Replies

1. 
   UncleDunc | Aug 10, 2004 04:55pm | #1

   Set it the same as the humidity in the room where the furniture will live.

2. 
   jackplane | Aug 10, 2004 08:29pm | #2

   50%.

    Wood, like any object affected by humidity, performs best when kept in a stable range. Since 50% is ideal though summer and winter,that's where I'd leave it, assuming you're woodworking for yourself/your area.

   
   

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   Edited 8/10/2004 3:47 pm ET by JACKPLANE

3. 
   drhamel | Aug 10, 2004 10:03pm | #3

   I'm going to have go along with Uncle Dunc.  I live in Utah where it only hits 50% when there's something falling out of the sky.  Usually we're in the 'teens but fairly frequently get into the single digit range - I recall one day in March when it was 3%.  I think the ideal humidity is very dependent on location.  what may be suitable for Houston would be less than ideal for Salt Lake City.

4. 
   jonsherryl | Aug 10, 2004 11:02pm | #4

   WP, you are actually addressing two issues here. The first is; what humidity level will best protect my tools from rusting? And the answer is you want to maintain a constant temperasture and humidity level whatever the quantitative values are. Rusting occurs when humitity and temperature values change and moisture condenses on to cold tools, because the air has warmed up faster than the denser tools have...So, rusting results from constant changes in heat and humidity, rather that simply what humidity or temperature the environment is at.

   The other issue is: what relative humidity is best with respect to minimizing the risks caused by wood's natural instability? The answer here is that it is best to approximate the humidity-temperature conditions that the finished piece will experience once it is put in use. Of course, this guideline would be infallible, if the in-use environment had perfect environmental controls and always maintained the same humidity and temperature...but that's seldom the case.

   So, in my experience, the practical answer is to work with wood that is slightly more desiccated that what it would be if it were immediately taken into the piece's final environment at the same moment you are assembling the piece and allowed it then seek what would be a higher equilibrium moisture content. In other words, you want it slightly drier than it would be if it were already in the end-use environment.

   This seems to work the best in that wood tends to fail (check or split) more severely when the wood cells are exposed to cross grain tension stress than when they are exposed to compression stress. True, joints may become a little overly tight, but the risk of wide panels splitting is reduced when tension stress is avoided.

   As for my personal experience, I've always lived in the north (suburban Detroit, at the moment) and I've always had a basement shop, which maintains extrtemely constant temperature, but vascilates widely in terms of relative humidity. What I've come to accept is that there seems to be a season to when certain types of furniture should be built. For example, I tend to save those projects requiring wide edge-glued panels for making during the winter months, when the furnace keeps my shop exceptionally dry. Outdoor furniture projects, or small items where wood stability is less of a concern, I try to save for building during the summer months.

   
   

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   Edited 8/10/2004 9:01 pm ET by Jon Arno

5. 
   JohnWW | Aug 11, 2004 12:19am | #5

   Depending on the the sources of moisture in the building, its airtightness, the climate and the size of the dehumidifier, you will probably find that you can only achieve a modest amount of moisture reduction even if you left the machine running full time.  So you might just start out setting the knob to 0% RH and see what is achievable after it has been running for a week or two, it will probably take that long to reach a stable RH if there's a lot of moisture in the shop when you start out. 

   If the building is on a concrete slab that can wick up ground moisture, the machine may not lower the RH very much at all in wet weather. 

   If you like to work with the doors and windows open in nice weather there's no point to getting the RH to much lower than the average outside RH.  If you have a very low indoor RH, opening the windows and letting in moister air will cause large and rapid changes in wood dimensions that will make quality work difficult. 

   Also the lower you set the indoor humidity, the longer it will take for lumber stored in moister environments to stabilize for working with once the wood is brought into the shop.  No matter how you maintain your shop's RH, you should design your furniture properly to accommodate wide moisture swings, from New England winter bone dry to southern states summer tropical.

   John W.   

6. 
   CStanford | Aug 11, 2004 02:33am | #6

   55%

1. 
   LeeGrindinger | Aug 11, 2004 04:02pm | #7

   55% will put your EMC at around 10%. Is that a good thing where you are?

   Here... http://furniturecarver.com/emc.html

   Lee

1. 
   CStanford | Aug 11, 2004 04:59pm | #8

   Yes.  And that would be a good number for a woodworker in Charlotte, NC as well.

   Edited 8/11/2004 10:00 am ET by cstanford

1. 
   LeeGrindinger | Aug 12, 2004 03:40am | #9

   Yeah, that sounds about right.

   You're deeper in the South than Charlotte as I recall. I wonder if the EMCs should be moved down with the advent of climate control. I live in the very high desert so humidity is a different sort of problem here...like when I build a table destined for Long Island

   Lee

7. 
   user-6909686 | Feb 08, 2020 07:57am | #10

   Bad link to furniturecarver.com. Leads to Chinese lottery site.

8. 
   DRBWWing | Feb 08, 2020 10:24am | #11

   jonsherryl ^^ nailed it.

   You'll have to play around with it. Its going to vary depending the time of year. IMO an AC unit will work just as well.

   I have used dehumidifiers in my bench room and not had very good luck keeping it below 55% (NE FL area). That said, I have not tried piping to the outside and leaving it running 24/7. The problem is the dh generates heat, which causes the AC to run more.

   Machine rusting revolves around temperature/humidity swings. My shop is not climate controlled keeping a fan running and the doors/windows closed is the key. The problem is machines getting cold overnight and warming up too fast during the day. Shouldn't be a big issue in an insulated shop.

   Re: lumber, & in relation to our environments in the east, its humidity swings, not the actual %. That said, furniture built in the shop at is usually going to shrink when it goes in the house. You have to take in to account what season of the year you are building, too.

   I have a separate insulated, climate controlled bench room where I build projects and store my hand tools. I keep my project lumber there for several weeks prior to the build, as well as during the build.

   Bottom line, with an insulated shop that size, I would install an AC unit and plumb the DH to the outside and leave it running 24/7.

9. 
   DRBWWing | Feb 08, 2020 10:34am | #12

   johsherryl ^^ nailed it

   Shop that size, I would install a window AC if you're going to use a dehumifier because it will only work well if you use it 24/7 it will generate a fair amount of heat. Be sure to plumb the reservoir to the outside.

   Machine rust is related to temp/humidity swings (and disuse). I a climate controlled shop, it won't be much of an issue. If you're leaving the shop unused for extended times you'll probably get a little rust built up.

   Personally, I've used dehumidifiers in my area (NE FL) I've not found any practical advantage over an air conditioner. That said, I've not left it running 24/7.