HVAC for workshop - Controlling rust?

[Brian Elfert]

I am in the early planning stages to build a 600 to 900 square foot shop next spring/summer.

HVAC is my biggest question right now. The shop will be fully heated and air conditioned. HVAC will be central, not window units or the like.

How do I control rust without pushing my energy bill through the roof? I live in the Minneapolis, MN area so the temps get real low in the winter and fairly high in summer with high humidity.

I don't want to keep the heat over 40 to 50 degrees in the winter except when I'm in there. Will the temp changes cause rust?

I also don't want to air condition under 80 degrees or so unless I'm in the shop. How can I remove enough moisture from the air to keep the tools rust free? I am thinking maybe two A/C units smaller sized so one can run all the time and both when I'm in the shop.

Brian Elfert

[RonB]

I am not an expert but I would think installing your central heating and air will be one great step forward in controlling rust. Many of us have to contend with heating, as best we can, during the winter and have few cooling options except fans. Any level of air conditioning will tend to remove moisture.

I suspect your greater challenge might be winter when raising and lowering shop temp might cause condensation. Not familiar with the extremes in Minnesota. I just try to keep things cleanded and metal tabletops treated.

RonB

[Swingman]

In this Gulf Coast climate it may well be the opposite. My shop is neither air conditioned nor heated and I never have rust on any surfaces. The few I know here who have AC'ed shops are continually fighting it.

.. and therein lies the reason, IME.

[Rob V]

I just went thru this - my shop is 1250 sqft

I had him add a dehumidifer in my shop. In the winter I keep the heat on 55 in the summer the air on 80. Ive had no issues at all w/ rust. (I used to be in a open garage where thing would rust by just looking at them.

I also have timers set to turn everything off at 8pm (heat and air that is) so if I turn things on during the day and forget to turn them off - they will go off automagically for me.

Anymore info let me know.

[Brian Elfert]

Why would you want to turn off the heat and air at night?

I know you aren't in there, but wouldn't not heating and cooling at night cause rust problems?

I plan to use a programmable thermostat. I can change the temp when I am in there and the program will change it to a higher/lower temp automatically.

Brian Elfert

[cselby]

I

I live 450 miles north of you. I wish I lived where you do. I could stay in my shop shop all winter if the temp was a balmy above freezing and not -30 -40 below.

Think about a de-humidifier. It should use a lot less power and if you like it, hook up a drain hose to the condensation tank so you don't have keep dumping it.

Pete from Winnipeg

[Charley]

I live in North Carolina and have my shop in a dedicated garage size outbuilding that's insulated and has a vapor barrier. It has a 2 ton window style heat pump that I run whenever the outside temps will be below freezing or when I'm trying to work out there in the summer and it's too hot and humid to do anything without it. I keep my cast iron tools clean and the tops treated and waxed and I don't have any problems at all with rust. My biggest problem is keeping the filter in the heat pump clean (I have to clean or replace it about every 3 days of use). I also have a de-humidifier, but seldom run it if I'm going to be in the shop and using the heat pump at least every few days.

When I lived in New York State my shop was in the basement of my air conditioned home. I had to run a de-humidifier constantly all summer in addition to the air conditioning and I had to constantly clean and re-treat the cast iron or I would have rust problems. Below grade shops have a constant humidity problem.

I think that your above ground shop will be fine if you insulate it well and put in a vapor barrier while you are building it. Keep the shop temps above freezing (to keep your glues and water based paints from freezing) and run a de-humidifier in the summer when you aren't using the air conditioning in your shop to keep the humidity low (air conditioners cool and remove humidity, but sometimes you want to remove humidity and not lower the temperature). Keep your cast iron tools lubricated and re-treat the tops a couple of times a year and you should'nt have any problems. Minneapolis has damp Summers, but they can't be any worse than NC. A change in temp when you heat or cool your shop to work in it shouldn't cause any problems if the humidity in your shop is kept at a low dewpoint. Your cold Northern winters will actually dry out the air in your shop, and raising the temperature from just above freezing to a comfortable work temperature will take some time and shouldn't cause any problems at all.

[Rob V]

Sorry - when I say turn off - I mean turn off the current setting and go to automatic mode. heat on 55 in the winter - air on 80 in the summer.

I keep the shop about 68 - 72 all year round (heat or air depending on the season) as long as im working in there - when im done, I hit the auto button before I leave - If I forget (which happens) the auto setting on thermostat kicks in at 8pm and does what its suppoes to do.

[Brian Elfert]

My shop is currently in the basement of my air conditioned home. I did have some minor rust problems the first year or two, but they have gone away. One thing that may have helped is epoxy coating on the floor.

My basement has a lot of drainage around the foundation and under the floor so it never feels damp or moist, but yet some tools rusted.

Brian Elfert

[Chris Friesen]

I live in Saskatchewan (see previous Winnipeg response for temperatures).

The garage is kept just barely above freezing (2-3 degrees C) in winter unless I'm working.

It was done on the cheap using a standard bimetal thermostat, but mounting it with just one screw. The thermostat only goes down to 10 degrees, but by twisting the whole body of the thermostat to align one of the corners with marks on the wall it can be set to lower temperatures.

As suggested earlier, a straight dehumidifier will be cheaper to run than an AC. You could then add an AC for when you want to work in the heat.

Chris

[Greg O]

My shop is shared with two cars that get driven daily, year round, in North Dakota. I heat at 45 degrees, unless I am using the tools, and cool only when I am using the shop. Zero problems with rust. No problems with condensation. The floor is often wet with melting snow from the cars, but still no rust. If you are building a shop for tools only, and not for the car, you surely will not have any problems! Greg