open allowing air to enter the chimney while bypassing the stove during high winds. If you don't have one installed real high winds can create a vacumn in your chimney system drawing extra air into the stove. This can cause excessive heat and allow the winds to draw flames from the stove into the chimney which can cause a chimney fire. It also helps the stove to maintain a steady draft/heat.

They normally sell for $40-50. Sounds expensive but is really pretty cheap insurance.

 

[haveawoody]

Well thinking about the oil furnace and it's direct air flapper in the house I would never run the woodstove on that system.
Just think of it you have a ripper fire going in the woodstove all is well the wind picks up and forces flaming air down the chimney right out the point of least resistance the oil flapper.
A normal woodstove can handle that sort of event in it's firebox and since it has a no pressure release stack effect it's rare to see happen, but flame going into the oil furnace or out the flapper in a similar event that now has a pressure release area would make for a bad day.

Old school sometimes isn't a good thing.
IMO if you have room in the chimney put another flex pipe up for the woodstove and remove the T and make the oil furnace connection direct to it's line also, if no room then new stovepipe dedicated to the woodstove all the way up and out a new location.

 

[NSMaple1]

If the wind is sucking flames up the chimney from the wood stove, how can it push them out the oil pipe?

I have had that exact thing happen to me on my old setup (gusts of wind sucking fire out of the wood side), and nothing ever took a turn into the oil pipe. Straight up it will go.

 

[GVS]

I'd run either, one at a time.NEVER both at the same time.The draft of each could be so different,one from the other. No telling what would happen when the stove door was opened to load or check while the oil burner was runing full tilt.I absolutely wouldn't do it.Those that say all is good by doing it,let them take the responsibility.There won't be many takers!

 

[artbaldoni]

Had this setup, wood boiler and oil boiler. I would sometimes get backdraft from the oil side into the wood stove. It may have had something to do with the 8"x8" flue size. The wood fire was nearly out or just starting and the water temp was low enough for the oil burner to kick in so both units were trying to exhaust at the same time. I agree that if you used only one at a time you should have no issues.

 

[Whitespider]

As a bachelor I lived in an old dilapidated, drafty, two story farm house with an oil-fired furnace in the basement (a converted coal burner). The brick 'n' mortar chimney was on an outside north wall. The 10 inch flue pipe came off the furnace for a couple feet to the barometric damper, then ran horizontally about 10 feet to the chimney. I set a barrel stove next to the furnace and ran the flue pipe just past the barometric damper and Y'd into the oil furnace flue pipe... about 8 feet from the chimney.

When it was cold that old oil furnace started/stopped 3-4 times an hour while the barrel stove was runnin' hot 'n' heavy at the same time. I had the loading door open on that barrel stove hundreds of times when the oil furnace was either running or starting-up. I don't remember ever having anything "reverse" direction in either appliance... I don't remember any draft problems at all. Obviously the oil furnace was getting enough draft because the barometric damper was always open some... even with the extra 6 inch stove pipe Y'd into it.

 

[NSMaple1]

Well, I ran my setup for 17 years. Installed to code, by pros. There were lots of times the boiler oil side would cut in when there was a wood fire going in the other side of it, when there was too much heat demand for what the wood side was putting out. Which is the way the boiler was designed to work. As long as you've got adequate chimney draft, things should be good. How long has it been setup & running like this? That's likely your proof.

Out...

 

[haveawoody]

NSMaple1,

Well not much pressure difference between flame going up the chimney and out the oil flapper.
When fires are starting or winding down in the woodstove the chimney effect isn't much so a good gust of wind can easily push flame back down.
The oil furnace would be 100% safe to run on that setup since the oil flame pressure wont allow backdraft on the flapper.
IMO though I would never run both at the same time and if I was running the woodstove I would be very careful about doing it on very windy or gusty days.
Really best solution is to bite the bullet and migrate the woodstove to it's own chimney or at least own flex in the chimney, both units will be more efficient and both much safer.

 

[Whitespider]

There's that word again... "safer".
Safer than what?? Safer than running them both in the same flue?? Well... just how "unsafe" is that?? It's likely "safer" than a lot of everyday things you do.
Buying your firewood is a damn sight "safer" than goin' out in the woods and felling your own trees... how many of you cut your own firewood?? Can anyone tell me the odds of being injured or killed while cutting firewood versus the odds of being injured or killed by running two appliances in the same flue?? Anyone??
Sure... some things increase the odds... but you do that every day also...
Can anyone tell me the odds of burning your house down using that damaged drop cord (that you repaired with black tape) versus the odds of a chimney fire burning your house down?? Anyone??

Rules, regulations, laws, codes and whatnot do not, can not keep you "safe"... they never have, they never will. At best, they protect the fool from himself... and believe me, the fool will still find a way to be foolish. Just being alive is a "risk"; you risk losing your life every second you're alive... but without risk there can be no gain. There ain't a damn thing government and it's rules can do to reduce the risks of life... only a fool would believe it could. Knowledge and awareness is the real power... something all these "safety" rules have caused people to lose.

The OP asked about an existing set-up. An existing setup they may have been there for decades, yet some are convinced the first time he fires it up his house will be reduced to a pile of ashes... or worse. Some are saying it will be "unsafe" to run both at the same time... when likely both have run at the same time safely for decades.

Would I advise someone to do a new install like that?? No, I would not.
Would I advise someone to not do a new install like that?? No, I would not.
I would tell them to check local codes first, I'd make them aware of possible problems, issues and whatnot, I'd tell them to do their own research on possible dangers and the causes... and let them make their own call.

@jpmako
You, and only you, are responsible for you and your family. You, and only you, can make the call on this one. Do not let anyone else make this decision for you... not me, not anyone on this board, and certainly not government (although possible fines and whatnot, if there are any, should enter into the decision making). If you decide to use the existing set-up... well... don't be a fool, educate yourself on the possible problems, issues, dangers and how to minimize them. Keep a close eye on things (especially at first) until you get a "feel" for how the set-up performs, keep things properly maintained, and don't ever become complacent... don't ever become complacent about anything in life, the dangers don't begin and end with your chimney. And above all, never forget that you, and only you, are responsible for you and your family.
*

 

[jpmako]

There's that word again... "safer".
Safer than what?? Safer than running them both in the same flue?? Well... just how "unsafe" is that?? It's likely "safer" than a lot of everyday things you do.
Buying your firewood is a damn sight "safer" than goin' out in the woods and felling your own trees... how many of you cut your own firewood?? Can anyone tell me the odds of being injured or killed while cutting firewood versus the odds of being injured or killed by running two appliances in the same flue?? Anyone??
Sure... some things increase the odds... but you do that every day also...
Can anyone tell me the odds of burning your house down using that damaged drop cord (that you repaired with black tape) versus the odds of a chimney fire burning your house down?? Anyone??

Rules, regulations, laws, codes and whatnot do not, can not keep you "safe"... they never have, they never will. At best, they protect the fool from himself... and believe me, the fool will still find a way to be foolish. Just being alive is a "risk"; you risk losing your life every second you're alive... but without risk there can be no gain. There ain't a damn thing government and it's rules can do to reduce the risks of life... only a fool would believe it could. Knowledge and awareness is the real power... something all these "safety" rules have caused people to lose.

The OP asked about an existing set-up. An existing setup they may have been there for decades, yet some are convinced the first time he fires it up his house will be reduced to a pile of ashes... or worse. Some are saying it will be "unsafe" to run both at the same time... when likely both have run at the same time safely for decades.

Would I advise someone to do a new install like that?? No, I would not.
Would I advise someone to not do a new install like that?? No, I would not.
I would tell them to check local codes first, I'd make them aware of possible problems, issues and whatnot, I'd tell them to do their own research on possible dangers and the causes... and let them make their own call.

@jpmako
You, and only you, are responsible for you and your family. You, and only you, can make the call on this one. Do not let anyone else make this decision for you... not me, not anyone on this board, and certainly not government (although possible fines and whatnot, if there are any, should enter into the decision making). If you decide to use the existing set-up... well... don't be a fool, educate yourself on the possible problems, issues, dangers and how to minimize them. Keep a close eye on things (especially at first) until you get a "feel" for how the set-up performs, keep things properly maintained, and don't ever become complacent... don't ever become complacent about anything in life, the dangers don't begin and end with your chimney. And above all, never forget that you, and only you, are responsible for you and your family.
*

Very well said. As an adult I take total responsibility for my decisions as well as my personal safety and that of my family. Like I said earlier I am a Volunteer Firefighter so that in itself provides many opportunities for me to either get injured or dead, but I continue to do it. A lot of things that I do are dangerous but I enjoy doing them. I will be trying the existing set-up when I get into the house and will keep a watchful eye on how things go. I would assume that this was used this way before the way that it is without issue. Hopefully I live to report back and let everyone know that everything is okay and it all worked out.

 

[nk14zp]

What part of Maine are you moving to?

 

[jpmako]

What part of Maine are you moving to?

Outside of Bucksport.

 

[DavidBrown1212]

NSMaple1,

Well not much pressure difference between flame going up the chimney and out the oil flapper.
When fires are starting or winding down in the woodstove the chimney effect isn't much so a good gust of wind can easily push flame back down.
The oil furnace would be 100% safe to run on that setup since the oil flame pressure wont allow backdraft on the flapper.

.

This is not the way the flapper works. It only allows one way flow into the flue. In no way could flames be pushed out of it. But I do agree, having separate liners for each appliances would be the best solution as far as safety and performance.

 

[artbaldoni]

My setup worked for 10 years. Just would get some smoke out of the wood side occasionally when the oil kicked on. I didn't really see a safety issue, only a too small of a flue issue for both, but only under certain circumstances and for a very short period of time when the oil first kicked on.

 

[farmer steve]

Hi Art.

 

[artbaldoni]

Hey FS. Did it make 70 out your way today?