# Is it allowable to run two flue liners up a single chimney?



## rosebud (Mar 12, 2011)

I would like to vent my pellet stove which has a 3" flue and my gas floor furnace which has a 4" flue through my chimney which has an 8"x8" opening.  Is it up to code to run two separate flue liners through a single chimney? Thank you.


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## checkthisout (Mar 12, 2011)

rosebud said:
			
		

> I would like to vent my pellet stove which has a 3" flue and my gas floor furnace which has a 4" flue through my chimney which has an 8"x8" opening.  Is it up to code to run two separate flue liners through a single chimney? Thank you.



Don't see why not because both still have seperate vents and flus.


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## Lousyweather (Mar 12, 2011)

make sure you can satisfy the EVL for the pellet stove....if over, say 15' of liner, you probably should go to 4" pipe for the pellet stove....if so, also, can you fit 2 4" liners in the 8x8 flue? And how are you terminating the cap?


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## DAKSY (Mar 12, 2011)

NO. From NFPA 211:

4.5.3 Space Surrounding Liner or Vent. The remaining space
surrounding a chimney liner, gas vent, special gas vent, or plastic
piping installed within a chimney flue shall not be used to
vent another appliance.


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## summit (Mar 12, 2011)

only allowable if you can install a masonry divider 4" nominal thickness between the 2.


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## Fsappo (Mar 12, 2011)

DAKSY said:
			
		

> NO. From NFPA 211:
> 
> 4.5.3 Space Surrounding Liner or Vent. The remaining space
> surrounding a chimney liner, gas vent, special gas vent, or plastic
> ...



Daksy, I always read that as you can not use the area as it is to vent another appliance.  But as two seperate liners it was allowed.  Got that "version" from a code enforcer decades ago...But, I am an NFPA member.  I guess I better give em a call Monday and hear it from the horses mouth.  I have done installs that way in the past and now you all got me thinkin.


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## smwilliamson (Mar 12, 2011)

DAKSY said:
			
		

> NO. From NFPA 211:
> 
> 4.5.3 Space Surrounding Liner or Vent. The remaining space
> surrounding a chimney liner, gas vent, special gas vent, or plastic
> ...



I believe that this can be interpreted both ways, in such a case though, where there is not solid understanding one must always default to the safer option. The OP is not suggesting that he vent into the air space surrounding a liner, but in fact contain gases in a separate liner shared within the same air space.

Though, if one cannot install L vent anywhere above a gas meter or lass than 3 feet from center...venting a pellet liner next to a gas exhaust I would assume could create a dangerous albeit very rare hazardous situation.


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## Lousyweather (Mar 12, 2011)

yea, the reason I asked how it would be terminated is because I was concerned about one appliance not running, allowing a conduit for CO back down the other pipe.....


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## yooperdave (Mar 12, 2011)

do you need to maintain any type of clearances with the liners?? if so, i don't see how you could run both liners up the same chimney.  i'm sure they would be touching each other at some point/points.


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## velotocht (Mar 12, 2011)

Rosebud:
Interesting question - and one which I cannot answer.  From a pure safety point of view, I can't see where it would be a problem.  Both vents are still isolated from the flamable materials of the house by the chimney liner and brick - and they're separated from each other by two walls of stainless steel.  Furthermore, the chimney is designed to handle the total flow capacity of 64 square inches -- with 4" two flue vents you are only at 2*(2*2*3.14)=~52 sq. inches of venting area.  That is - if you can squeze 'em both in.  

Now I undestand from Daksy's post why colde would not allow you to run a second vent up the middle of an active (8x8) chimney - THis could make for a very hot center liner - but conceptually two 4" inch independant vent pipes sharing the lined chimney space should be OK.   I have a feeling this one is going to open to the interpretation of the code by the inspector.  And, if your inspector is like most, he will take the safe, conservative, and low-risk choice - and reject the proposal.  No sense in sticking his neck out for zero personal gain.

Good luck.  Let us know what you find.

RonB


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## rosebud (Mar 12, 2011)

Thanks for all the imput.  It's an old house that I'm working on, so I'll need to have an inspector okay the gas line before a meter can be re-installed.  I'll mention my idea to him when I meet him.  And I'll be sure to ask about how the two liners should be capped if he does accept my proposal. (Though I would think that a similar issue regarding CO2 running down the second flue would arise with two clay liners running next to each other down a larger chimney.)

rosebud


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## Lousyweather (Mar 12, 2011)

rosebud said:
			
		

> Thanks for all the imput.  It's an old house that I'm working on, so I'll need to have an inspector okay the gas line before a meter can be re-installed.  I'll mention my idea to him when I meet him.  And I'll be sure to ask about how the two liners should be capped if he does accept my proposal. (Though I would think that a similar issue regarding CO2 running down the second flue would arise with two clay liners running next to each other down a larger chimney.)
> 
> rosebud



sure, logocally speaking, yes, but your question requires an inspector to actually stick his neck out and make a determination, then actually SIGN it, since it s a grey area code-wise.


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## nate379 (Mar 13, 2011)

Ok, but he is running 2 flues, not using the remaining space... ie... the area that the flues run through.


			
				DAKSY said:
			
		

> NO. From NFPA 211:
> 
> 4.5.3 Space Surrounding Liner or Vent. The remaining space
> surrounding a chimney liner, gas vent, special gas vent, or plastic
> ...


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## Nicholas440 (Mar 13, 2011)

I dont think this has much bearing on the question of the OP,   but  my home has a Natural Gas Furnace, and a Natural Gas hot water heater,  and both of them are vented into  one single brick chimney.  Two seperate gas appliances, venting into one chimney, and thats how the house was built.  Every home I have seen that has furnace and hot water heater is always vented up into one chimney I've never seen two chimneys to vent two appliances.  

I wouldnt think that using 2 seperate steel pipes in one brick liner would violate code, but  I'm not an expert on this subject so it's best to ask your local code people.


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## brawny84 (Nov 24, 2013)

Nicholas440 said:


> I dont think this has much bearing on the question of the OP,   but  my home has a Natural Gas Furnace, and a Natural Gas hot water heater,  and both of them are vented into  one single brick chimney.  Two seperate gas appliances, venting into one chimney, and thats how the house was built.  Every home I have seen that has furnace and hot water heater is always vented up into one chimney I've never seen two chimneys to vent two appliances.
> 
> I wouldnt think that using 2 seperate steel pipes in one brick liner would violate code, but  I'm not an expert on this subject so it's best to ask your local code people.



I know this is a dead thread, but I'd like to add clarification on gas/oil appliances, which have a little more flexibility in this area:
It is common to vent multiple gas burning appliances into a common flue. I believe it's even permissible (likely with more restrictions) to vent oil and natural gas appliances to a common flue. Though I trust the codes and inspectors to give good, safe rules, I would be careful with this one. The natural gas or propane mixes can sometimes introduce a lot of moisture into your flue gas which can mix with sulfur in the oil to form "acid rain" in your chimney and shorten the life of the liner and masonry.

Obviously, even with accepted practice of multiple Natural Gas appliances on a single flue, there are some general "red-flags" to investigate further. That is, some of these could be fine in a specific situation and given the full picture, but certainly should be looked at carefully:
Make sure the flue is sized properly (cross-section and height) to handle the total sum of the devices.
Don't mix forced draft (aka power-vent) with natural draft in a common flue.
Placement: Smaller connector above the larger one, but still on the same floor of the house, and not opposite to one another (especially not at the same elevation and opposite!)


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## Daytrp (Jan 24, 2014)

Hellow all.
I am new to the hearth forums. Although this is an old thread it is a commonly asked question.
I have been Looking at the nutec-upland 207 which is a natural draft stove with an avid following and great user reviews. To install this I would need to run another flue liner in my chimney along with my oil furnace's flue liner (one chimney with two liners in the same cavity). I researched the residential building codes to see if it was even an option. I know many people have had the same question so I Had to share my find:

2009 international residential code. Chapter 18: Fireplaces and Chimneys (pg. 495)
M1801.4 Space around lining. The space surrounding a flue lining system or other vent installed within a masonry chimney shall not be used to vent any other appliance. This shall not prevent the installation of another flue lining in accordance with the manufacturer's installation instructions And this code.

This is, of course, subject to local county and municipality building codes and regulations.


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## Daytrp (Jan 24, 2014)

Same chapter and subheading in the 2012 IRC. Page 517 in this edition.
This means that yes, according to the most recent international residential code you can have two liners in one chimney.


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## Mt Bob (Jan 24, 2014)

Can vary from state to state,they have a say.Some states do not allow solid fuel liner next to a gas liner.Also,the nutec is natural draft,sometimes not allowed next to a power vent appliance.Building codes are one thing but state and local regulations trump.


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## Daytrp (Jan 27, 2014)

I agree. The best solution is to check with your local building permitting office as they do have the final say.


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