Damp musty smell comming from crawl space

mthomas58 · 07-27-2026, 02:26 PM

We've had lots of rain lately and I've noticed a musty smell from the crawl space under the the kitchen sink coming up from through the plumbing penetrations. In addition, the clothes dryer has alot of condensation inside. So much so the lint trap is completely saturated.

The dryer vent line was replaced several months ago - not clogged blowing freely. Flex alum line runs down to the crawl space then out through the concrete block foundation wall.

Today I went into the crawl to check things.

We ocassionally get water in the crawl space during heavy rain seasons. There was no standing water but in several spots the concrete was wet - front of the house (high Spot)

I am going to re-route a couple of down spouts that go into the ground into drain tile I already have running on the side of they house running to low ground in the back of the house

The real problem appears to the the condensate pump at the A/C unit. Condensation on the outside of the unit and alot of water dripping from the unit. Condensation line may be clogged or pump has failed or both.

All of the A/C supply ducts (rigid round metal wrapped in foil cover insulaton were covered in condensation and dripping.

Never had a problem like this. Never had a crawl space de humidifier but may need to get one.

I've got a call into my A/C guy to check things out.

LWJ · 07-27-2026, 02:45 PM

Yes. Check condensate line and pump. Should be easy to do. This is a super high frequency failure item. You can troubleshoot it yourself.

stevej37 · 07-27-2026, 03:05 PM

I have a full basement with a dehumidifier. It's a 30 pint with no hose to a pump. It's full every day, so I just plan on dumping it in the morning. If I don't, the cement floor is wet.

Here in MI...it's only 4 or 5 months that I need it...but I wouldn't want to be without it.

masraum · 07-27-2026, 03:18 PM

I'd seal the plumbing penetrations with spray foam or something. I wouldn't want a direct route for anything (critters, air, humidity, etc...) through the penetrations.

zakthor · zakthor's Garage

Quote:

Originally Posted by masraum

I'd seal the plumbing penetrations with spray foam or something. I wouldn't want a direct route for anything (critters, air, humidity, etc...) through the penetrations.

His core problem is that the back side is wet. Leave it and your house will mold and rot.

masraum · 07-27-2026, 03:39 PM

Quote:

Originally Posted by zakthor

His core problem is that the back side is wet. Leave it and your house will mold and rot.

Right, the damp/wet crawlspace clearly needs to be resolved. In addition to resolving the damp crawlspace issue, I think the penetrations need to be sealed. My suggestion was not a fix to the problem, but was something additional to do "while you're in there."

Por_sha911 · Por_sha911's Garage

You need to have a qualified person inspect the area of suspected mold growth. This can be easily fixed but an extreme health hazard if left unchecked.

gregpark · 07-28-2026, 07:08 AM

Double up your ventilation

Zeke · 07-28-2026, 07:24 AM

Someone should mention getting a crawl space purpose built fan like they use in flooded houses. HF sells them. Getting things as dry as possible is the most important first move. Treating for mold preemptively is a good idea. Many recipes on the net using vinegar + ingredients. Molds are different, kill them all.

I've done this for a customer with good results. No reason to get insurance involved in her case.

One caveat: I don't live or work in humid areas of the country. I did one year in AL and I know things are done differently. Rather than learn, I got the hell out and ran back home to CA by way of Las Vegas, another hell hole.

mthomas58 · 07-28-2026, 09:15 AM

I was fortunate to get my A/C guy to come out today. Here is what he found contributing to the high humidity situation.

(1) The A/C Filter that was vacuumed out vs replaced 1-2 mos ago by tthe duct cleaning guys because I didn't have a new one was extremely dirty causing a severe air flow restriction. My bad for not replacing the filter ASAP. I ordered new filters just hadn't ventured down below to replace.

(2) The PVC drain line coming out of the A/C unit was sloped up coming out of the unit so it was not draining properly into the condensate pump.

(3) The condensate pump had failed and they replaced it.

I've got a YoLink Temp/Humidity sensor that I'm going to place on top of the A/C Unit to monitor the humidity and will probably run a dehmidifier down there as well to help dry things out.

mthomas58 · 09:58 AM

Just placed the temp/humiditiy sensor in the crawl space. Beginning reading 72 degrees 88% humidity and calculated dew point of 68 degrees. The only water on the floor is a small pool under the condensate pump just replaced. Condensation still on the outside of the A/C unit.

flatbutt · 07-28-2026, 12:10 PM

Quote:

Originally Posted by stevej37

I have a full basement with a dehumidifier. It's a 30 pint with no hose to a pump. It's full every day, so I just plan on dumping it in the morning. If I don't, the cement floor is wet.

Here in MI...it's only 4 or 5 months that I need it...but I wouldn't want to be without it.

I dump mine into the washing machine.

stevej37 · 07-28-2026, 12:15 PM

Quote:

Originally Posted by flatbutt

I dump mine into the washing machine.

Hah!...I never thought of that....makes sense instead of going down the drain.

I use one in the spring/summer in the garage also. When I empty that one, it goes in the turtle pond. That much less I have to add due to evaporation.

.

onewhippedpuppy · 07-28-2026, 12:41 PM

I would give things a day to dry out good before doing anything else. What do you mean by “condensation still on the back side of the AC unit”?

mthomas58 · 07-28-2026, 01:26 PM

Condensation on the outside of the A/C Unit i.e. water beaded up on the sheet metal of the A/C unit

mthomas58 · 07-28-2026, 01:27 PM

Quote:

Originally Posted by onewhippedpuppy

I would give things a day to dry out good before doing anything else.

Good suggestion! Thanks!

onewhippedpuppy · 07-28-2026, 02:57 PM

Based on the copper lines on the left side of the picture I assume that’s your a-coil. When your condensate line is plugged the water will back up into the a-coil and either leak onto the ground and/or freeze on the a-coil. It’s possible that the ice is melting and/or water is still drying and that’s why you see so much condensation on the outside of the housing. Give it a solid 24 hours and see if things have dried up in that area.

Also if you want to limit condensation you can put foam insulation on the low side line (bigger diameter and will be the cold one) and seal the openings around the a-coil housing with foil tape.

onewhippedpuppy · 07-28-2026, 02:59 PM

One other thing, Damp Rid packs are great for getting moisture out of the air, I use them in my boat over the offseason. Amazing how much water they draw in.

mthomas58 · 02:09 PM

Quote:

Originally Posted by mthomas58

Just placed the temp/humiditiy sensor in the crawl space. Beginning reading 72 degrees 88% humidity and calculated dew point of 68 degrees. The only water on the floor is a small pool under the condensate pump just replaced. Condensation still on the outside of the A/C unit.

Today's update: So it has been 24 hours since the Restrictive dirty air filter and failed condensate pump were replaced. I closed the crawl space door and monitored air temps and humidity. This morning and throught the day Humidity was pegged at 98-99% with condensation remaining and dripping from all metallic surfaces (sheet metal and all foil covered ductwork.)

I decided to make an attempt to dry out the crawl space buy placing a large volume fan at the craw space door and place a portable dehumidifier in the space. Since doing so (about an hour ago) humidity has dropped to 91% which is encouraging. Outside humidity is currently 47%.

I also contacted a Crawl Space remediation company and made an appointment for an assessment tomorrow afternoon. The name of the company is Crawl Spaces and More which I fear may be short for More $$$. This co was used my a neighbor. She did a full moisture barrier encapsulation, fan and humidifier solution that was half the price of the Big Guys.

If I can't get the humidity down to a reasonable level I may need to go the encapsulation route which is not uncommon for our area/neighborhood - we are on low ground very near the Chattahoochee River. The strange thing is that we have been in this house for 25+ years and have never had a crawl space humidity problem until now.

Shortly after posting this update humidity had dropped to 86%

mthomas58 · 05:04 AM

So, after several days of running the fan and dehumidifier the humidity has leveled out at 80 percent, obviously still way to high. We are now starting to accumulate mold on wooden item in drawers in cabinets with electrical, plumbing or gas line perferations into the crawl space. This is a divider from the knife drawer in the island.

Had craw space solutions co inspect 2 days ago and have elected to go the encapsulation. Front/ Street wall of the crawl space in the high grade as the lot slopes to the rear approx 4-5 ft with the crawl floor at grade level in the back of the house.

Four active leaks found in the front wall. Two from Water Main supply penetrations one foundation crack full height of wall and one 4' hole for sewer line never used (sewer line exits in the rear) that was never filled but just stuffed with a plastic garbage bag - dirt on other side. Also three metal support posts are rusted out on the bottom and need to be replaced. Very light active mold growth (not black mold) throughout on joists and subfloor that needs to be remediated (no where near the growth on the bamboo drawer seperator)

Will be going with full encapsulation, mold remediation, drain installation along front wall routed to a sump pump and a crawl space dehumidifier. Just waiting to get scheduled.