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Sealing leaky air ducts in crawlspace w/mastic - DIY?

Posted by mikesbikes (My Page) on
Tue, Apr 5, 11 at 20:46

In a recent energy assessment of our home, one suggestion was to seal the leaky joints in the ductwork with UL 181 mastic and tape.

We're on a budget, so I'm wondering if this is a feasible DIY project? I'm not super-handy, but am a quick learner. One of my concerns is that the ductwork in question is in the crawlspace, which is about 3' high in most places.

Any thoughts? Is it worth the expense to call a pro? Also, any idea of estimated cost? It's a 2300sf two-story house built in 2002, if that helps.

Follow-Up Postings:

RE: Sealing leaky air ducts in crawlspace w/mastic - DIY?

with duct sealing it is a low material cost and high labor.
but it isn't rocket science.
if during your audit you had been shown leakage sites
and given solutions as to how to seal them it would make it much clearer for you.
what type of ducts do you have?
is all the ductwork in the crawlspace?
with more infomation we can walk you thru it.
be prepared to get dirty.
will you be testing ductwork after the work is done?
can you post any pictures?

RE: Sealing leaky air ducts in crawlspace w/mastic - DIY?

All the ductwork that would be sealed is in the crawlspace. The auditor didn't mention specific leakage sites, just advised us to seal all the joints. I'll try to post pictures. Appreciate your help.

RE: Sealing leaky air ducts in crawlspace w/mastic - DIY?

If it is insulated already it will be more labor intensive and if it is not insulated you should insulated down the road. Sealing is the biggest improvement if not insulated by far.

The mastic products available are brush on and a tape product. I have no experience with mastic tape but have watched rolls of regular foil tape just fall off. Mastic tape is supposed to be as good as brush on but might be more expensive. I really liked the results I obtained with a handful of 99 cent chip brushes and a few gallons of mastic. I had a situation with a lot of leaks and some were large enough to stick 3-4 fingers in. I also sealed the return air side.

Any sealing should come before insulating. I would also not worry about 'sealing it up too good and the air will get stale.' This can happen and does cause issues but the chances of sealing to this point are extremely slim. If you were building a new house with house wrap and sealing as the house was built this would be different.

Your utility bills will drop.. your dust and dirt amount will be minimized and your comfort level will increase.

74 used to be comfortable in the summer and afterwards the unit was not running as much AND 75-76 is comfortable.

RE: Sealing leaky air ducts in crawlspace w/mastic - DIY?

Get a tyvek disposable jump suit and get ready to get filthy.

You can wash some of the suits a few times and re-use them (gentle cycle) or just use a new one when the old one gets excessively dirty.

RE: Sealing leaky air ducts in crawlspace w/mastic - DIY?

let us know the type- flex duct or hard pipe ducting
so that we know which method of sealing to detail.

RE: Sealing leaky air ducts in crawlspace w/mastic - DIY?

Looks like it's already insulated. If so, is it that urgent to have it sealed? Another priority is to blow insulation into our attic to increase it from R-15 to R-49. Would this be a better place to focus our energy/budget?

BTW, the auditor suggested finding a PTCS-certified contractor if we hire out to do the ductwork sealing. What is this certification?

RE: Sealing leaky air ducts in crawlspace w/mastic - DIY?

air sealing trumps insulation.
air seal from conditioned space to attic before insulating.
your bpi guy showed you where these leaks are??

thermal bypasses, recessed lights, cuts at bath fans
are a few of the leakage sites in attic.

back to ductwork.
silver wrapped duct is hard pipe, black is flex.
see the duct tape..this is not a seal.
remove duct tape seal with paint on mastic the flex
to hard pipe connection.
pull black insulation jacket and insulation to the silver
duct wrap use a locktie (pundit) to hold the insulation & jacket in contact with silver duct wrap. mastic seal.

follow the flex to where it enters the floor of the house
see gaps, cracks or openings around cut in floor or on the supply box & connections there..mastic seal.

I don' have a clue what ptcs means, prolly some other guy
who passed a test and doesn't have a clue as to how to educate the homeowner.

I'll go pic by pic later..heading out for work now.
best of luck.

glad to see that vapor barrier on the ground!

RE: Sealing leaky air ducts in crawlspace w/mastic - DIY?

had to google ptcs Performance Tested Comfort Systems
PTCS Certification is an important qualification for contractors working on HVAC systems such as furnaces, air conditioners, heat pumps, and ventilation ducts. PTCS certified contractors are trained � and held accountable through third-party inspections � to evaluate your entire house as a system when installing a new HVAC system. In many cases, you may be able to replace your existing furnace, air conditioner or heat pump with a smaller (and cheaper) unit if the installation is accompanied by air sealing, insulation, duct sealing and other efficiency measures.

The program is limited to the Pacific Northwest, including Washington, Oregon, Montana and Idaho. If you live in one of those four states, you should look for the PTCS Certification when evaluating a contractor to do any HVAC work for your house.

ok enough of that pic by pic comments:
Pic 1 hard pipe supply plenum (silver)
with black flex suppy duct see the failure of the duct tape?
the duct tape should be removed. black jacket and insulation folded back and take off mastic sealed to hard pipe plenum. not only the take off but also the inner liner of duct to take off. let dry. insulation and jacket
pulled to plenum in full contact and mastic sealed.
I would use paint on mastic for the seal to the plenum
and mastic tape to secure jacket to ductwrap of plenum.

pic 2 & 3
see above

pic 4
your vapor barrier should extend up on the walls of the crawlspace and be sealed to walls

pic 4 this is where the hard duct plenum reduces to smaller size..the joints here leak also.
but opening the duct wrap and mastic sealing these areas would be a LOT of work. you may want to seal major leaks first and see if performance improves before tackling the sealing of hard pipe.

It is curious that the pipes seem to be insulated with batt insulation rather than pipe insulation see pink insulation wrap on pipe going thru block wall.
this may be to condensing unit?

so do you think you may take this job on or sub it out?
if you sub it out make sure that you have duct leakage numbers before and test to get reduction numbers afte sealing. also take a look at the job in progress to make sure that mastic or mastic tapes are used.

best of luck.

RE: Sealing leaky air ducts in crawlspace w/mastic - DIY?

Thanks for this excellent information, I really appreciate it. At this point we're leaning towards subbing it out. I'll keep you posted.

RE: Sealing leaky air ducts in crawlspace w/mastic - DIY?

glad to help.
keep us posted
will you be testing for duct leakage reduction
after sealing work is completed?
make sure they use mastics for a long lasting seal.

best of luck

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