Workshop Humidity

[paul cottingham]

What is an acceptable level of humidity for a workshop in terms of wood warping and tools rusting? Mine is around 70%. Is that high, or am I OK?

Thanks,

Paul

[Jason Beam]

What's the humidity outside? What is the humidity in the areas your projects will be stored?


It's not so much about how high it is, but the difference between the levels in the various environments your stuff will be stored in.

[Cliff Holmes]

70% is kinda high. I'm in Florida and the indoor humidity stays around 50% in our house and my shop.

[John Coloccia]

I keep mine between 40% and 50% and 75 degrees. I don't like to go much below 40% because of static and gluing issues (everything just seems to dry out too fast). Much above 50% and you run into problems when moving finished items into dryer atmospheres. If you're not selling the items, or if they're staying local, it may not be that big of a deal. If you take something to Arizona, that's a different story!

This is just what I do, by the way. 70% seems high but may be OK for your environment. I would expect at least a little cracking, loose joints, warping etc when moving items to any sort of air conditioned environment. You wouldn't believe how low the humidity can get in an air conditioned area. For example, at my day job we have to run humidifiers all summer to get the humidty to creep past 30%. That's pretty dry. This isn't a blanket statement, but I personally believe that 40-50% covers a lot of ranges, biased a bit towards the dryer side because a little bit of expansion seems to be less detrimental than a little shrinkage, generally.

Of course, I'm looking at this from an instrument building point of view, and another part to this is to consider what it is you're building. If it's an outdoor Adirondack chair, I would guess 70% is just about right, perhaps, although I would still dry out the shop because I personally can't stand feeling hot and sticky :D

[Scott T Smith]

Paul,

There is a relationship between temperature, relative humidity, and the moisture content of wood stored in that environment. This formula is referred to as "Equilibrium Moisture Content" or EMC for short.

Presuming that your shop is at 75 degrees F and 70% RH, the wood stored inside it will reach an EMC of about 13%, which is too high for interior woodworking projects.

Here are some EMC references, all at 75 degrees F

66% RH = 12% EMC
58% RH = 10.5% EMC
51% RH = 9.3% EMC
44% RH = 8.2% EMC
37% RH = 7.2% EMC


If the RH% in the shop stays constant, as the temperature increases the EMC will decline about 1/2% for every 15 degrees increase in temperature.

[John Coloccia]

Paul,

There is a relationship between temperature, relative humidity, and the moisture content of wood stored in that environment. This formula is referred to as "Equilibrium Moisture Content" or EMC for short.

Presuming that your shop is at 75 degrees F and 70% RH, the wood stored inside it will reach an EMC of about 13%, which is too high for interior woodworking projects.

Here are some EMC references, all at 75 degrees F

66% RH = 12% EMC
58% RH = 10.5% EMC
51% RH = 9.3% EMC
44% RH = 8.2% EMC
37% RH = 7.2% EMC


If the RH% in the shop stays constant, as the temperature increases the EMC will decline about 1/2% for every 15 degrees increase in temperature.

Excellent point I forgot to make. That's exactly why I keep the shop at 75 degrees as opposed to the 65 degrees I prefer when I'm working. Does that count as suffering for your artistic integrity?

[Scott T Smith]

Excellent point I forgot to make. That's exactly why I keep the shop at 75 degrees as opposed to the 65 degrees I prefer when I'm working. Does that count as suffering for your artistic integrity?


Uh, no. Suffering only becomes involved when your temps are above 85 degrees in the shop!

Unless of course you have a dirt floor and certain critters such as fire ants, scorpions, etc to contend with. Then you're allowed to "suffer" at 75!

[Pete Kurki]

You also asked about tools rusting. I am using my current shop here in MN for the third summer now. No AC needed, as the thick concrete floor keeps the temperature steady 70 - 75 °F even during hottest 90 °F days outside. The first two summers I did not use a dehumidifier, and during nights when rH outside went to 90%+ the shop rH crept up to 75% or so. Some lower quality metal tools started creating dark stains (did not look exactly like rust but I presume it was some form of humidity induced oxidation anyway). This year I have had dehumidifier running all summer long. With 55% setting it keeps the 70' x 20' x 11' shop at 52% until I start my large dust collector which quickly pumps the dry air out raising the rH to 65%. After I stop the dust collector and close the doors it takes about an hour to get back to below 55%. I have not seen any more signs of rust or dark stains on any of my tools this summer, so this seems to be working out. With my $0.10/kWh electricity it costs me an average of $0.90 per day to run the dehumidifier (kill-a-watt measurement).

I would also be interested in hearing other experiences on relative humidity vs tools rusting from other creekers.

[Dave Hartunian]

Here in Michigan I recently moved within the same town and the basement shop humidity doubled from my previous home. Here is want I would do:

First off I got a Indoor/Outdoor Thermometer with Hygrometer from Radio Shack.
Their Web Site and the link to the page is http://www.radioshack.com/product/index.jsp?productId=2049773

Second I would get a Low-Temperature Dehumidifier. Don't get a non-low temp as the coils usually freeze over. I had ice 1 1/2 inches hanging off the rear of the unit. Can also be low on refrigerant, or old.

Third I would seal the floor with a good basement floor paint.

Fourth I would seal the walls with Dry-Loc which you can get at Home Depot, Lowes or your local paint store.

My humidity before adding the Dehumidifier was Temp. 69 degrees/humidity of 62 per cent.
Now it is 69 degrees/humidity of 34 per cent.
Good Luck,
Dave

[russell lusthaus]

60% RH is th cut off for mold growth. I set my dehumidifier to maintain 55% and find my tools dont rust at this setting either.

[dan sherman]

Scott has you covered on the wood side.


For the rust all you need to do is keep the temperature of your tools above the Dew point.check out this graph.

http://en.wikipedia.org/wiki/File:Dewpoint-RH.svg

[paul cottingham]

My shop is in an unheated garage, so maybe I need to start heating it. A dehumidifier sounds like it wouldn't hurt either.

[paul cottingham]

As an aside, if I'm reading the chart right, I need to keep my shop at 85 degrees. Sweet.

BTW thanks to everyone for the info. Its been most helpful.