Horizontal Venting 80% Furnace


Old 04-25-09, 04:46 PM
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Question Horizontal Venting 80% Furnace

Hi there.
We are currently remodeling our 1600 sf 1903 home by dorming out and finishing a third floor attic space. We'll be adding approximately 800sf to the home. Our furnace is an 80% Trane 120000 BTU which vents out a decrepid chimney along with our gas hot water heater. We are replacing the hot water heater with a tankless and would love to get rid of the chimney from third floor up since we'll be raising the roof, and raising the chimney along with it doesn't make financial or aesthetic sense.

We have been told by a licensed HVAC professional that we can vent our Trane horizontally as long as we use B vent and install an exhaust fan. Vent would run approximately 15 feet. We've also considered just running B vent up through chimney for first two floors then on third floor, boxing it in where the chimney has been removed. Knowing that our Trane is overpowered for the size of our house and thus incredibly inefficient since it constantly cycles on and off, we've also considered replacing with 93% furnace to vent horizontally, but price quotes for new furnace + installation are coming back at $5000--way too much money.

So here's the question, finally.
Is horizontally venting an 80% furnace with an exhaust fan safe?

Thanks for your time.
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Old 04-25-09, 06:29 PM
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Horizontal venting

There are specific instructions in the installation manual for horizontal venting. Follow them & you will be fine. Personally, I would rather have the B-vent boxed in. Natural draft is much prefered to mechanical.
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