Is keeping your tools in a heated area the most essential step in rust prevention?

[Larry Edgerton]

For the first time ever my tools were in an unheated space last winter. Bad deal! They rusted badly. Wax only helps the top, its the little moving parts "under" the machine that you can't get to are the worst. They will never be quite the same. I sprayed them down with Aerokroil storage, and it did not help. Keep the temp at at least 40 is my opinion.

Larry

[Jason Roehl]

Conditioned air would be the driest, whether heated, cooled or dehumidified. Also, a covering on the equipment, such as a cloth tarp or a sheet would help as condensation would settle on the covering, not the tool surface.

A dehumidifier is an air conditioner that's not split so that it doesn't expel the heat to the outside. Otherwise, the only reason an A/C would dry the air faster is because it's a larger unit. One could argue that if you had an A/C and a dehumidifier that had the same amount of refrigerant, and same size motor, coils, condenser, compressor, etc. the dehumidifier would dry the air MORE because it would also raise the ambient temperature. Since warmer air can hold more moisture, the relative humidity would be lower.

We often run a dehumidifier in our basement during the summer, but it really came in handy this fall because the temps were too cool to run the A/C, but the air was very humid (not normal for us in the fall). It definitely helps in both cases.

[Ted Reischl]

The problem is that the air warms up faster than the equipment. Just like a nice cold beer on a hot summer day moisture forms on the cold glass.

What has been working for me is to circulate the air in my shop. I suppose I could come up with some theory as to why it has been working but my brain is too tired.

I suppose what happens is that as the air moves across the equipment the equipment keeps pace with the air temperature avoiding the differential between the air and the equipment? Anyhow, it has been working for me. A while back one of my neighbors gave me an old time GE fan that moves air really well. I just have that blowing along a wall creating a circular airflow in the shop.

[Peter Quinn]

I don't think of this problem as an either or situation. You need to control both the temperature and the humidity to control rust. Iron will definetly rust in a well heated swamp. I worked for a guy that had a lot of wood in warehouses, he was consulted to keep them at 50 degrees minimum in cooler months to stay above the dew point. Let's the air hold more moisture, so no moisture is free for absorption by the wood. Otherwise the lumber becomes a willing sponge. It's about stability. Here in CT we don't generally have a humidity problem in winter but you can easily create condensation as noted by heating a space, particularly with wet heat like propane, then working in it and breathing all day.... Then dropping the heat rapidly by shutting off the heat....big dew point, wet rusty iron.

My home shop is in an old basement. Temperature is very stable seasonally thanks to the earth despite no heat or AC, no rust issue. I do have a serious dehumidifier to over come the moisture vapor that concrete can transfer to a closed in space like a cellar. Those small consumer grade units make more heat than moisture control and don't tolerate dust well, I burned out 5 of them in as many years before switching to a Sante Fe unit by Thermistor. Serious dehumidifiers are capable of maintaining a set humidity level if sized to the space and working down to cooler temperatures than some home models allow.

So if you are going to heat your space, you need to keep it always heated, and avoid temperature fluctuations of more than 12-15 degrees, or your iron becomes a dehumidifier. And if your RH rises much above 55% you probably want to control that too. Running the heat in summer won't keep the iron rust free in the garage! If you need cooling in the summer that will also dehumidify, but a real dehumidifier is cheaper to run and more effective at controlling humidity, might be a better deal at temps below 80, or whatever your personal comfort level happens to be. IMO, you really need heat, AC AND dehumidification for a fully effective rust control system and for the stability of your lumber and projects.

[Charlie Velasquez]

A dehumidifier is an air conditioner that's not split so that it doesn't expel the heat to the outside. Otherwise, the only reason an A/C would dry the air faster is because it's a larger unit. One could argue that if you had an A/C and a dehumidifier that had the same amount of refrigerant, and same size motor, coils, condenser, compressor, etc. the dehumidifier would dry the air MORE because it would also raise the ambient temperature. Since warmer air can hold more moisture, the relative humidity would be lower..

This...As I work with our school district's energy program, about all I do during the summer is try to control humidity the cheapest way possible.
Looking at the climate data for Philly, except for Jan. & Feb. it almost mirrors our climate in eastern IA
Probably from about late May to mid October the goal is to eliminate water vapor. Dehumidifiers do this the best and are less expensive to run. If you are not going to be in there, then a dehumidifier, set @ 50%, hooked up to some sort of a drain, or a 33 gal trash can if there is no drain (we use 65gal containers in our schools) will do a great job. Then when you go in, you turn off the dehumidifier and turn on your A/C.
The room will warm up some when you are not in there, but that is not necessarily bad. Air changes temp quickly, cast iron,-not so much. Your tools will be a few degrees warmer than the air when you start working. Should any moist air come into the room you have that temp difference as a buffer for a while. When you leave, turn the dehumidifier back on.

In the winter time dehumidifiers are useless (at least in Iowa). The moist air passes through coils at about 45 degrees. So they exit the dehumidifier at 100% RH at 45*F, then mix with the rest of the air to lower the space RH. Probably the dew point of Nov-March air is already lower than 45* so the dehumidifier really doesn’t pull any water out. The solution, then, is to heat your tools. About 20 degrees above dew point is a good estimation of 50%RH. We worry about mold, so that is a number we look at a lot. Rust may not need that low of a RH, but if you have books or organic stuff in your shop you may want to keep that number in mind.

You said your shop is well sealed. If that is the case any size dehumidifier will work. As an example during a construction project on our HVAC, mold was a very real concern. Our high school media center (20m X 62m X 6m) full of books, upholstered furniture, and carpeting, was completely sealed off for the summer. All ducts were sealed. We started with several dehumidifiers, but after the first week, one 30 pint dehumidifier draining to a custodial mop basin kept the space at 40% RH during a very humid Iowa summer. The first couple of days it will pull the max water out, after that it will pull less and less until it equalizes.

[Michael Peet]

Those small consumer grade units make more heat than moisture control and don't tolerate dust well, I burned out 5 of them in as many years before switching to a Sante Fe unit by Thermistor.

I have exactly the same story. The Santa Fe is in a completely different league than the ones we find at the BORG. Worth checking out if you want to manage humidity.

Mike

[Jim Becker]

I have never had an issue with rust on my cast iron in the shop...once in a blue moon, I will apply a little wax, but that's about it. My shop is not heated or cooled unless I'm actively working. That said, I'm sure that in some areas, excess moisture can be a problem so dehumidification, heat, etc., can be very helpful. Regular maintenance will also help keep rust at bay...cleaning and waxing, etc.

[Ryan Baker]

As mentioned, if your shop is small enough and well sealed enough for heating it to be an option, then heat it (at least to about 50 degrees or so). But if you heat it then keep it heated. If you don't heat it then leave it cold. You need to avoid the temperature swings up and down (either due to heating some of the time or just to ambient temperature changes at this time of year) where you end up with warmer, moist air condensing on the cold metal of the machines. Whatever you can do to avoid that combination will help. A dehumidifier may help in a sealed space, but probably won't make much difference. Machine covers may help if they don't actually trap the moisture under them. Any bare surfaces should be coated with something like paste wax to give a little more protection from any condensation before it has a chance to evaporate again.

[Michael Yadfar]

So if I added heat in the winter, I still don't need a humidifier, right? Just the summer is my concern?

[Charlie Velasquez]

So if I added heat in the winter, I still don't need a humidifier, right? Just the summer is my concern?

Correct. Right now at 3:40PM Central Time the dew point in Glen Mills is 31*F. If you heat your shop to 50* your RH would be about 50%, more than dry enough and warm enough to inhibit condensation.

A dehumidifier would not be any more effective than this, as the dew point is already lower than the expected coil temp of 45*.

Notice the forecast shows an increase in outside RH, to close to 80% in the next day or so. This will have NO impact on your RH inside. The Outside RH is going up because the temps are going down. The actual water vapor is not changing much. You are only concerned with water vapor compared to the inside temp of your shop, not the outside temp.

[Jim Becker]

So if I added heat in the winter, I still don't need a humidifier, right? Just the summer is my concern?

Yes, with qualification...what kind of heat you use matters. For example, unvented gas (like a typical propane wall or stand-alone heater) pumps out a lot of moisture as a by-product of its combustion. Vented gas, electric heat pump or electric resistance, etc., do not have this issue.

And as previously mentioned, regular maintenance and waxing can help a lot.

[Michael Yadfar]

Yes, with qualification...what kind of heat you use matters. For example, unvented gas (like a typical propane wall or stand-alone heater) pumps out a lot of moisture as a by-product of its combustion. Vented gas, electric heat pump or electric resistance, etc., do not have this issue.

And as previously mentioned, regular maintenance and waxing can help a lot.

Everything was just recently waxed. The kind of heat I plan to use is an electric oil heater which won't produce any moisture. I do have a tank top propane heater which is really nice because it produces a lot of heat, but I never used it in the shop due to what you just said. Plus I try to avoid open flames in the shop due to the fact there's a lot of wood and foamboard insulation