Portable Air Conditioner Question

I live in a 2 story condo which does have central air, however it doesn’t do a great job of cooling the upstairs (pretty typical for 2 story buildings from what I hear). Pretty much I can crank it down to 70 downstairs, and it’ll still be mid to upper 70’s upstairs where unfortunately my bedroom is. Looking for a way to “supplement” the cooling in just that room, hoping to bring it down by about 5 degrees or so. Cost to operate isn’t a huge concern, of course I’m not saying “spare no expense” (because then I’d just get a better central unit), but I’m OK with paying some higher energy bills for the 3 or so months I’d need to run this. I live in the northern part of the US so even during the summer its not always hot, I’m guessing about 30 days a year I’d need to run this “bonus” cooling system.

Window A/C units are not allowed by the condo association, so that’s out, however I’m considering a portable indoor unit. Main concern there is that I realize they still need a vent hose, typically out a window, but unfortunately the window isn’t the right kind (cranks out instead of sliding up and down). Looking for a plan B since I can’t go out the window. 3 options that come to mind would be into the central air return in the room, just venting into the next room (which is vacant), or venting up into the attic above the room. Not sure if any would actually work, looking for advice. I realize not venting to the outside may defeat the whole purpose, so maybe this is impossible.

So, any advice? I’ve already gone through the process of closing/opening vents in other rooms, had a buddy tune up the A/C, and running a ceiling fan, which did improve the situation, looking to finish this off and take the room from bearable to comfortable. More or less during the summer I’m not home that much, so its almost like there’s only 1 room I even care if is cool, and it happens to be the one most difficult to cool.

No real advice but to say that we’ve just inherited an indoor air conditioner and have the same crank windows. My father in law is very handy and is working up a custom plexiglass insert for the window with the outlet hose holes built in. Not sure how well it will work but that is an option.

I bought one this afternoon and I’ve just now turned it on. It’s 83 in here right now. Let’s see how it works!

Two-story houses that don’t have zoned control for the AC can be balanced by closing the first-floor registers. Try opening all the top-floor ones and closing all the bottom ones a little over halfway.

Also make sure that all doors are open or at least ajar.

Also keep in mind that AC works very differently from heating - it doesn’t just “blow cold,” but works in a balanced loop and can take time to stabilize. You also want a certain amount of runtime to dehumidify the air - having a huge AC unit that only runs 1% of the time will be completely uncomfortable, because you’ll have chilly, damp air.

So assuming that your AC is at least nominally sized and installed correctly (right number of vents in the right places, etc.) try the vent-balancing for a while. Keep closing down the lower floor ones until (about 24 hours after each change), you have comfortable temps up and down. What you’re trying to get is the heat from the bottom rising up to the top and being sucked through the system, without over-cooling the lower floor. It can be done in most cases but it takes a little patience and you can’t screw it up by assuming you can turn the AC off for two days, then get instantly balanced temps again.

81.2 woooot! I have it set for 77, I’m curious if it’ll get down that low. If I can have my apartment at 77 in the summer I will cry with joy. I live on the top floor in a south facing apartment. The sun is wonderful in the winter but in the summer it regularly gets up to 100 in here. I’m so excited!

Does anyone know if it’s ok that the seal isn’t air-tight in the window? I squished a small strip of cardboard in there. But are there any dangers or fumes I have to worry about?

I’m sure it’s an electric air conditioner so your only worry is general loss through any gaps, meaning cold air escaping and hot air making it’s way in.

ETA: also, bugs could get in through a gap

Thank you! I have birds so I’ve been keeping an eye on them, they seem fine but now I won’t worry. :slight_smile:

Check to see if you have 2 return air vents. ONe up stairs and one down stairs.
In the summer when the AC is running I restrict the downstairs one some. Do not cut down on the total amount of air flow or you will have other problems. I also put the fan on “on” rather than auto.

In my house as designed the 2nd floor return air was put low on a hall wall. I extended the duct to the top of the wall and put adjustable registers on the returns up stairs. In the winter top return closed bottom open. Summer top open bottom closed.

Would this one work for you? Looking at the pic of the window install, it seems like it may work.

Could you cut a piece of 2" thick foam the same size as the window, with a hole in it for the exhaust, and then just push it into the open window when the unit is in use?

Going back to (cheap) dorm living: Poor man’s Air Conditioning = aluminum foil taped, reflective side out, to cover the glass.
Is also good for us nocturnal types who sleep during the day.

OP: find cardboard, foan board (the stuff at Home Depot, sold as insulation would work - anything you can cut and get to jamb in the window opening (close the window onto the board) and cut a hole for the hose.

If the attic is well vented (don’t count on it), it could accept the hot air, but I wouldn’t bet on it - stick a thermometer up there.

And play with the vents, as suggested.

Your plan to vent into the return or a vacant room will work, I have seen this in business settings. I is not all that terribly inefficient because it’s easier to cool hot air then cold air, so the hot air exhaust will lessen the energy requirements of the central a/c. Not that it won’t cost you more, but it should not be way out there.

It may also save you money if you can turn up the central a/c temp at night and ideally just run the fan (using it to distribute the heat from the portable unit), while using the bedroom a/c for cooling.

The laws of thermodynamics are interesting on your world. What color is your sky? :slight_smile:


We also have casement windows (aka crank-out), adding central air to our house was something like $13K for 2 rooms (:eek:), and we weren’t about to cut a hole in the wall to put a standard window AC unit it. So a few years ago we invested in two free-standing AC units and had a window store cut custom plexiglass inserts for a couple windows. They work fine.

That said - they are not as powerful as the standard square AC units that sit in the windows, or central air. They will get the heat down to manageable levels (70s or so) but the don’t provide the cooling blast that the other types do. At least, our units don’t. They are about 8 years old now, it could be that the newer ones are better.

A/C guy told me to pick a temp, set it, and don’t change it but maybe twice a year if you just have to. Works for us.

Have left the fan on for long periods, up goes the bill but when guests are up stairs we do it for them if we are having a lot of door openings and closing…

Up stairs are vents ‘closed’ year round except when guests using it.

Replace filters or check them at least once a month or more, weekly is good/necessary in some conditions.

I have an upstairs office with a computer and a TV, and I generally keep the door closed so I can work in privacy. It can get very hot in there with the electronics, etc., when the door is closed, even with the central air fan set to ON instead of AUTO.

The room has two vents for the central air at floor level, but the returns are located in the hall. With the door closed, there is not much air circulation, and the cooler air tends to stay low and go out under the door.

I purchased two small fans that I can tilt upwards (like the ones from Vornado), and placed them near each of the floor vents. They pull the cooled air from the vents and blow it up towards the center of the room. Makes a huge difference.

Obviously your sky is pink. Extreme example, is it impossible to cool air below absolute zero.

The colder the air inside (the outside remaining constant), the more energy it takes to move heat from the inside to the outside.

Depending on the OP’s interior design there may be one more easy modification to help the air balance.

If your staircase is enclosed, install a curtain across it. All you need is an adjustable spring-rod and a simple fabric curtain. Target sells both. Install it wherever you can so it blocks the vast majority of the opening. Typically at either the bottom or top there’s a space which could conceivable have a door installed. Just put the curtain there. Ideal the rod is just below the top of the frame and the curtain bottom just drags the floor. But if you’ve got an inch or two gap at top or bottom or both it’ll still be a big improvement.

To use the stairs, just sweep the curtain aside with one arm as you pass through. For parties or moving big stuff, just take it down & put it back up when you’re done.

Doing this, plus adjusting the output and return registers as suggested above will massively improve your upstairs/downstairs temperature problem. And it’ll only cost $20-30. Much cheaper than buying a portable AC, jerry-rigging an exterior vent, paying for extra electricity every month, etc.

Of course, if you have an open plan unit with no way to wall off the upstairs from the down, then this idea is useless for you.

Do NOT get a heat/cool a/c. Find and buy a device that does only cooling. You want something that works well in one direction, not something that works badly in both directions.

There is a lot of difference between the units. The best one I’ve used does a good job of using the condensate (from the cold side) to cool the hot side, and blowa out humid air. Sometimes when the inside is too dry, I had to add water to the drip tray to make it work effectively.

I think the point is that if the portable a/c is not exhaust vented to the outside, whether it’s into the same room, another room, or into the central a/c return, it will increase the heat load on the central a/c beyond what the portable a/c is doing to cool things off.

It would be like opening the doors to the fridge and freezer in an attempt to cool off a hot kitchen.

Not only will it not work - it will make things worse. Because thermodynamics.

Also, to those suggesting that he adjust the vents to balance things out, from the OP: