I live in a very dry climate but I've run into an odd humidity problem.
My theater is located below the garage (suspended slab garage floor) and it's the lowest part of the house, including about 5' lower than the rest of the basement. Even during the summer when it's very dry and there is low humidity (the upstairs is below 50% humidity and the basement, which is unfinished, sits at about 55%. Because the rest of the basement is unfinished and because of pets we have to leave the door to the basement open, but the door down to the theater closed, all the cold air and humidity go to the theater. The theater has a heat pump for heating and cooling but the rest of the basement has no heating or cooling since it is not yet finished.
The humidity in the theater reaches 70% in the summer and about 80% during the winter. If I crack the theater door it goes to about 65% humidity and if I put a fan in the door, it goes to 57% humidity.
I think I have two choices and this is where I need help.
Option one is to get a dehumidifier but there is no water drain in the theater and that's a fair bit of extra power.
The second option would be to unseal the theater and build a hush box for a fan and continually vent the air in the theater with the rest of the home.
I'm leaning towards option 2 because the rest of the home has lower humidity, especially during the winter, and eventually the basement will be finished.
I'm also not sure what size of fan would be really needed to just keep the air from getting stale and humid down there.