I am going to agree with previous posters on several accounts: 1. Depending on where you live and how much annual precipitation your area receives, you may not need a humidifier. 2. Live in the house a little before you purchase a humidifier. This is a good idea for a couple of reasons, one of which is you will want to establish some kind of baseline by buying one of those little digital indoor climate readers that gives you humidity and temperature readings so you know what you're dealing with, and only then will you know the size of dehumidifier (or number of dehumidifiers) you'll need. 3. If you NEED a dehumidifier, do not go too cheap or too small. Read lots of online reviews and make sure you get the right size with the right drainage options. If you're not using the basement frequently (i.e., not planning to check on the unit several times a day during spring rainy season or the humid days of summer) and live in an area with a long summer + high humidity, you may need a larger unit with built-in pump options and a hose attachment that drains to a sink/sump pump. Too big and powerful with infrequently used pump and outlet hose options is better than too small with no pump and no hose options that you have to remember to dump every 3 hours to keep the humidity down to 70% (which is, BTW, waaay too high for most basements). You will end up spending a lot more in the end if you have to deal with mold/moisture remediation.

There are some threads at GW on dehumidifier brands. A central dehumidifier would be quietest, as it's part of the central HVAC system, which is usually in a separate room. However, the cost will be five-10 times that of a stand-alone unit. FWIW, I've always used basic stand-alone models from Woods. The EPA says 30-50%RH; CMHC (Canada Mortgage and Housing Corp.) says below 60%; Woods recommends 50%RH. This post was edited by worthy on Mon, Apr 15, 13 at 18:38

Get a dehumidifier. Here's the problem with what was said: Air that can hold more moisture is a good, not a bad, thing because you are talking about relative humidity -- the amount of moisture in the air relative to what it can hold at its temperature: So, by doing nothing other than warming air, you can lower its relative humidity. If you were to put a heater in your basement and warm it from, say, 65 degrees to 75 degrees, you would drop the relative humidity of the basement because, even though the air has the same absolute quantity of moisture in it, the 75 degree air could hold more than the 65 degree air, so the relative humidity is less. But a dehumidifier is even better than a heater because it removes moisture in two ways -- it drops the air to a temperature below its dewpoint, removing actual moisture, and then warms the air, lower the relative humidity further. An air conditioner is a problem for at least two reasons. First, because it cools as it dehumidifies, its ability to dehumidify is limited to situations where cooling is needed. If it's below 70 degrees or so outside, the a/c evaporator is liable to freeze, and at that point it'll keep running but do nothing as far as cooling or dehumidifying until it's shut off and the evaporator is allowed to thaw out. Second, because the a/c lowers the temperature of the air, it makes condensation on those walls and other surfaces more, not less, likely. Why? Because if the surface of a wall is, say 64 degrees, and the air is 65 degrees at a high humidity level, it doesn't take much heat transfer for the wall to pull the air near it down just one degree (and if the humidity approaches 100 percent, that might be enough to create condensation). On the other hand, if the air is 75 degrees with the same absolute quantity of moisture it had at 65 degrees, the wall has to drop the air 11 degrees to create the same condensation. Obviously that's much less likely. And that's the benefit you'd get from a heater alone. With the dehumidifier, the air won't have the same absolute quantity of moisture at 75 as it had at 65 -- it'll have less. Finally, the walls won't stay 64 degrees once you warm the room up. They'll gradually warm up too, further reducing the risk of condensation.

That's what I've been doing for decades in many homes and it seems to work well. Building Science Corp. research shows that stand-alone dehumidifiers perform this task efficiently.