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Fresh Air makup coming from attic...?


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AC, Furnace, HWH all share closet aproximately 3' deep x 10' wide x 6' tall (air return build into platform beneath) The door was not luvered, there was no way for air to be pulled into the room to allow the Nat. Gas furnace to freely vent. After I got to looking there were 2 6" class A vent pipes side by side coming down from the ceiling, one stopped about 6" from the ceiling and the other stopped about 8" off the platform aprox. 1' from the pilot access door.

I made a note of it so when I was in the attic i would look for them and figure it out. The 2 pipes just stopped open about a foot above the insulation.

In the attic there was a thermostatically controled fan, which actually moved quite a bit of air (4k sq ft house). Not sure if this means anything but it may suck that CO2 right out of there lol...

My question is, is this right? wrong? My experience is limited with gas products. My town of origin, gas cooktops, ovens, furnaces, and HWH are not very common, and for the longest time, I did not know what a gas dryer was.

Matt the typo king.

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If the attic fan is truly operating on a t-stat, it's probably only on in the summer time. That means the furnace wouldn't be in use. I wouldn't worry about the furnace.

The water heater might have a problem. A guy would have to do a combustion zone / draft test in the closet with the attic fan running to see what happens.

The 6" air supply ducts are probably too small. Usually, the ducts want to be 8" to satisfy the volume required by the water heater and the furnace mfr's.

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AC, Furnace, HWH all share closet aproximately 3' deep x 10' wide x 6' tall (air return build into platform beneath) The door was not luvered, there was no way for air to be pulled into the room to allow the Nat. Gas furnace to freely vent. After I got to looking there were 2 6" class A vent pipes side by side coming down from the ceiling, one stopped about 6" from the ceiling and the other stopped about 8" off the platform aprox. 1' from the pilot access door.

I made a note of it so when I was in the attic i would look for them and figure it out. The 2 pipes just stopped open about a foot above the insulation.

In the attic there was a thermostatically controled fan, which actually moved quite a bit of air (4k sq ft house). Not sure if this means anything but it may suck that CO2 right out of there lol...

My question is, is this right? wrong? My experience is limited with gas products. My town of origin, gas cooktops, ovens, furnaces, and HWH are not very common, and for the longest time, I did not know what a gas dryer was.

Matt the typo king.

That is called a "high/low" combustion air or make-up air system. The room was too small for proper make-up air so this was installed to provide "outside" air to the room. Yes, the attic is considered to be "outside" air as it is not in the conditioned part of the home. Without some photos, it is hard to say if it was installed properly.

Based on your description it sounds like it is OK. But, this depends on the amount of combustion air that is needed and this is based on the total BTU's of each unit and the cubic footage of the room. The 6" pipes might be enough, but 8" are more common as they do provide about 30% more make-up air. Do you know the BTU's??

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It might be OK, it might not. I don't think it will be safe with that fan in the attic and I think they should extend those pipes outside. Here's why:

If they're going to draw air from that attic and there's a fan in the attic, the attic ventilation (gable end vents, soffit vents, frieze vents, etc.) has to be capable of supplying enough incoming air to equal what the fan will suck out of the attic without depressurizing that room. That's a pretty tall order; if attic ventilation were already capable of adequately ventilating the attic they wouldn't need a fan, would they? Otherwise, the attic fan will cause air to reenter the house via the water heater flue and the water heater may establish a draft into the attic via one of those ducts. If that happens, even after the fan is shut down the water heater might continue to draft exhaust gases into the attic via the same path because the air in the flue above the water heater will have cooled and will be denser than the warm path the exhaust follows. If conditions in the house below then are sufficient to depressurize the house below what the attic is, the house could then draw the CO into the home from the attic.

I think you made a good call. I'd recommend they get rid of that fan in the attic, get nice tight seals on that door, make darned good and sure that with all of the fans in the home, plus the clothes dryer, running that the water heater is able to maintain it's draft. If not, then they'll need to consider making some changes.

ONE TEAM - ONE FIGHT!!!

Mike

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