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Old 01-09-2006, 05:35 PM   #1
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Flue Gas Piping and Proper Drafting


We have been in a home now for a year and since then installed a couple CO/gas detection units. Every now and then they are triggered and indicate gas is present. Upon a recent visit by our gas company to inspect the home, the agent indicated that our exhaust flue was improperly sized and there could have been leaking.

The exhaust flue has a 4" port from a small blower motor and was quickly reduced to a 3" pipe. The 3" pipe was fed into a larger 5" Tee manifold that connected with the 3" exhaust of the hot water tank and then both were continued to the outside of the home. He explained the issues of reducing the duct and this seemed logical, therefore I followed his advice and replaced the entire ductwork in the utility closet.

I now have a 4" line from the furnace exhuast flue that leads in to a 4" T manifold. Also into this T manifold is the 3" exhaust from the hot water tank. This is then fitted into the 5" duct pipe that leads outside the home. I also sealed all mating pieces with foil tape as added insurance.
I wanted to see if anyone can offer any insight or if there is a way to make sure the draft is correct. does the original setup sound as though exhuast gases could have been escaping back into the home tripping the detectors?
Thansk in advance for your input.
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Old 01-10-2006, 07:30 PM   #2
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Flue Gas Piping and Proper Drafting


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Originally Posted by DK75
We have been in a home now for a year and since then installed a couple CO/gas detection units. Every now and then they are triggered and indicate gas is present. Upon a recent visit by our gas company to inspect the home, the agent indicated that our exhaust flue was improperly sized and there could have been leaking.

The exhaust flue has a 4" port from a small blower motor and was quickly reduced to a 3" pipe. The 3" pipe was fed into a larger 5" Tee manifold that connected with the 3" exhaust of the hot water tank and then both were continued to the outside of the home. He explained the issues of reducing the duct and this seemed logical, therefore I followed his advice and replaced the entire ductwork in the utility closet.

I now have a 4" line from the furnace exhuast flue that leads in to a 4" T manifold. Also into this T manifold is the 3" exhaust from the hot water tank. This is then fitted into the 5" duct pipe that leads outside the home. I also sealed all mating pieces with foil tape as added insurance.
I wanted to see if anyone can offer any insight or if there is a way to make sure the draft is correct. does the original setup sound as though exhuast gases could have been escaping back into the home tripping the detectors?
Thansk in advance for your input.
It sounds like you have a catorgory 2 furnace.
That is to say that it is probally an 80 percent effiency furnace with a ventor motor.

What you really need is to have B-Vening from the top of your exhaust on the furnace, routed all the way over to your Y branch the branch
should also be made of B-Venting as well then when it goes into the chimney it must go into a flexible metel liner.

On catorgory 2 furnaces they have a tendacies to create vapour which will fall back down the chimney if this is not repaired properly.

Check the net for B- venting and get some ideas of why this happens
Also you mention that it goes to the outside . I hope you mean to the Chimney and then to a liner in the Chimney
Allan
Clarkson Comfort zone Heating Mississauga
weinstall.ca
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Old 01-12-2006, 09:04 AM   #3
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Flue Gas Piping and Proper Drafting


I do believe it is a category B furnace and not a high efficient. I am actually surprised how much heat is lost in the exhaust air.

The gas company rep said that the furnace and hot water tank exhaust should not join into a TEE because there is a chance the air flow could get trapped and create a backdraft. He said a "Y" union would be better.

After a trip to the local hardware store, I could not locate a "Y" union, therefore I purchased a TEE and configured in a way where both the exhuast flue from the furnance and water tank exhaust meet upwards on an angle and continue in an upward path to the main exhaust. I also made sure there are no restrictions to the path of air flow by reducing pipe sizes. Since hot air travels up, and through the path of least resistance, this approach seemed logical.

I did run the furnace for several minutes and the exhuast flue is hot to the touch. I also felt the exhaust pipe of the hot water tank and it is not nearly as warm, but the main exhuast pipe is hot. I guess I can conclude that the hot exhaust air from the furnance is maintaining a path to the outside.

And by the way, I am not sure exactly how the exahust is plumbed into the chimney. It is a townhome, and there is a large pipe into the wall and I am only guess it is leading to the roof.

Thansk again and any additional input is greatly appreciated.

DK
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