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alvanos 03-09-2008 04:20 PM

Tape vs. Sheet metal screws
Hi all, this topic has probably already been discussed here before, but a quick search of the key words came back with so many hits, I hope you'll all forgive me for asking again.

I've gutted a part of my basement in order to make for a full bathroom (before only had a 1/2). There is an existing rectangular duct run that I've tapped off of with 6" diameter duct, and which I'm running into the bathroom. No flex, all ridgid stuff. Using tin snips, I cut the circle into the existing duct. and I've used a number of 90's to reach my end destination. So ... I need some tape to seal the hole I cut out (where the first 90 comes off). There are SOOOOO many tapes, which one do I use? And for the 90's to 90, and 90-to-run, do I use the same tape or should I use a sheet metal screw? I remember when doing my dryer duct/vent that sheet metal screws were a BIG no-no, since lint could get caught and start a fire. Not sure about HVAC hot/cold air.


wire_twister 03-09-2008 04:44 PM

I would use sheet metal screws to be sure it did not come apart. The hvac man that put in my ac ran hard pipe, with 3 or more screws in each joint, then taped the joint with foil tape to seal any air leaks.

nap 03-09-2008 06:48 PM


tape to seal- better way- duct seal. A gooey pasty consistancy material that gets spread on with a brush. it seals better and easier and does not come off as it ages like many tapes will.

Lowes sells it. not sure where else (other than a pro HVAC supplier)

not sure about sealing the hole you speak of. Did you make the hole too big? Removed a duct?

If so, use tin for a patch, screws to hold and duct seal to seal.

alvanos 03-09-2008 09:31 PM


Originally Posted by nap (Post 105928)

not sure about sealing the hole you speak of. Did you make the hole too big? Removed a duct?

If so, use tin for a patch, screws to hold and duct seal to seal.

It was big enough to put the new duct into, with a little room to spare, so yeah a little to big. I'm talking about something like a 1/4" around the perimeter in the widest areas, in some places it's already pretty tight.

nap 03-09-2008 09:48 PM

For a 1/4 inch gap, I would probably pput a piece of tin in place or possible use a piece of duct tape then apply duct seal over all the tape and past the edge of it.

HVACguy 03-10-2008 12:21 PM

Controversial To Popular Beliefs - The Standard "Duck Tape" We All Know and Love, Is Not A Good Product For Galvanized Sheet Metal.

I Would Use "Tin Tape" Made of Thin Aluminum, and A Strong Adhesive - It Is Commonly Found With A White Backing.

This Product Will Stick Better - and Longer Than Any Traditional Duct Tape. I Would Recommend Using 1/4" Zip Screws - As It Is General Code For Any HVAC Install.

nap 03-10-2008 12:40 PM

the problem I see with the tin tape is it is difficult to make it conform to the angle and both pieces of duct at the joint without leaking. It is difficult to make a piece of metal with a 90 angle bent into it to wrap around a duct and set flat on the flange of that piece. That is why I use duct seal. The only reason for the tape in my suggestion is to provide a base for the duct seal to lay on until it sets. It needs to go beyond the edge of any tape.

In any commercial job I have ever seen, I have never seen tin tape spec'd. Either nothing is used (obviously a different type of joint that what we are speaking of here) or duct seal was used.

pcampbell 03-25-2008 01:26 PM

Mastic will do wonders. Most non professionals have no clue what this is and I only found out about it on here. It is some gooey stuff, very easy to work with though. It is water based so not very nasty. Washes off easily. Dries hard.

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