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Thread: Unoccupied Shop Temp

  1. #1
    Join Date
    Mar 2015
    Location
    Warsaw, Missouri
    Posts
    92

    Unoccupied Shop Temp

    I have a devil of a time with the cast iron on tools getting a patina of rust in no time at all, even though I'm pretty good about keeping surfaces dusted and wiped down with a bit of WD40 (I avoid wax just because I have had contamination issues at finishing time in the past). Especially bad on the ways of my new, big lathe. The bed of that lathe is right in the heater's path.

    I live in NE Missouri, so much of the winter is subfreezing, but only a few days of subzero here and there...

    I have a suspended, high efficiency propane fueled heater vented to the outside and with good drains also to the outside in my 30x30 slab floor shop. I am not having a humidity problem at all - it's quite dry in the shop.

    It has been my normal practice when not in the shop to set the temp at about 55...I spend some evenings and most weekends in the shop. The heater is probably oversized for my shop, it can bring the temp from 55 to 68 in about 7 minutes. I am wondering if I am inducing problems from keeping it so cool most of the time and then rapidly ramping up the temp. How much temp difference do you folks keep between unoccupied and working temps in your shops? Think I'm on the right track? I can experiment, of course, just hate to burn more propane than necessary when not in the shop.

  2. #2
    Join Date
    Mar 2006
    Location
    Fort Wayne, IN
    Posts
    555
    John,

    I keep my shop at 50 at night and take it up to 68 when I'm working. I don't have the rust issues that you seem to have. My heater is natural gas rather than propane. Don't know if that would be the difference. I'm in northern Indiana so my weather is probably similar to yours.

    Cliff
    The problem with the world is that intelligent people are full of doubts, while the stupid ones are full of confidence.
    Charles Bukowski

  3. #3
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
    Posts
    12,298
    Hmmm, interesting. I live in TN and in the winter keep the shop at 60 with a heat pump. The heat pump is designed to run a lot and keeps the temperature within one degree of the setting. (You can barely feel the heat in the air blowing from the diffusers)

    The HVAC guy had asked me if I wanted a larger unit at the same cost which would heat/cool faster but would cycle on/off more frequently but I chose the one sized better for the shop space. I am no HVAC expert but he said this smaller unit would tend to keep both the temperature and humidity more constant and that seems to be the case. Zero rust noted on any tool or cast iron surface in three years.

    When I use the shop I turn turn the heat up to 65 which is warm enough for me, then turn it back down when done for the day. BTW, this is easy with the heat pump thermostat which has a single "Economy" button which toggles the temperature setting 5 degrees.

    What is your actual relative humidity at the temperature extremes? The dewpoint tables could tell you what minimum temperature is needed to prevent condensation. If you search for "dewpoint, relative humidity, and condensation" there is a lot of information. This was the first document that came up:

    Preventing condensation - Vaisala

    https://www.google.com/url?sa=t&rct=...Wgut0y3l0veHKw

    Perhaps run a dehumidifier? It pulls a LOT of moisture out of the air! I run the dehumidifier in the summer when processing honey (to reduce moisture content), even if the dewpoint is high enough to prevent condensation.

    JKJ

  4. #4
    Join Date
    Oct 2013
    Location
    SE Kansas City Metro, MO
    Posts
    661
    Kansas City area, 40x40x10 pole barn, insulated (R-16 in the walls and R-30 in the ceiling) and drywalled. Automatic thermostat set to 50 degrees at night, up to 60 in the morning before I leave for work (it's so nice having my truck warm when I get into it!), back down to 50 during the day and then back to 60 at around dinner time till 10pm or so.

    No problems with humidity or condensation in the winter time, but *huge* problems with humidity and rust in the summer where I don't run the air conditioner enough to keep the humidity under control. I'm going to install a dehumidifier in the spring and let it try to keep the shop a little less moist.

  5. #5
    Join Date
    Oct 2008
    Location
    Columbus, OH
    Posts
    3,063
    Quote Originally Posted by John Nordyke View Post
    I am not having a humidity problem at all - it's quite dry in the shop.
    If you are getting rust then you must have higher relative humidity than you think. It must be high enough (55%) that when you drop the temperature to 55*, it rises to 100% and condenses on surfaces. You either have to raise the temperature to store more moisture in the air, or pull moisture out of the air with a humidifier. Maybe you are actually dropping below 55* before the heater kicks on?

    Propane heaters are known to generate quite a bit of water vapor, although I think all combustion creates water. I wonder if the venting is not working efficiently enough?
    Brian

    "Any intelligent fool can make things bigger or more complicated...it takes a touch of genius and a lot of courage to move in the opposite direction." - E.F. Schumacher

  6. #6
    Join Date
    Jul 2007
    Location
    Seattle, WA
    Posts
    1,495
    John,

    Is your shop insulated? In my experience, that's he most important factor. If your answer is yes, then you can ignore the rest of this post. If no, then let me share what I've learned:

    The rust is a result of condensation. Condensation happens when air goes from warm to cold, because warm air holds more moisture than cold air. The condensation happens on your machines because the cast iron has a lot of thermal mass- way more than air. So when your shop warms up, it takes a while for your cast iron machines don't warm up as fast. So when the warmer, moist air touches your colder cast iron, the air cools and drops its moisture. The key is to slow those temperature fluctuations down as much as possible so that the difference between the air temp and your machinery's temp is minimized at any given moment.

    When my shop was uninsulated, I was constantly battling rust. As soon as I insulated it, I never saw a spec of rust on my machines at all. I haven't been able to work in my shop for about a year now, and my shop has been un-heated the entire time. Still no rust.

    That said, my climate is very different than yours.

  7. #7
    Join Date
    May 2009
    Location
    Boston
    Posts
    1,740
    Consider putting in an insulated wood floor. Concrete tends to hold the cold so the warm air mixing with the cold concrete could be causing water vapor.

    I live 1/4 mile from the ocean and have fully insulated my shop. I have an electric heater which I only put on when I'm in there. So it may go from 30 to 55 then back down later. I have no rust issues to speak of. Maybe a dab on a chisel every now and then. I paste wax everything every few months.
    Don

  8. #8
    Join Date
    Sep 2013
    Location
    Wayland, MA
    Posts
    3,656
    No rust problems except for a few days in spring when it gets warm and humid outside and the shop is still quite cool inside. Can avoid that if I think to turn the heat on a bit. I keep the temp at about 42 most of the week when I'm not working out there, up to 60-65 on the weekends. Heat is a sealed combustion natural gas unit, building is insulated with spray foam, ~R24 walls, ~R48 ceiling, 2" (~R12) of xps foam under the concrete slab, 4" at the edges.

  9. #9
    I had a little bit last year in my attached garage. I insulated 80% and paste waxed most tools. Not only does the wood slide better across the tops but the rust has not come back since. I did read that a silicon wax will mess up finish you have to use a paste wax.
    I only heat the garage when I'm in there with a natural gas direct vent heater. They do produce vapor I read but the cost and ease of install was in my favor vs something else. We live in a small subdivision surrounded by fields so when it get's cold it gets really windy and cold so the temps go from maybe outside or close to it up to 50-60 range (no thermostat)

  10. #10
    I've always used TopCoat (Glidecoat) and have never had any rust issues. If I won't be in the shop for 2-3 days, I turn the furnace off, and it can get down to 20°-30°. I have a ceiling mounted Reznor natural gas furnace. I'll run it on the weekends, and leave it off during the week.
    On machines that don't see much use, TopCoat can prevent rust for many years without recoating.
    Gerry

    JointCAM

  11. #11
    Join Date
    Jun 2008
    Location
    Indianapolis, IN
    Posts
    231
    Quote Originally Posted by roger wiegand View Post
    No rust problems except for a few days in spring when it gets warm and humid outside and the shop is still quite cool inside. Can avoid that if I think to turn the heat on a bit. I keep the temp at about 42 most of the week when I'm not working out there, up to 60-65 on the weekends. Heat is a sealed combustion natural gas unit, building is insulated with spray foam, ~R24 walls, ~R48 ceiling, 2" (~R12) of xps foam under the concrete slab, 4" at the edges.
    Same here. I set mine to 50-55 when unoccupied depending what is setting up/drying, but only have issues when there are humidity issues, not in the winter. My biggest issue times are the same, spring/summer.

  12. #12
    Join Date
    Dec 2003
    Location
    Mountainburg, AR
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    3,031
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    You say you have had contamination issues with wax? Did you use car wax? If so, most if not all car wax contains silicone and will cause problems with the finish. If you use Johnson's Paste Wax you will have no such problems. It works very well to not only protect from rust, it also keeps things slick. It is cheap and available most everywhere. Of course there are anti rust products that will do a better job at preventing rust than Johnson's. But those are not nearly as cheap.
    Larry J Browning
    There are 10 kinds of people in this world; Those who understand binary and those who don't.

  13. #13
    Join Date
    Mar 2015
    Location
    Warsaw, Missouri
    Posts
    92
    Thanks all. I have paste wax and am going to apply that. I also had a DUH! moment after posting this - Even with dust and shavings brushed off everything, I've been in bowl-roughing mode for a couple weeks and WET SHAVINGS all over the floor arrghhhhhhhh

  14. #14
    I live near I-70 in Kansas, and have my furnace set at 45 when I am not in the shop. Having no problem with rust at all now. Used to just turn the furnace off, as it did not freeze in the shop, but resulted in rusty machines, no matter how much wax and boeshield I used. Did find I could wipe poly on the machine tables and it sealed well enough to stop the rust. Does wear off, but you can see when it does. But since leaving the furnace set at 45 no more rust.

  15. #15
    Join Date
    Feb 2008
    Location
    Prince Edward Island, Canada's Ocean Playground
    Posts
    232
    I am only home weekends and my shop is heated via radiant in the floor. I keep it at 45 during the week and 60 when I am home and in use. I keep all cast iron surfaces cover with paste wax and have never had a rust issue. Winter is long and cold but the shop stays nice and warm.
    [SIGPIC][/SIGPIC] Erik

    Canada's Atlantic Paradise - Prince Edward Island

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