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Old 08-30-2008, 11:30 AM   #1
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Basement humidity


Like most folks, my cellar has a high degree of humidity during the summer months. If left unattended, metal will slowly form rust and mold will grow on certain surfaces. I have used a dehumidifier for the past two years which has solved the problem by keeping the humidity at around 50%. Unfortunately this luxury of dryness is costing me about $60 a month or $300 per season. The dehumidifier, which is almost constantly on, is only two years old and comes with the green star of energy efficiency. Still, it seems a high price to pay for a dry basement. Is there an alternative solution I could use, such as slow moving basement window fans to circulate the air flow throughout the area? Any help greatly appreciated.

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Old 08-30-2008, 01:06 PM   #2
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Basement humidity


You're not alone - and even though that may be of little consolation and doesn't pay your bills, other people have the same problem and so it is reasonable that a liveable solution is around somewhere...look, first there are about 5 separate ways that moisture can enter your basement and oftentimes all 5 are in play. Sometimes you get lucky and perhaps only 3 are active but that still means the same outcome: mould and mildew...

Is the ground outside sloped away from your house? do the eavestroughs drain away from the house or down along the foundation walls?

But I think you'd best first tell us what size basement you have and how it is made, if you can see the walls, or it is a finished basement? is it insulated? in what part of the world are you located?

Actually what I can tell you for free, is that 80% of houses are under-ventilated and people work more at making them so than perhaps anything else. Some think that caulking around the windows and doors is all there is to lowering one's heating bills, while at the same time they don't do anything to remove the stale air they have just prevented from getting out of your house. They also surround themselves with plants and ignore the fact that they give off moisture too. So by all means, and especially in the basement, increase air circulation, by putting in fans or turning on the fan in your furnace. Anything to keep the air moving will reduce your humidity and mould levels.

At 50% relative humidity (RH) down there, you're on the borderline of damaging mould growth if the temperature is close to 65 deg and up. Therefore, your dehumidifier isn't being effective. Sure it's energy efficient and all that but saying that is the same as saying: why can't a Honda engine drive an SUV? It's not the right size, that's why. Efficient? sure is, but not the right size to move an SUV. It takes a bigger engine. Your basement may be 700 sqft and a 17-pint dehumidifier too small to dehumidify that area. It may take 45-pint or larger...size matters!

Knowing where you live makes a difference to one way of reducing the humidity problem.. Can we assume "MA" is in the Northeast US?

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Old 08-31-2008, 09:44 PM   #3
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Basement humidity


Please accept my apologies as I was in a bit of a rush to post the original message. My profile is updated to include the usual as well as regional location. The overall size of the basement is 1200 sf, is unfinished with a poured concrete foundation. I have had a minor to moderate flooding problem during very heavy rains and recently had French drains with a dual sump pump system installed. The jury is out until the next heavy rain storm as to if the new drains actually work or not. I have also graded the landscape to direct runoff away from the foundation as best as possible. The Honda, er, dehumidifier is labeled 50 pts / 24hrs, which Im assuming is adequate. Im disturbed to know that mold can flourish at 50% humidity at 65For >, which is the average ambient temp at this time of year. I havent noticed any mold or rust since Ive been using the non-efficient appliance for the past two years though. I was suspecting that if I drew the hot outside air into the cool basement with window fans I would be contributing to the moisture problem. If this isnt the case then Ill install the fans asap. But to return to my original question, does this electrical bill seem par for the course?
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Old 09-01-2008, 03:06 AM   #4
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Basement humidity


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Originally Posted by myca View Post
I was suspecting that if I drew the hot outside air into the cool basement with window fans I would be contributing to the moisture problem. If this isnt the case then Ill install the fans asap. But to return to my original question, does this electrical bill seem par for the course?
You most certainly will make it worse if you do this! Any air you bring in has to be drier than whats already there. Alot of times dep on where you live summertime is humid.If you just bring in more heat and humidity...you are making your situation much more worse as that is an even better growing environment for mold. Also just running the furnace fan many times will just boost the humidity of the entire house and not lower it one iota in the basement itself. I've seen this in my own place. If you can put it on intermittent circulation the total house humidity wont rise as quickly but the basement levels will nevertheless remain the same. what you need is a larger capacity dehum like a santa fe or aprilaire1700 but the will cost you. The elec bills you are paying seem a little high but that depends on its cost in your area. what you need to do is find out how many watts that dehum is using evry 24 hours and the price per watt. The larger capacity dehums are more efficient, and will actually lower the humidity for the entire house including the basement and wont run 24/7 to boot but they cost so you have to figure out your length of payback.
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Old 09-01-2008, 07:08 AM   #5
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Basement humidity


Your dehumidifier rating at 50 pints/24hrs should be well suited for the size of basement you have; above and beyond actual size is the efficiency of it, but that's a moot point. Some experts say dehumidifiers are most useful down to an indoor temperature of 65 F; temperatures below that cause some units to ice up, in addition to simply working less efficiently and wasting money. But all things being equal, your unit is doing what it should. How much water do you remove physically every day? a full container, or just a cupful or so?

You also seem to be doing as much as you can about the flooding in installing French drain and the sump pumps; that's excellent. The french drain system and the sump pump which are connected to it will take care of water underneath your house. If the sump pump pits regularly fill with water and are then pumped into the French drain system, that is what is happening and your basement will become drier with time. Of the 5 different methods by which moisture can enter your basement, you have taken care of 2. Next in line is that which is coming in via the walls.

Please note that we are not trying to turn your basement into the Sahara desert - just trying to keep the moisture level in check. Ideally, and most practically, the humidity level in the basement will be around 40% on average year-round. Less during the winter (say 35%) and more during the summer (say 55%). A cheap hardware store humidity guage is most useful here. But these levels will be slightly higher (by 10%) than the rest of your house, where there is hot air pumped around by your heating system - but less moisture coming in. So one way to dissipate that moisture is to have the fan on your furnace if you have one on all the time. Better yet are fans down there not necessarily from the outdoors in, just blowing the air around.

To bring in air from the outdoors, you'd have to turn on the fans when the RH outdoors is less than that indoors, so you'd have to either follow the weather forcast constantly, or get a guage for the outdoors, and the turn the fans so that the air is either expelled or brought in, depending. That's a lot of playing for most people.

The fact is that at 60% RH, moisture will promote mould growth if the air is still. Keep that same air moving and the chances go down. Lower to the RH to 45% is a good step to making sure it never happens...

OK; so now you're like millions of homes: manageable RH in the basement. Now you can set your sights on the walls where probably half the moisture is coming in. An easy DIY thing is to insulate the walls with the 2-inch pink T&G polystyrene boards (2'x8') glued together and glued to the walls, once the wall are made flat. Tape the joints with that red tape and bring the boards down to about an inch from the floor. Insulate the cavities between the floor joists with fibreglass insulation and your temperature will go up down there by about 5-10 degrees F. Then perhaps do the floors...by heating up that space, the RH will go down a bit and away from the danger zone, making the measures you have already taken more effective.

Ultimately, you may not need to run the dehumidifers as much; that saves you money in the long run, probably enough to pay for the foam boards you've just installed...

Make sense?
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Old 09-01-2008, 08:25 AM   #6
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Basement humidity


Adding the additional insulation in the basement sounds like a viable suggestion. Ill also set up a fan or two to help circulate air throughout the area. As far as extracted water goes, I was empting a full container (guessing about a gallon) per day but was told it was ok to let it drain into the sump pump well. I initially thought I would just be recycling the moisture from the air into the well and back into the air again but told this wasnt the case. I appreciate all the replies and feel more equipped to deal with the situation.
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Old 09-01-2008, 09:01 AM   #7
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Basement humidity


OK - so everything is working fine.

By my calculations, you have about 5 lbs of water in your basement air at this time and your dehumidifer is removing about that every day or so. Approx 10,000 cuft of air at 50%RH and 65 deg F. This also means that any object whose temperature is 46 deg F or less will act as a condensor. ie. that moisture will form on it much like moisture forms on a cold beer can on a hot afternoon.

So, if your walls are around 45-50 deg F - as many are - moisture will condense on them and then mould will start to form. Hence the insulation.

And yes, outletting the water into a drain is fine for removing water; at those temperatures it won't re-evaporate and become a problem. So good-bye H20!

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