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Old 01-08-2009, 09:02 AM   #1
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Does return duct width matter?


I have a return duct for my furnace (cold air return) and also for my air conditioner that is about 5' wide, with openings that are about 18" wide. I am tempted to reduce the width of this vent to accommodate electrical wiring. Does the width of the actual vent matter, or only the width of the openings?

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Old 01-08-2009, 09:39 AM   #2
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Does return duct width matter?


If you are thinking of changing just a straight section of return you need to be concerned with cross-sectional area and the duct material. Changing either could affect the performance of your system.

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Old 01-08-2009, 11:45 AM   #3
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Does return duct width matter?


Post pic.
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Old 01-08-2009, 11:52 AM   #4
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Does return duct width matter?


I will try to post a diagram when I have time, but cannot post a photo (this is inside a wall)

This is a straight section. Intuitively, airflow is limited by the narrowest cross-sectional of the entire vent. So slightly reducing the cross-sectional area of the vent where it is substantially wider than this should have no effect. However I don't know anything about HVAC so I thought I'd post.
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Old 01-08-2009, 02:02 PM   #5
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Does return duct width matter?


Oh great. Another Picasso diagram coming our way ...digital pic is much easier to read.


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Old 01-08-2009, 02:13 PM   #6
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Does return duct width matter?


Don't end up like most DIY projects like this
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Old 01-08-2009, 06:36 PM   #7
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Does return duct width matter?


Um, wow! No words that are suitable for this forum to explain that


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Don't end up like most DIY projects like this
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Old 01-09-2009, 08:50 AM   #8
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Does return duct width matter?


Quote:
Originally Posted by bvbellomo View Post
I will try to post a diagram when I have time, but cannot post a photo (this is inside a wall)

This is a straight section. Intuitively, airflow is limited by the narrowest cross-sectional of the entire vent. So slightly reducing the cross-sectional area of the vent where it is substantially wider than this should have no effect. However I don't know anything about HVAC so I thought I'd post.
Your semantics make it very hard to understand what you are describing.

You seem to use the word "vent" and "duct" interchangably, then also use "vent" and "opening" to describe the same thing in another post.

Furthermore your logic regarding the cross sectional area leaves out a very important piece of the puzzle - airflow. If piece of duct A has more cross sectional area then piece of duct B, it's probably because piece of duct A has more air flowing thru it. So you can't just reduce the cross sectional area of duct A based on the logic duct B is smaller...
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Old 01-09-2009, 03:29 PM   #9
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Does return duct width matter?


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Originally Posted by hvaclover View Post
Don't end up like most DIY projects like this
I wish I could have sold the flex on that job
I am a big fan of DIY, but that is NUTS
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Old 01-09-2009, 03:44 PM   #10
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Does return duct width matter?


Boy Isnt that a job to be proud of. I think I just puked a little.
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Old 01-09-2009, 04:31 PM   #11
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Does return duct width matter?


Quote:
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I wish I could have sold the flex on that job
I am a big fan of DIY, but that is NUTS

I think because we pros have seen so many jobs like that is the main reason we get a bug up our asses when a DIYer says he is going to install a furnace him self.

Then it is up to us to explain to the next HO that the job has to be ripped out and why it cost so much to fix it. Of course that makes us the bad guys then.

That is one reason I am trying to help out here. The biggest concern I have is some poor guy thinking he can just grad a used furnace from someplace and gas it up and put the electricity to and he thinks he's good to go.

Used furnaces are an accident waiting to happen if they aren't safety checked by a knowledgeable person.


Safety first always.
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Old 01-10-2009, 08:35 AM   #12
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Does return duct width matter?


Quote:
Originally Posted by hvaclover View Post
Oh great. Another Picasso diagram coming our way ...digital pic is much easier to read.


+1 for Picasso. hvaclover, I gotta tell ya, I have laughed for the last two days over your post

My customers are all over the country and there is not a week goes by that I don't hear "I will draw a picture of it and fax it to you" It rarely turns out well. When i saw your Picasso I burst

Thanks
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Old 01-10-2009, 10:14 AM   #13
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Does return duct width matter?


I agree.
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Old 01-11-2009, 02:03 PM   #14
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Does return duct width matter?




I am a boiler guy. What's wrong with that picture?

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