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Old 10-04-2013, 04:52 PM   #1
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Return air duct venting outside the house?


Hi guys,

I have a gas furnace, which was installed about 4 years ago. I noticed that part of the original ducts for the return air is going directly outside the house.

Basically on the side of the house, I have a 4 inch pipe which is connecting to my return air ducts.

When they installed my furnace, the basement had drywall on the ceiling so there was no way the installers could have seen this.

My concern is that this will bring in tons of cold air in the winter. Living in Canada, it gets very cold here during the winter.

Should I block this off or put a valve to open and close it when needed?

Any advice would be appreciated.

Thanks.

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Old 10-04-2013, 06:55 PM   #2
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Return air duct venting outside the house?


That is called a fresh air pipe and is there to bring in fresh air to get rid of excess moisture or cooking smells etc. some people don't have excess moisture or really need it. if you block it off then your windows may sweat. you can have a contractor install a motorized damper called a Hoyme damper which opens that pipe only when the heat is on. $3-400 job depending on the contractor.
http://www.hoyme.com/

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Old 10-05-2013, 06:21 AM   #3
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Return air duct venting outside the house?


That fresh air pipe also helps keep your home from going into a negative pressure when the dryer, bath fans, range hood,fireplace ect. are on.
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Old 10-05-2013, 06:50 AM   #4
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Return air duct venting outside the house?


The folks we bought our house from paid a bundle of money for radon gas mitigation back in the hay day of radon scams. Two and a half inch PVC pipes on both the return and supply ported to outside. I found better use for the pipe elsewhere.
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Old 10-05-2013, 10:02 AM   #5
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Return air duct venting outside the house?


Well one night the fresh air pipe brought in a lovely skunk smell in the house. It smelled like skunk when the furnace was on.

Mine is maybe 2 feet above ground level, not sure if usually they are installed higher.

In any case, having it always open even when the furnace isn't on just doesn't make sense to me.

Is it possible to install a damper myself that isn't motorized? Something that would open a flap with the pressure when the furnace is pulling air in?
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Old 10-05-2013, 10:08 AM   #6
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Return air duct venting outside the house?


There are some expensive spring loaded dampers but you won't have enough suction to open it so we don't use them for that type of job. The flap type is for clothes dryers and works the other way/forced open.
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Old 10-05-2013, 11:18 AM   #7
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Return air duct venting outside the house?


Thanks yuri.

I think what I will do for now is install a manual damper from the inside that I can close and open myself just to see how things go.

Will it cause a problem with the furnace itself if I leave it closed for a while?
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Old 10-05-2013, 12:05 PM   #8
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Return air duct venting outside the house?


It should have that damper and that is a good idea. I would leave it 1/2 open. In reality your house is NOT airtight anyway ( unless it is a very new house) and the furnace draws air in thru all the cracks around doors, windows etc and creates a negative pressure when running. So it is a good idea to let the air in thru that pipe and we need fresh air 2 B healthy. If U close it 2 much your windows may start sweating and you could end up with a mold problem. Try it 1/2 way open and take it from there. You don't want your house 2 airtight anyway. Mine is supertight and I have 2 run a HRV for ventilation at least 20-40 mins a day or U can tell the air is dead and stale.
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Old 10-05-2013, 12:22 PM   #9
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Return air duct venting outside the house?


Quote:
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It should have that damper and that is a good idea. I would leave it 1/2 open. In reality your house is NOT airtight anyway ( unless it is a very new house) and the furnace draws air in thru all the cracks around doors, windows etc and creates a negative pressure when running. So it is a good idea to let the air in thru that pipe and we need fresh air 2 B healthy. If U close it 2 much your windows may start sweating and you could end up with a mold problem. Try it 1/2 way open and take it from there. You don't want your house 2 airtight anyway. Mine is supertight and I have 2 run a HRV for ventilation at least 20-40 mins a day or U can tell the air is dead and stale.
My house was built in 1973, it's not a new construction. I have done my best to make it as airtight as possible, however I do understand your point of letting in some fresh air from outside.

Don't mean to be annoying, but there is nothing else I can do which would be cheaper aside from that motorized damper?
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Old 10-05-2013, 12:34 PM   #10
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Return air duct venting outside the house?


No. We started having humidity problems and putting them in in 1982 when the first Lennox G8E furnace came out that had a damper in the chimney to prevent air going up it in the off cycle. Houses cannot be airtight in our COLD climate w/o some fresh air but it really is an experiment to see how much you need or at all. Some homes are so leaky and drafty they don't need it but if you have done improvements/air sealing then probably you do. Hoyme has been selling those for over 25-30 yrs. If you are a smart guy and can do electrical and sheet metal then that damper is not hard to install if you can buy it from a HVAC shop. Not sure what the cost would be, probably under $100.
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Old 10-05-2013, 04:10 PM   #11
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Return air duct venting outside the house?


Quote:
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No. We started having humidity problems and putting them in in 1982 when the first Lennox G8E furnace came out that had a damper in the chimney to prevent air going up it in the off cycle. Houses cannot be airtight in our COLD climate w/o some fresh air but it really is an experiment to see how much you need or at all. Some homes are so leaky and drafty they don't need it but if you have done improvements/air sealing then probably you do. Hoyme has been selling those for over 25-30 yrs. If you are a smart guy and can do electrical and sheet metal then that damper is not hard to install if you can buy it from a HVAC shop. Not sure what the cost would be, probably under $100.
I really appreciate you sharing your knowledge of HVAC systems with me. It's nice to get advice from a real professional. I have done a lot of work in my home, I am a fairly handy person, so maybe I would be able to install it myself. My basement is completely open so I have access to all the wiring and ducts.

If you were in my area (Montreal) I would give you the job for sure.

Thanks for everything, I really appreciate it.
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Old 10-05-2013, 05:30 PM   #12
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Return air duct venting outside the house?


Yur Welcome and yeah that would be a bit of a road trip 4 Me.

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