Overnight Shop Temperatures — How Cold Is Too Cold?

Freezing and relative humidity are the prime concerns when you turn your shop heat off overnight. April 20, 2011

How cold do you let your shop get overnight? Where I am it gets to -30 outside in the dead of winter. Since electricity costs so damn much, I have been allowing it to get down to +5 at night. Not a great idea, I know.

Forum Responses
(Furniture Making Forum)
From contributor D:
The shop should always be 20 degrees above the outside temp. This will prevent dew point condensation on tools and wood that are stored there as the temperature falls every evening.

From contributor O:
I hope you're talking about Celsius temps. If you store glue in the shop, you need to keep it from freezing, since this can ruin it. Also, chilled materials can keep glues from curing properly and make finishing difficult. You'd turn up the heat while you're working, of course, but the materials can be much slower to warm than the air is. With this in mind, I set the thermostat around 50-55F / 10-13C at night.

From contributor J:
I put in a programmable thermostat and have it set for 52 F overnight. As stated, it's not good to let the finishing materials, glues, etc. get too cold and/or freeze. Not sure, though, if you're talking about Celsius or Fahrenheit? Makes a big difference in this conversation.

From the original questioner:
I'm talking Celcius.

From contributor L:
Cold hands and frozen glue have been my only problems. I would bring things up to a decent temp before finishing, etc.

From contributor E:
I let my shop go down to 45ºF. My spray room can go down even farther, but my drying area is heated and doesn't fall below 65ºF.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
I also like the 20 F above the outside temperature rule, but you must add that it should never go under 40 F, as freezing of some liquids can occur. However, what is really critical is the relative humidity, as if the RH gets too high over a long weekend, you will get moisture increases in the wood that can lead to swelling, and when the heat comes on, can result in shrinkage. You can get a fairly accurate RH gauge from Radio Shack for $30. In addition to monitoring the temperature, I suggest that you keep track of the RH and not let it go over 45 to 50% RH (maybe even 40% RH in the wintertime). Add humidity if the RH drops under 30% RH in the daytime while working.

From contributor M:
I try to never let my shop get to freezing. Between putty, filler, paints, primers and glues, it is too much of an opportunity for problems. The average night temp is around 40 to 45 degrees F in this area, so only occasionally (20 days a year) do we have several days of freezing weather. I had a pallet of melamine that sat through a freeze of several days. Even after the temp went up to 55-60 for two days, the inner sheets were still freezing cold to the touch. We had more chipping than usual and the edgebanding was a problem. I know you guys up north really have to fight this issue on a more serious level than here in the south.

From contributor A:
My shop is in St. Paul, MN, so I understand extreme cold weather only too well. All the responses above are well said, especially about glues, etc. freezing. I have a bit of a quibble with a small part of Dr. Gene's response. He recommends not going below 40F because of moisture problems. When the outside temperature hovers near or below zero, it gets dry. The shop humidity drops so darn low that it becomes a problem. I try to keep the shop about 50F and even occasionally throw a bucket of water on the floor to let it evaporate and raise the shop humidity. Extreme cold weather, in my experience, causes cracking, rather than swelling, problems in lumber.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
I suggest not going below 40 F due to freezing - pipes, liquids, etc. Of course, that is at night. During operating hours, the shop would be warmer and drier, which means that one must add moisture. Remember too that when the shop is heated back to 65 F, the adhesives, finishes, and lumber are much colder still, so they will not work as well until they are also warm.

From contributor B:
Some of you guys must be a whole lot tougher than me. I set my thermostat to 58 degrees F (day and night) and still think it's cold. Some days I wear two sweatshirts. Can't wait for spring.

From contributor I:
Check labels on your chemicals closely. We use a powdered veneer glue that is great, except it is supposed to be used above 65°. We had some problems and I called tech support, who told me we actually had a lot of latitude— the glue would stick all the way down to 60°, but below that it was toast. Made me understand what I was risking— sometimes the money for heat is worth it.