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SingleGuy 06-29-2012 10:41 PM

Repaired HVAC duct. What did I do wrong? What did I do right?
Three years ago, I had a Great Dane and had to put him in my garage while I went somewhere for the evening. When I returned after a mere three hours, he'd managed to do some extensive damage. One of the things he tore up was my flexible duct that runs from my intake ( where the filter goes inside the house ) to the blower/condenser.

Three years ago I didn't know duct tape wasn't really that good for ducts. Go figure! I commenced to putting up a new duct. But, I discovered the other day that the flexible duct had fallen down enough to become inefficient due to the duct tape failing ( it lasted 3 years though ). I noticed this because my house wasn't getting cooler and the unit was running longer .. sigh.

I bought some 3m tape designed for such a task and went to work this evening to fix it back up.

I'm hoping someone will chime in and tell me what I did wrong or right so that I can learn. If I've used the wrong terms, please correct me.

Here's what it looked like with the old duct tape. The duct tape simply stopped holding

I taped up the insulation to the inner duct to keep it from falling down

I started taping it up from inside the house

I taped the crap out of it making sure I didn't have any holes. I was trying to make sure to have a tight seal. I pressed as firmly as possible on the tape to ensure a good bond. This tape is awesome stuff.

The insulation is tucked nicely inside the metal duct

Finished the outside ( the top at least )

I still need to do the bottom but it's 102 degrees outside ( literally ) and I'm exhausted at this point

I figured out that this is my stand pipe to flush out the drain pan. I poured a bleach/water mixture ( 1:16 ) to help eliminate the musty smell. I've never done it in the three years I've lived here and i'm sure it had never been done by the previous owners. I noticed the clear lines immediately looking cleaner. The clear tubing was completely black/gray/green with algae. Why do they use clear tubing when black would eliminate algae growth so much better?

Thanks for looking!

Doc Holliday 06-29-2012 10:58 PM

Insulation is not supposed to be inside of those ducts. It looks as if you stuck the insulation under one connection. Tape on the inside is a serious no no. It will eventually get sucked up into the blower.

I wish you would've asked before doing any of this. I'd of simply used mastic sealant (a putty duct sealant that dries up rock hard) over all of the metal and then simply pulled the duct up and over, taped the inside liner to the collar and then zip tied around the entire thing and done.

That little turned up pvc 90 is a secondary drain that is not being used. If you have a drain pan under the unit with a secondary drain line running outside of the home (as is required in most cases), I'd turn it down. In the event your main drain (pump) ever clogs/fails the water is meant to come out of that drain. In other words it's shotty work as now backed up condensate water will overflow inside the internal pan and drip out through the casing of the evaporator.

Doc Holliday 06-29-2012 11:00 PM

And that main drain line should be insulated.

Doc Holliday 06-29-2012 11:08 PM

I just realized this was in the basement or in a garage and not in an attic, doh! You can have a float switch installed in that secondary drain line right at the evaporator. In the event the main drain clogs up and water passes into that secondary exit (where the little 90 degree pvc on the right is) it will shut the unit off, preventing condensate water spillage.

Doc Holliday 06-29-2012 11:14 PM

One last thing, that duct and it's insulation needs to come all the way up and over that joint, to the box.

hvac instructor 06-29-2012 11:23 PM

why not hard pipe it. i only like to use flex in hard to get areas

SingleGuy 06-30-2012 12:10 AM

That little box in the last picture is the float switch. The condensation drains to that and will ( and has due to it being unplugged ) shut off the whole unit. But, I understand that if the path to that box gets clogged, it's of no use lol

The outside temp hit 107 outside today and my house was 130 because I turned off the ac since I didn't want to have any potential damage to the unit with that duct hanging like it was :( I had to do something and quick otherwise I would have consulted this forum first :)

I'm going to redo that soon with the new knowledge.

SingleGuy 06-30-2012 12:12 AM

Interesting that you say it's shotty work. You wouldn't believe the things that are done horribly wrong in my house. The original work on that HVAC had tape on the inside to begin with. It doesn't surprise me. lol

SingleGuy 06-30-2012 12:14 AM

Just so I understand, the inner lining AND the insulation needs to go on the outside right?

Doc Holliday 06-30-2012 12:57 AM

Before I realized the unit had no place for a secondary drain line to run I thought it shotty. I'd still use that secondary flaot switch in that drain.

No tape on the inside and yes, the duct's insulation and outter liner on the outside, the duct's inside liner pulled up and over and duct taped to the collar all the way to the box.

scottmcd9999 06-30-2012 04:20 AM

First, be aware that in some municipalities you can't use flexible ducts on returns, and in general it's not a good idea. Flex duct can collapse (a return is negative pressure, after all) and cause you more troubles than you've got now.

Just so I understand, the inner lining AND the insulation needs to go on the outside right?
The coil tube "inside" the flex is the actual "duct". The insulation is just that - insulation. It looks to me like you may have the wrong size flex duct. It really shouldn't fit inside the hard pipe that easily. To determine your duct size, measure across the diameter of the duct. Ducts generally come in even numbered sizes (12", 14" etc).

The inner sleeve (the thing that looks like a slinky with black plastic wrapped around it) should be connected to the metal duct FIRST. Use duct tape, and also use a tie-wrap strap (you can get those from an HVAC supply house). Then, pull the insulation outer jacket up and over that connection, and use another tie-wrap strap to secure the insulation.

I've also had issues where the tie-wrap will come off the metal duct connection, so I've taken to shooting two sheet metal screws into that tie-wrap. Keeps it in place, and it's easy to remove if needed.

Finally, a good coating of mastic will seal up that inner joint nicely.

If you really want to do this right, however, use metal duct and cut it to fit the space.

biggles 06-30-2012 06:13 AM

need to trap that condensate line coming out of the unit and cap that fill..your sucking air in.when you do the flex connection it always goes on the outside of the metal ..peel back the insulation and pull the plastic flex over the metal then tape it with foil faced tape not that standard stuff.then zip some screws around it thru the fiol tape....

SingleGuy 07-07-2012 02:12 PM

Thanks everyone for the tips. I need to check with a business that does HVAC only because the box stores don't carry the size duct I need. It's always something right? lol

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