What's a resonable humidity for the shop?

[Marty Tippin]

I've bought a dehumidifier for my workshop in hopes of keeping the humidity levels under control and reduce rusting of cast iron surfaces. Planning to plumb it to a permanent drain so it can run unattended. So far, I've been surprised by the amount of water pulled from the air in just the first few days it's been running.

What's a "reasonable" humidity level to set the dehumidifer at, given I'm in the hot and muggy midwest? Need to find the balance between rusty surfaces and a dehumidifier running 24/7 all summer long fighting to reach a level that's not practical...

[Randall J Cox]

I don't think you shoot for a specific level but, find the balance between running all the time and what's comfortable. I've run dehumidifiers for many years and none actually have a % markings on any knobs. You will know after a couple of weeks. Also if your shop is open to the outside some how (windows, leaks, etc), it might run all the time. Is it a basement shop or above ground?

[Brian Tymchak]

Ideally, I think the shop should be the same relative humidity as the living area in a typical house in your area so that whatever you build doesn't have the "shock" of moving to a radically different humidity level. I did a quick google on the topic and came up with this page - Relative Humidity and Your Home that provides a few numbers.

[Bud Millis]

Currently in my shop in Upstate New York the temp is 72'f with a humidity of 37%. It has only slightly increased since winter when it was 33%. The humidity varies during the time of the year. During the winter of 2014/2015 it was as low as 27% - which is the lowest I've seen since recording it in my shop. Outside its 79'F with a humidity of 19%.

Proper care of the tools should keep it from rusting - wax or silicone things like your table was, bandsaw, etc and apply a coat of oil to hand tools.


Hope that helps,
Bud

[Ole Anderson]

Per Brian's link, 50% RH other than during the northern dry winter months is ideal. I would trust a digital RH gauge more than I would an old analog one. As with thermometers, when you buy one, make sure it matches several others.

[Mike Chalmers]

I don't think you shoot for a specific level but, find the balance between running all the time and what's comfortable. I've run dehumidifiers for many years and none actually have a % markings on any knobs. You will know after a couple of weeks. Also if your shop is open to the outside some how (windows, leaks, etc), it might run all the time. Is it a basement shop or above ground?

Interesting. Any dehumidifier I have run with a digital display offer the % as the setting value.

[Marty Tippin]

Thanks for the replies. My dehumidifier has a digital RH% setting, so I've put it at 55% for now and we'll see how it goes. The shop is an insulated and finished 40x40 pole barn but has 16x10 and 10x10 overhead doors that get opened frequently and probably don't seal as well as they could. Perfection isn't my goal, just a little less of the "tropical rainforest" effect I had going on last summer...

In the last few days, I've dumped about 2 gallons of water each morning and evening - and we haven't even started our summer weather yet. No telling what it's going to be like in another month...

[Malcolm McLeod]

Just sticking with the rust prevention topic, I think most of my issues have been a direct result of temperature swings. My shop was non-insulated garage. Blue norther blows in and its 20*F for three days and the TS and J/P tables drop to 25*F. Then the wind shifts, the Gulf of Mexico arrives at 85*F (>60%RH), and you need a swim suit at the saw.

I am now in a well insulated shop, and even with overhead doors, the temperature swings are minor. The cast iron's temperature never drops below the dewpoint of the air. So, no condensation and no rust. I've been in current environment for 5 years with no issues, and don't even see a need for cast iron surface treatments anymore.

If it's a comfort issue, Colorado Springs is nice in the summer...

[Mike Gresham]

Interesting. Any dehumidifier I have run with a digital display offer the % as the setting value.

That is true of just about any unit you will find at a big box store. I went through 3 of those in 18 months.

Then I got an Aprilaire and it has been doing well for 4 years now. It does not, as most of its industrial style brethren, have a % scale. Just numbers that you look up on a temperature table to see what % humidity it wil produce. You can buy a humidastat for some models, but the numbering system works OK if you have a fairly stable temperature like my basement.