Thread: Air handler plenum

Is Flexible duct OK to use as the plenum attached to the air handler? I have always seen insulated plenum attached to the air handler.

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The answer involves a question - HOW is it attached to the AHU?

That's like putting a round peg (the round duct) into a square hole (the AHU).

They have to have something between them.

Is this "just" an air handler or is there heat?
If there is heat, I think there is a stipulation in the IRC requiring at least an 18" plenum before flex ducts are attached, but that is just off the top of my head and I would have to research.
Jim

Nope, not in the IRC that I can find... must be manuf. instructions.
Jim

Thanks guys.

Jerry,

Interesting point. I never thought of that. There was barley enough room to fit my hand up there.

Bill,

How old / new was the house?

I could not find any reference in the code which precludes flexible duct from being connected to the AHU ... I thought there was, but could not find it.

May be in the installation instruction. Do you take a photo of the nameplate? If so, you might be able to download the instructions from the web and see what they state regarding it, if they state anything.

If you cannot find answers in the code but there is a situation you feel is "common knowledge" or even pointed out by another mfr. as long as it makes sense and is practical, you may want to still point it out. In this case, if you describe what it is you are worried about, it might help to make your case or clarify your concern. In other words, not just that you feel it is a problem but what is the hazard or consequences. Is it because the static pressure may cause the flex to collapse in on itself? Add too much turbulence and flow resistance? Not durable and easily damaged?

Following my theme of recognizing Red Flags, when you see something questionable like this, what else did they do goofy? Might want to take a closer look. I'd also try to get the mfrs. instructions. That way if anything should ever go Oops!, you can put some of it back on them.

Jerry,

The home was built in the 80's. The unit is an American Standard, installed 6 years ago.

Bill,

I guess the way to address this is that my report would state that it is incorrect based on standard industry practices (using their typical response against them) and that the flexible duct needs to be connected to a supply plenum which needs to be connected to the air handler unit, and, at the same time advise my client that if an a/c service technician says that the flexible duct is acceptable installed directly to the air handler like that - that installer needs to provide documentation from the Air Diffusion Council which states that such an installation is acceptable.

I can't tell from the picture but is this perhaps connected to the return side of the air handler? If it's connected to the supply side, I can't think of a reason why the installer would do that. It seems that it would be easier to create a supply side plenum using ductbard or sheetmetal.

>> oops, I didn't realize that the thread was 4 years old! <<