# Combustion Air - Help please



## sailingaway (May 24, 2011)

Background:
I am planning to wall off my mechanical area which will create a confined space, according to code definitions of < 50cu.ft. / 1kBtuh. Free advice from a HVAC pro acquaintance suggested putting grills on the new wall. However, I would have to vent two walls to make up the required space. If I am reading the code guide (not full code definitions) correctly, that would be four vents total since each wall needs two-one in the upper 12" and one in the bottom 12". On the new wall I would need to filter it since my woodworking shop is on the other side which produces saw dust and fine particles that probably are not ideal for combustion air. 

Question: I'd like to bring in the combustion air from outside. Code guide says a single opening is allowed. The ceiling of my basement is just above grade (> the 12" above grade req.) Can I get away with one pipe in the upper 12" of the mechanical room? By my math, it would take a 7" pipe to make up the required CA. Or, do I have to have two. If so, how would I get away with having one in the bottom of the room and one in the top. I have attached a layout of the room. Dimensions of the "fun room" are estimates.

https://picasaweb.google.com/lh/photo/Hly7e6Hst1Rg_RlptPM9LKKHuuq2nkCP0ygbl-VB1bM?feat=directlink

Thanks so much for reading. I really appreciate it.


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## nealtw (May 26, 2011)

I don't have the answers you are looking for, up here we would have a 6" pipe feeding the fire from outside. I am really surpized you have this in the garage where auto gasses can get to the furnace, That's a big no no. Closing it in is the right thing to do. I am sure answers will be comming soon.


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## inspectorD (May 26, 2011)

Well, I would ask my local building official before I start, what they want to see. This way there is no guesswork on your part. Pull a permit, pay the $$ and get them out there. I like to make them work.

And to get the lower vent in, you just pipe it down to the floor with some metal pipe. Then there is a lower vent at the floor level. I would put in what is called an HRV ( heat recovery ventilator) because it tempers the air comming in to be above freezing in a cold climate. It gets cold in there when the boiler or furnace is not running.
Good luck.


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## sailingaway (May 26, 2011)

Thanks. Looking at doing the "One-permanent opening method" as described here. This will help with grade issues. 

Chapter 24 - Fuel Gas


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## paul52446m (May 26, 2011)

sailingaway said:


> Background:
> I am planning to wall off my mechanical area which will create a confined space, according to code definitions of < 50cu.ft. / 1kBtuh. Free advice from a HVAC pro acquaintance suggested putting grills on the new wall. However, I would have to vent two walls to make up the required space. If I am reading the code guide (not full code definitions) correctly, that would be four vents total since each wall needs two-one in the upper 12" and one in the bottom 12". On the new wall I would need to filter it since my woodworking shop is on the other side which produces saw dust and fine particles that probably are not ideal for combustion air.
> 
> Question: I'd like to bring in the combustion air from outside. Code guide says a single opening is allowed. The ceiling of my basement is just above grade (> the 12" above grade req.) Can I get away with one pipe in the upper 12" of the mechanical room? By my math, it would take a 7" pipe to make up the required CA. Or, do I have to have two. If so, how would I get away with having one in the bottom of the room and one in the top. I have attached a layout of the room. Dimensions of the "fun room" are estimates.
> ...


You are on the right track, but it get a little complicated. That 38=Sq" is right for you BTU, but you need that much hi and low. This means if you are using one duct coming in horizontal it would have to be 76 sq".Then take you 38 hi and 38 low off that duct.
 One other thing. It looks like you have a dryer in that room. If so is it vented out side? If it is then the dryer is taking about 40 CFM of air out of that room, so this has to be included in your make up air. Check your code for dryer make up air. Even if the dryer is elect it still take air out.
   Paul


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