Mold Growing Around 3 Boots with Insulation inside of metal duct

[shamik51]

We have a house that is 2 years old. A couple of months ago I noticed there was mold growing from under one of the registers so I pulled the cover off and noticed that this boot was insulated on the inside and looked like it was wet. I pulled off 5 or 6 other covers and did not find another boot that was insulated on the inside like this, and no other boots had this problem.

I had the HVAC installer come out and take a look and he basically told me that they use insulation on the inside of the boot all of the time, and that in this case the boot was probably just faulty, and that cause moisture to get into the insulation and cause the mold. Not being an HVAC expert what he said sounded reasonable.

Now I have mold growing on 2 other boots in the house, and both of them have insulation on the inside of them. Somehow I doubt this is caused by 3 faulty boots.

We live in Frisco, TX which is NOrth of Dallas so it's fairly humid here. ALso, I live in a 2 story house and all 3 of the boots with the problem are upstairs. We have a couple of boots downstairs that are insulated on the inside and are not having this problem, yet.

SO my question, is it a good practice to use boots insulated on the inside in humid areas in 2 story houses? From the results I would say that the installation is wrong, but is this a common practice or a faulty installation?

[genduct]

Mold needs 2 things to live, water and Food ( dirt, wood all organic material)
The insulation is supposed to minimize the water/ sweat/ condensation problem so I wonder if the register is sweating because you are only turning the unit on when it gets warm OR why your home just doesn't get comfortable and dehumidified and stop sweating.

Seems you need to dig in and understand the cause and not just the symptoms

[kevinnn]

IMO, It is unusual that you would have some with and some without insulation. Many AC systems are insulated internally. By faulty boot I would think the person would be talking about the insulation being faulty, perhaps very old and worn allowing condensation to form. You say the insulation looks wet? It should not. Therein lies the cause I would think. Mold loves water and food. The food could be dust or the liner itself but this would not turn to mold without the water. So determining why there is water should point to the cause and solution because there should not be water. I would think something is wrong with insulation somewhere causing condensation to develop inside the duct. The total system airflow/ size of the system maybe another factor. For example if the airflow is too slow from??? ( a dirty filter) the total system air is going to be allowed to stay in contact with the AC coil for a longer time producing very cold supply air in the ducts. The colder the supply air is the greater the potential for condensation to develop where there are faults in the insulation. Were any solutions recommended like re insulating the boots.

[stvc]

As has been said, condensation is forming, because warm and cold areas exist, and a surface is reaching the dew point. It sounds like the upstairs ones are probably exposed to the attic, and am guessing those are the insulated ones and the ones with problems. That would make sense. I would start by taking a look in the attic, hopefully it is accessible [assuming there is one] Check for sealing the boot to the drywall and properly covered with insulation. Also, you didn't say if this was occuring when heating or cooling.

[mdm0001]

I had the same thing to the boots closest to the ac unit. Do you have overspray inside of your boots where they sprayed the ceiling? This was the food for the mold in my case. Here are the reasons I had mold inside my boots.

-overspray food for mold
-fan motor speed was too low trying to get humidity down
-boots were not sealed around sheetrock. Horrible cutting job left big gaps for the hot, attic air to suck in and mix with cold air
-My boots were wrapped with insulation on the topside in attic, but
-I didnt have enough insulation in attic to keep hot air away from boots.

I cleaned the mold out, sealed the boots to the sheetrock, blew in 16" of insulation and sped the fan motor up to where it should have been. Another thing I found was that I dont have enough soffit vents and the ones I have are covered with insulation. The attic is not breathing. In March im going to add soffits and some whirlybirds or some other type fan to ventilate the attic.

[energy_rater_La]

the mold is a symptom of another issue.
usually I find the item listed third in above post to be a contributor.
in homes with heating ducts only and central added later this is not uncommon.
but not your case.

I would proceed as follows.
remove supply grill inspect and possibly change insulation inside supply box.
mastic seal box to sheetrock ceiling. I use hardcast mastic tape for this,
while supply is off look inside duct to see if ducts are dirty past the supply box.
if so...change duct.
is your duct system flex duct? if so the
sealing of box to sheetrock ceiling is first step.
then box itself...corners mastic sealed
duct collar at box mastic seal..paint on mastic
duct liner and duct insulation jacket mastic sealed.
check for holes in duct on way to where it is taken off
plenum. duct take off on plenum should also be mastic sealed
same as flex to supply box.
plenum corners
supply plenum to equipment
return plenum to equipment
all should be mastic sealed.
return framing to framing members and to sheetrock ceiling
if r/a chase or closet should also be sealed.

somewhere the air in the duct and the attic air are meeting
causing condensation.
even if it is the box to grill leakage..this is an indication of the
quality of air sealing further into the duct system.
seal all air leakage and the problem goes away.
and the air you pay to heat and cool actually enters the living space.
mold is a symptom of another issue...fix the issue, change
moldy parts of system..mastic seal.

on new construction I regularly find 25-30% duct/return leakage
more on existing ductwork.

best of luck.

[Daltex]

Energy Rater is right on but I would like to add one extra thought that has worked for me in this situation. The outside (attic side) of the boot is reaching the dew point so you might want to add a can of spray foam to the outside of the boot(s). This will not only seal the boot to the back of the sheet rock but also provide the insulation needed to keep the humid air from contacting the cold boot. This will also seal the vapor barrier of the flex duct so the insulation covering the duct will remain dry.

This has worked for me and lasted for many years. The results are instant and it's a quick cheap fix. Hope the pro's will chime in if they see flaws with my thinking.

[stvc]

Energy Rater is right on but I would like to add one extra thought that has worked for me in this situation. The outside (attic side) of the boot is reaching the dew point so you might want to add a can of spray foam to the outside of the boot(s). This will not only seal the boot to the back of the sheet rock but also provide the insulation needed to keep the humid air from contacting the cold boot. This will also seal the vapor barrier of the flex duct so the insulation covering the duct will remain dry.

This has worked for me and lasted for many years. The results are instant and it's a quick cheap fix. Hope the pro's will chime in if they see flaws with my thinking.

I've used the two part foam and buried the whole thing from the attic, worked great.

OP hasn't been back to add more detail, so don't really know if these suggestions are possible.

[energy_rater_La]

Daltex,
thanks.

but I have to say that I don't like foam for ductsealant.
mastics are for ducts. not duct tapes, not foil tapes unless
foil/mastic or.. foam insulation.
mastics for duct sealants. materials made for extreme temps
and high air pressures.
when the hvac industry comes out with a foam insulation...
maybe then I'll get on board...but it will have to change a lot.

foam insulation does not always seal air tight..it is just so expanded
that you can't see the leakage sites. I've removed many a supply
grill and seen foam around the supply box to sheetrock. dirt trails
from air leakage in between the mounds of foam.

in older installs of foam you can see where over time in the hot attics
here that the foam shrinks..leaving an air leakage opening around foam to
sheetrock/wood. in my weatherization days I made carpenters caulk foam to
sheetrock/wood..but it is double working an area that is best addressed with
another product imo.

a few years ago I got a chemically sensitive homeowner's call. after builder, architect,
insulator..servicemasters..zerodraft..
in 10 years the lady of the house had gotten sicker and sicker. to the point where Mr
showered at the club because..well I think he just wanted to get a break, but she said
his humidity from the shower in the master bath made her sick.
anyhow..all sheetrock walls and ceilings no ceiling moldings recessed lights
high efficiency new central system, blown cellulose on attic floor vaccumed out and replaced with 5" open cell foam on rafters. when draft company came in they foamed the ductwork. supply boxes.2" all over.
big mistake.
at the gap between sheetrock and supply grill, under supply box and at areas they didn't get all the cellulose..the foam incapsulated the cellulose..condensation..food source
when I pulled open the foam insulation you could smell the mold. this was at all the supply boxes in the attic for master bedroom suite..bedroom..closets..bath
5 supplies in the area she complained made her sick.
she was right..she could 'feel' the mold.
bath fans were vented to exterior...but at cut between the housing and the sheetrock..
more cellulose.

they remediated the master bedroom suite..did some air sealing..all is good.

in the few houses I've been called to with foam sealed ducts and supply boxes
the duct leakage was still high. now the problem is that these areas have been
encapsulated creating an ecosystem that is not good.

I don't reccomend foam for sealing anything hvac..
having been able to see issues caused by others with this install.


best of luck OP

[Daltex]

Rater- Thanks for the input on the foam.

Understand 100% what you are talking about and with the OP being in a hot/humid enviornment I can see this being a concern.

One question- could you use the mastic to seal the duct to boot and boot to sheetrock and then foam the boot externally after that without the problems you mentioned?

BTW I think that it makes alot of sense that if you are getting condensation/mold on the internal side of the boot/grill then you must assume a high probability of a leak that is allowing the humid attic air to get pulled inside the boot.

Thanks again on your input on the foam suggestion comments

[energy_rater_La]

I usually seal the supply box from inside the house.
remove grill cut 3" hardcast into 1 1/2" width strips
and seal from sheetrock ceiling to inside supply box's
metal flange. this holds box in contact with attic flooring
seals gap with mastic and once grill is re-installed covers
mastic tape.

mastic and caulk don't stick to dirty surfaces.
in my experience when you move the insulation back from
the boxes in the attic..there is dirt & crap that keeps the
mastic or caulk from adhering well to the attic flooring.

with my method of sealing..it is a 100% seal
I've tested when boxes were mastic or caulked to
attic floor and the findings were what led me
to use the method above.

and no..I wouldn't use foam on any part of the hvac system.
in years to come to change out boxes with foam is a pita.
foam is not a product that I recommend to anyone to use for
hvac sealing.

have a good one.

[Daltex]

Good info Rater- Thanks again