Dehumidifier in basement

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  #1  
Old 10-20-18, 11:31 PM
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Dehumidifier in basement

Added a 40 Pint Dehumidifier to my basement because I installed a standing shower, my question is... even if the shower hasnt ran for days making it a basic basement one way down or up and no door so its an open 100sqft basement. the RH levels have yet to drop below 45% and thats with the humidifier running none stop. I live in Ohio and the past week its been in the 50s outside but the inside temp stays around 67-70 (including the basement) I dont use the collector pan, I use a water line that dumps right into a floor drain, so now for my question, is water evaporating out of the floor drain and just going right back into the air creating this non stop cycle of taking the same humidity out of the air over and over? is a 40 pint dehumidifier not big enough for 100 sqft? whats going on here. even after a shower the humidity only rises like 2 RH, is my humidifier even doing anything?! is 45% RH low enough to keep mold away? Thanks.
 
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Old 10-21-18, 04:20 AM
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Some water is evaporating from the floor drain but it's a pretty small amount. The bulk of your water vapor is probably coming up through the slab or through the walls.

45% is low enough to prevent mold and It's about as low as you'll be able to get. The further you get below 50% relative the more difficult it is for the dehumidifier to extract more water. So, if you set your dehumidifier on 30% if might run continuously and never reach it even though the machine is working properly.
 
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Old 10-21-18, 07:06 AM
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I just checked your current outside temp (37) and RH (60) and it gives a dew point of 21°. Once that air is warmed up to 65° it would have an RH reading of 21%, so clearly your moisture is not coming from air leakage.

100 ft² is small so what is in the rest of the basement?
Is that space open in any way to other basement spaces?

When dealing with humidity I always recommend to pick up a humidity and temperature meter. You need both reading at the same time and location to calculate dew point which allows you to compare different areas, lower is better.

As Pilot explained very possible your moisture is coming through the basement walls and floor. In some cases landscaping to direct outside moisture away from the foundation can help.

As for the drain, where is that water going. If just into the soil under the slab it might as you suspect be contributing. Can you collect it into a bucket for awhile to bot get a measure on how much is being removed and if dumping the bucket down the drain helps any?

Bud
 
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Old 10-21-18, 07:59 AM
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Originally Posted by H3re2Learn
the RH levels have yet to drop below 45% and thats with the humidifier running none stop. I live in Ohio and the past week its been in the 50s outside but the inside temp stays around 67-70
Well, unless you're in a very dry, windy location like a bald mountain top you're seeking normal humidity. Most neighborhoods with grass, trees, creeks etc will have humidity.

The big thing to remember is that the percentages are relative humidity, e.g. how close to saturation.
As long as you keep your home above ambient temperature, the warm air will pull humidity out of the surrounding cool air, the furniture, and any standing water.
And you'll get around 1 liter per person per day from just breathing.

Unless you get a really cold mass of air, which is really effective at removing humidity, or a forced hot air furnace which is really good at removing humidity, it's actually quite difficult to keep water vapor from diffusing into warm dry air.
 

Last edited by Hal_S; 10-21-18 at 08:42 AM.
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Old 10-21-18, 08:06 AM
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I do have a digital gauge sitting near the dehumidifier and it currently reads 47% rh and 66 degrees. The drain is a trap that leads to the street. Its the very top of the trap so it always has water sitting in it. The walls are block painted white and the floor is slab painted grey, there are 2 sumps that only run on heavy rains and have plastic covers over the holes. Its an open floor joist ceiling unpainted. And its an open floor plan, just the staircase in the center and 3 jacks. The home was built in 1923 so it's old 3d block that looks really cool, ive never seen them before. I dont feel any moisture on the walls or floor. Doesnt mean it's not there though I guess.
 
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Old 10-21-18, 09:07 AM
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To make sure that the humidifier is working properly, disconnect the drain hose and let the dehumidifier fill the collection container . Just because it is new does not mean it is working properly
 
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Old 10-21-18, 09:28 AM
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I started off using the container which holds 2 gallons and it would take about 6 hours to fill it. Then I would dump it in the floor drain. So is an average 50% rh low enough to stop mold growth?
 
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Old 10-21-18, 09:37 AM
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Doesn't sound like 100 ft², more like 1,000 ft². Big difference on how much moisture you would be dealing with. Just the open floor joist ceiling makes all space down there common.

As for feeling any moisture on the wall you won't with moisture vapor, it goes straight to the air.

Relocate your digital gauge to other areas to see if you detect more moisture. Trick I use is to enter temp and RH into that calculator to get the few point. I then enter that dew point and 70° to get a new RH at a common temperature for all locations. Much easier to see where the highs and lows are. If you find a high area that could indicate the direction the humidity is coming from.

Block walls pose a problem in that moisture can move horizontally. I have encountered several times blocks filled with water all the way around a basement, several blocks high. It was impossible to know where that water was entering but it slowly evaporated through the blocks, in some places leaving efflorescence.

Bud
 
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Old 10-21-18, 03:05 PM
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Good catch Bud, it is 1000ft2 I had forgot a "0". IF the moisture is coming from the walls, would covering them with drylock help? I will begin moving my gauge around through out this week. Thanks.
 
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Old 10-21-18, 03:52 PM
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Unfortunately no, despite their advertising. According to their own specifications it is not a vapor barrier. Basically moisture, vapor or liquid needs to be l=blocked on the outside or managed on the inside and in your case it is entering in the vapor form so dehumidifier is the appropriate solution. Below 50 is reasonable. If you want or need lower then a larger dehumidifier.

The moisture concern is usually a summer problem as homes naturally exchange a lot of inside air with the outside and currently that outside air is very dry, 21% @ 65° as I posted earlier. The good news is, as the temps drop your RH should go down. Bad news is, next years warm temps will bring it right back up.

Question, what are you doing in the rest of the house to reduce RH (or create it by mistake)? Here are some activities to be concerned about.
1 Drying cloths inside.
2. Venting the cloths dryer to the inside.
3. Storing firewood inside.
4. Fish tanks
5. Lots of cooking without running a kitchen fan
6. Failing to run a bath fan for 20 minutes after showers.
7. Running a humidifier (like one built into a furnace).
8. Lots of people.

There are more but I'm sure you have the idea.

Bud
 
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Old 10-21-18, 05:22 PM
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Thanks for all the help, I was just concerned because the "internet" suggested RH to be 40>. Is all.
 
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