Gas furnaces in a foamed attic

I did an inspection on a home from 2007. The homeowner removed the blown in insulation and hired someone to install foam insulation at the roof sheathing. They completely sealed the attic including foaming the gable end vents (as seen in the first/foamed picture). They did not make any changes to the gas furnaces which are now installed in a sealed attic. Typically when I’m in newer construction attics with no ventilation because of roof sheathing insulation (typical in the Phoenix area) the gas furnaces will be installed with a fresh air vent and exhaust vent through the roof sheathing insulation and roof (as seen in the second picture).

I recommended further evaluation by a licensed contractor and HVAC contractor to evaluate combustible air and because the gable end vents had evidence of leaking from the interior of the house. (I’m assuming the gable end vents weren’t properly sealed before foaming the attic and the water is running down the foam to the interior.)

This is the first time I’ve come across this situation. Am I missing something? Since the attic is now sealed at the roof sheathing the gas furnaces are now getting “Air from Inside the Dwelling” ?

From InterNACHI: All Air from Inside the Dwelling

If all combustion air is taken from the inside of the dwelling, then two permanent openings should be installed. One opening should be within 12 inches of the top and one within 12 inches of the bottom of the space. Each opening shall have a free area equal to a minimum of 1 square inch per 1,000 BTU-per-hour input rating of all appliances installed within the space, but not less than 100 square inches.

I apologize in advance, this is my first post and I’m not sure what I am doing. Thank you.

First, Welcome to the forums Cyril.

Not sure that I can see in your first picture about the furnace being a gas fueled furnace. All I see is is foam insulation and duct work. Any thing there that I’m missing in the first picture?

Sorry for the poor picture. I was trying to get a decent shot of the gas furnace with the foamed insulation. If you look closely or click on the picture to enhance you should be able to see the gas lines.

I think that the furnace is getting its combustion air from outside. You have an intake and an exhaust pipe from the furnace.

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The top picture is a different attic than the bottom picture. The bottom picture is getting it’s fresh air from the outside. Which is what I want to see in the top picture. The top picture is a foamed attic that has no air from the outside seeing how it’s sealed and there is no additional vents other than the exhaust vents.

Is this the gas supply you are referring to?

Yellow is a rigid gas line, turned to flex, turned to rigid before entering the cabinet.

If that is the case, as you describe, I would call in a HVAC guy. Pretty sure B Vent should not be insulated and the other questions.

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There should be at least an inch or two of clearance between the b vent and the foam. Does not appear to be fire rated foam that is in contact.

Just out of curiosity, is it common to have HVAC units suspended like that where you are? Where do the chains tie into the structure?

Yes, I would say this is the most common installation starting from the late 90’s or early 2000’s. Metal straps attached to the trusses with chains attached. The units are then suspended.

Also thank you for the insulation spacing information. I didn’t even think of that. I was too shocked by what I saw to be able to understand everything going on.

From what I understand from the Seller, this company is going around and sealing attics and making good money from it.

Normally when a home is going to be using Foam insulation at the roof decking, air tight construction along with HVAC systems fully enclosed in the structure. They are designed with that in mind. A ‘retrofit’ application poses many problems and if not addresses can really turn it into a “sick house” meaning high humidity, and basically unhealthy living conditions. Most of the “Air Tight” homes designed (to be like a Foam Ice Chest") will have a mechanical air (fan) system to bring in outside air, and an outflow valve/source. Theoretically a home built like this will need outside air for makeup and combustion…makes no difference how large of a room or Home the unit is in. It simply will run out of combustion/makeup air.

These Guys (either criminal or stupid) going around Sealing Attics are going to wind up killing people!

Larry is correct this is a crime!
Cyril this is serious stuff

  1. The gas fired appliance MUST have combustion air. Using all air form inside will not work
  2. Minimum 1" clearance from the double wall B vent to combustibles (foam and wood)
  3. The foam must at least have an ignition barrier. Some closed cell foams have this built into the foam but not all. If not there are liquid applied ignition barriers available
  4. To prevent condensation a minimum R-value is required depending on your climate zone.
    Best of luck

Thank you very much. That is how I felt. I did inform the Sellers and even had them call the company that did the job. They told me they would get on it, but when I called my Clients for an update it turns out they refused to make any changes.

My next question is, should I do anything more? I would hate for a second home inspection to happen from another buyer and this issue not be recorded.

Not much else you can do. You reported it to your client and the sellers apparently are aware. It’s in their court now.