Crossover duct sizing.....

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Casper2016
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Joined: Mon Aug 15, 2016 3:10 pm

Tue Aug 16, 2016 10:24 pm

I'm a recent owner of a DW with an airflow issue on one side of my house (opposite of furnace).

I replaced the 12" flex duct with 2, 90 els and new R8 insulated 12" flex and supported with straps. I haven't found any major holes, collapsed duct, or blockage on the main supply duct. Problem still exists (low airflow opposite side of furnace). So I'm trying to figure out if the flex (crossover duct) should be reduced in size to compensate/equal the approximate size of the metal supply ducts (12x5").....? If my theory is right, I would need approximately 9" round duct. Does this make sense? I don't know if this side of the house has ever had ample airflow and the previous owners just dealt with it. I'm thinking I need more velocity. Any feedback would be appreciated!

Thanks,


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Greg
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Wed Aug 17, 2016 6:48 pm

Sizing ducts correctly is a science. I would try contacting a hvac professional and see if they can get things correctly sized.

Greg
"If I can't fix it, I can screw it up so bad no one else can either."

HouseMedic
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Wed Aug 17, 2016 9:29 pm

I would temporary close off the vents on the good side and see if it changes. It seems that crossovers never seem to work right for some reason. Like Greg said, duct work is a science and can be very difficult to figure out even with a computer program.

Ron

Casper2016
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Thu Aug 18, 2016 11:26 pm

Thanks for the replies guys. For the moment I think I'm going to do some more research with a snake camera. Seal up all my registers with mastic. If all else fails, trial and error with a 9" round duct. If that doesn't work, I may call for an HVAC company to fix the issue. Just like saving money on labor since I'm capable. If only I had to knowledge to know exactly how this was meant to be designed.... I'll post my results when I get it fixed.

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Greg
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Tue Aug 23, 2016 4:57 pm

Unfortunately the way it was designed and the way it will work correctly are usually two different designs. If there is a way that you can use metal duct over flex plastic I would go that way. Many times they just connect plastic flex duct and lay it on the ground so critters can chew through it.

Greg
"If I can't fix it, I can screw it up so bad no one else can either."

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