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Thread: dehumidifier help

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    DIYFK member mcaquatic's Avatar


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    dehumidifier help

    Hopefully someone can steer me in the right direction. My fish room is about 22 ft by 14 ft and holds a little over 2000 gallons of water. The room is kept between 74 and 80 degrees. During the summer the humidity was kept in mid 70's % with a ventilation fan out the window. Since I sealed off the window to help trap the heat for the winter my humidity has been sticking at 85-90%. I want to get a Frigidaire dehumidifier but do not know what size to go with. The 70 pint seems to big. Will the 30 pint be enough or should I go up to the 50?
    thank you

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    DIYFK member Meep's Avatar


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    The bigger question is how often do you want to empty it? Or can you drain it right into a floor drain and thus avoid constant empyting?

    I have one that is about 30 pint capacity in my basement (100+ year old farm house rock wall basement, so not exactly as dry as modern basements) and during humid weather it can fill up every day, and I don't currently have any tanks in the basement that is just natural moisture...

    Evaporation is dependent on surface area, so you need to take the surface area of all your tanks and estimate about 5-6mm of evaporation a day and see how many pints of water you can expect those tanks to give off each day...

    To put this in perspective, lets take a common 180g factory tank... Top dimensions are 72.5" x 18.5" or about 1341 square inches if we estimate about 0.25" of evaporation a day it comes out to about 335 cubic inches of water, or 1.45 gallons (11.6 pints) of evaporation a day... With that said if you had that single 180 gallon tank in your basement you could expect to empty a 30 pint dehumidifier every 2 days just for the tank evaporation, plus some extra depending on how much the ambient humidity is that could easily mean emptying it every day...

  3. #3
    DIYFK member mcaquatic's Avatar


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    Click here to enlarge Originally Posted by Meep Click here to enlarge
    The bigger question is how often do you want to empty it? Or can you drain it right into a floor drain and thus avoid constant empyting?

    I have one that is about 30 pint capacity in my basement (100+ year old farm house rock wall basement, so not exactly as dry as modern basements) and during humid weather it can fill up every day, and I don't currently have any tanks in the basement that is just natural moisture...

    Evaporation is dependent on surface area, so you need to take the surface area of all your tanks and estimate about 5-6mm of evaporation a day and see how many pints of water you can expect those tanks to give off each day...

    To put this in perspective, lets take a common 180g factory tank... Top dimensions are 72.5" x 18.5" or about 1341 square inches if we estimate about 0.25" of evaporation a day it comes out to about 335 cubic inches of water, or 1.45 gallons (11.6 pints) of evaporation a day... With that said if you had that single 180 gallon tank in your basement you could expect to empty a 30 pint dehumidifier every 2 days just for the tank evaporation, plus some extra depending on how much the ambient humidity is that could easily mean emptying it every day...
    thank you for the great reply as always. The unit would be draining into a floor drain so emptying is not an issue. Not sure if size affects efficiency? . I have all tanks covered to minimize evaporation but I need to go back and get tighter fits. I have a ventilation fan I use in the summer but can't in the winter since allows too much cold air in. The floor drain and efficiency influence your thoughts at all?
    I know these are expensive to run should I be looking at an air exchanger? Can they be bought and installed reasonably?

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    DIYFK member Meep's Avatar


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    Click here to enlarge Originally Posted by mcaquatic Click here to enlarge
    Not sure if size affects efficiency?
    Hard to say, read the specs on the two models and compare overall dimensions, also if they have 'energy' ratings check those... Just a guess but I suspect that in many cases they are the same size condenser just bigger water holding tanks

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    DIYFK member PaulPerger's Avatar


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    Meeps calculations seem accurate, so you need to determine how much evaporation you need to deal with. The capacity, 30 litres, 50 litres, etc. are generally the maximum volume of water that unit will remove, not necessarily it's holding capacity. I had a unit in my previous home that was rated at twice it's holding capacity because it was intended to be drained directly and basically bypassed the tank. Also keep in mind that you probably want about double the capacity you need or your unit will run constantly.

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    DIYFK member cornclose's Avatar


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    The less the relative humidity of the air in the room the more evaporation will occur, all other things being equal.

    If you place a dehumidifier in the room you will force more evaporation to the extent that dehumidifier will always fill/always be taking water out of your tanks. Unless the moisture is not predominantly as a result of evaporation from the tanks of course..

    Why do you want to reduce the RH in the room ? Apologies if I missed that..

  7. #7
    DIYFK member Meep's Avatar


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    Click here to enlarge Originally Posted by cornclose Click here to enlarge
    Why do you want to reduce the RH in the room ? Apologies if I missed that..
    Because when you get that much water in a enclosed space like a house it will drive up the humidity in that enclosed space, the risk of promoting mold growth, condensation, musty smells and what increases exponentially resulting in the potential for serious damage to the house... There are also real life heath issues that come into play with high humidity in your house... High humidity promotes and causes bacterial, viral, fungal and other potential 'baddies' to thrive... High humidity also causes some unwanted critters to thrive, mites for example thrive in 80%+ humidity but mostly die off or have a very hard time surviving in 50% or less humidity... And last but not least, high humidity destroys modern electronics, humidity issues are one of the leading causes to electronics failing... So you are left with two options, vent the room to control humidity or use a dehumidifier to control humidity, ideally you want the space to be between 40%-60% relative humidity sure keeping the room at say 50% humidity will cause more evaporation then letting it rise to 70% humidity but on the flip side maintaining 50% humidity has many other advantages...

    Of course how serious this can be and become varies by region and setup...

    For example, if you live in an area that experiences freezing temps, even a few 55 gallon tanks in a room can cause excessive humidity build up that causes the windows to condensate and thus promote water damage to the surrounding area... Depending the setup this can jump things like bubble wands, floating bed systems, trickle towers and what not exponentially increase evaporation rates...

    If you want to decrease the evaporation rate of the tanks as you reduce the ambient humidity in the room with a dehumidifier, it's best to put hoods and/or lids on the tanks to isolate them a bit...

  8. #8
    DIYFK member mcaquatic's Avatar


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    i vent the room in the summer and it works ok. I wish I could use the ventilation fan in the winter but I loose too much heat/cold air rushes in and cools the room too much

  9. #9
    DIYFK member Rodent's Avatar


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    An air exchanger may be a good way to go if you have the space. If you get one with heat recovery it won't cost as much to run as one without. But they can be quite expensive if I remember correctly. Here is one units website...

    http://www.broan.com/products/produc...a-c2cc54599220

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