crawlspace ductwork


Old 02-19-04, 07:33 PM
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crawlspace ductwork

Just had a new HVAC system (4 ton) installed by a national brand dealer. It's a downflow, airhandler is in a closet in the house, newly installed ductwork runs through the crawlspace underneath. There is a major (2 ft. dia.?) supply trunk down the center of the crawlspace, all roooms are fed off of that via 6" insulated metal duct. Supply trunk and 6"duct are wrapped in foil faced insulation.

Question 1. Should the ductwork be suspended from the overhead? The way it is now, the feeders are suspended but the main trunk is laying in the dirt.

Question 2. The air filter at the handler is 20x25 (500 but the air return intake grill at the wall is only 35x10 (350 There were no restrictions on the size of the grill, so the final size and configuration were at the discretion of the installer. Is it likely this reduced cross section will hamper the airflow?

Thanks in advance.
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Old 02-20-04, 09:01 AM
Ed Imeduc's Avatar
Join Date: Aug 2002
Location: Mountain Williams Missouri
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I hope you havent paid for this job yet.

No that duct should not be laying on the ground at all.
Id look and see what code calls for there.

We would do a job like this with metal duct and 6" round pipe off it to the registers. All hung on up on the joist also 2 small registers down in the crawl space for heat and to help dehumidifi.

The ground should have a 4 or 6 mil poly on the ground over lap 2' and tape the seams ,also up the wall 2'. Then a 2"or3" polystyrene on the wall up to the joist. A block of R19 insulation cut and put up there in the joist space there on the sill plate all around the home.Dont vent it at all to the outside . This will give you a warm floor and dry in the summer.

The cold air return dont sound to bad,if its open all the way.
For a 4 ton AC a tight job would be like 240" and a real good job 320" on the duct work and cold air return

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