So, I have built a room inside my shop, a clean room for finish and airbrushing. I want to cool this room as I spend more time in it than the rest of my shop (garage) So, I get a portable unit. Block walls, no possibility of a window unit. The room I built is false..that is to say it's not correctly framed, finished, insulated, etc. It's just insulation panels, so it's not, nor will it ever be air tight. The portable AC unit seems to make it more humid in the room - my theory is it's pulling the hot, humid air in from the shop and not really helping. So .. my question.

Can I put the unit in the shop, and run a duct for the cold air into the room I want to cool? I have an exhaust fan (on the way) that I will install in the room to exhaust the air.

  • This is more of a buying type question and I don't know. But I have seen window units that have areas to run a duct line. I doubt that these will cool much unless you are spending a lot of money because these unites don't usually have blowers.
    – DMoore
    May 4, 2015 at 18:41
  • He's talking about a portable, which is a floor unit and has an exhaust for the hot air, I believe. Sep 5, 2015 at 12:04

2 Answers 2


I've seen several unique installations of portable type air conditioners. The true difficulty comes as you need to have a separate location to exhaust, which will get both hotter and more humid. Fundamentally, an air conditioner is increasing the temperature gradient between the cooled side and the exhaust side. This exhaust side is typically meant to be outside, as the way most of these uprights are built, blows a healthy majority of condensate out as water vapor. I discovered this after I disassembled mine completely out of curiosity.

To get more directly to your question, unless you have a good and thorough seal between the area you're cooling and area your exhausting to, you will actually just be disturbing more air and creating some odd microclimates.

It matters less if you pipe the exhaust out, or if you pipe the cooled air in. What matters is that you contain the cooled air and prevent it from re-mixing with the unconditioned air.

However, these units can create a bit of negative pressure near them as they exhaust some air from the conditioned space, over the heat exchanger. So your suspicion that it is pulling in the air from your shop that it sounds like is both unconditioned AND it sounds like you're exhausting to.

I would surmise, that creating a positive pressure from blowing in the conditioned air might feel more comfortable, but know that you're creating a fairly small space with both a dry cool area and a warmer, more humid area. This could cause problems with things like condensation, mildew, corrosion, etc. if there were enough moisture throughout.

It might be good to pair this with a dedicated dehumidifier also.

Also, it's worth noting, that the recovery time for these type of units is quite poor. It makes more sense to let them run as much as possible, and the larger/more hot and muggy the room you're conditioning, the more lead time they'll require.

I would also go ahead and check how the exhaust vent line is attached. If it's misaligned, has a tear etc, you would just be blowing heated and moistened air near your unit.


The portable, roll-around floor unit is indeed drawing air into the clean room. It does this because the exhaust hose is only an exhaust and it moves a good deal of air. Probably you have it exhausting into the garage immediately outside the clean room so it is indeed pulling humid hot air into the somewhat cooler clean room.

Even if you sealed up the clean room very well, hot and humid air would continue to be drawn into the clean room somehow: under the door, through the ceiling, through the hole beside the a/c exhaust hose, etc.

The solution is to either modify the a/c unit or replace it with a more suitable version. There are two hose portable units—no longer very popular—that would work much better. Or if your current unit is suitably designed, you could modify it into a two hose unit. If those aren't workable, replace the portable with a window style or heat pump style air conditioner. Those isolate the airflow and move the heat far away. You would have to install limited framing in your clean room to safely support either.

enter preformatted text here The pictured unit is here, but it is certainly way overkill for your needs. Here are smaller, more suitable units.

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