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HVAC & ductboard #5421204 05/04/20 09:18 PM
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Donald Offline OP
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I am in the process of moving to my retirement home in DE with a HVAC. Prior homes always had hot water baseboard.

The HVAC guy was there today and told me some of the ductboard was looking old and might need replacement.

I assume others have had similar issues. Are there ways to repair the ductboard with tape or mastic or does one just replace it. In my case I think they used ductboard to turn a floor joist cavity into a duct.


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Re: HVAC & ductboard [Re: Donald] #5421226 05/04/20 09:51 PM
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Originally Posted by Donald
In my case I think they used ductboard to turn a floor joist cavity into a duct.



Are you talking about the cold air return? If so, that's common. A lot of HVAC installers use a mylar-covered cardboard (the brand name escapes me) to nail over the joints to form the return air cavity.
If this is the piece you are talking about, installation is simple. It's nailed up and the seams are taped.

Re: HVAC & ductboard [Re: Kruse] #5421236 05/04/20 10:04 PM
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Donald Offline OP
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Originally Posted by Kruse
Originally Posted by Donald
In my case I think they used ductboard to turn a floor joist cavity into a duct.



Are you talking about the cold air return? If so, that's common. A lot of HVAC installers use a mylar-covered cardboard (the brand name escapes me) to nail over the joints to form the return air cavity.
If this is the piece you are talking about, installation is simple. It's nailed up and the seams are taped.


I have not been in the crawl space in a month or two to verify. But I was told its installed as you mention but is used for both return and supply. I would have thought it should be used for return only.


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Re: HVAC & ductboard [Re: Donald] #5421245 05/04/20 10:10 PM
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irad Offline
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I believe it is called panning duct. This is the most leak prone method of installing duct. Surprise, it is the quickest and least expensive.

Re: HVAC & ductboard [Re: Donald] #5421274 05/04/20 11:21 PM
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Duct board is a fiberglass ridgid duct material. It has a foil face on the outside. Its used for supply and return air trunks.

Panning is what is used to close in a joist space to make it a return air duct. It can be sheet metal or foil backed cardboard called thermopan.


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Re: HVAC & ductboard [Re: CDX825] #5421434 05/05/20 08:24 AM
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Donald Offline OP
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Originally Posted by CDX825
Duct board is a fiberglass ridgid duct material. It has a foil face on the outside. Its used for supply and return air trunks.

Panning is what is used to close in a joist space to make it a return air duct. It can be sheet metal or foil backed cardboard called thermopan.


Any reason not to use sheet metal when replacing?


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Re: HVAC & ductboard [Re: Donald] #5421442 05/05/20 08:37 AM
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Donald Offline OP
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And if the joists are closed in with panning for a supply duct why is that bad?


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Re: HVAC & ductboard [Re: Donald] #5421447 05/05/20 08:49 AM
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Fitter30 Offline
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Duct board is its own insulated duct. Sheet metal has to insulated. Since this is a crawlspace are mice a problem?
At least with metal and no flex duct mice would have less of a chance of getting in. You will miss your baseboard heat.

Re: HVAC & ductboard [Re: Fitter30] #5421453 05/05/20 09:00 AM
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Donald Offline OP
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Originally Posted by Fitter30
Duct board is its own insulated duct. Sheet metal has to insulated. Since this is a crawlspace are mice a problem?
At least with metal and no flex duct mice would have less of a chance of getting in. You will miss your baseboard heat.


Yes, but with HVAC comes central AC which I don't have with baseboard. And the heat source is a heatpump. I am all for reducing the use of fossil fuel, so a heat pump is good unless you loose power and need to run on a generator. In that case you need a large generator.


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Re: HVAC & ductboard [Re: Donald] #5421518 05/05/20 10:43 AM
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JohnG Offline
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Quote
The HVAC guy was there today and told me some of the ductboard was looking old and might need replacement.

I assume others have had similar issues. Are there ways to repair the ductboard with tape or mastic or does one just replace it. In my case I think they used ductboard to turn a floor joist cavity into a duct.


Down here in Florida, probably 95% of all ducts are made from this stuff, unless the premade fiberglass tubing is used. Nearly all of the ducts go in the attic, since there is no basement, and even crawlspaces are very rare.
This board, or fiberglass round tube is pretty good at insulating things, so I'd say it would be a good choice to replace it IF IT IS DAMAGED OR LEAKING. I don't know how "looking old" impacts the efficiency of your A/C.

The guys that do this work down here are TRUE Artists at it. They work quickly and efficiently. So as tempting as it might be to do this work yourself, just let the heating/cooling guys do the work. They can check pressures and flow as part of the deal.
I had a home in Pennsylvania that had a floor joist converted to a duct. After years of wondering why my bedroom floor was always cold, I discovered that the builder (in like 1951) chose one joist opening on one end (the register end), but hooked the furnace ductwork to the ADJACENT joist on the other end!

Re: HVAC & ductboard [Re: Donald] #5421591 05/05/20 11:56 AM
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It depends on how bad of a shape the duct board is, back in the day they used 1", nowdays the standard is 1.5" thick but can also find 2". Ive noticed that ductboard quality itself is not the same, some is sturdy and some other brands can crumble easy. Duct board isn't ideal for use in crawl spaces because it is more exposed to the elements, rodents, and does not last as long as it lasts in attics or in between floors. Even in Florida where duct board is widely used it is not recommended for use in mobile homes, they use metal boxes and black flexible duct.
To answer your question, it really depends on how bad of a shape the duct is in, if it has a few small holes you can tape and mastic over it, if it is falling apart than you have to replace it.


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Re: HVAC & ductboard [Re: Donald] #5422663 05/06/20 01:00 PM
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So related to this topic, should I move the supply duct from a joist covered with ductboard to a normal duct? Thats more effort than just replacing ductboard over the joist.

I assume there is some skill or experience required to be able to make the cuts to turn a flat piece of ductboard into a rectangular duct?


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