Dehumidifier in my basement workshop

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Forum topic by Charles Culp posted 11-03-2009 05:15 AM 6485 views 0 times favorited 8 replies Add to Favorites Watch
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Charles Culp

13 posts in 3819 days

11-03-2009 05:15 AM

Topic tags/keywords: dehumidifier lumber moisture content

Does anyone suggest for or against adding a dehumidifier to my basement workshop? We have had about 1.5 weeks straight of rain, and I have water everywhere. My basement leaks and there’s really nothing I can do about it.

I wasn’t able to find any information about whether this is a good idea or not. Before my basement turned into a woodshop, we were already contemplating getting one to control the humidity down there (just to keep mold away). Now that there is wood and wood dust it sounds like an even better idea. I just want to make sure there isn’t a hidden issue. Also, if it is a good idea, I’m surprised I’ve never heard of it before.

So what do you all think?

-- Charles Culp,

8 replies so far

View ChunkyC's profile


856 posts in 3897 days

#1 posted 11-03-2009 05:19 AM

I’ve always wonder the same thing, great question. I have one in my basement shop set @ 50%.

-- Chunk's Workshop pictures:

View lew's profile


12961 posts in 4398 days

#2 posted 11-03-2009 05:47 AM

I run a dehumidifier in the basement shop all summer. The only down side I can find is that you have to remember to clean the filter often.

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

View bigike's profile


4057 posts in 3931 days

#3 posted 11-03-2009 06:55 AM

well i had the problem with the moisture and i got an A.C. and this works fine for me plus its cheaper in price well mine was anyway and i only have to run it when im in there now first i ran it for a day or two then it was just ran once a day for a week but now its all good u might want to get some high pressure cement to patch all the holes that leak and check for the down spouts outside and make shure there takeing the water away from the house so there is no standing water around your house then go and patch all the holes u can get cement from home depot or any home store like that hope this helps keep us posted.

-- Ike, Big Daddies Woodshop, http://[email protected]

View ADKAmateur's profile


9 posts in 3770 days

#4 posted 11-03-2009 07:07 AM

This will work. I run a humidifier in a basement and also in my workshop which is in my garage. The nice thing about it is that it will throw off a bit of heat, which combined with the lower humidity will make a big difference in the amount of rust on your cast iron surfaces.

The best way to set it up is to buy one that allows you to insert a bypass hose that you can route to a floor drain. Then you never need to worry about emptying the bucket.

View bill merritt's profile

bill merritt

203 posts in 3932 days

#5 posted 11-03-2009 06:23 PM

Very humid here in Ga. I run one in my basement, it helps alot.

-- Bill Merritt -Augusta Ga. woodworker

View SwedishIron's profile


142 posts in 4284 days

#6 posted 11-03-2009 06:37 PM

I ran one in my “rubble stone foundation” basement shop in Mass. @ 100% during the summer and just let it drain into the sump pump… worked great cutting down on surface rust and condensation on the old tools.

-- Scott, Colorado

View ondablade's profile


105 posts in 3841 days

#7 posted 11-03-2009 10:10 PM

The issue you would probably want to watch out for is not to over dry the air or this might over dry your wood – which could lead to expansion problems when a finished item is put in more humid conditions.

Your humidifier should be set at an appropriate %RH – the ideal range to avoid problems in a house is reckoned to be 30 – 50% RH, although in practice it varies with the season, and with the part of the country. It’s said the % RH in a workshop should roughly match that of the building where the wood is to go. Here’s a useful looking info page on humidity and its measurement and control:

There are different measures of humidity. Relative humidity or % RH is the one you want – because it determines how much ‘wetting’ effect the air will have on timber. How it’s calculated is a bit complicated (it involves partial pressures), but it’s a measure of how much water the air contains vs. what it can hold. (100% RH is basically steam or air so full of water that it’s about to start condensing out in the form of droplets or fog)

Specific humidity is the number of pounds water vapour per pound of dry air, and is a fixed value for a given sample of air. % RH is different, it varies with temperature. As you cool the air sample the %RH increases until you reach 100% or saturation, and you get fog. (this is the dew point, the temperature at which it happens is the dew point temperature) Cool further and it stays at 100% RH, but more fog drops out. Warm up the air and the %RH reduces – because air can hold more moisture at higher temperatures.

% RH is measured using a low cost device called a hygrometer. The basic ones are mechanical meters, and are not regarded as being very accurate. One low cost and pretty accurate way of measuring it is using a device called a sling hygrometer. (available from air con suppliers) This has two thermometers, one dry, and one with the bulb covered in wet lint. Evaporation from the wet bulb causes it to read a lower temperature than the dry bulb – how much lower depends on the %RH of the air. % RH is calculated from a table using the wet and dry bulb temperatures.

Raising the temperature of the air in a room reduces the % RH and so makes it harder for wood to take up water from the air, but to get the RH low enough for really effective drying (as in a kiln – where it’s necessary to remove water coming out of the wood too) it’s normally necessary to use a de-humidifier to remove water from the air (to reduce the specific humidity) as well.

Corrosion of tools become a problem in winter because the drop in temperature can drop the air in a workshop below the dew point – with the result that the water in the air turns from a gas to a liquid and condenses out on cold metal. (this is actually how a de-humidifier works – the cooling rad is cold enough to do this) Bringing a cold tool from outdoors into a warm room may cause temporary condensation too.

Whether or not the dew point is reached depends both on the air temperature, and the amount of water in the air. (the specific humidity) Warming a workshop may be enough to stop condensation.

Wood in air at a given % RH over time reaches what is called an equilibrium moisture content. i.e. it takes up as much moisture as it can at that % RH. Drop the temperature or add moisture (e.g. from water ingress to a basement) to reduce the specific humidity and increase the % RH and it will take up more moisture, and vice versa.

Manuals like the Encyclopedia of Wood contain lots of information on equilibrium moisture content and how wood responds to changes in humidity and its wetness….


-- Late awakener....

View Charles Culp's profile

Charles Culp

13 posts in 3819 days

#8 posted 11-04-2009 05:39 AM

Thanks for the tips everyone. My wife has wanted one for a long time, she’s paranoid of mold. I just want to keep my new wood collection from twisting.

My basement stays pretty warm, so I’m definitely going the dehumidifier route, and it will be run straight to the floor drain. I just have to find one that is quiet enough.

-- Charles Culp,

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