Damp smell? Need help

[2CRUZ]

Hey Fellas
I need some advice. I can't seem to get any help around here where I live.
My problem is the duct worrk to my furnace/central air runs under the house and it stays damp under there in the summer time. The central air ***** that damp smell up into the house along with the cold air. The duct work is all insulated but it still pulls that damp smell up into the house. I had one fella tell me to put plastic under the house so I coverd all under ther with plastic.
I have all the vents in the foundation open and I put a screen over the crawl space in hopes of drying it out under the but no luck. I sure could use some professional advice. Most of the heating and air guys around here are a bunch of jack of all trade guys with no professinal training.

Thanks guys

 

[DEnd]

You need to seal and insulate your crawl space, and possibly do some radon mitigation.

http://www.buildingscience.com/docu...-light-in-crawlspaces?topic=doctypes/insights

The smell is likely coming from mold and/or mildew, so you could very likely have other issues as well.

 

[LS6 Tommy]

Your ductwork shouldn't pull odors into the space no matter where it's located. You have something else going on.


Tommy

 

[CWO4GUNNER]

Your ductwork shouldn't pull odors into the space no matter where it's located. You have something else going on.Tommy

Agreed. Your insulated flex duct should be sealed, so your either having condensation migrating from the evap coil down the ductwork instead of to your drip pan/ drain lines or a varment has torn a hole into your ducting and making a wet home. Check your pan/drain lines for proper drainage and entire ductwork under the house for holes from all sides and underneath. You can also send in a toy webcam to take a look all inside.

 

[Gerald O]

If the makeup air inlet is in the crawlspace then odors would be pulled in from that.

 

[CWO4GUNNER]

Im always thinking in terms of the desert where I live. In Southern Illinois where you live there may be a crawlspace humidity problem. My Last address in Ches VA, homeowners with crawlspaces instead of slab foundations had to place fans and dehumidifiers inside otherwise mold would infest from ground moisture. Like I said with a slab foundation I had no first hand experiences, just within earshot of co-worker complaints.

 

[James-W]

I am certainly no expert on this subject, but it would seem to me that if the duct is properly sealed and insulated, there should be no damp smell coming from it. As others have suggested, I think you have more problems than you are aware of.

 

[pseudorealityx]

That's a HUGE *IF* in the above statement, especially in residential construction.

Depending on the house, the return duct may be in the crawl space, and since it's under negative pressure, it can pull air/odors/moisture if not sealed well.

 

[DEnd]

Your ductwork shouldn't pull odors into the space no matter where it's located. You have something else going on.


Tommy

I am certainly no expert on this subject, but it would seem to me that if the duct is properly sealed and insulated, there should be no damp smell coming from it. As others have suggested, I think you have more problems than you are aware of.

Duct work causes depressurization of the space it is pulling from. This is because all duct work leaks. If it is then located outside of the space it is conditioning it depressurizes the conditioned space. This will cause odors from outside that space to be pulled into the conditioned space. In this case the odors may not be coming from the air ducts themselves but MAY be more noticeable when the system is running. The solution is to seal and insulate the non-conditioned space where the duct work is located and provide a return air path between the spaces. If the duct work is relatively well sealed then some conditioned air may need to be provided as well. The test is if you have at least 1 cfm per 50 sqft of area duct leakage in the crawlspace then you only need the return air path. If your ducts are tighter than that you need to supply that air in another way, such as a register from the HVAC system or a fan between the house and crawlspace. Also sealed crawlspaces tend to "create" higher radon levels in the house, therefore it is a good time to put in some radon mitigation while you are sealing the crawlspace.

While sealing the crawlspace basically solves the depressurization issue the crawlspace may not be the only source of the damp smell so it's a good idea to perform a thorough inspection for other sources as well.

 

[zmaxmotorsports]

Put a dehumidifier down there for a while and see if that helps.

 

[MScott]

Perhaps a power ventilator is needed to get rid of the moisture. You certainly don't want to seal the crawlspace.

 

[zmaxmotorsports]

 

[DEnd]

Put a dehumidifier down there for a while and see if that helps.

So you want him to dehumidify the entire outdoors? It would help some, but the ventilation in the crawl space would keep him from being able to really dehumidify the space.

Perhaps a power ventilator is needed to get rid of the moisture. You certainly don't want to seal the crawlspace.

A powered ventilator would just add to any moisture problems that may be under there. If there is a condensing surface powered ventilation would just ensure the moisture level in the space remains at atmospheric moisture levels resulting in more moisture accumulation on the condensing surfaces.

Ventilated crawl spaces are fine, but you can't have ducts there and you need to air seal and vapor seal the floor. If you have ducts in the crawl space (or attic) then that space needs to be conditioned, and thus insulated and sealed. Ducts in unconditioned space just cause problems.

 

[Gerald O]

Ventilated crawl spaces are fine, but you can't have ducts there and you need to air seal and vapor seal the floor. If you have ducts in the crawl space (or attic) then that space needs to be conditioned, and thus insulated and sealed. Ducts in unconditioned space just cause problems.

Exaggerated hyperbole (yes, I know that's redundant). While not 'ideal', ducts in unconditioned space are the norm.

 

[yeldogt]

I have seen ventilated crawl spaces with no problem -- but only when they are completely dry .. and really could have been sealed. In many parts of the country the outside air has too much water (humidity) in it for too much of the year. You can't dry out a crawl space with humid outside air,

The only way to correct this is to remove any water and completely seal the crawl. Before you put down the plastic did you see any water?

many require a dehumidifier - or be conditioned.

You may have to remove the insulation as it may be holding odors.

 

[zmaxmotorsports]

So you want him to dehumidify the entire outdoors? It would help some, but the ventilation in the crawl space would keep him from being able to really dehumidify the space.



A powered ventilator would just add to any moisture problems that may be under there. If there is a condensing surface powered ventilation would just ensure the moisture level in the space remains at atmospheric moisture levels resulting in more moisture accumulation on the condensing surfaces.

Ventilated crawl spaces are fine, but you can't have ducts there and you need to air seal and vapor seal the floor. If you have ducts in the crawl space (or attic) then that space needs to be conditioned, and thus insulated and sealed. Ducts in unconditioned space just cause problems.

Try it and see what happens,Depending on the results he can seal up the crawl space if need be.
Air circulation couldn't hurt either to help dry the place out,last time I looked outside after it rained a good breeze helped to dry things faster.
If he was closer to me Id be happy to jump in my service van and drive over to look at it and give him some more options,but all any of us have is the little bit of info that weve been given here to go buy.

 

[DEnd]

Exaggerated hyperbole (yes, I know that's redundant). While not 'ideal', ducts in unconditioned space are the norm.

Just because it is the norm does not make it right.

In field duct leakage testing shows most homes have between 20% and 30% duct leakage. (http://www.paltech.com.au/datasheets/Duct_Modera_ASHRAE_152.pdf) Even well installed ducts regularly test at 10% leakage. Even if the house lucks out and has none of the other associated problems with ducts in the crawlspace (or attic), the homeowners are still throwing money away because their ducts are most likely throwing 20-30% of the air they spent money to condition outside.

Ducts and HVAC equipment do not belong in unconditioned space.

 

[zmaxmotorsports]

I don't belong in an unconditioned space either,but sometimes I too must go outside!

 

[DEnd]

Try it and see what happens,Depending on the results he can seal up the crawl space if need be.
Air circulation couldn't hurt either to help dry the place out,last time I looked outside after it rained a good breeze helped to dry things faster.
If he was closer to me Id be happy to jump in my service van and drive over to look at it and give him some more options,but all any of us have is the little bit of info that weve been given here to go buy.

If the crawlspace is sealed I don't have a problem with putting a dehumidifier down there. It's a decent way to keep the relative humidity down. Without doing some purposeful work to air seal the crawlspace however the air leaks will let in as much moisture as you remove. Don't believe me? How about a Physics Ph.D. who does energy auditing training: http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/27157/Turn-Off-That-Dehumidifier

As for increasing air circulation, it is a bad idea. The breeze works by increasing the moisture content in the air. If he has mold in his crawlspace it is because he likely has condensing surfaces on the structural members of his house. Increasing the moisture content of the air will only add to the moisture condensing on those surfaces. It's a quick way to rot your house. He could have other moisture sources as well and those should be fixed, adding a fan there is not fixing the issue.
http://www.greenbuildingadvisor.com/blogs/dept/building-science/beware-expensive-ventilation-scam
http://www.greenbuildingadvisor.com/blogs/dept/guest-blogs/problems-crawl-spaces

 

[MScott]

As for increasing air circulation, it is a bad idea. The breeze works by increasing the moisture content in the air.

I'm not sure where this convoluted idea comes from. Since you haven't chosen to indicate your location in your profile, I'll have to assume that you live in an area of high humidity such as the deep south where drawing in outside air could increase moisture content. It does not apply for large parts of the country or for other areas where humidity is not as high.
I do know that a friend of mine who had a cottage in this area with a crawl space was having a problem with moisture and dampness until vents were placed in the foundation and a power ventilator was added. Problem solved. YMMV

 

[yeldogt]

The moisture is coming from some place. The only way ventilation works is when you are in a dry climate -- and then normally you don't have crawl space issues.

Have to find and eliminate the source of the moisture.

This time of year when overnight temps fall, humidity in the air can condense inside of the cooler crawlspace in the morning -- this can be enough to cause problems. The only solution is to close the vents. If you have moisture coming up from the ground inside the crawlspace the only solution is to install a proper barrier.

Having proper conditioned air coupled with a correct dehumidifier will solve the problem -- as long as the space is sealed to the outside.

 

[bbrz]

What is your filter type, and location? The pleated filters will stink after just a few mos. of inactivity (re no air flow). Crawl spaces or damp basements. Start small and work up.

 

[Fechmup]

I have seen ventilated crawl spaces with no problem -- but only when they are completely dry .. and really could have been sealed. In many parts of the country the outside air has too much water (humidity) in it for too much of the year. You can't dry out a crawl space with humid outside air,

The only way to correct this is to remove any water and completely seal the crawl. Before you put down the plastic did you see any water?

many require a dehumidifier - or be conditioned.

You may have to remove the insulation as it may be holding odors.

Exactly...

I can tell you with most certainty, that the cool air of your crawl space is being mixed with warm, highly humid air coming in through the vents and you're having issues related to the condensation of atmospheric moisture.

Close off your foundation vents, put in a dehumidifier, and seal off any moisture that can be wicked up from the sub grade....

Science applied, problem solved... My step dad deals with building deficiencies for a living. He has a successful business that started with damp crawl spaces.

Best wishes.

 

[sourdough]

I am somewhat confused by all the comments concerning vented/unvented crawl spaces.

Just one, to wit:

Ventilated crawl spaces are fine, but you can't have ducts there and you need to air seal and vapor seal the floor. If you have ducts in the crawl space (or attic) then that space needs to be conditioned, and thus insulated and sealed. Ducts in unconditioned space just cause problems.

I have a triple-wide 2100' modular ranch home in SW WA State that has a very well vented 18+" crawl space. This is code in WA State. It sits on a 6" slab and the home was placed on a black plastic vapor barrier prior to elevating and leveling. It has a Rheem forced-air downflow propane furnace. As it was built at the factory, it consists of 3 sections bolted together and the ducts are round, insulated, flex connecting between the sections. The furnace is in the center section, thus the ducts split off left and right from there.

After we had just moved in September 2007 to this area, we were subjected to a catastrophic area flood due to extreme rainfall in December 2007. Our total damage, being on a very wide floodplain, was restricted to 3" of water in the crawlspace and none in the elevated 2-car garage.

The ventilated crawlspace worked well to dry it out in the following few weeks and further inspection found no black mold on the modular structure, and the skirting framework/fiber cement siding showed no damage whatsoever.

Just checked them again this summer and the ducts have no rodent damage and there is ZERO mold on the complete underside of the home.

We have since never smelled any musty/damp smells nor have we had any other problems associated with this or any other weather event.

 

[zmaxmotorsports]

 

[DEnd]

I am somewhat confused by all the comments concerning vented/unvented crawl spaces.

Just one, to wit:



I have a triple-wide 2100' modular ranch home in SW WA State that has a very well vented 18+" crawl space.

We have since never smelled any musty/damp smells nor have we had any other problems associated with this or any other weather event.

The difference is you don't have humid summers, thus due to your climate you are unlikely to have condensing surfaces under your house (that does not mean that it won't ever happen however). In your case you might not save much if any money sealing your crawlspace, and since you live in a flood plain it would not be recommended anyway. However your duct location is not ideal, if it is in the crawl space. Ideally you want it inside the conditioned space, however with your climate it may not make sense to increase your conditioned space by approximately 20% (and increase your insulation envelope by ~3%) to encapsulate your ductwork. At least according to the studies I've seen on houses in the Southwest, that likely holds true for the Northwest Marine climate as well. If you were able to move your duct work into your existing insulation envelope I'd wager you'd see around a 10% or more reduction in your heating and cooling bills. You'd get even more savings by reducing the air leakage rates in your house as well.

For the OP's climate he is at risk of damaging his structure due to condensing surfaces, and he is wasting money by having his ducts in the crawl space. If his property is unlikely to be flooded his least expensive course of action is to air seal and insulate his crawl space, and provide proper air sharing between the house and crawlspace. This takes care of any duct leakage related mold issues he has under there and will very likely save him 15%-20% on his heating and cooling costs.

 

[yeldogt]

A properly built crawl space is nothing more than a short basement. A ventilated crawlspace is a basement with the windows open. Lots of vents -- A house on stilts.

Building a house and placing the HVAC in the attic or a vented Crawl is almost like installing it outside -- the unit will be subjected to hot or cold temps and the normal insulation on ducts and equipment is less then R6. The efficiencies are much lower in this configuration .. and this is not factoring the duct leakage that almost all systems suffer from -- or the real possibility that the system is pressurizing or depressurizing the space (depending on the often poor design)

Years ago crawls were built with nothing more then a few vents and sand on the bottom -- some worked some did not. Heating systems were grossly oversized for most houses -- placing a few vents into the heating ducts warmed the crawl and minimized the problems in the winter.

Its the summer when people had issues -- more moisture and most of the time the air coming into the vents was moisture laden ... then it would go away with the colder dryer weather and dry heat from the heating system

Proper construction is to provide drains under the slab and if the possibility of flooding occurs -- a proper drain inside the space ... this is no different than a basement.

 

[zmaxmotorsports]

What he said

 

[DEnd]

Its the summer when people had issues -- more moisture and most of the time the air coming into the vents was moisture laden ... then it would go away with the colder dryer weather and dry heat from the heating system.

I fully agree with most of what you said except for colder dryer weather. In most places it may or may not be dryer in colder weather, but the humidity is still high enough to cause problems. The major difference as far as fungi growth is concerned (fungal growth is the major cause of rot and decay) is the lower temperatures. Fungi need energy from heat in their environment in order to grow. In a well insulated environment, such as a compost pile, the exothermic reactions that fungi use provide enough heat for the organisms to grow. In a less well insulated environment, such as the underside of an open crawl space, or if that compost pile were spread out on the ground, the cold air removes that heat thus limiting fungal growth even with humidity that might otherwise cause problems.