# Fresh Air intake



## JBM (Mar 31, 2011)

I have never felt when putting in a fesh air intake, can we just call it a F.A.I? that I really had a system for it.

My current way of doing it is with 4" sheetmetal pipe, using a hole saw through the plywood when I form the hearth and the builder needs to have a duct run outside with some sort of acceptable looking vent/hood gismo. 

So my current thinking is I have a back to back fireplace to do, with one in the upstairs bedroom as well. Center chimney. The downstairs fireplaces can just be run out of the cellar somewhere, but for the one upstairs, im thinking I will need to run the duct through the chimney into the cellar as well.

Can anyone off the top of your head confirm that 2-3 FAI's can be ducted together into 1 pipe? This would make it easier to vent the upstairs fireplace if I can join into one of the other ducts.

Then again, if one of the fireplaces has a significantly larger fire than the other joined fireplace it could pull the draft from it, to a degree perhaps? Or if the other unit was not in use, it would possibly pull air from that fireplace as well.

Any input?


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## raskolnikov (Mar 10, 2008)

JBM,
I would keep the upstairs fireplace separate from the downstairs and I would steal the fresh air from above. A brick louver vent in the stack above the roof would be all you would need and few would notice it if it's done well. I've installed at least a half dozen in this manner and it's worked out every time.

D.


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## JBM (Mar 31, 2011)

Ahh, so you run a duct inside the chimney up after the lead is on and put in a louver in the brick?


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## raskolnikov (Mar 10, 2008)

JBM,
Correct, although it's always more of a pain in the ass to go up as opposed to exiting where the chase is. Keeping the flexy pipe ahead of what you're doing is tough but certainly not impossible. In the end it's a better fit for the 2'nd story box in my opinion.

D.


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## JBM (Mar 31, 2011)

Good idea, ill let you know how it goes


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## dom-mas (Nov 26, 2011)

Kind of late but you could also have a 6" duct rather than 4" which is over twice the volume of 2- 4" ducts, you could then tee off from the there with 2- 4" ducts and have one between the block and the facing ( assuming there's enough room.) 2 runs but only 1 intake.


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## CJKarl (Nov 21, 2006)

I would not tie them together. I think you would be asking for trouble.


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## dom-mas (Nov 26, 2011)

Why? Are you thinking that the closest fireplsce will suck more air? Unless one of the rooms was sealed off from the rest I can't see a problem.


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## 2low4nh (Dec 12, 2010)

yes one will back feed the other. the bigger fire will draw more air possibly causing a down draft. go light a fire then turn a fan on see what the fire does.


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## CJKarl (Nov 21, 2006)

2low4nh said:


> yes one will back feed the other. the bigger fire will draw more air possibly causing a down draft. go light a fire then turn a fan on see what the fire does.


The make up air is going to take the path of least resistance. Could draw air down one intake vent to supply a larger fire/firebox. That in turn could cause a lazy draft in the smaller firebox.


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## CJKarl (Nov 21, 2006)

My house does not have a cold air intake for the fireplace. I'm too lazy to retrofit one.
So I cannot burn my basement woodstove and 1st floor fireplace at the same time.
Unless I open a COUPLE windows.
The smoke will be drawn down my furnace flue and pulled out the draft damper in my furnace stack. ...And my house isn't even that tight.


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## dom-mas (Nov 26, 2011)

I'm having a hard time visualizing this. Air is always going from outside to the fireplace when the fire is burning. When either one is burning it will suck as much as will pass through, it's still burning the air from the room as well. I can see the closest fireplace receiving more air but not causing any kind of a down draft, the fire will still want to suck the air. 

Unless you're saying that the larger fire will suck air from down stream as well as outside. I guess possible but not likely. 6" air intake is pretty big. Depends on the size of the firebox though I guess


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## 2low4nh (Dec 12, 2010)

atmospheric pressure and 6" is huge way to big a raccoon will be in your living room


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## dom-mas (Nov 26, 2011)

Ha, maybe, but it would get stopped by the T


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## JBM (Mar 31, 2011)

Here is some information taken from the Rumford website, a site I consider an authority on fireplace/chimney construction.

I had known about such issues as is below, but had never read it in the serious manner in which it was written here. To consider that on a windy day a fresh air intake could cause my fireplace to have puffs of smoke or throw ashes/embers out into the area beyond the firebox bothers me to say the least.

In mass air inlets as well as gasket-ed glass doors are now code and being enforced. It also appears that Superior Clay is not selling the wolf heads any longer either, I will call them at some point soon.

With regards to joining more then 1 air inlet in the same vent, I dont think so. A fireplace in a bed room, a slam of a door, this could cause rapid air movement. Too much of a liability, and its simple enough to just build 2 small chases inside the chimney.

Here is the International Residential Code on exterior air:

R1006.1 Exterior air. Factory-built or masonry fireplaces covered in this chapter shall be equipped with an exterior air supply to assure proper fuel combustion unless the room is mechanically ventilated and controlled so that the indoor pressure is neutral or positive. 

Combustion air ducted from outside directly into the firebox is inadequate at best, does not improve efficiency, can lead to bad smells and blowing ashes, can cause the fireplace to smoke and, in some cases, if it can back draft, it can be a fire hazard. For the last reason, it's a controversial code issue.

So the best solution is to make sure the room is "mechanically ventilated and controlled so that the indoor pressure is neutral or positive" and then don't provide exterior air specifically for the fireplace at all, as code permits.

We recommend not installing combustion air directly into the firebox unless you are required to. Section R1006.5 allows the vent to be within 24" of the firebox opening but some officials insist on the vent in the firebox if glass doors are installed. If you are forced to install exterior air, the most unobtrusive way to do it is with the Outside Air - Ash Dump Kit set in the inner hearth. Then keep the vent closed to avoid the bad smells, blowing ashes, smoky fireplace and fire hazard.

Now, that doesn't absolve you of providing a balanced ventilation system. In fact the code implies as much when it exempts exterior air if you have neutral or positive indoor air pressure. Ideally you should provide as much clean, tempered outside ventilation air as you exhaust through various appliances, fans and leaks. See Balancing the Ventilation System.

Related discussions at Exterior air code issues and smoky fireplaces and Balancing the Ventilation System

http://www.rumford.com/tech7.html


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## bytor (Jan 23, 2010)

Some preliminary studies have been done in Canada that show the standard 4" fresh air inlet is far from adequate. In fact, for a 'passive' make up air system to maintain a neutral indoor air pressure, the passive make up air needs to be one and one half times the size of the flue venting the wood burning appliance (different rules apply to appliances designed to be burned with airtight doors).
There is a very real risk that a roaring fire in one fireplace will draw makeup air from both the outdoor vent as well as the other fireplace if it needs to, and in turn, draw smoke from a smouldering fire in that second fireplace back down it's flue and into the room it is in.
We have had problems like this in well sealed houses with two distinctly separate fireplaces on different floor levels. It does take time for a negative pressure to build in the house, but when it does, smoke will be drawn down the flue of the fireplace with the least active fire.
Throw in a powerful kitchen or bathroom exhaust fan and look out...


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## JBM (Mar 31, 2011)

Jeesh some good info there Bytor!


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## dom-mas (Nov 26, 2011)

I don't want to belabour a point but I feel I have to. 

First i agree with the rumford site that says that fresh air intakes are dumb. It's just a hole in the house that has a direct lead to the fireplace. Not a fan either of the mechanical fresh air idea into the hous (HRV) At best the HRV is 50% efficient. Why bother tightening up a house then pumping in cold outside air. I do feel that a mechanical air supply directly to the fireplace is a good idea. That way it is mostly that air that can supply (and partly control) it, similar to a damper on a wood stove.

with a typical FIA the firplace isn't burning the air from the FIA exclusively, the FIA is just making up for the air that is burnt, so regardless of where it's origin is that air will still be made up if the volume is there. I can't see having one source as an issue, and a fireplace sucking air from the other fireplaces means to me that there isn't sufficient air supply to that larger fire in the first place. 

And if you do feel the need for multiple inlets, why not run them through the floor system to outside rather than using the chimney, which if there is a huge draw could suck in smoke and CO2 rather than fresh air


For these really tight homes the entire air quality system must be balanced, HRV's, bathroom and kitchen vents, and any type of furnace. If that's the type of house it is then I can't comment because there are too many factors to consider.


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## joulian (Dec 9, 2011)

Ok i am trying to understand. So what is the best place to get air from? 

It seems it would be better to get air from outdoor clean out in fireplace rather than suck it from a window or door very far from the heat source once you get the fire going that is. 

If that door or window happen to be in a bedroom that person(s) would be at a great disadvantage of obtaining heat from the fire.

Do Rumsfords have air vents built in bottom of them usually. I live in the southern states. So fireplaces are really more decorative than for function.


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## joulian (Dec 9, 2011)

JBM said:


> Here is some information taken from the Rumford website, a site I consider an authority on fireplace/chimney construction.
> 
> I had known about such issues as is below, but had never read it in the serious manner in which it was written here. To consider that on a windy day a fresh air intake could cause my fireplace to have puffs of smoke or throw ashes/embers out into the area beyond the firebox bothers me to say the least.
> 
> ...


I think what could be happening is the cold air is more dense. Therefore it expands rapidly when heated therefore causing your potential mishaps. Why not have the outside air being routed by the firebox to heat it first. There might be issues at first until the bricks warm enough to heat air. But someone is usually around for that part of starting a fire.


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## dom-mas (Nov 26, 2011)

fresh air intakes are generally in the hearth directly in front of the firebox or can be part of the cleanout which takes the place of a firebrick towards the front of the firebox. That is typical but as JBM points out the FIA can be within 2' of the firebox.

there isn`t always room between the firebox, 7.5"s of semisolid masonry and facing to route something through. Plus it has to come from somewhere and from below along a joist is easiest/most pratical. It could come from above I suppose but it's most practical to have it exit around the hearth.

warming the air is probably a good idea though just like it's a good idea to warm the chimney before starting the fire. But it is quite rare in my opinion that outside air has a higher pressure than inside air on days when people are likely to make a fire. The possibility of air from the FIA causing any real smoking is unlikely on anything but a day when wind is howling to an extreme and blowing in just the right direction to cause vacuum on the FIA and that vac would have to overcome the draw of the fireplace. Best thing is to not have an FIA (or have one just to satisfy code) unless your house is built extremely tight. 

All my opinion, I'm not a fireplace expert by any means but I have had some schooling in fireplace theory.


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## Paul B (Mar 10, 2007)

I don't see in the IRC where outside air for combustion is necessary. Am I missing it or it a local thing in some areas?


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## dom-mas (Nov 26, 2011)

The Ontario building code demands it. Not sure about international. 

It's purpose is so that when someone falls asleep with a roaring fire the fire doesn't consume all the oxygen and the person can wake up again.


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## JBM (Mar 31, 2011)

Paul B said:


> I don't see in the IRC where outside air for combustion is necessary. Am I missing it or it a local thing in some areas?


Mass is enforcing it now.


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## JBM (Mar 31, 2011)

dom-mas said:


> The Ontario building code demands it. Not sure about international.
> 
> It's purpose is so that when someone falls asleep with a roaring fire the fire doesn't consume all the oxygen and the person can wake up again.


WOw I wonder how we made it all these years without Govt to keep us alive....


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## BrandConst (May 9, 2011)

JBM said:


> WOw I wonder how we made it all these years without Govt to keep us alive....


I think you have it backwards, should read: I wonder how the government made it all this years without us to keep them alive.


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## dom-mas (Nov 26, 2011)

JBM said:


> WOw I wonder how we made it all these years without Govt to keep us alive....


I agree 100%. i believe in fresh air intakes about as much as I believe in weep holes


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