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DIY Duct Sealing, Pls Evaluate

Posted by cebury (My Page) on
Mon, Sep 5, 11 at 13:14

About 2 years ago I improved my ducting by tying it down, tightening joints then sealing with mastic and metallic tape.

Last week, a duct test revealed ~14% leakage (just under our Code/Reqs). The local vendor can install new ducting that targets 9% or the top-line at 6%. They are going to run numbers for me on costs/benefits.

1) Would you consider 14% a poor/adequate/good job for a DIYer?

I'm wondering if there are points of leakage out of my control, such as within the gas-pack or the sheet metal interfaces between the roof.

2) If I slightly increase tonnage (+0.5) on new HVAC, I may replace it all anyway (vs. just increasing return and a few new supply lines). Outside of that decision, would you think it's worth upgrading ducting to gain a 6% improvement just on its own? It's probably going to run a couple/few thousand.

Opinions? As always, thank you for volunteering your time.


Duct Details: I'm in Central CA, have 20yr old grey R4 flex duct in the attic, with a 14" return feeding about 10 supply vents to condition ~1150sqft. The original Carrier 48NLT gas-pack on the roof is still in place (replacing soon with a 14seer).


Follow-Up Postings:

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RE: DIY Duct Sealing, Pls Evaluate

Hmmmmm. I would be a little suspicious if the tester wants to sell you the ductwork job. Ask yourself, "what makes type A ductwork better than type B"? Or, is the difference in the quality of his workmanship. No duct should grossly leak if one takes the time and trouble to do a quality job.

You need to do some of your own testing. Go to a hobby store and buy a thin wooden dowel (about a yard long). Take a facial tissue and cut a strip (longwise) about an inch wide and tape the end to the end of the dowel.

Turn your blower on high and with the 'telltale', probe around every accessible joint and along seams. Don't forget the tops of trunks and also the returns and filter housings.

Supply leaks will cause the flag to blow; return leaks will suck in the flag. Maybe your leak rate isn't as bad as was reported.

You would have to have a lot of holes to rack up that leak rate.

Is your current unit a 4 ton unit? Don't know if there are any 4.5 ton units. Why do you want to increase tonnage? Has a documented heat calculation been done? If your current ducts can't deliver the air, you will make matters worse.

Good Luck.

V

P.S., disclaimer: I am not a PRO.


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RE: DIY Duct Sealing, Pls Evaluate

Thanks for the suggestion, I'm always suspicious of the test/sell approach. But my original ducting is supposedly horrible compared to the newer stuff (I think the minimum code is R6). I researched tight ducts before hand and do believe they are as good as they claim and I do trust the company that tested would install correctly.

About testing myself: I did that when I originally sealed it myself. There were no detectable leaks (which are EXTREMELY obvious in a still, dusty, 130F, attic when I'm all sweaty) at any joint and all the outer grey plastic was undisturbed. More than half the joints I sealed and taped are now buried in lots of cellulose insulation, so not an easy thing to get at now. I watched them take the readings and do the math to obtain the 14%.

>>> You would have to have a lot of holes to rack up that leak rate.

That's the part I'm looking for guidance on. That would SEEM true, but I'm pondering there must be a large acceptable threashold for "non-leaking" ducts if new ones are only 9% and the top-lines are 6.


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RE: DIY Duct Sealing, Pls Evaluate

14% is not bad, its just not good either. There are naturally going to be places that you just can not seal and being a DIY project you may have missed areas that you did not know how to access or that you should seal them.

What I am VERY curious about is why are they upsizing your system? It is common practice to downsize after sealing but if your system is working well now, why make it larger? this will just cause more problems.


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RE: DIY Duct Sealing, Pls Evaluate

The instrumentation device can easily be 10% in error. 14% of total air flow. Two areas to check, but difficult. Under the ceiling grills. And inside the return air intake.
Have a HERS Rater give your house duct leakage test. You can us a smoke test also. Pressurize your duct system with stage-smoke [ u can rent these at the rental store and a leaf blower [electric] ..blank off all the vents with 3 in painters tape, the beige color professional, Sherwin Williams ..blue is too expensive. blow it into the
return vent...will need some cardboard and duct tape to attach. Good Luck...oh bty, if you have floor vents, inside, under the floor grill ..will need mastic or mastic butter.


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RE: DIY Duct Sealing, Pls Evaluate

14% leakage is not bad.
average new construction leakags minimums often start at 30%.

diy ductwork is not rocket science.
mastic tapes, paint on mastics work well
it is just the degree of difficulty to get to them
after blowing in insulation it is harder, and messier.

concentrate on return, and supply boxes.
these you can seal from inside.
remove supply grills use mastic tape to seal from sheetrock ceiling into metal supply box.
use paint mastics to seal returns.
if chase returns are what you have,
things to look for are open wall cavities
at supply grill. mastic tape & duct board.
never foam products.
spiderwebs pinpoint leaks also.
seal 2x's at walls and to floor of return
if return floor is wooden caulk 2xs at floor
mastic floor (paint on mastic) and put a piece
of ductboard on floor of attic use button cap nails
or roofing nails to hold in place and mastic to walls of return chase.

make sure your paint on mastic is water based
and apply with 2" paint brush.
best of luck.


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RE: DIY Duct Sealing, Pls Evaluate

Chuckfh:

>>> The instrumentation device can easily be 10% in error.
I knew there must be some +- factor due to instrumentation (or usage) but that is never shared. Is that an industry accepted amount?

>> HERS Rater give your house duct leakage test.
I assume that's to SHOW where the leaks are, therefore the smoke? That's an interesting idea... I may just do that if I don't purchase new ducting.

>>> floor vents, inside, under the floor grill ... need mastic
No floor vents, all either in the ceiling inside attic or in the internal wall directly above the door.
I DID seal all the gaps between the metal Boot and the dry wall cutout. I could've done a better job, but the thermal pictures from the blower door tests showed only one was a little bad though.

Thanks for sharing!


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RE: DIY Duct Sealing, Pls Evaluate

Energy_Rater_LA:

>>> average new construction leakags minimums often start at 30%.
The BPI auditor said his experience w/local homes of this age & style are at @ ~40% with the very worst being 60%. Thanks for confirmation.

>>> it is just the degree of difficulty to get to them.
My return and all supply vents are simple: flex duct sitting in open attic space connects to a boot, mounted in ceiling or horizontal above bedroom doors (near a drop ceiling).

So I made sure duct was secure & used plastic/metal ties as needed. I spread ~1/4" thick grey mastic on *every single* connection where flex duct attaches to a boot, reducer, or the plenum. Two boots were difficult as two sides touched framing and ceiling sheet-rock, so my application was messy and lacking on just those two.

The only exception: A 20' chase holds the 14" flex duct travels through the living room (raised plant shelf). I packed insulation around both of the attic-side openings and also cut out a 1'x1' hole so I could examine the ducting from the interior (of course I put a hinge on the removed sheet rock & applied weather stripping to make a tiny sealed door).

>>> remove supply grills use mastic tape to seal
>>>> never foam products.

Already done, except I used spray foam to fill gaps between the boot and the sheet-rock. Why not foam and what should I do now?


As I said in my previous reply I may do the smoke test myself if I don't upgrade any ducting.

Thanks for the answer and tips.


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RE: DIY Duct Sealing, Pls Evaluate sky

Skyheating: Thanks for the reply.

A man J was done 18 months ago (when I knew nothing of home heating/cooling) that recommended I go with 4ton, but they said "maybe 3.5ton". Come to find out that particular vendor is shady and was trying to oversell me on a $10k unit (without upgrades to the ducting). So I can't trust the man-J results either.

If I increase from existing 2.5 to 3 ton it would be for additional supply vent to a walk-in closet and to increase maybe an inch on duct into a particularly hot bedroom and increase it in the living room with cathedral ceilings. These are my opinions at this time but I'm not installing anything until I get my home audit done, then work with an hvac company I can trust that will advise me correctly on the sizing, ducting, and I'll pay for another man-J to confirm it. By then, I'll have actual duct and home leakage numbers to plug into the software.


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RE: DIY Duct Sealing, Pls Evaluate

Already done, except I used spray foam to fill gaps between the boot and the sheet-rock. Why not foam and what should I do now?

why not foam..because it isn't an approved hvac product.
I've seen the results after a few years.
when you remove the supply grill you can see from the dust
collected that the area is not totally sealed.
foam's don't fill gaps like mastics.
they are not approved materials for hvac.

you can't easily remove the foam now but you can
seal it from inside the house.
I use a mastic tape and remove the supply grill from inside
the house, tape goes on sheetrock and in to supply box
pressed well to seal. corners reinforced. tape has to be
covered when grill is replaced so stay within area that grill covers.

I do a lot of ductsealing. after so long I can achieve the 5% that my state's efficiency program requires.
using the mastic tape to seal equipment to plenum connections works well because it provides a continous seal for areas you can't always fit a mastic brush into.

look for hardcast brand #1402 mastic tape
hvac supply will carry, hd lowes carry a thinner
mastic tape that tears easily. polyken is the brand
I don't recommend it. hardcast will cost you about $30
a roll. but worth every penny.

best of luck


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RE: DIY Duct Sealing, Pls Evaluate

Just so I know I'm explaining this correctly, here is what I'm referring to. This is a bedroom vent above the door next to the drop ceiling hallway. If you click to see the detail, the foam is visible on the bottom gap.

Photobucket

I only did a tiny strip of foam from the interior. I did NOT apply mastic on the Boot to Sheetrock from the attic side.

Is that where my mistake was? Or can I just go around on the interior and apply the mastic tape?


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RE: DIY Duct Sealing, Pls Evaluate

I'd go from the interior with the mastic tape
and cover the foam. but make sure the tape will
be covered by the grill..it is next to impossible
to get off once it sticks.

you did a neat job, I just worry with foam
and heat cycle. if you look closely
you'll see the places the foam didn't seal
completly. but like I said..neat job.

looks like they blew the drywall finish with
the supply boxes uncovered..huh.
your boxes must be insulated on the exterior?
(attic side)

best of luck


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RE: DIY Duct Sealing, Pls Evaluate

energy_rater_la: OK will do. That won't take me more than a few minutes per vent.

>>> looks like they blew the drywall finish with the supply boxes uncovered..huh
Yeah, it's crazy. That pic reveals over spray from both the knock-down wall texture and the ceiling acoustic/popcorn texture. Other vents are worse: the texture goes all the way into the visible part of the ducting. When I first examined it (a neophyte home ownership/DIY) I thought ducts were supposed to look like that.

>>> your boxes must be insulated on the exterior?
I'm having trouble w/memory recall here, but I think they are NOT insulated whatsoever. They are just straight metal boots. Now, they are all surrounded by at least 12" of cellulose, some cases 18". But there is no outer insulation to protect from conductive heat transfer from attic framing.

Thanks for all the contributions folks. Very helpful in a few different ways.


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RE: DIY Duct Sealing, Pls Evaluate

I had places on my boot to floor areas that had over an inch of gap and the only thing I could think of at the start of sealing before I knew about mastic was foam. I later went over the foam which had shrank away but only had 1/8" gap or less and gave everything a double coat of brush on mastic.

It is a lot of work to seal each individual connection you can get to but a small leak here and there adds up quick. I had like 400 register cfm of return air at the start of my ductwork rebuild on a @1200 cfm 3.5 ton system. The rest was being sucked out of the attic and basement. I don't remember my supply numbers but they were stupid low also.
The house was built in 2006 and now has a 15 seer 3 TOn Ruud matched system with sealed ducts and the only time it hasn't maintained temp is when it was over 100 degrees and it raised from 77 set temp to 79. The previous system was a builders grade 3.5 ton unmatched with horrible ductwork that was installed when the house was built. The previous system had to be set at 75 degrees to be comfortable and would start to lose the set temp at anything over 90 degrees. I did do the duct sealing and reconstruction while the old system was in place and it made an incredible difference. This new system is all the better.


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old style ducting

My house was built in 1950. The duct system leaked badly until we got after it with mastic and tape.

My HVAC contractor buddy mentioned my old rigid ducting
was better. He explained it this way. The old sheet metal
has a smooth interior wall therefore less resistance to air flow and more air where you want it delivered.

He went on to say the 'new' flexible ducting is MUCH easier to install so all the HVAC companies say it is 'better' because it is a faster install.

Here in California the regulations require that a different company test the duct system for leaks (it can not be the outfit which installed the heating/cooling system)
Poorly fitting systems are very common and leaks and energy waste cost the home owner/renter for decades.

Thoughts?


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RE: DIY Duct Sealing, Pls Evaluate

Here in California the regulations require that a different company test the duct system for leaks (it can not be the outfit which installed the heating/cooling system)

this is a good practice imo. wish we had those standards in place here.

flex people diss hard pipe
hard pipe people diss flex.

here is my experience.
flex leaks at the plenum and the supply box.
hard pipe leaks at all 90's the long seams
and all connections.

most hard pipe that is unwrapped has dust marks
at the leakage sites where air has moved thru
insulation. flex usually is dirty at plenum
and supply box.

hard pipe is more expensive, and is wrapped
when installed, leaving little time to mastic seal.
and once it is covered up...who knows how well it was
sealed?
sealed hard pipe is a beautiful thing.

flex does have more resistance to air flow,
but the ducts are usually sized to overcome
the resistance.

pros and cons for both. try to avoid the companies
that bad mouth the other ducting.
make sure that connections are mastic sealed.
not duct tape, foil tape. paint on mastic or
mastic tape.

I test both types, unsealed hard pipe leaks
much more than unsealed flex due to the sheer
amount of leakage areas.

both can be well sealed. just takes the want to do so.

best of luck


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countrybomo's post

"I had places on my boot to floor areas that had over an inch of gap..."

always remove ceiling/floor/wall registers and seal
the cut to the supply box/boot. I use Hardcast brand
mastic tape. trace lightly around register before
removing and keep tape within area covered by register.

you'd be amazed at how much leakage there are at these
areas. in the attic these supply boxes are surrounded
by insulation which enters the house when unit runs.
keeping these particles & attic air out of the house is always a good idea.


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RE: DIY Duct Sealing, Pls Evaluate

There are also some new caulks that will expand and contract huge amounts and will stick to about anything which in this application would be awesome.


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RE: DIY Duct Sealing, Pls Evaluate

I just replaced the unit and was able to investigate the transition area in the roof. The new unit is a Coleman 2stage 16/14(s)eer DBYX-F036D110 (ecm/scroll), and I upgraded my return vent from 14" to 18" and added a new supply vent -- everything is still in balance.

So before, my duct leak rate was 14%. But the 3rd party test (who said he "calibrated yesterday") shows it's now only 6%! And BTW I still haven't gotten around to putting tape on any of the registers!

I did notice quite a few gaps up inside the transition area/adapter when the old unit was pulled off. Just what I had suspected in the OP -- the majority of the leaks were probably in that area, which I couldn't get into. Before they dropped down the new unit, they applied reflective/sealant tape everywhere indicating they made more effort to seal it up well. Of course I was standing over his shoulder and talking the whole time about how much effort I put into sealing everything ;-)

Thanks for all your replies


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RE: DIY Duct Sealing, Pls Evaluate

>just takes the want to do so. <

Les Miles influences us all, eh energy_rater_la? :)

What is this mastic tape you speak of, and what exactly does it attach to? I guess it must stick to the drywall to get a seal, and I guess it would be the surface drywall within the area covered by the register?

I used caulk around a few ceiling penetrations with really bad gaps in my house, but I haven't done the supplies. I've also thought about using the soft DAP foam-in-a-can. Any thoughts on that? Any problems with condensation around these sealed supply boxes?


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RE: DIY Duct Sealing, Pls Evaluate

>>> I guess it must stick to the drywall to get a seal, and I guess it would be the surface drywall within the area covered by the register?
Yes, that was the idea. As far as mastic tape, I don't know the brand names but even the bigbox stores carried a couple types: the plain alumin foil w/adhesive, and the foil tape with a thin film of what looks like mastic (dark grey stuff that will conform into smaller spaces and remain somewhat flexible).

Not sure what he'll say about condensation, but very little worry in my area. However for whatever condensation already develops between the boot/attic layer, I doubt sealing up the small gap between the register boot and the drywall would make matters any worse. If so, there are bigger issues or other implementations for tackle that problem.


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RE: DIY Duct Sealing, Pls Evaluate

this is how I seal supply boxes.
hardcast brand mastic 1402 tape.

foil tape fails, hardcast with black
backing & blue writing fails. I've only
found the 1402 to last long term.

condensation on grills was how this
sealing method evolved.
sealing this gap eliminates condensation
on grills. now if the condensation
drips from the center of the grill..that
is a different problem.

don't use foams. they exacerbate rather
than solve the problems. somewhere I have
pics of supply boxes that were caulked.
caulk came off when register was
removed.

best of luck


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RE: DIY Duct Sealing, Pls Evaluate

Thanks for the picture and tape recommendation. I asked about the condensation because someone said somewhere it could be a problem because without the attic air infiltration, the register got too cold. I was kinda doubtful about that.


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RE: DIY Duct Sealing, Pls Evaluate

I have to admit..had to google Les Miles...


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