80% efficiency furnace in a foamed / sealed attic space
We have an 80% furnace that is in a walk up attic space we are planning on foaming, insulating and sealing up. I am trying to determine what steps we to take to determine if there is sufficient combustion air or if we will need to provide outside air. The space will be a conditioned storage space. We are planning to replace the furnace in a year or two.
The furnace is an American Standard Silver 80 100,000 BTU.
From the manual and ANSI Z223.1 the furnace is a class 1 fan assisted combustion device.
From ANSI Z223.1 220.127.116.11 with an unknown ACH (I assume ACH50, but the standard copy I have doesn’t clarify), you need 50ft^3 per 1000BTU. The space contained within the drywall is 5370 ft^3, so we technically have enough space. Should I worry any further? This formula assumes a .33 ACH (from 18.104.22.168 ft^3=15ft^3/ACH*(BTU Device/1000 BTU)), which seems unlikely to achieve with interior spray foam, caulking, and drywall.
Should we have a CAZ test performed? I can DIY this to know I we are safe, but the inspector is going to want someone professional. Who is most cost effective to perform this test?
I can have a blower door test done, but that is generally whole house.
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