Musty Crawlspace Smell Coming Into House - HVAC - DIY Chatroom Home Improvement Forum

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Old 09-17-2008, 07:25 AM   #1
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Musty crawlspace smell coming into house

Hello. I have a problem I'm sure someone here can help me with.

For about a month, I've been noticing a musty, damp odor in my home. I'd come inside after a while, and it would really hit me (unfortunately, no one else in the house notices this smell). I climbed down into our crawlspace, and it's dry as a bone except immediately under our furnace (we have a split-system heat pump). There was water just dripping from the furnace. I really didn't think this is enough to create the smell, but it's not good anyway, so I called my favorite HVAC guy, Clyde (yes, his name is Clyde). Clyde came out and cleaned out the condensation drain because it was stopped up.

Well, then I began to notice that, whenever I happened to be standing near register inside and the AC kicked on, there was a very strong musty smell right away. So once again, I called Clyde.

Clyde came over yesterday and spent about an hour under the house. He said the ductwork appears to be in good shaped (clean inside, sealed up tight, etc.). However, he said the inside of the furnace is covered in mold and mildew. He said the unit has been sitting in the moisture for such a long time (because the condensation drain had been plugged), that even the coil is covered in rust. He said that this would cause the musty smell in the house.

His solution is to spray the inside of the unit with something to kill mold and set a fan in front of the unit to help dry things out more quickly. He said he'll probably have to come back at least once more to spray for the mold to make sure it's gone. Also, he recommends installing a pump/monitor so that we are sure the condensation does not sit in the pan and is always removed.

So my questions are:
1. Would the mold inside the unit cause the musty smell inside?
2. Does this sound like the right solution?
3. What would be the best product to use to spray for the mold?
4. What else, if anything, can we do about this problem?

For obvious reasons, I'm very concerned about this. I want to do this right. Please help!!!!

Thank you!!!!


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Old 09-17-2008, 09:16 AM   #2
Mold is not my friend.
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You definitely want to address the mold, and yes it can cause a musty smell.

One of the best products you can get right now is Shockwave from Fiberlock . You'll want to make sure you have access to all parts of the inside of the unit. Spray anywhere that you see visible mold, making sure that the affected areas remain wet with the product for 7-10 minutes. You may want to employ Clyde to cut an access panel for you for future sprayings, as you will most likely not be able to completely and permanently get rid of every bit of mold, and the drip pan is an excellent breeding ground during the summer when the AC coils drip on it daily.

Allow the Shockwave to dry completely, then follow up with a 50/50 solution of bleach and water (we have extremely hard water here so I used distilled). Someone on this site (ccarlisle) recommended that the bleach treatment be used first so that may be the better process to follow, but both are effective. Scrub off any visible mold and mildew with a 3M scrub pad or sponge and let dry completely. (this thread has been very helpful in dealing with a mold problem in my walls the last few days)

You might also look into sealing any leaks in your returns that could draw basement air into your system. Usually HVAC caulk and foil tape are effective at the duct joints, but if you want a complete sealing process, look into Aeroseal.


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Old 09-17-2008, 08:16 PM   #3
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Originally Posted by Rubu View Post
One of the best products you can get right now is Shockwave from Fiberlock
This is just a Quat cleaner (with a mild fragrance added, and possibly a small amount of a deodorant) and you can buy virtually the same thing for $4 a gallon at sams club. It's called Sanitizer, and it will have the word Quat listed in the ingredients.

Every janitorial supply store will have at least one Quat cleaner available.

For that matter, you can even use regular lysol or some kinds of Mr. Clean, look at the labels, there are many of them that are Quats.

Some have water soluble deodorizers in them, which can help with odors, but in the case of mold, aren't really what you want to do, as they don't really solve any problems.

Diluted bleach really works at least (if not better) as well as anything else, but is more caustic, so if it is going to be used on a regular basis, the quat cleaner is much less damaging.

All disinfectants rapidly lose there efficacy in the presence of organic contaminate. i.e. Clean the surface as much as possible prior to attempting to disinfect.

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Old 09-02-2009, 01:12 PM   #4
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Musty smell coming into my house

I also have a musty smell in my house.i had some flex pipe that was not connected and i replaced them with new flex pipe.i was still getting the smell so i had plastic liner put down,but i am still getting the crawlspace is dry but i get the smell worse when it rains and in the winter when i use the heat.i do have a sag in my drain line from my furnace could that cause the smell.i have only found one very small place were i found mold
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Old 09-02-2009, 03:23 PM   #5
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In my case, the entire problem was caused only by a clogged condensation drain for my HVAC unit. Once that got cleaned out and the coils were cleaned out, everything was fine. Of course, I also don't have any drainage issues around the foundation, nor are there any plumbing leaks--my crawlspace is the most dry I've ever seen (and I do not have poly laid down).

I am told that those condensation drains should be cleaned out twice yearly. Mine is particularly long (probably about 15 feet or so), and it doesn't have much of a fall, so it's susceptible to clogging.

Hope this helps.
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Old 09-02-2009, 05:34 PM   #6
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Installing a safety float switch is a good idea. It should shut the A/C down if condensate backs up before any water damage is done.
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Old 08-20-2015, 09:46 PM   #7
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We have the same problem tmpyankee (Aug 2008) had: clogged condensate drain, mold in condensate pan, etc. We’ve had the pan & line, blower assembly, and coils cleaned (and also sprayed with bio fresh cd). We also had the ducts cleaned, and I’ve taped the seams on the ducts. Unfortunately, we still have a sour/earthy smell coming from our registers when the AC kicks on.

Our HVAC guy is unconvinced that there still should be a problem (even though he seems unwilling to do a smell test). I worry that there’s still mold on the underside of the coils, which he didn’t access, although his experience is that the external side is mold free, the underside should also be mold free. I talked to a couple other HVAC guys, and neither of them had any solutions.

Is there something else I’m missing? Should I consider getting new evaporator coils?


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