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Old 05-25-2011, 07:30 PM   #1
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Best Way to Dehumidify Basement?


My wife and I have recently moved into a three-bedroom townhouse. There is a basement, first floor with kitchen, bathroom and living room, and an upstairs with the three bedrooms and another bathroom. I presently run my online business from the basement (where I store a great deal of merchandise - which I don't want affected by moisture.) The townhouse is equipped with a HVAC central air system. There is a pipe leading from the first floor into the basement which blows cold air into the basement when the AC is on. As far as I can tell there is no return from the basement back upstairs.

At present the townhouse is comfortable enough to not need the AC on. The air in the basement feels damp and the air temp down there is always cooler than in the rest of the house.

I'm trying to get rid of the humidity in the basement and am wondering if it's better to run a dehumidifier in the basement and keep the AC off, or if it's better to just run the AC all the time, without the humidifier in the basement. Like I said, there is a pipe which puts cold air into the basement, but no return back upstairs. I'm not sure if running the AC AND the dehumidifier at the same time will just cancel each other out (and cost double in power).

Any help someone can provide on my best solution would be greatly appreciated!

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Old 05-25-2011, 07:51 PM   #2
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Best Way to Dehumidify Basement?


A GOOD quality Simplicity de-humidifier with a digital display so you can set it at 40% RH is what I recommend and use in my basement. As it de-humidifies it gives off heat which is a bonus as it warms the basement. We NEVER want to shoot cold air from the AC into the basement. Hot air rises and cold air settles so you want to force it upstairs. Dehumidiifers are rated in pints/day removal so by a medium capacity one and not the smallest or it won't keep up and will never stop.

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Old 05-25-2011, 08:08 PM   #3
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Best Way to Dehumidify Basement?


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A GOOD quality Simplicity de-humidifier with a digital display so you can set it at 40% RH is what I recommend and use in my basement. As it de-humidifies it gives off heat which is a bonus as it warms the basement. We NEVER want to shoot cold air from the AC into the basement. Hot air rises and cold air settles so you want to force it upstairs. Dehumidiifers are rated in pints/day removal so by a medium capacity one and not the smallest or it won't keep up and will never stop.
I have a old dehumidifier with a 1-10 dial on it that works pretty well. I plan on hooking it up and draining it into the floor drain near the washing machine.

You said it's not a good idea to AC the basement - should I block the AC vent into the basement?
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Old 05-25-2011, 08:34 PM   #4
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Best Way to Dehumidify Basement?


Getting the air moving down there and pulling the moisture out with a de-humidifier works. Also, having a cold-air return in that space helps also to cycle the air. I only run my dehumidifier in the early spring and mid fall when our air conditioner & heat are not running. Humidity stays between 55-65 down there all the time, temp around 62 in Winter, and 72 at the highest point in the Summer.
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Old 05-25-2011, 08:57 PM   #5
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Best Way to Dehumidify Basement?


I would block the vent to the basement or you will find out in a hurry that your rooms on the top floor are going to be very hot. Hot air naturally rises quickly and those rooms are always difficult to cool at the best of times due to them being the furthest from the furnace and having the most pipe and restriction to airflow. The basement does not need cooling. I can keep my humidity down to 40% in the basement but I live in a semi-humid climate. Average outdoor humidity is around 50% RH where I am. I like to keep it lower in the basement so no mold grows and any clothes or other items I have down there don't get a moldy skunky smell and ruined. If it is an old dehumidifier/over 6 yrs old you may want to buy a new one. They can use a lot of electricity and the newer ones are more energy efficient. They are nothing more than a small bar fridge with a fan. They have a compressor and freon and a cooling coil and the compressors wear out. Then they run non stop and don't cool well but give off heat. Mom's unit wore out and ran non stop but did very little cooling/dehumidifying. You can put your hand on the cooling coil above the drain bucket with the bucket removed and running and it should get very cold. If not it may be worn or lost some freon and not worth repairing.
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Old 05-25-2011, 09:24 PM   #6
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Best Way to Dehumidify Basement?


Actually incorrect Yuri. If the system is designed properly, letting air into the basement is not going to cause any side effects to the main floor. Only time the upper spaces get hot, is if there is insufficient air flow, improperly placed cold air returns, and sun allowed to heat the South side up during the day, and west side during the late afternoons. That with improper amount of insulation, and air leaks not sealed also cause cooling & heating problems.

Opening up one or two vents in the basement and having a Cold air return, or not closing the door going down to allow air movement is the best solution, along with running the de-humidifier to get the space down to a good RH & temp. Telling people to close the vents in a space is the worst way to not keep the space conditioned & kept warm during the Winter.
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Old 05-25-2011, 09:51 PM   #7
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Best Way to Dehumidify Basement?


Closing the vent increases the static pressure and forces more air upstairs. We also don't take any return air from the basement. Guess it is just a different way of doing business/HVAC across North America. There is not a single house in Winnipeg with an open AC vent in the basement. Most runs to the upstairs are done in 5" and with 6 or more elbows and 20-40 feet of pipe it is awfully hard to get air up there. If I had it my way they would all be 6" but the builders save $$ and don't design ductwork for proper airflow. Architect makes a wonderful looking house and the HVAC contractor has to work around his work of art. Furnace gets unceremoniously dumped under the stairs or in a corner. House construction techniques and layout varies greatly across North America but we don't AC our basements here.
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Old 05-25-2011, 09:54 PM   #8
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Best Way to Dehumidify Basement?


The townhouse in question is a rental unit so just adding a return in the basement isn't an option. Is there a reason why there would be a pipe with AC heading to the basement but not a return back to the upstairs?
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Old 05-25-2011, 10:00 PM   #9
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House construction and ductwork theories vary a LOT across Canada and North America. Some builders try use the stairwell for return air as it settles and don't run return ducts upstairs. I don't like that idea. Saves $$ for them. They cut 1" off the bottom of the doors and use the stairwell. We leave our doors uncut and run RA ducts. Costs more and I don't like the central return stairwell and grill concept but you may have it. If you don't have enough supply vents closing one can overload the blower as it needs to move air thru a minimum amount of vents. I would have to see if they are sized correctly. If not enough air is moved the AC coil can freezeup. Recommend you get the freon level checked and get the tech to check the airflow if you want to try close that vent.
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Old 05-31-2013, 02:36 PM   #10
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Best Way to Dehumidify Basement?


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Originally Posted by gregzoll View Post
Opening up one or two vents in the basement and having a Cold air return, or not closing the door going down to allow air movement is the best solution, along with running the de-humidifier to get the space down to a good RH & temp. Telling people to close the vents in a space is the worst way to not keep the space conditioned & kept warm during the Winter.
We are in Chicagoland and have a full finished basement that is way to cold and humid during summer with AC on. We have vents and cold air return in the basement. I will heed your advice and leave a couple vents open. I would have thought the AC cycling would remove much of the moisture in the basement but for some reason the humidity level doesn't seem to go much below 50% with temperature around mid 60's. Does this mean I need to have a dehumidifier to keep the moisture low? Thanks

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