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Topic:   Condensing Furnace - 1577 visits (1 today, 2 this week)

Darren Miller
Member


Posts: 317
From:Succasunna, NJ
Registered: Mar 2001

posted December 18, 2005 12:51 PM            

Does anyone have any written source that states a condensing furnace cannot be vented into a masonry chimney?

Darren
www.aboutthehouseinspections.com

John Arnold
Member


Posts: 604
From:Philadelphia PA
Registered: Dec 2001

posted December 18, 2005 02:17 PM            

Darren - I imagine you're looking for something more official than this, but the quote below is from the website http://homeenergy.org/archive/hem.dis.anl.gov/eehem/94/941108.html

"Why can't a condensing furnace just vent into a chimney?
The exhaust gases from a condensing furnace are cooler and therefore aren't buoyant enough to create a draft in a chimney. As a result, they would condense inside the chimney and corrode conventional chimney materials."

John Arnold
Member


Posts: 604
From:Philadelphia PA
Registered: Dec 2001

posted December 18, 2005 02:22 PM            

Also this, from http://www.hartandcooley.com/vent/sizing%20guides/Gas%20vent,%20chimney%20sizing%20&%20application%20guide.pdf

"All Condensing Type—Category IV (High Efficiency) Appliances—are NOT ALLOWED on TYPE B venting systems. Condensation will leak out and damage the structure and contents."

Darren Miller
Member


Posts: 317
From:Succasunna, NJ
Registered: Mar 2001

posted December 18, 2005 03:25 PM            

Thanks John;

I had a 10 yr old Goodman condensing furnace (w/PVC pipe) tied into a masonry chimney. Of course I had an arguement with the realtor (she didn't have a clue as to what I was saying, but hey, it's been that way for 10 years, passed a home inspection last year, you know the same BS). I'm looking for something I can fax to my client (who is a 'friend' of the realtor).

Anyway, my report also states when repairs are made, the chimney may have to be re-lined due to just the water heater being present.

Thanks

Darren

Bob Harper
Member


Posts: 254
From:Drexel Hill, PA
Registered: May 2005

posted December 18, 2005 04:32 PM            

A category IV furnace is under positive vent pressure and requires a vent approved for positive pressures. Masonry chimneys and B-vent are not. These chimneys work off natural draft. There is no draft with condensing appliances--only condensation and gases.

The chimney or vent must meet the class of service. Condensing furnaces can use PVC or AL29-4C stainless steel liners & vents listed to UL 1738.

Can reference NFPA 211, 54, ASHRAE handbook, and Int'l mechanical and gas codes.

When in doubt, you can always refer to the mfr. for what type of vent that appliance is listed for. Its right in the listed instructions.

Darren, if you have an orphanned water heater, it needs a liner of its own. If you common vent a condensing furnace in with a water heater into a masonry chimney, the furnace will power vent out the water heater draft hood and kill somebody.

------------------

John Arnold
Member


Posts: 604
From:Philadelphia PA
Registered: Dec 2001

posted December 18, 2005 04:39 PM            

There is a good gas venting artice at Journal of Light Construction http://www.jlconline.com/cgi-bin/jlconline.storefront/43a5ffba0017680b27177f00000105cc/Product/View/0302vent
well worth $2.95 in my opinion.

Eric Barker
Member


Posts: 157
From:Lake Barrington, IL
Registered: Mar 2001

posted December 18, 2005 05:38 PM            

How about the furnace manufacturer's spec.? That will supercede any other information that you might find.