Am I Cutting/installing This Duct Wrap Correctly? - HVAC - DIY Chatroom Home Improvement Forum

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08-02-2020, 05:04 PM   #1
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## Am I cutting/installing this duct wrap correctly?

The instructions say to measure P+13 inches, where P is the circumference of the pipe, and cut a 2" tape flap on the side and end.

6" circumference is 18.8 inches + 13 = 31.8 inches. I rounded down to 31 inches here:

It's really loose, but if I am reading this correctly, it's how they are saying to install it. There's like a 2 inch gap in some spots... I exaggerated the looseness here by pulling up in the first pic, but if I center the pipe it's not as bad.

I know there is supposed to be some air gap, but I'm I doing this correctly? I'm assuming I am, but wanted to check to make sure, or see if there were better methods.

Also are there any quick formulas or methods for cutting 6" elbows?

08-02-2020, 05:46 PM   #2
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## Am I cutting/installing this duct wrap correctly?

P+13=
6+13=
19 total, then remove a 2 section of insulation for the overlap.

I would want it in contact with the metal all the way around to eliminate possible condensation.

Last edited by ServiceCall; 08-02-2020 at 05:48 PM.

08-02-2020, 05:58 PM   #3
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## Re: Am I cutting/installing this duct wrap correctly?

Quote:
 Originally Posted by ServiceCall P+13= 6+13= 19 total, then remove a 2 section of insulation for the overlap. I would want it in contact with the metal all the way around to eliminate possible condensation.

The packaging says that P is the circumference of the pipe.

A 6" pipe has a circumference of 18.8"

P + 13" = 31.8".

08-02-2020, 06:34 PM   #4
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## Re: Am I cutting/installing this duct wrap correctly?

Here's a pic of it installed on the duct:

08-02-2020, 11:13 PM   #5
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## Re: Am I cutting/installing this duct wrap correctly?

I wonder how much of the formula shown in Figure 1 was for the Oval ducts instead of Round. Assuming the thickness of the insulation was ~2" it seems the cut width should be closer 8*pi + a couple of inches for the overlapping flap. But that may to too short if the insulation layer bunches up and takes up more room when folded into a tube.

It does not look bad in that install photo, but I think I would trim them just a little bit shorter/tighter. Seems that it should be installed without compressing the insulation, but also without much of an air gap.

08-03-2020, 03:46 PM   #6
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## Re: Am I cutting/installing this duct wrap correctly?

Quote:
 Originally Posted by RustNeverSleeps I wonder how much of the formula shown in Figure 1 was for the Oval ducts instead of Round. Assuming the thickness of the insulation was ~2" it seems the cut width should be closer 8*pi + a couple of inches for the overlapping flap. But that may to too short if the insulation layer bunches up and takes up more room when folded into a tube. It does not look bad in that install photo, but I think I would trim them just a little bit shorter/tighter. Seems that it should be installed without compressing the insulation, but also without much of an air gap.

Thanks Rust... yeah I contacted the manufacturer, and they said it should be snug but not tight... so I will cut it smaller and remove the air gaps.

Not sure why they instruct it to be cut so loose, though...

08-03-2020, 04:31 PM   #7
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## Re: Am I cutting/installing this duct wrap correctly?

Quote:
 Originally Posted by tireshark Thanks Rust... yeah I contacted the manufacturer, and they said it should be snug but not tight... so I will cut it smaller and remove the air gaps. Not sure why they instruct it to be cut so loose, though...

Thats my thought. If you get 18.5 circumference why would you add another 13 to the measurement.

08-03-2020, 04:35 PM   #8
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## Re: Am I cutting/installing this duct wrap correctly?

IIR to do metal forming or tubing bending the thickness of the material has to be calculated into the measurement for each bend. Their formula is correct for their rectangle and it will be long for your round duct. You could do a rectangle cardboard mock up to check that by adding the insulation thickness for each bend.

Edit: Edit

Last edited by SeniorSitizen; 08-03-2020 at 04:37 PM.

08-03-2020, 08:39 PM   #9

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## Re: Am I cutting/installing this duct wrap correctly?

Its not actually suppose to fit loose.

For a 6" pipe, using 2-3/16 thick roll of insulation. You would cut it to 29", giving a slight compression down to the 1-5/8" thickness.
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