combined exhaust flue for hot water heater and furnace?


  #1  
Old 03-08-05, 06:38 PM
greenmoss's Avatar
Member
Thread Starter
Join Date: Jul 2004
Location: Northern Virginia
Posts: 16
Upvotes: 0
Received 0 Upvotes on 0 Posts
combined exhaust flue for hot water heater and furnace?

Hello

I have an old furnace and hot water heater that both vent through the same flue. I am about to replace the hot water heater with a tankless/on-demand heater that has fan-assisted exhaust.

Several contractors I have talked to said that I must put in a new flue for the hot water heater since it is fan-assisted. Otherwise the exhaust from the hot water heater might flow down the furnace exhaust instead of going up the flue and outside.

I was quoted about 1500$ for the new flue (about 8' of flue straight up and out the roof). Alternately, I was wondering if it would be OK to re-use the existing flue with some kind of air flapper system. I was thinking of a one-way mechanical flap that would be forced open by exhaust from the furnace so it could escape. When the furnace was not running, gravity could push the flap shut so that the water heater exhaust would be unable to go down the furnace exhaust pipe. Is this a reasonable/workable idea? If so, where can I find this kind of hardware?

Thanks for any answers.
 
  #2  
Old 03-08-05, 07:08 PM
Jay11J's Avatar
Member
Join Date: Sep 2001
Location: Rochester, Minnesota
Posts: 16,984
Upvotes: 0
Received 0 Upvotes on 0 Posts
Is the new water heater vented by PVC pipe? If so, it should not share the same flue as the furnace.
 
  #3  
Old 03-08-05, 07:51 PM
greenmoss's Avatar
Member
Thread Starter
Join Date: Jul 2004
Location: Northern Virginia
Posts: 16
Upvotes: 0
Received 0 Upvotes on 0 Posts
No, it sounded like the exhaust from the tankless heaters (maybe a Bosch 250) required stainless steel duct. I think this is what I have now shared by my current hot water heater and furnace.
 
  #4  
Old 03-09-05, 08:46 AM
Ed Imeduc's Avatar
Member
Join Date: Aug 2002
Location: Mountain Williams Missouri
Posts: 17,505
Upvotes: 0
Received 1 Upvote on 1 Post
Thumbs down

There is no way you can put a water heater that has a fan assisted exhaust into the same flue with a gas furnace.Id say what you have now could be Gas B vent pipe for the furnace and water heater

Is this a reasonable/workable idea? If so, where can I find this kind of hardware?
No way. Code would come down on you also your insurance company would cut you off.

ED
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: