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pulling combustion air from attic


jodil
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It is done here all the time (assuming you are talking about cellulose insulation) with no problems.

You will have floored attic around the unit and walkway to the equipment with batts and the unit should be mounted above the insulation, so I have never seen an issue for furnaces.

Drawing combustion air from the attic is approved but attic venting to the exterior will need to take furnace needs into account.

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Hi Jodi,

Cells (the linty stuff) is literally saturated with borate so it will not burn. It's not "sucked in" at all, in fact it settles rather rapidly and consolidates so well that it's one of the best combination insulators/vapor movement inhibitors you can find. I'd say that the only thing one would have to be concerned about is whether borate will cause a furnace and flue to corrode; I can't imagine that it does, since literally millions of attics are insulated with cells and many thousands of furnaces garner their combustion air from attics. Still, if you want to stick to your position, you'll need something more than your preference to prohibit it.

I usually take down the model and serial number of every furnace I inspect; that way, if I need to back up my findings with something more substantial, I can call the manufacturer, explain the issue over the phone and get backup - or not, depending on the manufacturer's point of view. That's what I suggest you do.

If the manufacturer can't provide you with substantial reasons for why scavenging combustion air from a cells-filled attic shouldn't be done, I'd call the builder, meekly apologize for being so stubborn and invite they guy down to the local café to laugh it off over coffee and a cruller.

ONE TEAM - ONE FIGHT!!!

Mike

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It's done quite a bit actually. If, for example, he is running two 6" rounds into the attic just make sure there are a foot or so above the insualtion and there should be no problem. If it is the PVC that feeds the fan on the furnace same thing, make sure it's a foot or so up above the insulation. Also, if it is the later, the attic must meet the requirement for the CF per BTU.

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Originally posted by jodil

Having a disagreement with a builder about pulling combustion air from the attic.. He says its fine I say no. The home has the paper like blown insulation thats very linty. I would not want that being sucked in by my furnace...

Whats your opinion?

Thanks

Nothing wrong with pulling combustion air from the attic as long as you have adequate ventilation up there.

The insulation will settle down and won't be an issue unless you have someone up there stirring it up all the time.

Not an issue.

- Jim Katen, Oregon

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Originally posted by Brandon Whitmore

Here's why I don't like it (when furnace is in living space):

Energy loss concern

Insects/ Bees enter attic and have free reign of the house (not to mention birds, squirrels, etc.)

Dust issue--- during high winds fibers / dust will blow around

Galvanized steel mesh; it's a wonderful thing.

OT - OF!!!

M.

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Originally posted by Brandon Whitmore

Mike,

Look at firgure M1702.2(2) in my link above- --- no screening is allowed........

You can put the mesh on the attic openings, not the combustion air opening.

If you've got insects, bees, birds & squirrels in your attic, that's a separate problem that you need to fix. The same goes for wind stirring up your insulation -- it shouldn't be happening if the attic is properly vented.

- Jim Katen, Oregon

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If you've got insects, bees, birds & squirrels in your attic, that's a separate problem that you need to fix. The same goes for wind stirring up your insulation -- it shouldn't be happening if the attic is properly vented.

Best case scenario, I agree. I see very few houses that don't have a gap at least big enough for a bee to enter. As long as we have starlings[:-bigmout, I see problems.

Even in places I inspect where I don't see large insects, I end up seeing quite a few smaller dead insects in an attic space.

The same goes for wind stirring up your insulation

I'm not really talking about chunks of insulation, just airborne fibers. During windy days, it seems like there are a ton of fiberglass fibers floating around. I'm sure those fibers don't everyone, but my system does not like them.

Anyway's, in the grand scheme of things it is not a big issue. I would not pull combustion air from an attic in my own place.

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