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lizhsharpe 04-06-2011 09:24 AM

foam insulation and venting
We live in Atlanta area. We are having foam insulation installed
and getting mixed signals on whether new venting is needed with
air conditioner to ensure combustion...supposedly with encapsulating attic with foam, that is an issue. This is not a new construction, house built in 1993. Foam people want HVAC to sign off on this or add venting, but
not all insulation companies even address this issue.
What's code on this in Georgia?

tcleve4911 04-06-2011 09:26 AM

I don't think this is a DIY question.
The HVAC contractor should know.

lizhsharpe 04-06-2011 09:32 AM

Wanted practical advice from someone who's gone through this...yes,
I'm checking with HVAC people too and not getting straight answer....just
YES< we can do vent for you. Not a big help!

Rory Read 04-06-2011 10:49 AM

not quite enough information

I am not a HVAC contractor, but attic venting, insulations types and vapor management are common enough contractor issues.

I am not sure how the spray foam is being installed in your house. Is your attic being converted from an unconditioned, vented space to a "conditioned," vented space?

If you are moving the house's heating/cooling envelope you may in effect be moving a piece of machinery that used to be "outside" to the "inside" of your home. You definitely do not want the condenser "exhausting" hot wet air inside a closed attic (and ideally the compressor which generates heat would be outside as well).

For gospel on attic venting:

I hope this helps,


Arkitexas 04-06-2011 11:27 AM

Your insulation contractor is wise in addressing this issue.

Houses built twenty years ago often did not provide outside combustion air for flame fired heater systems (HAVC or water) but rather simply drafted house air. Although this is not a good method, it was often done because houses were loosely constructed and infiltration (air leakage) could make up the difference. Among the bad points of this arrangement are that unconditioned outside air is drafted into the house through cracks, windows, and doors to make up for the air drafted for combustion and that air must be heated; the amount of combustion air is not controlled (may be too little); flames can be backdrafted out of the heating equipment housing; and efficiency and safety are compromised. After houses became more air-tight, combustion air supply became a very important component not to be left to chance.

The simple answer is YES, outside combustion air should be provided where flame fired equipment is used. Codes establish the size and location of the combustion air supply. The equipment room should be sealed from the rest of the house. The source of combustion air should be outside, not the attic nor the house interior. If your combustion air is now coming from the attic and the insulation contractor is sealing up vents, then you may have problem. Local codes may also require an second outside air vent near the ceiling of the equipment room. These issues should be referred to a local licensed HVAC contractor for evaluation and recommendation. Your safety and that of the house are not worth the cost of proper venting.

lizhsharpe 04-06-2011 12:01 PM

Thanks for your help...that was detailed! Can't figure out why some
of the insulation companies didn't address this FIRST though..they
should know codes....
That was a BIG help...

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