Keeping woodshop (garage) above dewpoint

[srv52761]

William - The dehumidifier makes sense.  That is easy to accomplish too.

Jim, it is 2*F here today.  will be -20*F before the middle of Feb.  Heating my shop to 68* would be much more than $30/mo.  Besides, I am a hobbyist and I don't work in the shop every day.  I do hear what you are saying about the leg.  I have heard the same from many people.

Dehumidifiers work similar to air conditioners, a fluid removes heat from one place and blows it to another. For the sake of discussion we will dispense with the part where the heat goes and concentrate on the cooling part-the part that removes water.

A coil is cooled, air blows across the coil, the air is cooled. Any moisture above the holding capacity of the air at approximate temperature of the coil condenses and the resultant air has less water vapor than previous air.

Ok, let's look at this in more detail with some hypothetical numbers.

Let us say the coil gets to 40*F (not uncommon). The area near the coils will be 40-43 or so. As the room air is blown past the coil the coil will "give up some of its coldness" (actually the opposite, the room air will give up its heat, but the other makes explanation easier). So the coil and adjacent area will be about 45-50. So any moisture above a dewpoint of 45 or so will condense. The resultant air will be 100% relative humidity at 45 degress. This will mix with the warmer air in the room to produce some relative humidity based on the temperature of the room.
If the room temp is 65F, then we are looking at a RH of about 50%, if the room temp is 85F then we would be looking at a RH of maybe 35% or a little lower.

But what happens when the ambient temp is in the single digits, your 2F, for instance
To protect your equipment from water that will condense at 2F, you must remove enough water that condenses at maybe 1 or 0, as it will mix with the air that didn't pass through the coil.. So your coil must get down to a few degrees below zero.
But your coil can't get that low. The ambient air (say 25F during the day) has already condensed the water vapor in excess of the capacity of the coil.

Most dehumidifiers start to lose effectiveness at about 55F. They do make low temp dehumidifiers that work down to about 36F, but these are three or four times the cost of the regular residential models.

Dehumidification may not give you the results you want.
A tip I got from this forum a number of years ago has already been mentioned. A clamp light with a 100w or bigger incandescent bulb on the inside keeps my tablesaw top condensation free all winter long (it also helps in the summer, too).

If you want to play around with the numbers some here is a handy dew point, rh, temp calculator
http://www.calculator.net/dew-point-calc...&x=56&y=16

edit: as an example,
I mentioned in a different thread we had a hvac unit freeze up on us over the Christmas break and water dripped on and under our hardwood gym floor. A company specializng in remediating this problem set up blowers and dehumidifiers. Their dehumidifiers are the low temp, commercial models-big ones. Our gym is about 11,000 sq.ft. 30ft high.
Outside temp was 12F daytime to -11F overnight, inside temp we kept at 68-70. About 24 hrs of dehumidification produced almost no water...and we think this was water already in their equipment.

[Willyou]

i think i read somewhere that a ceiling fan to keep air moving helps keep moisture off of tools.

I agree. Before I had my insulated shop, I found that keeping a small fan running kept the air stirred up enough to keep condensation off the tools. This alone was enough for my situation at the time. Good insulation should be the next step. After that, all the suggestions above.

[TDKPE]

A tip I got from this forum a number of years ago has already been mentioned.  A clamp light with a 100w or bigger incandescent bulb on the inside keeps my tablesaw top condensation free all winter long (it also helps in the summer, too).

My marginal electric rate is about $0.10/kW-hr all-in (energy, delivery, taxes, and fees, not counting fixed monthly costs or first-tier stuff, which I'll pay no matter what), so a 100W bulb would cost me a penny an hour more than not using it.  That's pretty cheap insurance against rust.  Good tip.  


My shop is in the basement, so zero rust issues, but my last shop was in the garage, and my next probably will be also, and in a warmer, more humid location.  So I'll keep that in mind for the future.

[Dave Diaman]

When I was working out of a two car garage my first step was to insulate it. I put r38 in the ceiling and 2” rigid foam on the doors. After that something I found that worked wonders was one of the small radiant oil heaters. I set it under the outfeed wing on my jointer and just left it on. The heater was very efficient. This warmed the whole end of the jointer so the heater was doing double duty. That little bit of heat kept the slab warm and the shop only ever dropped below 55 if it got really bitter outside. When I would go in the shop I had a 220v electric heater that would bring the shop up to 65-70 degrees in about 30 minutes.

[MichaelMouse]

William - The dehumidifier makes sense.  That is easy to accomplish too.

Jim, it is 2*F here today.  will be -20*F before the middle of Feb.  Heating my shop to 68* would be much more than $30/mo.  Besides, I am a hobbyist and I don't work in the shop every day.  I do hear what you are saying about the leg.  I have heard the same from many people.

Dehumidifier makes no sense to me.  Two reasons.  First, absolute humidity is LOW in cold weather, and warming the air even a couple of degrees would result in an even lower RH.  Second, the coils cool the air to condense moisture, and they'll frost over.  Of course, when frosted, they are at absolutely zero efficiency, which means running the compressor is strictly a heat source, not diminished by the cold in the coils.  Any other form of electrical heat would be more efficient.

[Richard D.]

 The bike has made a big difference making me tolerate indoor 55-60 degree temperatures.