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  1. When my husband and I moved into an older house it had a really bad musty odor. We could not figure out what was causing the odor. We tried doing repairs, but nothing worked. The neighbor across the street (also with an older house) told me about a odor eliminator that she uses. It’s called Room Shocker and it worked great! It is environmentally friendly too! You can find it at

  2. Hi- I’m at a loss right now because my parents went away on a cruise and I’m stuck taking care of the house. I have a house with no basement/crawl space with the ducts built into the concrete slab. After big storms, like this week’s Hurricane Irene, our bottom floor vents get filled with water. I used a wet/dry vac to suck up the water (it was about 2 inches). This process took two days because I didn’t have electricity for some time. However, now there is a mildew smell in the house when I run the fans and I am afraid of mold. Is there anywhere I can spray something to get this smell out? My parents just bought a new air conditioning unit (A-coil and central air condenser) about a week ago. There is an attic space in the upstairs master bed room. Is there a way I can get to the ventilation up there to spray something to get the smell out? Any help would be appreciated.

    • Hi Antoinette,
      The longer the air ducts located under the slab are wet, the higher possibility of their contamination with mold. Since this isn’t the first time the air ducts got flooded there might be mold already. It feeds off of the moisture and prefers dark areas making wet in-ground air ducts a perfect mold growing environment.
      Not having standing water inside the visible portion of the air duct does not indicate that there’s no water / moisture along some lower sections of the ducts / you might not see it after removing the register(s). If the grounds are heavily saturated this might be the case and even constantly running the fan won’t help in drying it nor removing that musty air duct smell.
      The best option would be to consult an HVAC contractor about eliminating floor air ducts / registers, rerouting them to the ceiling / wall, and sealing-off the floor openings with concrete or expanding foam. Might not be an easy task to do but if your parents plan to stay in this house for a while, it would completely eliminate musty smell and air duct flooding problem.
      Spraying some scented aerosol into the air duct will only help to eliminate this musty smell for a short period of time, which is only as long as this scent stays active. Longer lasting solution would be to attach scent emitting devices (just like the one you put in your car) or scented wipes on / under each of the air supplying registers.
      Even if you’re not constantly using air conditioning system, set the fan to ON position (there should be such option on the thermostat) and let it run constantly. The AC will still kick in on its own whenever the thermostat calls for it. Circulating air will speed up drying process lowering possibility of mold growth inside the air ducts.
      There are chemical agents that can be used to kill the mold spores inside the air ducts but complete process involves cleaning the air ducts interior surface first and then applying this chemical onto the cleaned surface. There are also “fogging” devices that can distribute mold killing chemicals with the air stream as well. However, without completely eliminating the source of the moisture and air ducts flooding all types of chemical delivery would be only a very temporary solution and waste of money.
      Let me know if you have more questions.

      • Hi Dariusz,

        The advice you gave Antoinette seems right on for my issue too. Have the slab and after all the rains there was a swishing thumping sound from the vents indicating water has creeped in to the ducts. The sound is gone, smell remains so my question is approx how much will this cost to repair? (sealing the ground vents with foam then concrete and have new vents placed in the attic for redirection of air flow). Fan is running and smell is decreasing.
        Thanks in advance

        • Hi,
          Difficult to estimate without examining your property. Sealing of the floor registers is the least expensive part of the job, all you need is a bag or two of concrete per register and / or some expending foam. Register covers can stay in place so you wouldn’t have to cover those openings with carpeting or whatever floor finish you have. For re-routing the duct work you’d need to bring an HVAC contractor (I’d try at least 2-3) and explain your situation. There might be more than one way of doing it and different contractors may have a few suggestions. If the attic is open and accessible it is just a matter of getting the main air feed up there and installing insulated / flexible air ducts (quicker and less expensive than sheet metal work).

  3. Hi! A couple of yrs ago my husband decided to paint the basement walls. He scraped them down w/o
    wetting them first & DID NOT turn off the A/C sytem. Now we are experiencing a really heavy musty
    smell when the A/C is on. What can we do? We are linited in funds so this will have to be a diy job.
    Thank you.

    • Hi Wanda,
      I’d need more information to give you some advice on that musty smell from your air ducts. Where are the air ducts located? – ceiling, walls, floor. If under the floor (sometimes partially), is there a partial crawlspace (wet/dry) in the house and they are suspended under the floor frame, or the air ducts are partially under the concrete slab / ground. Did you open the floor level registers and look inside the air ducts for moisture / water (using mirror, flashlight and or simply by taking pictures with digital camera).

      Is your furnace / air handler located on the lowest level and blowing air down, to the air duct system beneath the floor surface, is it in a crawlspace, attic, basement. Do you use central humidifier attached to the air distributing system (for cold season… if you have a cold season at all)? Did you check your air filter?

      When was the last time your AC system (“A” coil compartment) was opened and checked / cleaned by a professional? Can you see condensate draining from your coil when AC is operating? Do you have a sump pump / drainage system in / around your home? Have you recently experience long periods of rain… Describe everything in as much detail as possible. I don’t believe that painting your basement 2 years ago has anything to do with that musty smell. Let me know those details so I have a better “picture” of your situation. Thanks.

  4. Are there any foundation worries if you just seal the vents when water has entered as a solution for slab with no crawl space where ducta have water in the floor?

    • Hi Sean, I’m not sure if I understood correctly… Your house is on a concrete slab (no crawl / no basement) and the air ducts are embedded into that concrete slab / partially (most likely) into the gravel, sand, dirt under the slab. There’s either a high water table or whenever it rains the air ducts fill up with water.

      I’m not sure how much water are you getting but the air ducts probably don’t overflow inside your house? Ideal solution would be to develop a drainage system around the house foundation and divert all that excess of water away from the structure as far as possible before it penetrates the foundation wall.
      This is assuming that the air ducts aren’t constantly flooded which would be the result of a high water table (you’d most likely need a sump pump in that case) or sometimes a broken water line – I’ve seen that a couple of times.

      After the drainage system installation you could seal the vents with concrete or some other material.
      Right now, that water inside the air ducts evaporates (probably) naturally and with the forced air system’s help (I know that it isn’t healthy). If you seal the air ducts without taking care of the drainage issue there might be water standing inside the air ducts constantly, possibly saturating the concrete and elevating moisture levels inside your house (unhealthy too).

      I don’t know how deep your foundation is, what type of a structure it is supporting (single story or more), if your home is in the freezing zone, how is it positioned (terrain surrounding the house), and how much water penetrates your air ducts. Therefore, I can’t really answer your question concerning the foundation. I would suggest consultation with a local drainage contractor and foundation specialist. Let me know.

  5. well the ducts in the master bedroom must be blocked there is no air coming out of them and the other two rooms to the west have about one inch of water standing in them.well i am puzzled?

    • Maybe there’s a lower spot inside the air duct, not visible for you, where the water level is higher than 1″ / blocking the entire air flow…

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