Dirt in A/C Ducts, sometimes damp

[jeffw_00]

Hi - Happy Holidays everyone. I started a thread on this a few months ago but it went in a lot of different directions and I have more information now so let me start over.

Preview: I have dirt in my A/C ducts in the attic. When ducts get damp dirt turns to mud. I'm trying to decide best long-term solution. I will use a contractor, but the consensus opinion of this forum often turns out to be more right than a single contractor's opinion (or put another way, posting here gets me questions to ask the contractor that might help us find the best solution).

House is in New-England. Forced-hot-air gas furnace with duct system in basement. Separate A/C-only system in attic with separate own duct system. Duct system made up mostly of 8 x 20 alumimum mains, and 8" insulated flex duct, circa 1987.

Both systems are Bryant Evolution systems, both have Spacegard 2000 filters.

Last summer (late August), I had reason to pull one of the flex ducts off the main and noticed it green muddy type substance in the flex. It didn't seem like mildew (because mildew usually is sticky and this wasn't).

I know that moisture gets into the A/C ducts in the winter - can't be prevented. I have a humidifier on the furnace (need some humidity for health reasons), and the moist air floats up into the A/C ducts.

Today I finally got around to doing some exploration and pulled a few other flexes (feeds, not returns). They all look the same (see picture). However, in the aluminum mains, there is just a fine coat of dusty dirt, no "mud" per se.

Interestingly, my Allergist (top guy at Mass General) wasn't concerned, as he didn't think it was mold. He said if I was really concerned I should run the house at like 85 Deg for several hours and that would kill any bacteria.

Anyway - I suspect this is accumulated dirt over many years, and that there's no way to keep the ducts dry. I notice that it accumulates only on the flex duct. Still, although I can see why the feeds might be moist in the winter, but DRY in the summer (doesn't the A/C have a drying effect?). Today it was 40 Deg out, so there was no condensation.

I'm not sure if I should care, as long as it's just dirt, and I'm not sure what I could do to fix it. Maybe replace all ductwork with metal? (I had a quote to do that for a couple of K).

Any/all comments welcome.

NOTE: I am NOT trying to avoid paying a contractor. I have called a few contractors and unfortunately I couldn't get anyone to come out and look at it thoughtfully themselves. They'll replace the ducts if I want them to but can't afford the time to do a diagnosis. Too busy. That's the way it is here in MA. So I need to do the diagnosis myself and be sure exactly what I want the contractor to do (even if it's a specific test that I pay him for).

Thanks all VERY MUCH for your help.
/j

[jwiehagen76]

I would have all duct system removed and replaced. If it is wet or moist mold will grow. Have a contractor do a load calc see your system may be oversized. A/c that is over sized will cause a cold clammy feel and have poor moisture removal. Hard piping runs and sealing and insulating well should provide better air flow and less dirt in duct providing you change your filter!

[jeffw_00]

Hi - I've had a load calc done - A/C is technically slightly over-sized but less than 1/2 a ton, and the Spacegard filter is religiously changed every spring. Current ductwork looks well-insulated. I've been here 21 years and no cold/clammy feel yet.

I could replace the flex but I'm not sure if hard duct or double-insulated duct is better. I need to prevent condensation or I'll get more moisture in the winter.

How does so much dirt get into the feeds anyway? System ALWAYS had the Spacegard filter. will replacing the ducts solve this?

Thanks - good comments
/j

[jwiehagen76]

The return must be sealed as well. possible just have low end flex duct. I use hard pipe almost always little extra work but no complaints. less restriction

[jeffw_00]

not sure what you mean by "sealed". Currently it's insulated (I.e., jacketed with duct insulation).
thanks
/j

[m-cooling]

Hi - I've had a load calc done - A/C is technically slightly over-sized but less than 1/2 a ton, and the Spacegard filter is religiously changed every spring. Current ductwork looks well-insulated. I've been here 21 years and no cold/clammy feel yet.

I could replace the flex but I'm not sure if hard duct or double-insulated duct is better. I need to prevent condensation or I'll get more moisture in the winter.

How does so much dirt get into the feeds anyway? System ALWAYS had the Spacegard filter. will replacing the ducts solve this?

Thanks - good comments
/j

I was wondering that too.
If the a/c contractor did'nt cover the register holes while the house was being built it can get really nasty stuff gets swept down into the holes .

[jeffw_00]

A/C system was added 27 years after house was built. I don't know, the duct system looks well sealed and wrapped. and there's ALWAYS a Spacegard filter in place. But there's always dirt in the air, and the air from the house can always waif up into the A/C ducts when the system isn't running. In fact, I'm sure moist air DOES make it up into the ducts and sometimes condense.

Still - I'm not sure how normal dirty ducts after 21 years is, and whether I need to do anything about it.

thanks
/j

[m-cooling]

It's totally up to you Jeff.
You see whats in there if your fine with it and can live with it then OK.
If not then get the whole duct system redone to todays codes.
Its different insulation,tape,procedures nowdays.
better ,for efficency.
Its probably R4 flex in there. Go back with R8 which is twice as thick insulation

[m-cooling]

Could be better for your allergies to get it replaced.

[jeffw_00]

Thanks M-cooling that may well make sense.

2 qns -
1) does new code require rigid? Should I go with rigid anyway?
2) what about the mains? The system includes 40-50' of 8x20 mains. Does it make any sense to replace the flex if I leave the mains alone? and then,what about the boxes around the air-handler? Can the mains and boxes just be re-insulated?

And, the silly question - won't the new ducts get dirty after a while as well?

I'll talk to my allergist. He seemed to feel if there wasn't mold'/bacteria, then dirt wasn't really a problem... (and if the dirt was getting circulated into the house, it wouldn't still be in the ducts? 8-})

thanks
/j

[m-cooling]

Thanks M-cooling that may well make sense.

2 qns -
1) does new code require rigid? Should I go with rigid anyway?
2) what about the mains? The system includes 40-50' of 8x20 mains. Does it make any sense to replace the flex if I leave the mains alone? and then,what about the boxes around the air-handler? Can the mains and boxes just be re-insulated?

And, the silly question - won't the new ducts get dirty after a while as well?

I'll talk to my allergist. He seemed to feel if there wasn't mold'/bacteria, then dirt wasn't really a problem... (and if the dirt was getting circulated into the house, it wouldn't still be in the ducts? 8-})

thanks
/j

A contractor will know those questions. Did the doctor test that ?how does he know what bacteria is there?
Look beyond ducts to fix your issue.
The humidity needs to be addressed first

[jeffw_00]

The humidity isn't a "problem" (i.e., unwanted and not-understood), I know where it comes from. On cold nights we use our humidifier for keeping the house from getting too dry, which makes us all more comfortable. On those cold nights, the temp in the attic is below freezing. Thus, as the warmest moist air rises into the ducts (which, although insulated, aren't as well insulated as the house), it condenses on the insides of the ducts (hmm, perhaps carrying dirt with it?). I agree that R-8 duct insulation will help, but I don't think this can be stopped totally when it's 0DegF outside. (unless I insulate the ducts to R-15, or insulate the underside of the roof - no small project!)

All of this stuff has solutions, and I wish I was wealthy enough not to think about cost, or to just blindly trust a contractor (read my other thread http://www.hvac-talk.com/vbb/showthread.php?t=96183 to see what happened last time I did that 8-{)). I know there would be people who open the duct and say "oh my god, dirt!" and call a contractor and tell him to replace everything, but I'm trying to spend my $ more thoughtfully/wisely than that.

I agree that the dirt could be a health detriment (though less so than mold, etc). What I don't yet understand is how replacing the ductwork keps the dirt from coming back - I mean, the dirt got in the ducts once. I'd hate to spend the $, and 2 years later pull a duct and, well, see dirt again...

thanks!
/j

[m-cooling]

Why you keep bringing up the same thing jerk off?
I had a feeling yous a diyer

Post 7 says the same thing I did so what answer are you looking for?

Here I am posting to help u running in circles on the same issue
waste of time

http://www.hvac-talk.com/vbb/showthread.php?t=102571

[m-cooling]

http://www.hvac-talk.com/vbb/showthread.php?t=102571

[jeffw_00]

Hey - chill out...
I'm not a DIYer, and not asking 'how' to fix things, but no one has yet explained how so much dirt got there, and no one has explained why it won't recur. Aren't you pro's always saying "don't just do something, fix it right"? So how does replacing the ducts stop the dirt? - are you saying the new codes make them that much tighter??
3
On the post you quote - I did actually have mold on one register. We cleaned it off (yes, I admit I didn't call a pro to wipe it with tilex and a rag 8-}) and it hasn't come back on that, or any other duct. Luckily, not an endemic problem (like the dirt).

thanks!
/j

[Gunnery Sergeant Hartman]

Replace the duct, seal it, then have a blower door test performed to determine leakage.

You will get dirt and dust through leaky ductwork.

I'd hate to be your contractor.

Cotty Gee!!!!!!!!!!!!!!

[jeffw_00]

Thanks - and actually my contractors like me - I'm informed, reasonable, and respectful, just like I try to be here. Always a pleasure to get input from you guys. 8-}
/j

[drk]

Sorry thats not dirt it is mold! Replace the flex. Keep fan on in winter to help remove thr RH.

[jeffw_00]

Hey drk - I'll believe you, but one qn - I always thought mold adhered, I was able to "clean" a spot by just pushing the stuff away with my finger...
Believe me, if it adhered, I'd already be getting replacement quotes.

Question: Running the fan in the winter makes the house cold and drafty, as I'm pulling the warm air through the colder ducts. Is the lesser evil the best I can do here?

thanks!
/j

[drk]

Mold would come off of the plastic liner easily. The flex duct should be pretty tight so there should be no holes. When you replace the flex make sure they go back with R-6 this should help some. Running the fan also helps even temps in each room and filters the air.

[jeffw_00]

Thanks - you know - an easy way to be sure - I can try some Tilex on it and see what happens 8-}

I've called a contractor - still not clear on whether I want double-insulated flex or rigid alumimum.


Also - I really really don't want to run the A/C fan through the winter, even on low, it makes the house cold and drafty and the heat runs more often than it should. Will this really be necessary?
/j

[drk]

I thought this was a gas furnace?

[jeffw_00]

yes - gas furnace in basement with its own duct system, but when I run the A/C fan in the winter, pulling hot air up into the ducts in the attic, where it gets cooled a bit, and then blown down back into the house, it makes the house drafty and the heat runs more often to compensate. Not real comfortable. Wish there was a better way
j

[drk]

OK so unit in the attic is AC only! Take plastic bags fill with news paper and stuff them in each supply grille. You can do the same thing for the return.

[jeffw_00]

all the registers have fins. I would have to unscrew and pull them to stuff in anything 8-{

[m-cooling]

Sorry thats not dirt it is mold! Replace the flex. Keep fan on in winter to help remove thr RH.

He knows what it is
GSH cotty gee OMG

[jeffw_00]

actually, I was hoping it wasn't 8-}

So why isn't there any mold in the mains? Is it something about the old flex that attracts it? Would new flex be mold-resistant? or do I need to go with rigid? and if I do get rigid, can I get it as well-insulated as the flex (I have to get this all well-insulated as I cannot keep the moist air from passing through it in the winter). Is it also reasonable to ask the contractor to increase the insulation on the mains? Do I need to?

thanks
/j

[dash]

Looks a little like mold.

Is the Spaceguard attahed to the air handler,is it sealed air thight between the air handler and the Spaceguard?If not there's a source of dirt.

Is there any dirt/mold in the air handler?

If the return air part of the air handle is not tightly sealed,some sstuff can b pulled in thru there.

Thinking maybe programing the fan for limited run times,on low,might be a solutiion,if possible.

[jeffw_00]

Spacegard is sealed tight to AH. AH is new (2 yrs) and new one looks clean. can't comment on old one.

thx

[drk]

Its in the flex because that is were it is condensing in the winter. Metal would do the same. Air has cooled down by the time it hits the main duct.

[jeffw_00]

That makes sense, unfortunately.

So would I have to run the fan (even on low) like ALL winter 24/7? Or, what, 6 hours on, 6 hours off? Or a couple of hours a day? or?

Thanks!
/j

[drk]

Id try the news paper in the grille trick first is that does not do it you will have to go the fan route.

[jeffw_00]

I don't mean to be dim, but my registers look like the picture below. how would you stuff newspaper in them?

Also - and this is a really dumb question. Three of my ceiling A/C registers were installed adjacent to the Main. I.e., the "duct" run is about 6" (a 90Deg bend from the main to the duct). I'm going to pull a register today, but wouldn't I expect to see mold in the main at those points? If I do, replacing the longer flex lines solves only 1/2 the problem. If I don't, then there's something about the flex (as opposed to the main) that attracts the mold.

and this is even dumber: Wouldn't condensation be more likely to occur on the aluminum main than in the plastic flex? I mean, metal conducts cold much better than plastic, and the jacket on the main looks no thicker than the cover on the flex (about R-4). I understand the comment that the mold is more likely to grow closer to the register (i.e., where the moist air gets into the system), but most of my runs are less than 10', wouldn't some moist air make it to the main, where the aluminum would be nice and chilly?

I'm not understanding something basic here, and even though I'm inclined to take the advice and replace the flex, I hate not understanding how it all works 8-}

Thanks! and happy new year
/j

[jeffw_00]

I just pulled the register in the duct in the ceiling of the master bathroom. It's a 6" duct with a very short run to the main. I would have expected more mold here than elsewhere (more moisture in bathroom)? but I didn't find any. Mirror says duct is almost totally clean (though there were a few mildew spots on the back side of the register).

now I'm really confused. Why is the problem confined to the long flexes?

/j

[jeffw_00]

The local HVAC supply place recommended a local professional who came by yesterday. Seemed like an experienced, knowledgeable guy. He thinks that what's in the flex ducts is a mix of dirt and mostly dead mold. He suggested that moisture captured the dirt/mold on the sides and it drifted into the bottom of the flex where it dried out. He said that there's nothing in the mains but dirt and dust. His recommendations:

1) I should replace the flex feeds, and close the registers in the winter. He thought R4.2 or R6 was fine because the R8 and R10 stuff is "too expensive". He said he would do it for T & M. We agreed it was a day and 3 to 4 25' boxes of flex duct, but he couldn't give me an estimate because he didn't know how much a box of the duct costs. He has to call me. I'm concerned about replacing the flex with something no better insulated than I'm using now.

2) He thought I should consider get the ducts cleaned because they're dirty (the returns more than the feeds). He recommended a local company that he has recommended before, but has never gotten any feedback from a customer, either way, so he couldn't comment on whether they do a good job.

3) He said I should consider replacing all the returns, although he agreed that with the Spacegard filter there's little risk of dirt/mold from the returns being a health issue.

I think the bottom line on all this is that I'm going to replace the feeds. Either because they're dirty, or because they might be moldy, or because better-insulated ones have a lesser chance of getting moldy in the future (pick your favorite reason). I still think it's worth using R-8 or R-10 (is it really much more expensive?).

I wouldn't mind getting all the dirt out of the mains and returns, but I've read (even here) that duct-cleaning can be a scam. Is there really any good way to get the dirt out? What method should I be asking for?

Thanks guys, getting closer now.

/j

[supernova72]

I ran into a problem with duct work getting wet in the summer due to lack of air flow. the issue there was insulation colasping onto both sides of the blower. I wonder what the blower is doing on this unit. Does your ac keeps up during the summer? How's the airflow? As for duct cleanings, the company i work for is very successful at pulling dirt out a duct system and using sanitizer to kill bacteria. Indoor air quality is not all about what you can see. shop around some more for duct cleaning services. How old is the flex duct?

[jeffw_00]

Flex duct was put in in 1987. Airflow is more than sufficient (in fact, my static is a bit on the high side). What do I want to ask a duct-cleaning service to see if they know their stuff?
Thanks
/j

[teddy bear]

Confusius Say-He who puts a/c ducts in attic in cold climate has mold during cold weather unless he warms them up for several hours each day. Enough dust is everywhere to grow mold. Damp for several days grows mold even on glass. An "air cycler" operating the a/c fan long enough to dry them out every couple hours will keep mold from growing.
Your allergist does not have a clue. Most do not understand the mold/dust mite problem. Moisture for health reasons? Health problems because of mold problems is more likely. After avoiding extended hours continuous dampness, mold will go dormant. Most people are not sensitve dormant mold. This means you must keep the duct dry winter and summer. You need extra a/c fan operation year around. There are some posters that have given good advice, some not. Mold growth any place in home can be a serious problem. This includes the basement and all the ducts. Keep all of these areas <50%RH and condensation free. Regards TB

[jeffw_00]

Thanks Teddy - I can set my A/C fan to run a couple of hours a couple of times a day (2hrs out of 12?) if that's all I need. I don't see you telling me to replace anything or that it's worth paying up to put R-10 feeds in.

Clarification: In dead of winter (0DegF outside), we run humidifier for "health reasons" (maybe comfort reasons is better term) because it gets so dry we get raw throat, etc.

Thanks again
/j

[energy_rater_La]

am I the only on that sees the red flag with this?
"The local HVAC supply place recommended a local professional who came by yesterday. Seemed like an experienced, knowledgeable guy."
The contradiction is this:
He thought R4.2 or R6 was fine because the R8 and R10 stuff is "too expensive". He said he would do it for T & M. We agreed it was a day and 3 to 4 25' boxes of flex duct, but he couldn't give me an estimate because he didn't know how much a box of the duct costs.

R-8 too expensive?
working for time and mateirals?
professional but doesn't know the cost of a box of flex.

and the duct cleaning thing is just wrong.

I'd keep shopping..this sounds like a diy for hire to me.

good luck OP!

[jeffw_00]

Thanks - he's actually legit -runs his own small company (might be just him) and been around for a while, checked out BBB, etc. Still, for all the reasons you mention, I got a recommendation from a GC I know and will talk to him this evening.

thanks!
/j

[jeffw_00]

Hi - I had another contractor out today. This one was recommended by a contractor/friend. He (the guy who came out) seemed to know what he was doing. he offered me two options

1) for a reasonable sum, replace all my A/C flex feeds with R-8 flex. R-10 isn't available in any of the supply places around here. We agreed that I would try the place recommended in this thread for R-10 and if the price is reasonable we would trade up.

2) Do #1, but go on to do more work: For significantly more money (but a reasonable amount based on what he's proposing) he would also
-seal all the seams on the mains with sealing "paint" (?),
-vacuum out the mains with a shopvac, and
-replace the 1" jacket on the mains with an R-8 jacket.

i'm sure I'm going to do #1.

As for #2 - I can't argue that these are all good things to do, but as this project drifts into 4-figures I'm wondering (with 2 kids in college) if these are things I -need- done. I understand that with my condensation concerns it's a good thing to keep the duct as well sealed and insulated as possible, and I doubt there's a pro on this forum who wouldn't recommend doing #2 with someone else's money ;-}. However, since there's only a thin coating of dust in the mains, and no visible mold, I'm wondering, if I'll get a return on the larger investment.

What do you guys think? do I -need- to redo the mains?

T H A N K S ! ! ! ! !
/j

[energy_rater_La]

I guess mains are plenums and junction boxes?
These may be internally insulated to R-4, any external insulation would not be a bad thing to do.

the money is well spent to have his crew seal all the seams and ducts with mastic as they replace them. and to do additional mastic sealing like end caps, returns andsupply boxes etc. mastic sealing (paint on type in a bucket..or mastic tape) will last for years as opposed to duct tape or foil tapes. It is a worthwhile investment for them to do this as they work.
shop vac out any visible debris, also in any return chases.

I'd take the time to do this work, even though it will cost a bit more than expected. The crew will be replacing ducts..what better,
and easily acessable time to seal the ducts..won't be easy to do later when it is all put back together, and would cost you more to hire them back out later, just to seal.


Most people don't have any idea of how much their ducts leak. In my area houses I test have more than one ton of duct leakage on the average. I won't tell you anything stupid like you will see a 40%
drop in your utility costs, but I do think you will see a drop in costs.
Indoor air quality may also be improved due to sealing of ducts and supply boxes.

good luck with your decision.

[jeffw_00]

system consists of 8x20 aluminum mains (aka plenum) (no internal insulation, system is circa 1987) and 8" flex. (with a little 6" flex).

No one has suggested replacing the mains, plenum, or replacing the flex on the returns. (spacegard filter keeps return debris in the returns). The only thing he proposed replacing were the flex feeds.

"Indoor air quality may also be improved due to sealing of ducts and supply boxes."

I don't mean to be dense - but there's positive pressure in the feeds, I understand how sealing improves efficiency, but not air quality - how does debris "leak" in when the air is pushing out?

thanks!
/j

[teddy bear]

you will never get these ducts tight enough or insulate them enough to avoid winter condensation. Nice to have them tight and well insulated but you must warm them up and circulate dry air through them everyday. The cirulating duration must be long enough to dryout all of the condensdation. Regards TB

[motoguy128]

Why not properly connect the two systems together. I don't understand where there are 2 seperate units for the heating a cooling functions. Use a relay to run the blower on the A/C air handler when the furnace is running. It will waste a little electricity, but you'll get better air flow and air filtration, without any condensing in the ducts. Or like mentioned, use a off-delay timing relay and just have both blowers run for a few minutes when the furnace first start's up.

[jeffw_00]

heating system is in the basement, uses 3.5" branch ducts off a single main.

A/C system is 2 stories up in attic, uses 8x20 mains.

But you're saying - run a duct (how big would it need to be) from heating system to A/C system so that a little heat blows through A/C system in winter....

What an interesting idea - how much CFM would I need?

thanks
/j

[jeffw_00]

I'm going to -bump- this because the contractor needs an answer soon. Please see my post #44.

I contact Anco products and they quoted me a price on R-12 8" flex comparable to the regular R-8 price, so I'm going to replace the feed flexes with that. I'm trying to figure out whether to vacuum out, seal, and re-wrap (with R-8) the mains at the same time to reduce the chance of condensation. I know it's a good thing to do, but I need to explain how it will actually improve things to convince the spouse.

Any/all comments welcome - thanks guys
/j

[jeffw_00]

topic has shifted, starting new thread - thanks!

(ps - I'm getting R-12 flex from Anco and contractor will replace feeds a week from monday!)

[jeffw_00]

problem resolved nicely here

http://hvac-talk.com/vbb/showthread.php?t=191982