How do you know if you need a Dehumidifier???

I just bought my first home and have a ton of questions. The first being how do I know if I need a dehumidifier? The previous owner had one in the basement. The basement is dry but does have a drain in the floor which goes to the city system. Some days, the air in the basement is a little damp. The basement is 3/4 finished (of course with nasty 1950's panelling).
If I do use one, do I need to use it year round? Also, what size would I need, basement is about 700-750 Sq. Feet.
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If you do not have central air or ventilate the basement with it, the basement air is cooler, which cannot hold as much moisture. With an unfinished basement it is easy to tell if you need a dehumidifier, by condensation on cold water pipes or other dampness. With a finished basement, you do not want to wait for stains to appear, so a device that can measure relative humidity helps. I do not know how accurate they are, but something is better than nothing.
When removing humidity, the comfort range is considered 40-60%, so you generally want to get it below 60%. Also make sure that you maintain gutters to dump or direct rainwater away from the home.
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Joe wrote:

"The basement is dry", but "Some days, the air in the basement is a little damp" Decent dehumidifiers have a humidity detector that turns the dehumidifier on and off as needed. They also can be adjusted for the amount of dehumidification wanted. The dehumidifier would only be cycling on and off on those days when the basement is damp. My basement (~900 sqft) 25 pint Westinghouse dehumidifier hardly ever goes on in the winter, since there is less humidity in the ambient air. Since your basement is somewhat finished, I would spend the ~$130 or so, to keep the paneling, stored items, furniture, and other materials, from absorbing all that damp air.
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Get the biggest unit Sears makes on sale for $200. Set it for the level you want and let it drain into the drain. Worry about other stuff.

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Joe wrote:

The prior responses I think did a good job of answering your question. I will try to answer your next question.
When shopping for a dehumidifier be sure to find out that specifies that it is designed for cool damp areas and/or basements. One would expect that a dehumidifier would be designed to work in ... well cool damp areas, but not so.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
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The top of the line Sears Kenmore can do it.

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If the carpet is damp and there is mildew on the walls, that's a pretty good indication. HTH :-)
Bob
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