Why can't they share a chimmney?

[Brianna]

Ok so trying to understand why....
We have a mason lined chimmney one for the upstairs fireplace and one for the oil furance. We want to put on an add on wood furance downstairs and tie it into the same chimmney as the oil furance as they would each have their own flues. We where told you can't do this. Why not?
What are our other options? Can you block off the upstairs fireplace somehow and then use that one or it our only option a pipe out the side of the house from the basement. Any help would be greatly appreciated and if I need to provide more information to get some answer let me know! Thank you so much for any feedback.

 

[jtp10181]

We want to put on an add on wood furance downstairs and tie it into the same chimmney as the oil furance as they would each have their own flues.

You mean you were planning on using the same chimney space for both but each would have its own liner? That itself is a code issue, others probably know exactly why. They definatly can't share the same liner or chimney because of down drafting.

I think I have heard other people mention power venting oil furnaces? Then you could hook the wood furnace up to the chimney.

 

[nshif]

The person who should answer this is Elk as to the why but youve been advised properly per code as I see it. My take on the why is as jtp said if one was running and the other not you could backdraft exhaust from the running one back into the house which was the purpose of the flue in the 1st place.
the second thought I had was overheating the masonry and flues when both were running. But Ill defer to Elk

 

[kevinmoelk]

Hummm. Also is going to depend on how the chimney itself is constructed. The chimney my oil furnace uses is an old beast, but then again it was originally built with the idea a coal burning furnace would be attached. I believe the chimney requirements for an oil burning appliance is lower than for a wood burning appliance. My point being is that just because it's made of masonry does not mean the chimney is suitable for a woodstove. As others have stated, a single chimney cannot have 2 appliances. If it were me and the chimney were okay for a woodstove (after inspection) I'd use the chimney going to the basement. The oil furnace will probably be the cheaper of the two to run a new exhaust.

Having said all of this, many questions come to mind. What are you doing downstairs? Is this a basement remodel? Do you have pictures? What are your expectations for the woodstove in the basement?

Welcome to the forum Brianna.

-Kevin

 

[Xena]

Are you sure the fireplace and
the furnace share the same flue?

Our chimney has two completely separate flues inside,
one going down to the furnace, the other to the fireplace.
They are not connected at all. I'm no "ekspert" by any
means, but it would seem odd to me that
a chimney with a furnace in a basement and
a fireplace up in the living space be built without
two separate flues.

 

[nshif]

Zeta
sounds to me as if its 2 separate chimineys one for the fireplace one for the oil burner. each with one flue and they want to add a flue to the oil buner one. not legal

 

[KeithO]

Why not ? Because the flue gasses from wood burner downstairs could "exhaust" through the oil burner (the thing is not 100% airtight after all) and kill you.

Its kinda funny to read about "airtight" stoves when it obviously consumes air that it has to get somewhere, generally from the same room that it is in. Because of the fact that none of the appliances is sealed (nor could it stay that way for any time), each needs its own flue. Hopefully, if the fire smolders and makes CO, it will be venting it safely straight up through its own flue and not out through the nearest other appliance (illegally) connected to the same flue. Alternatively, if the oil burner were to run rich, it too may be starved of oxygen and make CO that could vent out of the wood burner. Bad deal both ways. CO kills.

 

[nshif]

Keith
They are talking 2 flues in the same chiminey. think of a masonry fireplace with 2 liners. You have the right idea but the wrong application

 

[KeithO]

and tie it into the same chimmney as the oil furance

It does sound like they have 2 flues currently. Also sounds like they want to share a chimney with the oil burner with the add on. Whats the likelihood of getting 3 liners down a masonry chimney ?

 

[nshif]

No if you reread it they have 2 chimineys each serving one item. they want to add a second liner to one of them.

 

[webbie]

OK, well - first of all, it is 100% normal and fully within code to have multiple gas and oil and other burners sharing the same flues - it is detailed in the owners manuals. It is also legal to use a multi-fuel unit which can actually burn both fuels at the same time - wood and oil or wood and gas, all into one l6" chimney (see HS Tarm boilers, etc.)

Even more interesting, years ago our state (MA) actually wrote an exception into the state code which allowed for residential wood burning furnaces and boilers to be vented into the same flue as an oil burner AS LONG AS THERE WAS ENOUGH CHIMNEY CAPACITY......

But, to answer the original question - presently, that code appears to be no longer in force. One chimney is needed for each appliance. The reason is simply this - since there are so many brands and types/capacities, allowing multiple units in one chimney is asking for trouble "in the field". In a perfect world, an expert could rate chimney capacities, condition, height, appliance maximum outputs and more...and make a judgment. But this is not that perfect world.

Strangely enough - way back when the testing was done with an oil boiler and a wood boiler into the same chimney, the chimney stayed cleaner than just the wood burner alone! I think the testing was originally done at ETLM (Maine), and then accepted by Ma. due to pressure (partially) from the Tarm importer - who used to be located in Conway......

How's that for trivia?

 

[Xena]

I re-read and I see now. Need sleep.
Shouldn't be on the computer.

 

[elkimmeg]

Even more interesting, years ago our state (MA) actually wrote an exception into the state code which allowed for residential wood burning furnaces and boilers to be vented into the same flue as an oil burner AS LONG AS THERE WAS ENOUGH CHIMNEY CAPACITY......

I did read this code in the 1978 edition of codes but it never was brought forward into the 1982 code edition From I982 forward one flue for one appliance.

Craig is right a multi fuel appliance tested and listed and approved for one chimney connection is perfectly legal but Ad on using different fuel may not be code compliant

There is the dynamics's of a Bevent draft hood that easily can be back drafted due to open air intrusion of the draft hood Then there is the oil burner using a barometric damper which vacuum of another soiid Vent appliance may change the nature of its draft and effect the safe performance of both appliances connected to that flue.
then the is the volume issue inside an 8/8 masonry flue area is about 45 sq inches 28,25 X 2 6" draft pipes in 56.5 " far exceeding the volume requirements Then what if the oil burner is tank less hot water and the demand call at the time the wood boiler is running Remember already established n not enough capacity to draw both appliances.

The real question is what the listing is tested listed and approved for the venting. Code will not allow venting of appliances using different fuels Code with the exception of low volume water heaters will not allow two appliances in one flue .

A property od gas combustion is moisture having moisture in a chimney with wood smoke is asking for a creosote problem.

Maybe the best reason is, no permit can be issued for a direct code violation or listing violation

 

[keyman512us]

OK, well - first of all, it is 100% normal and fully within code to have multiple gas and oil and other burners sharing the same flues - it is detailed in the owners manuals. It is also legal to use a multi-fuel unit which can actually burn both fuels at the same time - wood and oil or wood and gas, all into one l6" chimney (see HS Tarm boilers, etc.)

Even more interesting, years ago our state (MA) actually wrote an exception into the state code which allowed for residential wood burning furnaces and boilers to be vented into the same flue as an oil burner AS LONG AS THERE WAS ENOUGH CHIMNEY CAPACITY......

But, to answer the original question - presently, that code appears to be no longer in force. One chimney is needed for each appliance. The reason is simply this - since there are so many brands and types/capacities, allowing multiple units in one chimney is asking for trouble "in the field". In a perfect world, an expert could rate chimney capacities, condition, height, appliance maximum outputs and more...and make a judgment. But this is not that perfect world.

Strangely enough - way back when the testing was done with an oil boiler and a wood boiler into the same chimney, the chimney stayed cleaner than just the wood burner alone! I think the testing was originally done at ETLM (Maine), and then accepted by Ma. due to pressure (partially) from the Tarm importer - who used to be located in Conway......

How's that for trivia?

..."Okay that was as clear as mud."

OK, well - first of all, it is 100% normal and fully within code to have multiple gas and oil and other burners sharing the same flues -

Want to clarify web??? Do you mean 6 gas furnaces all sharing the same flue....or could one put 4 gas burners and two oil burners all into the same flue???

From what I've heard you can't "mix fuel types".

So what's the answer (curious on this one).

 

[keyman512us]

Ok so trying to understand why....
We have a mason lined chimmney one for the upstairs fireplace and one for the oil furance. We want to put on an add on wood furance downstairs and tie it into the same chimmney as the oil furance as they would each have their own flues. We where told you can't do this. Why not?
What are our other options? Can you block off the upstairs fireplace somehow and then use that one or it our only option a pipe out the side of the house from the basement. Any help would be greatly appreciated and if I need to provide more information to get some answer let me know! Thank you so much for any feedback.

Some more info would help.

Let me see if I "read this right"...two existing heating appliances...you want to add another for a grand total of 3???

What did you 'propose'???

Fireplace stays in it's own flue??? Oil burner and wood stove get connected to the same flue???

If the local AHJD won't "let it fly"...Put in a "power venter" for the oil burner and use the flue for the stove... simpliest way out IMHO.

 

[nshif]

Brianna
If you even understood half ot that your better off then me
The simple answer is no you cant do it. Ramifications of doing so might lead to deneil of an insurance claim, a problem selling your house in the future or worst of all somebody may die.
Your options :
1) run a new line outside
2) move the existing oil vent outside ( probably smaller ) and install the new vent in that chimeny.

 

[webbie]

Do you mean 6 gas furnaces all sharing the same flue....or could one put 4 gas burners and two oil burners all into the same flue???

From what I've heard you can't "mix fuel types".

This answers the multiple gas part of your question.......

 

[webbie]

And this one is from the Metalbestos Class A manual

 

[nshif]

Thats all fine but it doesnt deal with a wood burner
How much do we want to confuse this girl?

 

[stoveguy13]

the code only allows it if it is all on ther same level of the house for example all the units must be located in thhe basement. wood burning or soild fuel applineces are one appliance per flue. with excepiton like the tarm

 

[elkimmeg]

Note to the code one gas appliances are governed by the National gas code Not by NFPA code period. Their venting is also covered by the International Mechanical codes
I can't find that graft or pictures in either of the governing code bodies for gas appliances. Also Note the NFPA codes are not a fully adopted code

Also note there are codes that apply to relationship of sequence of entry the smaller venting appliance usually the gas hot water heater must enter bove the larger volume appliance.

in a typical 8/8 masonry flue 26.25" is used by a 6" round connector pipe a 4" gas hot water pipe may use the same flue because it only needs about 12.5" Added up they equal 39.75"
blwow the vollume frow of the 8/8 45 sq inch capacity

Larger applications are only found in the Insterenational Mechanical codes and not in the residential sections of the one and two family dwelling codes.

Also not addressed is Code dealing with different fuel burning appliances which is prohibited

NAFA 31 Oil burner code Chapter 6 Venting of combustible fuels

6.5.1.9
Solid fuel burning appliances shall not be connected to a chimney flue servicing another apliance burning other fuels unless specifically listed for such connection

6.4.1.4
Connectors serving appliances under natural draft, shall not be connected into any portion of a mechanical draft system

6.5.18
Oil- burning applainces that are connected to a common venting system shall be located within the same story of the building

6.5.1.7
Two or more oil-burning appliances shall be permitted to be connected to
a common venting system provided the following conditions are met
1. Each appliance is equipped with a primary safety control
2. The Venting system is designed to meet the volume requirements of the code application

6.5.1.5
If two or more openings are provided into a chimney flue, they shall be at different levels and the smaller connector shall enter at the higher level consistant with the available head room or clearance to combustible materials..

The National Gas code has similar language when time alots I will supply tomorrow.

I would hope that the code quoted is from the recognized governing codes and not from unrecognized souses. All the above code is from the NFPA 31 governing Oil burners

 

[stoveguy2esw]

6.5.1.9
Solid fuel burning appliances shall not be connected to a chimney flue servicing another apliance burning other fuels unless specifically listed for such connection


this is the one that counts. the wood unit cannot be installed in the same flue that any other appliance is also being vented through. you will need a seperate flue for the wood furnace that will not service any other unit.

 

[mkmh]

So from this thread I am pretty sure I am reading that a Propane Strorage Water Heater could not legally vent into the same masonry chimney(same flue) as a Pellet Stove, correct?
Personally, I am avoiding this situation by going to an electric storage water heater, but was interested in hearing why this would be unsafe. I don't understand why this set-up would be against code, while my old oil burner and propane hot water heater co-existed (legally) for many years.



Don't blast me...just want to understand the difference from a safety perspective. (not purely code)

 

[elkimmeg]

my old oil burner and propane hot water heater co-existed (legally) for many years.

I don't understand this statement they never legally existed read the above code Maybe they were installed prior to most code in the 50's even so I doubt it is either the original burner or hot water heater so at some point illegal installations were made time and time again.

Next you also have another opr tion up grade to a high direct vent high efffeciency gas hot water heater then you can free up the flue of other appliances

 

[webbie]

The answer to the wood question is obvious - unless it is a listed multi-fuel unit, it is one chimney per appliance. My point in confusing the issue was to show that these things have changed vastly over the years. Today most gas units are direct vent through the wall anyway (at least around here), so the multiple connecting applies mostly to commercial and industrial applications.

So, simply speaking, with wood or pellet or coal, one chimney (or vent) per appliance.