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  1. #1
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    Nov 2019
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    Whole House Dehumidifier/Attic sealing Question

    Hi I live in Miami Beach in a low lying area which has continual flooding and a water table that is inches below my dirt crawl space. Our crawl space has water coming out of the ground during rainstorms and water events in the summer through king tides. I have a sump pump that constantly is going even when it hasnt rained for days, so there is no way to stop the water from coming up. I decided to spray closed cell foam on the underside of my flooring to act as a vapor barrier as opposed to put one on the ground. Since i moved in a few years ago we have experience higher than normal humidity ranging from 50% to 70% depending on the time of year. It is a two story house and the 2nd floor is much more stuffy. We have closets that at times can get 95% humidity where the towels will get moist. I have 15 year old HVACs that dont run very long, it seems as though they arent de-humidifying because they arent on that long, so we bought some portable dehumidifiers to help as a bandaid. I have consulted some local hvac people and one went into our attic and suggested that the eaves and soffits are allowing too much humid air into the attic and causing a lot of the humidity to come down into the house. He suggested sealing the attic completely and also putting a dehumidifier in the attic and also putting carrier hvac units with dehumidification capability to help with the issue.

    Obviously with a 1.5 yr old i am concerned about healthy air and we have REMY Halo filters in each of our units. I wanted to know if this guys suggestion is generally accepted solution, or should we consider a whole house humidifier system which regardless of the a/c units, will continually dehumidify the house. I am not sure what to do at this point. My AC/s are definitely old so it probably makes sense to get the new units, but what about the attic?

    any advice would be appreciated and if anyone knows a really good south florida service provider that has experience with whole house dehumidifiers i would welcome that info as well.

  2. #2
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    A crawlspace that floods is the toughest problem. I suggest a bubble pack plastic like on a pool. The plastic would float on top of the water. Fasten the plastic to the wall with a strip of plastic. I assume that you do use the crawlspace for anything. After plastic that can rise and fall with the water level, close the vents and provide some dehumidification.
    Your foam idea is ok but you will need a plastic vapor barrier below the foam because foam is not perfect. Also the space below the vapor barrier will be a mold farm and probably stink. Plastic floating on water if air tight will not grow mold.
    Plastic on water water with the vents sealed will not be difficult to control with a dry home above.

    Attics are damp, but if well vented with soffit vents and ridge vents with well insulated ducts usually get by.
    Your a/cs need a good setup to assure that the cooling cools are cold enough to remove moisture during normal high sensible cooling runs. By measuring the a/c return air temperature/%RH from the home to the a/c and a/c supplies, the amount of moisture removed by the a/c can be checked. Measure and report temp/%RH return and supply.
    A well setup a/c can remove +3 lbs. of moisture per ton per hour. By adjusting the air flow of the a/c, the amount of moisture can be increases. During evenings and rain days supplemental dehumidification is needed.
    Correct installation of the dehumidifiers in your home can also warm the cold supply ducts to avoid sweating ducts in the attic. The idea is that the dehumidifier supply is routed to the a/c supply duct. This warms the duct a few degrees to avoid condensation in the attic.
    Sizing also critical.
    Find an a/c contractor willing to listen to advice and all this can be worked out.
    Enough for now. Your thoughts?
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  3. #3
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    Nov 2019
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    Thread Starter
    Thank you - this is really good feedback. I guess the challenge would be to be able to hang some type of dehumidification in the crawl space so that it didnt impede the plastic vapor barrier from floating on top of any water below. It sounds like you are opposed to sealing the attic and dehumidifying it, I have spoken to a few people who have different engineers telling them that sealing and insulating the attic and then dehumidifying was the way to go.

    Drew

  4. #4
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    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Just to make sure that you understand a bubble plastic pool insulation that will float on top of the water in the crawlspace will contain the moisture under the plastic that will grow mold and will rise and fall with the water keeping everything above the plastic bubble pack dry. The same dehumidifier that will keep the home dry will also keep the crawlspace dry. The vents are closed and water is below the bubble pack that is fasten to the wall. This is the same way we handle an indoor pool surface.
    A 100 pint per day whole house dehumidifier will handle 2,500 sq.ft. home and the crawlspace, maintaining <50%RH throughout. This would include a 100 cfm of fresh filtered air to purge the indoor pollutants and renew oxygen.
    Comfortable and healthy.
    Keep us posted on your thoughts.
    Regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  5. #5
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    Nov 2019
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    Thread Starter
    Are we talking about a whole house dehumidifier system hooked up through my AC ductwork? I am just curious how the crawl space which will be sealed will benefit from that dehumidifier if there is no connection to the house. Or are you saying there should be a dehumidifier in the crawl space itself?

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
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    Quote Originally Posted by Dakworks View Post
    Are we talking about a whole house dehumidifier system hooked up through my AC ductwork? I am just curious how the crawl space which will be sealed will benefit from that dehumidifier if there is no connection to the house. Or are you saying there should be a dehumidifier in the crawl space itself?
    Depending on the size of the crawlspace. If less than 1500 sq.ft., a supply from the main whole house may handle the space. A separate dehumidifier makes it simpler. Where are a/c air handlers located and how big are they?

    A fresh air change in 4-5 hours when occupied is suggested to purge indoor pollutants and renew oxygen. Maintaining <50%RH controls mold/dust mites and is comfortable. This is critical.
    Keep us posted.


    regards Teddy Bear
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  7. #7
    Join Date
    Oct 2019
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    The area you live in and the circumstances really calls for a perfect humidification control. sealing the crawlspace as tedyybear suggests will only aggravate the situation and i think you will have to deal with the stale smell of water as well. If you are considering buying humidity control systems and also changing your HVAC then why don't you consider ductless HVAC system that has inbuilt dehumidifying system and its anti-fungal system resist build of mold. If your attic has high humidity you can add one there too and adjust timing for it from the online app that controls the system. You can have separate for every area and this way you can improve the air quality as well as regulate humidity levels. Moreover. you can get heating in the winters and cooling in summer. So there will be a three in one solution for you .

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