Author Topic: DIY Duct Work For the Inexperienced  (Read 1529 times)

slipslop

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DIY Duct Work For the Inexperienced
« on: August 17, 2019, 11:10:12 AM »
So I'm fairly inexperienced with DIY around-the-house and wanting to start with a few small things. I have a 40 year old central HVAC system and my ducting seems to be very leaky. My ductwork is mostly accessible through the attic, crawlspace and garage.

After several how-to sessions on YouTube I'm at the point of "yeah, I think I can do that." I certainly doubt I could make things much worse. So as a first step I'm looking at the trunk of the ducting that goes up through my garage. It's accessible, seems like a reasonable scope and, even better, I think the kids might be able to help (and enjoy doing so.)

My understanding is that the dirt pattern on the fiberglass is indicative of air leaks. My thought is:


And my questions:
  • Is this a reasonable approach?
  • Would it be better to actually find specific leaks and seal them, instead of just coating the whole trunk in mastic? If so, how would you recommend sealing them? Metal tape and mastic?
  • Would it be better to just replace this part of the duct work completely, instead of sealing it?
  • Any thoughts on whether this is even a worthwhile project? Any votes for a full, professional, replacement of the ducting instead?

If it makes a difference for answers, I'm inland from the west coast with fairly moderate temperatures (daytime between 55° and 90° most days.)

« Last Edit: August 17, 2019, 11:30:33 AM by slipslop »

BTDretire

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Re: DIY Duct Work For the Inexperienced
« Reply #1 on: August 17, 2019, 11:19:38 AM »
Don't any of the videos recommend Duct tape?
 Normally I see aluminum tape used.



 If the attic does not have a floor and is just joists, I would not have my kids up there.
It is to easy to step in the wrong place and put a hole in the ceiling, or worse yet have
a kid go through and hit the floor.


slipslop

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Re: DIY Duct Work For the Inexperienced
« Reply #2 on: August 17, 2019, 11:31:40 AM »
If the attic does not have a floor and is just joists, I would not have my kids up there.

Heh. No kids in the attic. Just for this first part on the garage floor and maybe a step-stool.

I might let them go into the crawl space and clear the bugs out before I go down there myself, though ;)

Don't any of the videos recommend Duct tape?

They do. My thought was that, just coating everything in mastic, I won't need to spend time investigating where the leaks actually are. I don't know if that's dumb or not, though.
« Last Edit: August 17, 2019, 11:33:24 AM by slipslop »

CowboyAndIndian

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Re: DIY Duct Work For the Inexperienced
« Reply #3 on: August 17, 2019, 12:53:30 PM »
How old is the ducting? Looking at the picture it looks like something quite old.

In that case, I would worry about asbestos. Asbestos was banned after 1978, so installs after that date should be safe.

Removing and getting rid of asbestos is a professional job and I (or my family) would not want to be there. As long as asbestos is firmly embedded and not disturbed it is not a danger.

It might be worth getting a professional to look at it if you are in doubt.
« Last Edit: August 17, 2019, 12:56:23 PM by CowboyAndIndian »

Papa bear

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Re: DIY Duct Work For the Inexperienced
« Reply #4 on: August 17, 2019, 01:14:49 PM »
Use mastic.  Tape won’t hold as well on old dusty ductwork. Do NOT use duct tape.  UL 181 metal tape is fine for new ductwork. 

Use mastic on the seams where ductwork meets, over the screws, and on the adjustable 90’s. If you want to go overkill like a commercial job, then also mastic over the seems of the round pipe on the long ends. 

Just get a crappy paint brush, wear gloves, and be liberal painting on the mastic. 




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Papa bear

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Re: DIY Duct Work For the Inexperienced
« Reply #5 on: August 17, 2019, 01:18:09 PM »
On the “is it worth it” I’m of the opinion that, at least for heat, you are heating a box.  Who cares where the heat end up coming out of the ductwork as long ad the envelope is insulated appropriately. 

AC is a different story, and I’m more concerned about getting cold air where it’s intended to go (upstairs) and getting hot air back down (returns near ceilings on top level back down to blower.


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Fishindude

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Re: DIY Duct Work For the Inexperienced
« Reply #6 on: August 17, 2019, 01:30:02 PM »
The photo looks like about the most lousy duct work and insulation installation I've ever seen, or right up there.
I'd tear all of that insulation off, see what you have and then start replacing accordingly.   Might be, you have some decent sheet metal duct under that insulation mess?
Stay away from using any of the cheap flex duct, that stuff really impedes your air flow because it's not smooth like sheet metal.

If you need to go all new, any reputable HVAC supply house can create a duct plan and supply all of the components.

BTDretire

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Re: DIY Duct Work For the Inexperienced
« Reply #7 on: August 20, 2019, 02:48:49 AM »
I zoomed in on the picture you posted. It looks to me like it's just wrapped with fiberglas insulation.
If that is true, it would not take 5 minutes to remove, and start fresh. Also if it is fiberglas insulation, I don't see how you could apply mastic.

PS, I've been in Florida to long, all the duct work is in the attic,
when I was in Michigan it was in the basement or crawl space.
« Last Edit: August 20, 2019, 02:51:27 AM by BTDretire »

Jon Bon

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Re: DIY Duct Work For the Inexperienced
« Reply #8 on: August 20, 2019, 11:07:20 AM »
Utility knife and throw away that insulation pronto.

I like tape over mastic. For the same reason i like screws over nails. One is alot easier to remove and fix your mistake than the other!

If your in the basement I would not worry too much about insulation. (attic is another story) You are going to be chasing diminishing returns in a hurry. Insulation on duct work is really only a required in uninsinuated spaces.

You can do it, but any insulation you apply would be MUCH more efficient applied to the envelope of the structure.




lukebuz

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Re: DIY Duct Work For the Inexperienced
« Reply #9 on: August 21, 2019, 08:08:29 PM »
I work at a tape factory that makes all types of HVAC tape.  For old leaky ductwork, you need to use the best of both worlds.  A FOILMASTIC tape.  Exactly what it sounds like, it's a butyl adhesive/mastic that is foil backed.  One and Done!  I'd go with the Polyken or Nashua 367-17 or 360-17.  If you have more money, get a flashing tape; the kind used to seal mobile home roofs that are leaky.  Polyken 626-35 is similar to the 367, but twice as thick, so it'll go over more grime and irregularities.  I resealed all of my ductwork with freebie tape from work myself.  PM or post here if you have any questions.

slipslop

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Re: DIY Duct Work For the Inexperienced
« Reply #10 on: August 22, 2019, 10:02:35 AM »
Thanks All!,

It sounds like tape is the way to go. Lukebuz, I'll look at your recommended tapes specifically.

If your in the basement I would not worry too much about insulation. (attic is another story) You are going to be chasing diminishing returns in a hurry. Insulation on duct work is really only a required in uninsinuated spaces.

This is in a south-facing garage that isn't insulated, so I'll need something covering the ducts. I'm not too worried about that part--anything I do will look prettier than how it is now. Hopefully it will insulate better, too.

I zoomed in on the picture you posted. It looks to me like it's just wrapped with fiberglas insulation.
If that is true, it would not take 5 minutes to remove, and start fresh.

Yep, that's exactly what it is. Shouldn't take too long coming down or putting a replacement back up. My presumption is the mastic would be applied directly to the metal ducts underneath at any leaky parts. (The seams seem likely.)

BudgetSlasher

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Re: DIY Duct Work For the Inexperienced
« Reply #11 on: August 24, 2019, 09:21:35 AM »
Use mastic.  Tape won’t hold as well on old dusty ductwork. Do NOT use duct tape.  UL 181 metal tape is fine for new ductwork. 

Use mastic on the seams where ductwork meets, over the screws, and on the adjustable 90’s. If you want to go overkill like a commercial job, then also mastic over the seems of the round pipe on the long ends. 

Just get a crappy paint brush, wear gloves, and be liberal painting on the mastic. 




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I prefer to use mastic (my experience has been impressive of how much leakage is sealed).

Rather than a paint brush I like to use heavy duty rubber gloves (regular latex gloves will tear) and smear it on by hand. I find this easier to get into tight places and to feel that the seams have been covered.

SweatingInAR

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Re: DIY Duct Work For the Inexperienced
« Reply #12 on: August 27, 2019, 05:06:56 PM »
I prefer to use mastic (my experience has been impressive of how much leakage is sealed).

Rather than a paint brush I like to use heavy duty rubber gloves (regular latex gloves will tear) and smear it on by hand. I find this easier to get into tight places and to feel that the seams have been covered.

I 100% agree! I tried a brush too, but ended up smearing it around with gloved hands. If you are trying to cover a big gap (maybe 1/4" to 3/4"?), bridge it with fiberglass tape or a high quality foil tape first, then coat with mastic.

Even outdoors, the tape+mastic works.

slipslop

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Re: DIY Duct Work For the Inexperienced
« Reply #13 on: August 27, 2019, 11:02:41 PM »
Two big leaks sealed and hopefully a few smaller ones, too. Next step is to get under the house and see how bad the ducting is down there...

zolotiyeruki

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Re: DIY Duct Work For the Inexperienced
« Reply #14 on: August 28, 2019, 10:08:01 AM »
I'm late to this party, but I'll add my voice to those who advocate mastic.  It's surprisingly easy to apply, and very effective.  Earlier this year, I sealed many of the ducts in our basement, and DW says that it has made a difference in the comfort level in the upstairs bedrooms.  It's not necessarily an energy conservation issue, it's a matter of getting air to the specific locations that need it (and sucking it back from those locations).

I'm no longer a fan of the aluminum-backed tape--many of the joints were (often half-heartedly) sealed with that tape, and it was falling off in many places.  It's possible that the installer was using subpar materials, and he/she was certainly doing the bare minimum to pass inspection (i.e. no tape on the back side of the duct where the inspector wouldn't see it, and it's harder to apply).

 

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