Now that heating season has started our shop is running from the high
teens to the low twenties in R.H. I'm wondering if blowing a fan
across a 55 gallon drum full of water can raise the humidity into the
The shop is about 50,000 sq ft and maybe 1 mil cu ft and the temp
ranges from 60 to 70 F.
You've got 2 of 3 parts to a traditional humidifier. There's also a
filter media that's primary purpose is to act as a wick and spread the
moisture out before the fan blows it in the room.
The drum and fan will have some effect, but you might need a towel or
something to use as a wick.
If you're quiet, your teeth never touch your ankles.
To email me directly, send a message to puckdropper (at) fastmail.fm
Think of it this way, as the air steam from the fan is somewhat like a
cylinder, and the water pan slices a part of the air stream across the
surface of the water. Only that small part of the air stream in contact
with the water pan will assist in water vaporization. Yes, it can be
done but at what efficiency cost.
Room humidifiers use some sort of water wick that alternates between
being dunked (immersion) in the water and being presented to the fan as a
much larger damp surface area for the air stream to effectively assist in
water vaporization. Much more efficient.
Actually, Sears sells several room humidifiers (difference is mostly in
the gallons the tank holds and the size of the replaceable wick) that
actually work quite well. My Sears room humidifier has lasted almost 20
years with normal maintenance of the occasional V belt, wick replacement
annually and a drop of oil in the motor.
There is no reason you could not improve on the Sears design and make you
own version. I suspect the 1st design improvement will be to come up
with a filter on the fan's input air to cut down on the saw dust that
will clog the water wick.
Don't forget the bacteria bit on room humidifiers. Room humidifiers are
famous for growing nasty bacteria that ends up as congested lungs on your
part. Tablespoon of household bleach each week helps out. Just make
sure no shop pet gets a mind to drink.
Just ignore the Neanderthal woodworkers who claim a dry woodworking shop
is justification for bending wood. Bending wood requires a steam box,
boiling water, and a heat source to boil the water. Way too much extra
work just to add some humidity.
Presumably, that's not half air/half water, but rather 50% relative
humidity that you're talking about. Why that target?
Is your shop really always fully heated? Mine isn't.
Wouldn't it be better to humidify to a point where fully-dried
wood has neither uptake nor loss of moisture?
The interesting quantity is EMC (Eqilibrium Moisture Content).
The USDA wood handbook has a formula, equation 3-3, for this:
M = 1800/W *(K *H/( 1 - K*H) + (...other terms) )
where M is the percent moisture content (something around 7% is
common for fully-dry furniture), and W is a temperature function
W :== 330 + 0.452 *T + 0.004157 *T**2
K :== 0.791 + 0.000463 * T + 0.000 000 8447 *T**2
H :== relative humidity (50% would mean H = 0.50)
where T is Fahrenheit temperature.
In other words, one cannot keep wood stable at varying temperature
with constant relative humidity. When one changes, the other does
too, OR the wood starts to shrink/swell/cup/warp.
USDA wood handbook, FPL-GTR-113, is available online, is
about 14 MBytes in size.
I was curious so I plugged the above into a spreadsheet to check it out.
It turns out the effect of temperature isn't all that large.
For relative humidity of 30% the EMC varies by 0.2 when you change the
temperature from 32F to 107F.
At RH of 50% the effect is larger, but it still varies by less than 0.4
over that temperature range.
Yes, if it weren't, wood wouldn't be much of a useful material, after
The RH in an inhabited space may as well simply be controlled for
comfort and economical heating/cooling considerations and for a shop
somewhat the same w/ the primary emphasis on avoiding condensation in
unheated areas for rust prevention.
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