Question about desiccants (e.g. silica gel)

I want to keep humidity and condensation out of a large closet. If I get some kind of desiccant, like a box of silica gel or something, is there a way to quantify how long I should expect it to last before it loses its effectiveness? Obviously, it depends on both the volume of the closet and the average ambient humidity, but I am just looking for some sort of rough guideline for how often to replace the desiccant.

No need to replace…I’ve heard that silica gel can be recharged/dried out by baking in an oven for 2-3 hours at 200 deg. I’m also seeing hints that a microwave can be used to recharge the bags.

Also here’s a source for large bags of dessicant: http://www.amazon.com/Silica-Desiccant-Dry-Packs-Prevent-Corrosion/dp/B004N6JQFW

There is a product made for doing what you aim to do, that’s not just “a box of silica gel.” It’s called DampRidand I believe each version of the product has info on how long it will last.

Looking around the site I see some are 60 days, some 45 days, some 75 days.

Do a search for ‘rechargeable desiccant’ and you’ll find different examples.

I have a unit almost like this in a large safe. Paraphrased from the description: ‘It will absorb about 6 oz of moisture which takes about 6 to 8 weeks’. You can tell when it needs to be recharged because the window turns from blue (dry) to pink (wet). Then you plug it in for 12-14 hours to dry out the crystals and it’s ready to put back in your closet. You don’t have to fire up your oven.

There are also vented cans of silica instead of bags like this. You can see the crystals change color through the window in the lid. The description says ‘it provided protection for up to 57 cubic feet’. While the model above can be plugged into the wall to recharge, the cans you have to throw in the oven.

I’d probably go with DampRid or a similar product. Fairly cheap, though not regenerable, and basically just calcium chloride. Sure, you can regenerate a number of desiccants with heating in an oven, but I’m not sure that’s really any cheaper or easier in the long run.

I think you’re better off with a small dehumidifier. This is what I use in my closet.

Interesting. It’s got a good rating. How often do you have to empty the tank?

ETA: Also, does it emit much heat?

I empty the tank every week or so, maybe up to 2 weeks in winter. But I’m sure it’s strongly dependent on the humidity and how well sealed the closet is. The closet does not feel noticeably warm compared to the rest of the room.