# Confused about humidity levels in basement - a math problem

I can't work out the math on this one.

I have a basement. The size is about 10,000 cubic feet (about 35 by 32 by 9). I bought a dehumidifier that says the humidity is 70 %. I want to get this below 50 %. The temperature in the basement is about 70 degrees (Fahrenheit). Now, here is where I may be doing something wrong.

at 70 degrees 100 % each cubic foot of air should contain about 0.0011 lb of water. I get that from here

https://www.engineeringtoolbox.com/maximum-moisture-content-air-d_1403.html

So at 70 % there should be about 0.00077 lbs of water per cubic foot. At 10,000 cubic feet this would be 7.7 lbs of water in the air in the basement. Since I started running the dehumidifier yesterday, the humidity has dropped to 65% (so not a lot). In that time (so about 24 hours), the dehumidifier has produced about 5 gallons of water. But five gallons of water has a weight of 42 lbs.

And that is what I don't understand. If there is only 7.7 lb of water in the air, how can the dehumidifier take out 42 pounds of water and only lower the humidity by 5%?

The basement is sealed of pretty good. There is a crawl space covered in plastic. It doesn't smell bad and I was a bit surprised with the 70% humidity. I thought it was less. The numbers above are very rounded, but 7.7 lbs is nowhere near 42 lbs.

• When I start my dehumidifier it slowly drops the humidity level. It takes several days for it to go down 15% - 20%. In the first day 5% seems about right. – Platinum Goose May 21 at 3:31
• @SteveSether: You got me thinking a bit more. Does this mean that it is feasible for me to dry out the walls? The basement really is sealed off from air pretty well. – John Doe May 23 at 20:51