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tideview

join:2013-03-01
Palo Alto, CA

High Efficiency Furnace Vent Adapter

A horizontal installation of a 66,000 btu, 93% efficient natural gas furnace is planned in my garage. A 2” plastic flue was proposed to run horizontally 20 ft. to exhaust through the garage wall. Closer to the proposed furnace location is a 3 inch vertical metal flue that exhausts the hot gases of a gas water heater. The 2” plastic exhaust pipe cannot be tied directly to the much hotter 3” pipe. If a section of high strength ceramic tube is used to make the connection between the plastic and metal flues, it would prevent heat conduction to the plastic pipe. Is this exhaust scheme reasonable? Are other options available for making the connection?

robbin
Premium,MVM
join:2000-09-21
Leander, TX
kudos:1
The condensate of a high efficiency furnace is acidic. That is why PVC is used and not metal for the flue.


Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4
reply to tideview
The new furnace is force draft. You should not tie it into the water heater. combustion gases can and will spill into the space.

dick white
Premium
join:2000-03-24
Annandale, VA
reply to tideview
I'm not an expert on these things, I only know what I see mine doing. My HW heater exhaust is hot enough to keep rising through the flue until it exits above the roof. The exhaust from my HE furnace is barely warm as it exits the plastic pipe through the wall. I cannot imagine it actually rising the full height of the flue before it cools completely and sinks back down and out the bottom of the flue back into the utility room, and from there into the rest of the house. The idea is to get the CO and combustion gases out of the house.

dw


tp0d
yabbazooie
Premium
join:2001-02-13
Carnegie, PA
kudos:5
If you dont want a penetration thru the wall of the garage, have the installers run a new hole thru the roof. Either horiz or vert vent is legal..

-j
--
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currently on FiOS (kick aZZ!)


Grumpy
Premium
join:2001-07-28
NW CT
Reviews:
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reply to tideview
Local building & fire codes often prohibit sharing combustible / flammable fuels exhaust vents and flues for the reasons listed above.

Every device that uses fire also uses air to complete the combustion. When CO laden exhaust air may be forced back through air inlet porting via a shared flue, the results can be deadly. If memory serves, CO poisoning can occur via long term small amount accumulation in the body, in addition to sudden large volume exposure.


jack b
Gone Fishing
Premium,MVM
join:2000-09-08
Cape Cod
kudos:1
reply to tideview
You cannot join Category-4 and Category-1 vented gas appliances exhaust together.

National Fuel Gas Code prohibits you from doing this for safety reasons.

Don't do it.
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