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bman03
Venting complex roof and attic situation
bman03

Recently moved into home in Eastern MA(Zone 5?) and have a 2 story 3K sqft home. There are 3 gas furnaces and AC units. One of the furnaces is in the attic. The roof is a "T" shaped Gable roof. The roof at "top" of the T has soffit vents and a ridge vent. The "stem" of the T has soffit vents and *no* vent at top. The furnace is located in the stem. That roof has a flat roof top. The furnace itself has a vent stack penetrating through the flat roof; label reads "American Standard Freedom 80 Single Stage". I don't see an intake pipe so I'm assuming it's not a sealed burner. What's concerning is that there is no venting of the attic area where the furnace is. Roofer suggested installing a powered gable vent. Will this be an appropriate way to vent this area? Will there be conflicts with the ridge vent in the other roof system? Will there be issues with the furnace or pull air from the living space?

Top Attic measurements: 30' x 25'
Stem Attic measurements: 24' x 34'

Thanks

llmotoll
Re: Venting complex roof and attic situation
llmotoll

Thumbs down on a power vent for any reason.

Recommend adding a couple hats vents (most economical choice) or ridge vent (match existing conditions) on Stem roof section.

Fencepost
Re: Venting complex roof and attic situation
Fencepost

The problem with a powered vent is that if the furnace is not a sealed burner (it draws its combustion air from the room), the power vent will tend to draw air backwards through the combustion chamber of the furnace, causing the furnace to operate inefficiently AND bringing combustion byproducts including carbon monoxide into your house. BAD idea. A passive vent is a better solution.

If a powered ventilator is installed, there MUST be other passive vents also installed in that same space to "make up" both the air drawn out by the power vent, AND the air drawn by the furnace burner.

bman03
Re: Venting complex roof and attic situation
bman03
Fencepost wrote:

The problem with a powered vent is that if the furnace is not a sealed burner (it draws its combustion air from the room), the power vent will tend to draw air backwards through the combustion chamber of the furnace, causing the furnace to operate inefficiently AND bringing combustion byproducts including carbon monoxide into your house. BAD idea. A passive vent is a better solution.

That's one of my concerns.

Fencepost wrote:

If a powered ventilator is installed, there MUST be other passive vents also installed in that same space to "make up" both the air drawn out by the power vent, AND the air drawn by the furnace burner.

There are soffit vents in the same attic area. However, there are no vents at\near the top of that attic section.

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