Trying to make exhaust quieter


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Old 10-17-09, 12:41 PM
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Trying to make exhaust quieter

I've been trying to find a way to reduce the sound of the exhaust from my high efficiency condensing furnace. It's kind of close to my neighbor's bedroom and when the second stage kicks in it can get pretty loud. The furnace was installed with an exhaust pipe that sticks out horizontally about 10 inches. Today I added 90 degree elbow on the end of it and set it at an angle which seemed to reduce the sound some. If I add about 1 foot of pipe to end of the elbow that that made it even more quiet. I didn't glue anything together yet.

Good idea ? Bad idea ?

If this is a bad idea then are there any other options besides rerouting the exhaust up the chimney?

Thanks

 
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Old 10-17-09, 01:03 PM
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Probably against code to have a downturn. Never see it on the exhaust, - only on the intake. Likely due to possible condensation freezing and building up inside.
 
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Old 10-17-09, 03:26 PM
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You would have to refer to the installation guide of your furnace (not this example's). Consider the lenth of your vent, and allow for the extra footage of any 90's. If in doubt call a factory authorized dealer of your furnace.

This is a Trane TUH example...

 
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Old 10-18-09, 02:55 PM
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When in doubt refer to the installation manual. Should have thought of that earlier. Here is the appropriate section from my Amana AMV9 manual. So I guess I'll see what effect it has on the sound if I end it with a T. I think having a 60 degree elbow pointing down would be quieter than the T but my furnace manual does not show that as an option.

I had hopes that there would be such a thing as a 'vent muffler' but it does not look like such a thing exists. I am curious about why the vent pipes have terminate a certain way. As ecman51 suggested it might be due to the condensation turning into ice and plugging up the pipe. But my intuition says the exhaust would be warm and it would melt any ice away so that shouldn't happen.

 
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Old 10-18-09, 04:02 PM
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you might speak with the manufacturer to ask about a diffuser. It may cause too much back pressure but the manufacturer would be the place to see.

you might try tossing on a T such as in the pic. That may allow enough of the airflow to flow each direction so as to allow a gradual pressure drop which would be heard less.
 
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Old 10-19-09, 12:26 AM
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Follow the specifications in the manual.

Exhaust vents ARE prone to freeze ups. Your elbow down is an invitation to plugging the vent and shutting the furnace off when it snows or sucking up leaves or other debris, which will likely also shut off the furnace.

Follow the manual.
 
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Old 10-19-09, 07:36 AM
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Originally Posted by nap
you might try tossing on a T such as in the pic.
That does indeed make sense. We have a 4 -pex that has those tees, since perhaps the exhaust points right at another 4-plex about 25 feet away.
 
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Old 10-19-09, 02:00 PM
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Thank You for being considerate of your neighbor

We had a neighbor that had a system that sounded as if it were a truck between the buildings. You could hear it two rooms away in our bedroom. His "expert" heating contractor kept telling him it was installed to specs. The afternoon of the night that the neighbor was to a appear in court to face the sound level surveys the problem was fixed by the "expert" routing it out the back. No more problem. By the way, 1) condensation runs down 2) correct installation calls for the termination to be at least 12" (sometimes 18") higher than expected snowfall. It will not "suck" up leaves. If it is not high enough, getting it high enough is the first concern to prevent shutoff 3) the T will result in the sound being diffused by splitting it 2 ways -- somewhat canceling each sound wave against the other. Termination in a T is the best sound solution.
 
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Old 10-19-09, 02:12 PM
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The incoming combustion air can indeed suck up leaves. Or a leaf --- one is often all it takes to shut off a furnace.

Prudence call for keeping vent pipes away from plants that might cause a problem.
 
 

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