Setting Shop Temperature

A long discussion about how warm (or cool) to keep a shop, whether to turn the heat down at night and over the weekend, and the effect on costs, productivity, and quality of different practices. December 24, 2012

What do you guys set the heat at in your shops? My shop is approximately 10k sq ft and has overhead forced air gas fed heaters. Do you turn them down at night or leave them at a steady temp?

Forum Responses
(Business and Management Forum)
From contributor C:
Our shop is kept ideally about 63 - 64 degrees. I use a programmable thermostat, but only set back 5-7 degrees at night or weekends. If I drop it anymore I have machine issues. I am between two neighbors, so I recover pretty quick with a 2500 sq ft shop. I do not have CNC/router.

From contributor B:
62 to 64 in the shop during the day. Setback thermostat takes it 50 at night. Lumber storage area is insulated but unheated. We make sure the wood has been in the heated area of the shop long enough to warm up prior to applying glue.

From contributor G:
68 degrees days, nights and weekends, 10,000 sq. ft. If you are going to take your business seriously you have to treat it seriously. Over the years I've read about shop owners bringing their glue into their house so it doesn't freeze overnight. Are you a real business owner or a tightwad? If you can't afford to heat the shop you might want to step back and ask if this is really the business for you. Setting back overnight and weekends is fine, but don't overdo it.

From contributor L:
63-65 while I'm there. Getting too old to do 61-63 like I did years ago. Heat gets turned off at night unless I have finishes drying that can't be stored in the drying room. Temps rarely get below 45 in the winter from shutdown to startup.

From contributor J:
I'm in New England so there's no way I'm leaving heat up when I'm not in the shop any more than I leave the heat up at home overnight. Sorry, but heating your unoccupied space to 68 degrees is not a necessity to treat your business seriously, in my opinion. More like a waste of money and natural resources, but to each their own I guess.

I have a programmable thermostat which helps a lot. I run 52 overnight/weekends, and 62 during the days. The thermostat kicks the heat up about a half hour before I get there. Though I will often kick it up to 65 on the really cold days. My shop is 2k sq. ft. uninsulated block building with gas fired forced hot air.

From contributor A:
I am from New England as well. We would always let the temp get down to 50 during the week overnight and 45 on weekends. I kept the glue and finishes at 70 in an insulated warm box. As a tightwad, I have always kept the epoxy in a warm box. It helps it flow out, besides keeping it from freezing when the power goes out and your heating system shuts off.

From contributor B:
We also have a heat box for the glue bottles. Even at 60 to 65 it helps the glue flow better.

From contributor O:
We did very well yesterday. I got the shop up to 41 degrees. We have wood heat and it doesn't keep up.

From contributor Y:
Contributor J, I think I'd do some insulating. Block buildings are basically wind breaks! My Dad had one for his shop. Ice used to form on the inside of the walls.

We've got infrared gas heating. Works pretty well. Insulated building with 18' side walls. My prior shop had ceiling mounted unit heaters. Really didn't like them. We keep temp above 60 all the time, 64 during the day. All materials stored inside.

From contributor U:
No heat. In San Francisco, so it never gets too hot or too cold. It's generally mid-fifties in the winter and mid-sixties in the summer. I share my shop with artists, so they don't want to pay for heat. I use Titebond 3 since it can be used down to 45 degrees, and use a heatable darkroom or a heating blanket when I'm using plastic resin glues. Sucks for about a month in November/December, then I get used to it. Plus side is rent plus utilities just got raised 15% to $685 per month. What do you guys pay for heating in the seriously cold places?

From contributor J:
Contributor Y, mine's not that bad, but it sure doesn't hold heat! If I owned the building there's a lot of things I'd do. But I've already got thousands into it between painting, lighting, and electrical (space was pretty rough when I took it), so I'm not looking to put too much more into it now. Rather buy something down the road if I ever save up enough!

My heat usually costs between $2-3K a year. It's not uncommon to drop below 0 degrees Jan - March up here. But the snow looks pretty.

From contributor N:
I'm a real business owner wrapped in tightwad. If I'm in the shop it's 62 - with the wife it's closer to 70, but If I'm not in the shop, which can be for days, the heat is off. Even with freezing temps outside the shop seems to hold at 45/50 with no heating. If for whatever reason it gets colder I'll kick the heaters on a tad just to satisfy my conscience.

From contributor Y:
Heat bill in coldest months $1500 - $1600/month, 25,000 sq. ft. Natural gas, 10 infrared heat units, 1,500,000 btu total.

We've got 5 large OH doors and 2 dock doors, 7 walk in doors. All doors are insulated but OH doors are still not really good. It does get chilly here, Nebraska.

From contributor G:
Sorry to sound harsh. Like I said I've read these kinds of posts over the years and just shake my head at how low temp some keep their shops. I used to do that but don't anymore and like it much better.

Do you really save much by setting the thermostat back 10 to 20 degrees or more at night? Seems to me most of what you save you'd lose trying to heat everything back up in the morning. When I used to do that the furnace would run a long time to reheat the place and then kick on frequently because the contents were still cold and would cool the shop down quickly. About the time it was comfy, the day was over.

I should say I burn wood, sawdust briquettes and shop scraps, so I don't worry about the heat bill anymore. We lose more heat in our 10,000 sq. ft. during the day with the finish room fans running than we do at night, so that also affects my heat choice.

I made a mistake. I looked at the thermostat (don't do that much anymore) and it is set at 66. Floor heat, so it usually feels warmer than that.

From contributor L:
I have 2600 sq ft and they are split 50-50 by a wall and heated by separate units. I tried an experiment and instead of putting the temp at 45 at night, I put it at 55. Big difference. I used 180 gallons more in propane during that period and I never got to feel the heat while I wasn't there.

When it is at 45, that is just about the break point where the low temp hovers naturally. So when it is set at 45, sometimes it comes on at night and sometimes it doesn't. At 55 it comes on a lot more and uses a lot more fuel. So, yes, 10 degrees is a big difference.

From contributor G:
How long was your test period? Also, how well is your shop insulated?

From contributor L:
One heating season. Yes. Modern steel building with r-15 insulation (I think, could be more). The middle bay is mostly sheetrocked with 6" walls that are insulated. The experimental side is 25 w x 55 L x 26 t. So I have a lot of cubic ft to heat.

From contributor G:
Not to be argumentative, but 180 gallons @ $1.70 (which is on the high side here for LP) amounts to $306 a year. For that I would rather come to work in the morning to a warmer shop... but to each his own.

From contributor L:
Starts out at 2.69 and goes up to about 3.50 by the dead of winter. The shop heats up in less than an hour. 175K BTU makes for a quick heat up. It's just the fact that for 6 years I got away with 3 fills during the heating season and now I had to do 4. Plus I have the other side of the shop that has the same insulation factor but is the end bay, so it is exposed to the outside temps, while the center bay has bays on each side that buffer the area. The outside bay is 25-35% less efficient at holding the heat. I heat it much less as it is storage and finishing. But when I am finishing it is kept at 70 and sometimes at that temp 24/7 for a week at a time while finishes are curing as the project progresses. So it is not just a matter of $300/yr.

From contributor Q:
Many of us serious business owners actually study the laws of thermodynamics before choosing our heating protocols. My high output propane heater could bring the building from 50 degrees to 65 degrees in 30-45 minutes. Versus running the thing on a cyclic basis overnight from 5pm-7am = 14 hours. The savings are huge over the course of a long, cold New England winter.

Most buildings that have a decent insulation value and heat mass (machinery and wood) will reach an overnight equilibrium temp of about 45 degrees when it is 32 outside. It costs nothing to leave the building at 45 for a couple of days.

Your delta-T maybe lower than us Yankees. Where are you sweating at 68 degrees?

From contributor G:
I don't understand the last sentence in your post. What does "delta-T" mean? I am in the upper Midwest where we have our share of subzero weather.

From contributor L:
Delta T. Change in temperature.

From contributor X:
What is the best way to make a hot box to keep glue warm? I was thinking about making a box with rigid insulation and maybe putting a low wattage light bulb in there.

From contributor B:
I use an old 1950's flip top milk box for my glue warmer. They were common back in the days when the milk man came a few times a week and left milk bottles on the front porch. The boxes were insulated (not a clue what with) to keep the milk cooler in the summer and prevent freezing in the winter. A 25 watt light bulb on a line voltage thermostat is the heat source.

From contributor Q:
Old single door refrigerator. Build a few ply shelves paint can/glue bottle height. $15 small cube ceramic heater with adjustable thermostat and fan. Digital thermometer to know the temp. The freezer is handy for solvents and, yes, the vodka. Stains, fillers, dyes, catalyst, etc. go in the door shelves. I never found a use for the egg crate.

From contributor O:
30 to 60 seconds in the microwave for a quart sized glue bottle. Just gets it warm, not hot. If it's really cold in the shop overnight I'll throw a furniture blanket over the gallon bottle of glue. Seems to work. But I'm not in the Mid-West either.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
There are three issues with shop heat.

First, when employees are present, the work area must be warm enough so that they are not cold. A cold employee is prone to having an accident.

Second, the temperature of the wood is as important as the glue temperature. Cold wood does not glue as well. Note that every adhesive will also have an optimum gluing temperature… perhaps 65-75 for both wood and adhesive. If colder, a few changes when gluing must be done. Similarly, if hotter, a few changes.

Third, as the temperature drops, the humidity goes up, which means the surface of the wood will gain moisture. The reverse when the temperature goes up. Two days cool and more humid will require two warm days to offset or dry the surface. Whenever wood changes MC, we can get warp. Surfaces prepared for gluing that go through an MC change will often not be flat enough after the change to make a premium joint. Also, note that a cool shop will potentially have humidity much higher than the customer's home or office. So, when an item leaves the cool, higher average humidity shop, and then is exposed to the warmer, probably drier customer's environment, the wood will dry, warp, open joints, etc.

If you have wood that is a few percent MC too wet, it will be happier in a more humid, cool shop. But you will be only postponing trouble until the customer gets the product. I would rather have a shop close to the customer's conditions (temperature and humidity) so any problems will show up before the piece leaves the shop.

Note that wood can be placed in a small sealed room and even though the heat varies, there is no moisture exchange with the outside, so the wood's MC will be constant. Alternatively, such as in a tropical country, the wood can be stored and work in progress can be stored in a room with a dehumidifier that will keep the humidity fairly constant. Unfortunately, most small DH units work only above 65 F. You can buy a small humidity device for $30 at Radio Shack so you can see exactly what is going on.

From contributor L:
I have more than one of those humidity gauges in my shop and I find that as the temperature drops, so does the humidity. Most of the winter the gauge is at or below its lowest level (20%). I have several of them and they usually read within 2% of each other, so I assume they are pretty accurate.

I find the warmer weather brings on much more humidity in the shop. I prefer the cooler temps than the warmer for several reasons. Mostly dry time of my products, slower. Glues don't lock up as quick and give you more time and finishes don't flash as quick, giving a more uniform coating without retarders. The downside is it costs to heat the shop.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Humidity must increase as the temperature drops. It happens every day outside, as an example. Some RH devices will not work well when under 65 F.

If you cool air, the RH will increase until condensation occurs or fog forms.

Likewise, if you have a dust system that brings in outside air, even if it is 100%RH outside, heating the air by 25 F will drop the RH to about 30%RH. The wood MC at the surface would be about 28% MC at 100% RH, and 6% MC at 30% RH. Temperature does not affect the MC if the RH is constant.

This drop in RH and MC when heating is why a customer's home or office is so dry in the winter and we can see shrinkage issues if the wood is too wet. It is why humidifiers are often installed in homes in cold weather climates. This is also why a humidifier is not suggested for a shop, as humidifying a shop will create more humidity than the customer has and will postpone moisture problems until the customer gets the wood pieces.

A note to contributor L. Put your devices outside, protected from direct sunlight, and then check the local weather conditions (often 65% RH) and see if they agree. Readings under 20% RH would be very rare.

From contributor J:
I have a cheap humidity gauge and I'm not sure I've seen it go down to 20%; seems pretty low. Right now it's reading 60 degrees at 34% humidity, for whatever it's worth.

From contributor Z:
75 all the time, though I heat with wood.

From contributor L:
Sounds like mine is accurate. Pretty sure contributor J lives in the same state I do. 62.5F @ 34% in the shop.

From contributor Y:
I suspect there is some confusion about where the temp was dropping in contributor L's post. If he meant that as the outside temp dropped, the relative humidity in his shop dropped, that would be true. Cold air holds less water than warm, so when you move that cold air from out to in, its relative humidity drops. Its quantity of water in absolute terms stays the same, but warm air can hold more water. That's where the "relative" part comes in.

From contributor L:
That sounds about right. Temps in the shop are between 45 and 65 throughout the winter. Outside temps are between 0 and 40. Temp in the drying room is usually 70, which usually has the lowest humidity levels.

From Carl Hagstrom, Systems Administrator at WOODWEB
This is a topic I've spent a number of years learning about - a great deal of the knowledge coming from paying attention to Gene Wengert's posts at the site, and his countless articles on EMC (Equilibrium Moister Content). My observation has been that most buildings in a heating climate tend to establish a negative pressure heating routine... If there's a heating source that requires a flue/chimney to exhaust combustion gases, this sets up a negative pressure scenario where the air movement required to vent the combustion gases out the chimney creating a need for replacement air, which typically finds its way into the building as air leaks.

This replacement air is colder than the air in the interior of the structure. As this colder air finds its way into the building, it warms up... and anyone who's paid attention to physics understands that the humidity of this incoming/warming air drops significantly. The greater the temperature differential, the greater the decrease in humidity. So, in the winter, the colder it gets outside, the larger the temperature differential is between the exhausting air and the replacement air, and greater the drop in humidity will be. This also happens in buildings without an exhaust/chimney type of heat. A heated structure applies a positive pressure of sorts, pushes the heated air out of leaky spots in the areas of least resistance while the incoming colder air finds its way in through the leaky spots not being used by the outgoing air. Picture a day when the wind is blowing hard out of the NW. The heated air is finding its way out on the NE side of the structure while the wind is pushing the colder air in on the NW side.

My reading indicates that the most effective way to counteract this humidity issue is to build as tight a building as possible. Tight buildings have been around a while now, and the short description is that when you construct a really tight building, you have to provide make-up air (super tight buildings will cause wood stoves to back draft when the kitchen/stove exhaust fan is turned on). But as we all know, most commercial buildings (wood shops) are not built with extreme building shell tightness in mind. The result is a significant loss of humidity in the ambient interior air in the heating season, and the drop in humidity is directly related to the difference in outside air temperature compared to inside air temperature.

Unless you have a really tight building shell, the only way I'm aware of to counteract this effect is to add supplemental humidity. In other words, the leakier your building is, the more supplemental humidification you're going to need to maintain a humidity level that will prevent MC issues in the shop.

I have a room with a number of acoustic guitars, some which I prize highly. I keep a humidifier running in the room during the colder portion of the heating season (and it's a pretty tight room), and I can tell you that the colder it gets outside, the more I've got to ramp up the humidifier (ideal humidity being 50%).

My advice to all who are interested is to get a couple of decent hygrometers (humidity gauges... digital ones aren't very expensive), put them in a couple spots in your shop, and pay attention to them. You'll likely be surprised at how the outdoor and indoor temperature differential can make those hygrometers quickly change.

One of the benefits of being involved with WOODWEB over the years is that I've been able to follow what Gene Wengert has written regarding EMC, MC, humidity, etc. While it's true there is solid science that describes how it all works, there's also the common sense aspect that goes along with it, and that's where the Wood Doc really shines… describing the science in way we can understand and act on. And hopefully, if I've made any mistakes in my descriptions above, Gene will let us know.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Nice, accurate discussion, Carl. Also, we have had others contribute accurate info, including contributor B, contributor Y, and others.

What would be the cost of one repair due to drying in the customer's home? How does that cost compare to the cost of heating to a reasonable level (65 F) 24/7? It is most critical for large flat surfaces - table tops, doors, etc.

The brass desktop humidity gauges are worthless. Get a digital from Radio Shack and read the description to find the temperature range. These are usually plus or minus about 3% RH, which is fine for wood, as 5% RH is 1% MC.

From contributor J:
I think the only problem I have with Wood Doc's argument is that even if you could keep the temp and humidity at an absolute level year round in the shop, the work is going to end up in a customer's home. And at least here in New England, homes are anything but stable. We go from bone dry in mid-winter to dripping wet mid-summer with every variation between.

In my own house we put our heat on when we get home, usually about 68 degrees, when we go to bed 62, and during the day 56 or so. Fairly common practice around here. We also use the a/c pretty conservatively.

So if there's going to be such swings in conditions of the home, why would we want to expend our limited resources to keeping the shop more stable and comfortable than our own homes?

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Good points. With a finish, the changes in outside RH do not change the MC as fast, so we are concerned about the average RH and the resultant EMC. Daily and hourly swings are no longer an issue, unless they are severe.

The RH in winter must be controlled, as stated. However, in summer, the higher RH will not be as severe due to hysteresis. Also, the change from dry winter to more humid summer is weeks and months and not a day or two, and likewise, summer to winter. Very few shops control summer RH except in real humid conditions. This is why I hear many complaints in October when a shop with unfinished wood makes the transition from humid to dry.

From contributor L:
And that is why all my panel tongues get stained so when shrinkage happens, it doesn't look like a bright white line.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Staining of tongues and also edges is indeed strongly encouraged. Also, with 6" and wider staves, a longer tongue is suggested just in case.

From contributor L:
One of the other things I do is to seal the end grain of the tongue with lacquer to slow the moisture transfer down. Since I started doing this, I have very few problems with expansion of panels.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
Good idea although two coats are much better than one. As stated previously, a slow moisture change is often not an issue, while the same moisture change done rapidly is a problem. So, a finish helps slow things down.

From contributor L:
Never heard of anyone else doing it, the lacquer on the end grain of the tongue. Only a few will do the staining of the tongue, I do the backside also. I pad the lacquer on the end grain so it goes on pretty thick, much more than the 5 mil recommendation. Don't plan on doing any more coats than I already do as it goes far and above what most people do... nothing.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
There is or was a commercial product, I think thinned varnish, that did exactly what you are doing. I cannot recall the name, but I think it was made in Grand Rapids, MI. I recall one company that covered the end grain with masking tape. I also worked with a door company that used an in-line moisture meter and rejected wet pieces of lumber in the wintertime. Their reject callbacks went from over 100 to just three in the winter. It is all about moisture and humidity in the shop and in the customer's dwelling.

From contributor L:
Best thing to do is dip it in wax. The only thing that will stop moisture transfer instead of just slow it down. But since you only cover everything else in lacquer, it is still only a stop gap measure. But it is much better than nothing. Since I have done that, I feel much more confident.

From contributor K:
It's true that in New England unconditioned homes experience wide swings in humidity through the year, resulting in installed wood MC levels from perhaps 5-10% from winter to summer. Generally speaking, changes of 2% are negligible, and moisture losses greater than that have worse consequences (splits, checks) than moisture gains (doors sticking). For that reason it's wise to try to keep work going out the door in the mid range of expected MC in use, say 7-8%. That indicates a relative humidity of around 40-45%. Ideally we'd be humidifying in winter and air conditioning our shops in the summer. That rarely is the case, and often lumber enters and leaves the shop before ambient conditions change its MC significantly, so we need to concentrate on controlling the moisture content in the wood by proper sourcing, conditioning as necessary prior to processing, and controlled storage conditions. I know this is a bit removed from the original question, but it's worth pointing out that heating the shop adequately for gluing and finishing without humidification may result in lower RH than is ideal for wood moisture content.

From Professor Gene Wengert, Sawing and Drying Forum technical advisor:
I would suggest that because shrinking causes more problems (cracks, splits) than swelling, it is better to target a bit lower MC than contributor K suggests. I suggest nothing wetter than 7.0% MC especially in the wintertime. The effort here is to avoid any large drying and shrinkage issues when the piece goes into the customer's environment. It is rare, due to excessive condensation on house windows, and the risk of condensation in the walls, and mold in cold corners or bathrooms, to have a home at 40% RH or higher in the wintertime in a cold climate. So, the EMC of the air will be under 8.0%.

Further, due to hysteresis, a gain of moisture will have a lag, so a little higher RH will not be an issue for slightly drier wood.