Thread: Fireplace Combustion Air Intake

New here and new at this...please bear with me.

The homeowner wants to penetrate concrete block inside his chimney chase about 18" below grade with an 8" piece of PVC, which would then turn vertical and go up and out of the ground about 2-3 feet. This basically would create a "chase" for a 6" combustion air intake to run through. His plan is solid and well thought out. I actually think it would work just fine, but I told him, no. Is that right? I can't really back it up my "no" with codes references, but I can't support it with codes references either.

Normally, the intake would come off the fireplace turn 90 degrees upward (inside the chimney chase) and turn 90 degrees again and penetrate the chimney chase wall to the exterior above grade. He doesn't have the room to make a 90 degree turn inside the chase, which is why he wants to go straight out the side of the chase below grade. It's the issue of exiting the below grade that is my question here.

I suggested that he install a window well so he can penetrate the chimney chase where he wants to AND be above grade (inside the window well) then run it up the outside of the chase a couple feet to get above the snow line. Any issues with this scenario?

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Welcome to the board Chris.

There are many DIY projects a homeowner can safely undertake themselves. Modifications to wood burning fireplaces do not fall within that realm. He's talking about using a piece of combustible PVC material in the chimney. For safety and proper operation of the fireplace, he's best leaving this type of work up to a pro.

I never like it when a homeowner asks for repair design ideas or if I think such-and-such will work.

Originally Posted by Nick Ostrowski

Welcome to the board Chris.

There are many DIY projects a homeowner can safely undertake themselves. Modifications to wood burning fireplaces do not fall within that realm. He's talking about using a piece of combustible PVC material in the chimney. For safety and proper operation of the fireplace, he's best leaving this type of work up to a pro.

I never like it when a homeowner asks for repair design ideas or if I think such-and-such will work.

I totally agree. However, in this instance, he isn't modifying the fireplace at all. If the fireplace sat 18" higher or the ground outside was 18" lower there would be absolutely no issues. It's really a question or penetrations through the concrete block below grade that is in question. And it's a cold air intake, so it's not like he's trying to do this with b-vent or something...kind of a unique deal.

Based on your response to Nick, I'm going to assume you are the homeowner. If not you are FAR TOO involved to be an objective HI. The statement that "he isn't modifying the fireplace at all" is utter nonsense. You are modifying the fireplace by adding a component or installation that wasn't part of the original manufacture. Has anyone done research as to whether this fireplace unit needs exterior combustion air? What size is PROPER. If not properly sized or other room conditions it could act as a vent tube sucking flames into it.
The idea that IF X "there would be absolutely no issues" is also nonsense since it doesn't take other variables into account. Why is this being discussed at all. Homeowner Joe saw a show and thought that's a good idea? Or more likely there are humidity or carbon monoxide issues in the home and this is someone's solution.
"It's really a question or penetrations through the concrete block below grade that is in question. Really, that's all? Do you know how to make a hole without compromising the block, do you have a core drill, what if there is rebar, how are you going to seal the exterior side so there is no water intrusion? Dumb, pesky little questions .
And it's a cold air intake, so it's not like he's trying to do this with b-vent or something...kind of a unique deal. Oh yeah, why use a metal, non-flammable pipe when you can use a flammable pipe that gives off toxic fumes when burned. No problem. If not properly designed the pipe can and will act as a flame conduit. Using PVC is NOT recommended.
I realize there is no good way to say this but honestly, are you stupid or what? I really hope you aren't a licensed HI. As a DIY homeowner you are par for the course. I apologize for insulting you. If you are an HI, WAKE UP. I make no apologies.
There's more to this. Nobody decides they are going to do something like this because they have too much time on their hands. Whatever the other issues are in the home, they must be addressed in conjunction with the fireplace issue.

Markus Keller,

FYI, MN does not license, register, or regulate HIs.

That being said, I do not disagree with the direction, tone or content of your post!

NFPA 211 defining the chimney and "fireplace".

Don't hold back Markus. Tell us what you really think.

Chris, what you're saying the homeowner plans to do is a modification of the fireplace in the sense that adding a combustion air intake pipe will effect the performance of the fireplace. And that effect may be either positive or negative if it is not done properly (see many of the points raised by Markus above). And the fact that he wants to use combustible PVC pipe is a big no no no no no no no.

Back to your original question. You said......."His plan is solid and well thought out. I actually think it would work just fine, but I told him, no. Is that right?"

The homeowner's plan isn't right. Using combustible PVC pipe in any part of a fireplace chimney is not a solid and well thought out plan.

Originally Posted by Nick Ostrowski

Chris, what you're saying the homeowner plans to do is a modification of the fireplace in the sense that adding a combustion air intake pipe will affect the performance of the fireplace. And that affect may be either positive or negative if it is not done properly (see many of the points raised by Markus above). And the fact that he wants to use combustible PVC pipe is a big no no no no no no no.

Thanks for a meaningful response Nick. Let me clarify. The fireplace requires combustion air intake. There is no modification to "add" it. Also, there is no PVC being used. That was his inital "plan" which I told him isn't allowed. I shouldn't have even mentioned it, I just wanted to give some background.

The galvanized intake pipe will go through the block into a window well then run vertically out of the window well, so no part of the vent pipe is underground.

Originally Posted by Nick Ostrowski

Back to your original question. You said......."His plan is solid and well thought out. I actually think it would work just fine, but I told him, no. Is that right?"

The homeowner's plan isn't right. Using combustible PVC pipe in any part of a fireplace chimney is not a solid and well thought out plan.

Thanks. Point taken.

Your latest proposed IS STILL WRONG.

Originally Posted by Markus Keller

I realize there is no good way to say this...

Then shut the hell up, unless you DO have a good way to say it and actually be somewhat helpful!

If someone else has some actual useful thoughts here (Like Nick did), I'll love to hear it. But, if all you are looking to do is trash people, move along!

Thanks.

Originally Posted by H.G. Watson, Sr.

Your latest proposed IS STILL WRONG.

Oh yes, very helpful - thanks. You this helpful on the job site too?

HEY Newbie DIYer member, I referred you to NFPA 211, which BTW you can view on-line for free at NFPA.org, or at your local library, MUCH EARLIER IN THE THREAD.

Guess what? Its a reasonably SHORT publication, and SPECIFICALLY ON POINT to your "issue".

Try READING IT, you just "might" LEARN something (for example what a "thimble" is).

Meantime hire a pro. You have no idea what you're doing messing with a chimney, site built or factory built insert or appliance, solid fuel or other, or its foundation, since you haven't identified, even remotely, what YOU have.

This is NOT a DIY site, and I don't believe for a second you are a professional HI, acting in a professonal capacity on this subject.

Chris, I think you might have done better using a more humble approach to this site. Your posts have, quite honestly, been rather awkward and stumbling to say the least. You failed to declare your position or relationship in this case, which is deceitful and counterproductive. You should understand this is why the suspicion and contempt here. Had you made full disclosure, you probably would have gotten a little softer response.

In spite of your rhetoric, you have been given good information here, as painful as it may seem. However, when you're bringing fire into a home, an increased level of caution and attention to codes is certainly warranted.

To address your issues:
A masonry chimney is the entire structure. A chase is a hollow enclosure, such as for elevators or factory built fireplaces. BTW, once you get over three stories it becomes a 'shaft' which must be of fire rated construction.

If this fireplace has already been constructed and you are adding a combustion air kit, then you are, in fact, modifying it. This means that regardless how it was originally built, any new work must meet the current codes. Now, codes do not guarantee performance but you must abide by them.

To undertake a project such as this, you must have a grasp of several seemingly unrelated disciplines. For instance, to penetrate the CMU block foundation wall below grade may require some sort of thimble or sleeve and recoating the dampproofing. You should be getting drawings of this approved by your AHJ and pull a permit. Note that you are penetrating with dissimilar materials. They will move at different rates, which means there is a high likelihood it will open a gap. If you use plain galvanized steel pipe through a masonry chase, it will rust out in just a few years. If you route it vertically, it will very likely generate a draft and backdraft heat, smoke, and possibly open flames out this kit. You failed to discuss what type of termination/ intake you propose to use. Use of the wrong component can result in fire or failure of the system.

As a certified F.I.R.E. Inspector, NFI Certified Master Hearth Professional, etc. etc, I strongly recommend you turn this over to a professional before someone gets hurt or property damaged. This is NOT a DIY project by any means so hire a pro and step aside.

In the future, I recommend you not come onto a technical help site and snap back at those trying to help you from yourself. Yes, Markus WAS trying to help you---you just didn't like what you were hearing. Nick warned you, too just softer.

Originally Posted by Chris Johnson

New here and new at this...please bear with me.

The homeowner wants to penetrate concrete block inside his chimney chase about 18" below grade with an 8" piece of PVC, which would then turn vertical and go up and out of the ground about 2-3 feet. This basically would create a "chase" for a 6" combustion air intake to run through. His plan is solid and well thought out. I actually think it would work just fine, but I told him, no. Is that right? I can't really back it up my "no" with codes references, but I can't support it with codes references either.

Normally, the intake would come off the fireplace turn 90 degrees upward (inside the chimney chase) and turn 90 degrees again and penetrate the chimney chase wall to the exterior above grade. He doesn't have the room to make a 90 degree turn inside the chase, which is why he wants to go straight out the side of the chase below grade. It's the issue of exiting the below grade that is my question here.

I suggested that he install a window well so he can penetrate the chimney chase where he wants to AND be above grade (inside the window well) then run it up the outside of the chase a couple feet to get above the snow line. Any issues with this scenario?

Yes I have an issue. All you are adding is another chimney. Anytime you add a vertical air intake with out a trap it will be another chimney vent.

I have seen a few where that becomes laden with creosote by venting some of the combustion air products.

This does not sound like it is well thought out.

Chris- I have been on this site for quite a while now. I watch and learn more then I post. One thing I have learned over time is there are a lot of very smart and helpful people on this site. If you supply them with accurate info or answer follow up questions you will get an answer. H.G. is one of the top people on this site. But he is a teacher, he will make you think about what you are asking. Watch his reply and you most often will not get just a simple answer, he will direct you to the information you are in need of. By doing this he is trying to teach you two thing, the answer to your question and where and how to find the information. By following his advice you will do just that you will learn. If you follow his direction and do not understand what it said or means he will work with you to make it clear as will many other qualified people.

In regards to the fire place if it is new construction, the contractor installing it should follow manufactures specs and local code. MN is not licensed for HI but contractors are and permits are required. If this is not new construction it is a modification.

I know what my liability insurance cost me, and my response to such a question would be to consult with a licensed qualified conatractor.

One thing that most of the comments have completely overlooked is the location of the outside air intake port. If that opening is to be "18" below grade", or "in a window well", how is it going to be protected from blockage by snow, leaves, or other debris? If the area gets two feet of snow, that fireplace is going to be used a lot -- but if the air intake for the fireplace -- supposedly to make the woodburning fireplace more efficient by NOT sucking cold outside air through cracks around the rest of the house -- is covered with 6" of snow (or more), then it simple won't function, and the homeowner may not even realize that the fireplace is then sucking the warm (and humid) air from out of the main house, completely defeating the purpose of the outside air intake directly into the firebox.
Also not mentioned in these comments are the potential side effects. Wood-burning fires in our home are limited by my wife's and daughter's sinuses! Although we have an permanently installed Aprilaire humidifier with its own water source and humidistat, burning an extended fire substantially dries out the house (particularly on colder days) and causes wood shrinkage in doors, cabinets, etc., not to mention the health issues involved with dry sinus conditions. A proper outside air supply to the firebox eliminates most of that cold, dry outside air seepage from around the rest of the house by pointedly supplying the air that drafts up the chimney without greatly affecting the air in the rest of house --either from combustion particles (smoke is very irritating), cold air seepage in other areas of the house, or the overall humidity in the house.

Originally Posted by Ron Keeney

One thing that most of the comments have completely overlooked is the location of the outside air intake port. If that opening is to be "18" below grade", or "in a window well", how is it going to be protected from blockage by snow, leaves, or other debris?....

The OP said this in the first post:

"I suggested that he install a window well so he can penetrate the chimney chase where he wants to AND be above grade (inside the window well) then run it up the outside of the chase a couple feet to get above the snow line."

Well, if we're going to resurrect a thread.....

The modification originally contemplated would require a permit and the AHJ to sign off. There was no mention of where or how the air was to communicate to the firebox or if there was to be any sort of damper or control installed. BTW, outside air on masonry fireplaces must be of non-combustible material with a 1" clearance to combustibles for the first 5 feet. That ought to tell you something. If this was to periscope from above grade down then back up 18", it probably would never work anyway.

Now, let's look at some physics since this was just brought up. The code requires the air kit be sized to provide all the air for combustion. It does not include makeup air, which takes in dilution air and excess air that together comprise the typical 400-600cfm up the stack lost. What size pipe flowing at what rate do you think it would take to provide this amount of air? I can tell you it would have to be about 8"diameter with an inline fan.

Fireplaces draw their air from the room. Air kits have been proven by ASHRAE not to work. Passive makeup air is a joke. Only mechanical ventilation is reliable. Your typical 4" air kit with a short run and one broad radius ell with a -5 Pascal pressure gradient can deliver about 12-14 CFM on a good day. Now, when you look at the juncture of most factory built fireplaces, you will see this aperture grossly restricted or reduced. The screen on the intake cowling further reduces air flow even when not clogged.

Let's say this air intake is located in a downwind or leeward pressure zone. It will draft air out of the house instead of supplying air, which is why the non-combustible w/ 1" clearance requirement. These kits have caused enough fires from wind depressurization.

So, install the kit per code but close it off once inspected.

Originally Posted by Tim Twite

H.G. is one of the top people on this site. But he is a teacher, he will make you think about what you are asking.

He didn't in this instance:

Originally Posted by H.G. Watson, Sr.

Your latest proposed IS STILL WRONG.

The answer just seemed combative. I've never posted here before but I've been a long time lurker. It seems to me a number of replies are of this nature and I don't see a point in it. He asked a question and I agree he seems out of his bailiwick and he is literally messing with fire and would better off having a pro do this. At the same time it doesn't seem productive to respond with the level of nastiness as H.G. seems to frequently do in posts. In my mind it smacks of unprofessionalism.

Like I said I am just a lurker and the community is made up of the people that post regularly, they are the ones that set the tone. I'm just offering up my two cents.

But he is a teacher, he will make you think about what you are asking. Watch his reply and you most often will not get just a simple answer, he will direct you to the information you are in need of.

NFPA 211 defining the chimney and "fireplace".

The source of the needed information was supplied. If a question about NFPA 211 was posted I think it would have been answered or another source to get the information would have. I did not say H.G. would make it easy, but learning to find the answers is part of learning and you will remember more if you do your own research instead of getting a quick answer.

I do not think the replies were trying to be combative, I know I am not combative, just careful. If advice is given to someone not knowing what they are doing and they do it wrong it can result in property damage, injury or death. I would rather not be part of that.