Question about the air intake in my garage

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Old 06-19-14, 08:46 AM
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Question about the air intake in my garage

OK, I have a question about the air intake in my garage. I have a gas water heater and gas furnace on my garage, so there's a vent in the wall to bring in combustion air. I'm reorganizing the garage and might want to park a large rolling tool chest near the vent. I'd like to keep the chest as close to the wall as possible, while of course allowing enough space for air to come in the vent. So, my question is, how far do I need to stay out from the vent without creating a hazard or code violation?
 
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Old 06-19-14, 09:27 PM
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Here are a couple of pictures. Each vent is 8" by 14".
 
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Old 06-23-14, 09:22 AM
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Anybody?

I think the combustion air vent and it's size is covered in the building codes or maybe NFPA, but what would be required to keep it free of obstruction is less clear. Obviously you can't plug it or cover it, but what about nearby objects that may partially affect the air flow? I can't find anything on it.
 
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Old 06-24-14, 07:11 AM
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it's probably best not to put anything in front of those vents -. if u must, leave something like 6"
 
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Old 06-24-14, 07:27 AM
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Hi Gary, not my best topic, but I'll share as best I can.

First, those vents look like they are rather obstructed. Even the grills when clean will significantly reduce the air flow. Check the required net free area and location of those vents to be sure they will do the job.

Are these gas appliances located in a separate room inside the garage? Naturally drafted gas appliances are essentially open flame appliances and I would be concerned having them share the same space with cars and other gasoline vehicles. In Maine wood stoves are not allowed in a garage for the same reason.

Assuming this is a separate furnace room, then I would be looking for two vents, one high and the other low, both vented to outside.

As for your question, if the vents are part of a code requirement, then they would need to be unobstructed to whatever degree the local code official will require.

Again, this is outside of my area so hopefully others will step in and correct me where needed.

Best,
Bud
 
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Old 06-24-14, 09:10 AM
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it's probably best not to put anything in front of those vents -. if u must, leave something like 6"
Thanks for the reply. Why do you say 6" ?
 
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Old 06-24-14, 09:32 AM
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First, those vents look like they are rather obstructed. Even the grills when clean will significantly reduce the air flow. Check the required net free area and location of those vents to be sure they will do the job.
Yes I know they look that way, but it's partially because of the angle of the louvers and the angle of the photo. Still, they probably could use some cleaning.

Are these gas appliances located in a separate room inside the garage? Naturally drafted gas appliances are essentially open flame appliances and I would be concerned having them share the same space with cars and other gasoline vehicles. In Maine wood stoves are not allowed in a garage for the same reason.
No, they are on an elevated platform in the garage, per code. This is how many homes are built around here. If it was me building a new house, I'd give them a separate room.

Assuming this is a separate furnace room, then I would be looking for two vents, one high and the other low, both vented to outside.
From my reading on this, I know this is considered "best practice", but I believe at the time this house was built (~2004) this was code-compliant. One option I have considered is moving the vents, but only if necessary.

As for your question, if the vents are part of a code requirement, then they would need to be unobstructed to whatever degree the local code official will require.
And, as they say, therein lies the problem. I can find nothing in any code about obstruction of combustion air vents. Now, I'm sure completely blocking it would render the vent useless and therefore be a violation (and a safety hazard), but short of completely blocking it, I can't find any practical guidelines or advice based on actual experience.

Please see the attached photos. This came from another web site where the homeowner wanted to limit the cold air from the make-up air vent flowing onto the floor of the basement. The solution was to put it in a large bucket that kept the incoming air off the floor, while not obstructing the vent too much. This may be one of those questions with no real answer, and any opinions might be based on the thinking of an individual inspector or regulator. I've read that a closed (completely blocked) make-up air vent is one of the most frequently found problems by home inspectors.
 
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Old 06-24-14, 09:55 AM
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From 2012 IRC

G2407.11 (304.11) Combustion air ducts.
Combustion air ducts shall comply with all of the following:
1. Ducts shall be constructed of galvanized steel complying with Chapter 16 or of a material having equivalent corrosion resistance, strength and rigidity.
Exception: Within dwellings units, unobstructed stud and joist spaces shall not be prohibited from conveying combustion air, provided that not more than one required fireblock is removed.
2. Ducts shall terminate in an unobstructed space allowing free movement of combustion air to the appliances.
3. Ducts shall serve a single enclosure.
4. Ducts shall not serve both upper and lower combustion air openings where both such openings are used. The separation between ducts serving upper and lower combustion air openings shall be maintained to the source of combustion air.
5. Ducts shall not be screened where terminating in an attic space.
6. Horizontal upper combustion air ducts shall not slope downward toward the source of combustion air.
7. The remaining space surrounding a chimney liner, gas vent, special gas vent or plastic piping installed within a masonry, metal or factory-built chimney shall not be used to supply combustion air.
Exception: Direct-vent gas-fired appliances designed for installation in a solid fuel-burning fireplace where installed in accordance with the manufacturer’s instructions.
8. Combustion air intake openings located on the exterior of a building shall have the lowest side of such openings located not less than 12 inches (305 mm) vertically from the adjoining finished ground level.
 
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Old 06-24-14, 10:00 AM
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The bucket in the basement as a cold air trap is one of those myths that gets traction and can't be killed. The duct to the floor is a siphon and the bucket is a restriction (180° turn) and diffuser that mixes the incoming cold air making it less objectionable. But that's another topic.

As far as blocking the incoming air, any opening larger than what is shown would add zero to minimal restriction to the incoming air. But you are correct, local code officials have the final word.

Is the garage well sealed, most are not. If leakage around the door/s is leaky, then that air will add to whatever those vents are providing. But I don't have a code to quote so I'll wish you good day and go away .

Bud
 
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Old 06-24-14, 10:17 AM
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Thanks Bud. I'm trying to make optimal use of the space in the garage for practical purposes, while still leaving easy access to the 2 cars. The garage was not built with a lot of extra space so this is a challenge. I've seen a lot of garage where people put in shelves and whatnot, and it's almost impossible to get in and out of the car without banging something.

I'm torn between:

1. Going ahead with my planned garage arrangement, with the rolling tool box about 3" in front of the vent. My concern is that at some future time an inspector or whatever would say that the vent is too obstructed, and this would mess up my whole garage layout. Of course, worst case would be a fire or whatever that would raise this as an issue.

2. Do a new garage layout leaving the vent totally unobstructed. This would require some serious compromises in my shelves and toolboxes.

3. Or, RELOCATE THE VENT!

I like to do things once, correctly.
 
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