Latest Discussions : Electrical & Lighting


06:37AM | 02/04/08
Member Since: 09/03/07
32 lifetime posts
Can the coils of a dehumidifier get moldy? When running it on my 1st floor level (multi level house) I kept getting black in the pan where the water runs down. I was cleaning every other day because of that. I empty my dehumidifier pans every day whether they are full or not. The one in the basement does not get that black coming down. The one that does is on a carpeted area with the front door level with the driveway and level with the very busy street. I vacuumed the grill but can not open it.

Please, any suggestions??? I have Concrobium mold control that is non toxic but don't know if I could fog the unit.



08:27AM | 02/04/08
Member Since: 11/11/02
2267 lifetime posts
** Can the coils of a dehumidifier get moldy? **

A portable (roll around) freestanding dehumidifier??

I suppose if such a unit was left off for an extended period of time, the moisture on the coils might develop mold or mildew. I don't recall ever running into such a case though.

** I kept getting black in the pan where the water runs down. **

In the bucket itself or the trough that funnels water TO the bucket?

Either of those would be more likely to develop mold and mildew than the "coils" of the dehumidifier which are bare aluminium. But again, I myself don't recall ever seeing a case.

** [it] is on a carpeted area with the front door level with the driveway and level with the very busy street. **

It may just be pollution particles settling out on the unit's coils and getting flushed into the bucket with the recovered humidity.

** The one in the basement does not get that black coming down. **

Have you tried swapping the units to see how they perform in the other's area?


Dan O.

The Appliance Information Site



11:19AM | 02/04/08
Member Since: 09/03/07
32 lifetime posts
Thanks for replying.

1. Yes it is a roll around dehumidifier.

2. The black is in the bucket and as I mentioned I can clean it out one day and it is back the next so I don't really think mold would grow that quickly in the bucket and I thought it may be in the coils and running down.

3. I have not had it running for the winter months although the humidity down there is around 50%....the basement is only 40% so go figure.

4. No, I haven't swapped them around but the one in the basement was originally up there last year and I noticed a brown staining in the bucket similar to the black in this bucket in the same spot. It was a new carpet last year.

I have a feeling the carpet is contributing to the humidity but under the carpeting is some tiles with a lot of them missing and it is bare cement where they are missing. I don't have the money to remediate asbestos and since the house is 60 years old the tiles may be asbestos so is there any way to fill in the bare spots and put tile or linoleum over it. It surely would be easier to maintain. Hubby had carpeting put back because of the missing tiles but that was a big mistake since it is like a vacuum when we open the door -- everything flies in -- leaves, dirt, napkins from the ice cream stand across the street (which is not paved), etc. because it is level with the street, I guess.

Would really like to fill in the large amount of bare spots somehow.

Thanks much.


12:11PM | 02/04/08
Member Since: 11/11/02
2267 lifetime posts
** I thought [the mold] may be in the coils and running down. **

Very unlikely IMO.

** under the carpeting is some missing tiles... is there any way to fill in the bare spots to put tile or linoleum over it. **

I'm sure there is but that is not my field. Try asking in Bob's "Floor & Tile" forum:


Dan O.


01:54PM | 02/17/08
Member Since: 02/16/08
1 lifetime posts
Mold can not be prevented where moisture collects.

RH can not be controlled with humidifiers and dehumidifiers.

If you disagree, don't read below because you are smarter than applied scientific fact and no amount of reason is worthy of your time.

The only method to control relative humidity is to precisely control temperature.

Heating and cooling methods with "on-off" control can not be effectively used to control RH. The best one can do with "on/off" temp control is to install a very expensive but cost effective temp control with small deadband. If the deadband is small and controls temp swings within plus or minus 1 deg F or better, then the RH will swing about 10% as the temp swings 2 deg F. Controlling room temp within 1 deg F is tough throughout the whole house with on;off controlls. If RH is controlled at 50% RH plus or minus 5% rh, the rh will swing from 45%RH to 55% RH which is about the best available on/off temp and RH control with conventional electrical HVAC control.

To precisely control RH at a healthy 50% RH and comfortable temperature of choise throughout the entire house - install a NESCO Amaizablaze cornstove with cornplace mantle at an installed cost of $1000 to $3000, depending on house size. or the NESCO,

If you have money to throw away,

have a home health concern that requires 50%RH (such as hospital and medical personnel) my suggestion is to install a cornplace cornstove.

If not, purchase a PID controller for the heating system of choice. For the PID controller to be economically viable, you will also need to install smaller heat pumps that actuate in stages. The first One to actuate should be small enough to runn full time - think small room fan size or window a/c size. The PID should actuate a second small HVAC system when the first one needs help. The PID control should actuate the third and subsequent when the former need assistance and so forth.

Humidifier and dehumififiers are not healthy choices and will not control room RH nor whole house RH. Physically impossible - sorry. Check the psychrometric chart.

Now to address the original black mold concern. Install a small $50 UV light inside the HVAC coils to control the black mold problem. The UV light must be installed inside to prevent inadvertant eye contact. Human eyes should be protected with UV sunglasses when in the presence of UV light.

BTW: The cornstove effectively controls room temp and room RH because the fuel and air flow are each individually controllable in an analog control system that never goes off. To control RH with a tennesseecornplacecornstove simply and slightly bump the fuel up or down until the RH becomes a fixed 50%RH with no swing.

One other technical fact about measuring Room RH. The reason you falsely perceive room RH to be stable with humidifiers and dehumidifiers is simply because the measuring device for $H has a time delay of 20 minutes or more. Room temp swings occur within less than 20 minutes and the humidistat never responds even though the room RH is swinging wildly.

To verify, either borrow or lease an $10,000 room humidistat or simply chech out a psychrometric chart on line.


06:20PM | 02/17/08
Member Since: 04/25/05
1915 lifetime posts
Unless one has million dollar artworks or antiques then one does not need tight control over the RH level in a house.

And if one wanted to control the humidity level that closely in a house then it will take a lot more than just having heat source that puts has proportional controls.

The tempature in every sq inch of the house would have to be exactly the same. Most houses don't have near the air distrubtion systems needed to maintain that constant of tempature.

Then there is the question of different sources of moisture addtion to the house. Bring 1/2 dozen people and the RH will go up. Likewise cooking and bathing add moisture. You don't want to have to raise the air temp just to keep the RH level down.

In most cases a simple exhaut fan is all that is needed.

But before one starts adding or changing out equipment the question of where the moisture is coming from. If there are any leaks in the house, if there is proper ventalation.

And insulation. Often all is needed for humid basements is to install a low perm insulation (foam sheets) which will raise the surface temp of the wall and reduce the RH.


01:03PM | 02/21/22
All right I have a similar situation in a couple of questions. Are these foam sheets supposed to be applied to the floor or the walls? I have some that are supposed to go under laminate but I had a flood recently and I had to remove all the laminate floorboards and their garbage. I have some extra foam sheets which I never installed. My floor is basically like a sort of natural stone tile. I live near the sea and this house is old and it seems like the humidity is rather high, I have issues with paint bubbling and well rotten furniture I guess you could say. I recently bought two dehumidifiers within the past several months I noticed one of them the drip hand seems to be filling with this sort of dirty water. I don't think it's necessarily mold but it is sort of like a grayish blackish residue when I pour out the water on the inside of the drip pan. Did your panel so has a sort of lid on top and I noticed the part where the water comes in it has the black residue there so it seems to be coming from the machine itself not just growing from inside of the water reservoir. The other machine I have is new I just started using it this week but so far I haven't noticed any sort of black residue in that one. It's hard to take these machines apart of course I take off the screen to clean it regularly but I haven't seen anything from the part that I can view that looks like mold or I don't know it's really weird. I guess I'm going to try to contact the manufacturer and see if they have any idea. I had another dehumidifier previously at another house and I don't remember it having this sort of black water dripping problem.

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