Firestopping the ceiling of a HVAC closet in a single story?

Gas fired furnace in an HVAC closet with an open ceiling to the attic. There is definitely combustion air issues, but lets say they supplied combustion air through the wall to the exterior. Would the closet require firestopping at the ceiling of the closet, if there isn’t any livable space above?

What happens wen the HVAC is idle? It is a big insulation, energy waster as the air that was conditioned in the home leaks up through the attic. Can’t speculate a whole lot without pictures.

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Good point, the door isn’t tightly sealing right now but even if it was, its not an insulated door.

I’m asking because I got ahold of the pre-listing report that was done for my property today and the previous inspector called it out as missing fire stopping… It turns out my client recently had a house fire so she is, naturally, very concerned about electricity and fire hazards.

Thanks for the clarity about energy efficiency, but i’m more concerned with missing a fire hazard issue.

My understanding is that firestopping is only needed between floors of livable space, correct?

Not a whole lot to see. The second pic is “improper clearance from combustibles” with the exhaust going through the drywall, but you can see that the ceiling is open to the ductwork/plenum above:

Don’t know the age of the home or the codes in your area, But I do know that many homes built when energy was cheap (60s and before) have a similar arrangement where the “wet wall” and the chimney share a space that opens into the attic. Terribly inefficient, no fire stopping required. Fire stopping would fix the energy problem may or may not prevent fire spread, depends on the home construction. Fire stopping prevents the movement of hot air and gasses primarily, has a very limited fire containment capability. Your client needs to be educated and stop being preoccupied with the “fire” in fire stopping.


its 1960.

ill let it go, they have to figure out a whole lot anyway. any correct arraignment will be very different than it is now - there isnt even room to bring down two combustion air tubes into the closet (and i was just asking before, its in a central closet with no easy way to get air from the exterior.) Much of the home doesn’t even have attic space, its vaulted ceilings with a roof on the other side.

I’m not certain what those combustion air issues would be.

I would call out Flue clearance and Door sealing/insulation issue.

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So this diagram is of a water heater, but isn’t it the same idea? Combustion air supplied to 12” within the top & bottom for proper air flow?

Where is the combustion air intake on that unit? What does the mfg say?

As a rule of thumb :+1:, you need 50 cubic feet of air for every 1000 BTU.

Through the front grill.

Manual says: follow NFGC NFPA54/ANSI Z223.1–2012 Section 9.3

That eventually leads me to 3 sections, two of which require me to know the air infiltration rate for the home, which I do not. The other section says:


One of the other sections, while it does require me to know the infiltration rate to be less than .40 ACH, says what I was thinking:



If you JUST meet the air requirements and a dryer is located nearby you can have back-drafting from dryer use (about 150 cubic feet per minute) starving the adjacent appliance.

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duh, thank you.

the water heater in the home was in a sealed off laundry room and there was multiple pieces of evidence for improper draft. which I reported, but that is probably the biggest factor, huh?

So, I guess my question is, does that big open attic satisfy the combustion air requirement? And does that 1960 home have to be upgraded?


I’d have to guess - the furnace says 110k BTU/hr input, 90k for output. I assume we’re talking about input? that would be a required 5,00ft³/hr. tells me that’s the volume of a 25’ x 25’ room with an 8’ ceiling. That’s really hard to say. There was no ceiling, but there’s duct-work up there going into a very low profile attic space. The closet ceiling opening was pretty well obstructed.

Would you not have mentioned it?

The key to older homes is they are drafty. As soon as you start insulating to modern standards you need to re-evaluate the HVAC needs.

The key to Home Inspection is to simply report what you see. Don’t try to figure out the remedy just be aware of the ramifications. That is what you report.


Attic has soffit or Gable venting, probably not. But you are noting obstructions and other concerns. So, I wouldn’t object to your conclusion.

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