Humidifiers and Dehumidifiers - Humidity Issue

Hi folks, just joined up--I apologize if there's a better spot for this question.

So I started running a dehumidifier in my basement about a week and a half ago. The basement is half finished, half not, with a couple of closed doors between. The dehumidifier is in the finished half.

I've got the unit set to keep the RH at about 45-48% as measured by a seperate hygrometer. Without the dehumidifier I was getting about 65-70%. The unit runs almost constantly, and when I turn it off (I'm terrified of this next electric bill) the humidity shoots up *really* quickly...gets back to the mid/high 50's in a matter of 15-20 minutes. There's no standing water to be found. There are only two small windows at about ground level, one in each half of the basement, which are both closed. I keep the door leading down to the basement closed as well, but it's not an airtight seal.

My question is: is this normal? Is there something I can do to slow the re-humidification (is that a word?) I really want the room down there to be usuable with no mold or musty smell, but it's going to be really expensive to run this thing 20 hours a day. When I first started using the dehumidifier I had the doors to the unfinished half of the basement open, looking to dehumidify the whole area. I closed it off about 4 days ago thinking maybe the unit would be more efficient with a smaller area. So far, it's made no difference.

Thanks for any info,

Padraic

How big is the dehumidifier? Do you have AC? Do you cool the basement? Do you have returns in the basement?

Hi Padraic and welcome to the forum. Follow airman's Q&A, but there is another, perhaps bigger issue you should be reading up on and this forum has a ton of posts, links, and advice to help. It is the process of finishing a basement. There are so many steps that need to be taken BEFORE you start to finish inside. So many times I am asked about that musty basement smell, or worse, the resulting mold problems, yet when I look around I can't see an inch of foundation wall. Preparation, starting from landscaping and drainage outside, to air sealing, dehumidification, and proper materials inside. I have seen basements where years of finishing work all went to the dumpster. You've got airman's attention and he is one of the best, so ask away.

GL
Bud

Thanks for the quick responses, guys!

Airman: I'm running a 50-pint Frigidaire FDB50R1. I've been good about emptying the bucket before it fills until yesterday when I connected a drainage hose. The unit is definitely moving a lot of air and pulling a lot of water out. No AC, and it's unlikely I can afford to install it. I have crank windows that open like a door, so I don't know about a window-mounted unit either. I don't do anything to cool the basement--without the dehumidifier spitting out warm air it stays much cooler than the rest of the house on it's own. I'm not certain what you mean by returns, but I assume it's a vent for air circulation? Correct me if I'm wrong, please. There's no ductwork in the home--the heat is done with hot-water baseboards and there's no cooling. There are no vents between the first floor and the basement, or from one half of the basement to the other. The doors between these areas are typically kept shut, but are certainly not airtight. I hope that was enough info to answer the question!

Bud: I didn't do the basement refinishing. The previous homeowner is a home-builder by trade. His wife was recovering from cancer, so I know (hope, anyway) he would have done his best to inhibit mold. I do know that they did run a dehumidifier down there. This isn't to say that your point isn't possible, and I will certainly read up on any info I can find on these forums. But if it comes down to "specifically how was this part of the process done," I'm afraid I simply won't know the answers for the most part. If it's helpful, I can tell you that the interior refinished wall seems to be about 4-ish inches from the concrete foundation, made of drywall with knotty-pine over the lower half. There's fiberglass insulation between the studs. This info is from just one spot where I can see behind the wall a little, so I suppose it's possible that it isn't uniform all the way around. I suspect it is, though. The carpet is laid on a spacer, not right on the concrete. There's also a hanging ceiling with tiles and metal framework. A couple of the tiles have been water-damaged, but not terribly so. I found one pipe up there that was sweating a bit and insulated it. I've been throwing any silica-gel packets I get from product purchases up there. Dunno if that will help anything, but it seemed like a decent idea =P

50 pint is most likely to small. Dehumidifiers are sized at 80 degrees. At 65 degrees (common basement temp) your dehumidifier will be closer to a 30 pint unit. Unless your basement is very small, it will be to small. Make sure your downspouts run away from the home. Make sure the gutters are working.

Bah, those sneaky dehumidifier raters!

My basement has been around what you said, 65-70 degrees. Tending more toward 70 with the warm discharge from the dehumidifier. I guess it's not *tiny*, but certainly isn't huge either--I'd put the finished portion at pretty close to 300 square feet with a 6'10" ceiling. The unfinished portion is a bit smaller but there's not a lot of airflow between the two. The dehumidifier does get the RH down to where it needs to be, it's just how quickly it comes back up that concerns me. If 50 pints is too small, how big do you think I should look for? Is it a case of "Bigger is always better?"

I'll check the gutters and the downspouts. To my knowledge they are all in working order and diverting rain about 4 feet from the foundation, but I'll make sure. We have had a ridiculous amount of rain here the last few weeks, so I suppose this could be a case of bad timing too.

Thanks for your help. I hope such a basic question hasn't been a waste of your time!

Id make sure your downspouts go at least 10 feet from the home. Also take a look at Residential Dehumidification - Santa Fe and Ultra-Aire Dehumidifiers by Therma-Stor (http://www.thermastor.com/Residential-Dehumidification/) Worth every penny! Will save you money with electric rates.