Dear PoPville – Does anyone use a portable air conditioner (not a window unit) to “boost” the coolness of their top floor?

Photo by PoPville flickr user caroline.angelo

“Dear PoPville,

Does anyone use a portable air conditioner (not a window unit) to “boost” the coolness of their top floor? I have a 3 story rowhouse with central AC. The thermostat is on the 3rd floor. I keep all the vents on the first 2 floors closed and covered and am comfortable with the thermostat at 78-80 – but the folks up there need it set around 76 to really be cool – so I am too cold down here.

I have good windows and thermal shades to keep the sun out. I tried a window unit up there, but the only good window is south facing & over a roof so despite all sorts of sealing attempts, lots of heat pours in around the unit, defeating the purpose.

I’ve read about 100 online reviews of 100 models of portable air conditioners and am more confused than ever. Has anyone actually used one for this purpose?”

53 Comment

  • I’m looking forward to the responses here…

    I have my contractor coming over tonight to look at this. The AC flow on the second floor master bedroom is poor. I’ve tried closing vents, keeping blinds closed all day/night, etc and nothing works. I’ve even removed the vent cover for maximum flow.

    Home Depot and Lowes sell a register booster product– it looks like a small fan which is placed over the register and is plugged into an outlet. My register is on the wall, near the ceiling so this won’t work. I’m considering having the contractor increase the size of the vent and possibly the duct to the vent.

  • I used to have the same problem in a similar type rowhouse. My HOA did not allow window units, so I bought a portable unit. It was a great decision. It made a huge difference and I don’t remember seeing a huge increase in power bills. They are kind of large and many requiring periodic emptying, but it it completely worth it.

    I can’t remember the model, but I bought a relatively cheap one.

    • For the original poster or others considering a portable A/C unit:

      Try to find a model that does NOT require periodically emptying a tray/container thing that fills with water.

      It’s annoying when the unit stops in the middle of the night and won’t restart until you’ve emptied the water. And it can also be tricky to carry the water-holding device to the nearest sink without accidentally spilling some of it.

  • me

    How did I not know about these? I am in a house with a heat pump, so the a/c isn’t horribly great. The basement is nice and cool, but the bedroom on the top floor is almost unbearable at night, even with the ceiling fan going. I’m sorry I don’t have anything really substantive to add for an answer, but I would really like to know this as well. Thanks, OP.

  • I don’t know if this counts, but I’m using a portable air conditioner (not a window unit) because my regular HVAC (heat pump) is broken.

    In my opinion, it’s not as good as regular forced-air air conditioning, but it’s much, much better than nothing at all or using window fans.

    Have you tried getting the air ducts cleaned? I vaguely remember reading that a lot of duct-cleaning companies are sketchy, but if your air ducts are in fact clogged, maybe that would explain why the air flow is so poor.

    • Whoops, the part about the air ducts was intended for Anonymous 2:34 p.m., not the original poster.

      • This particular duct line is less than 3 months old. It’s a newly remodeled suite which included new duct work. I have some exposed duct work on the first floor…I need to check it for leaks.

  • Buy them a window unit and a fan and call it a day. A portable unit will spike your utility bill and it won’t run during Pepco “brown-outs”. They can also put a lot of strain on your electrical system and ruin floors with condensation dripping. Window units are quite powerful these days, they can stick it in their bed room to stay nice and cool 5000-7000BTUs should do the trick, anything more is overkill for a 800sf floor in a rowhouse. If all else fails use a circulating fan to blow air up through the stairwell.

  • I have to wonder if the existing system can somehow be adjusted to equalize the flow.

  • pablo .raw

    There are too many variables here, but basically if your duct system was designed properly you shouldn’t need to close vents. Looks like what you really need is to make sure that the hot air on the 3rd floor goes back to the unit to be conditioned, and that happens through a properly sized and located return duct. The return grille is usually located in the hallways, but if 3rd floor doors are kept closed, then air is not going back to the unit to be conditioned. I think you need to talk to an HVAC specialist.

    • +1. A skilled ductician could probably remedy the problem, but the solutions often vary in complexity.

  • Not to hijack a post, but I have a related question. I have heard/read differing accounts of whether vents should be closed in unused rooms or, for example, the basement. Some articles claim it will not lower Pepco bills and will decrease the efficiency of your system, while others say what seems to make sense intuitively — it is cheaper to cool fewer areas of your house. (DC Victorian rowhouse, brand new heat pump systems, one upstairs, one downstairs/basement.)

  • I just went throught this two days ago.

    Issue: 3 story Victorian. Thermostat and main AC unit/furnace-thing on first floor. Hot third floor while cold first floor.

    Intended Fix: purchased a cheap AC window unit at home depot and planned to install it.

    Actual Fix: Ran my hand around AC unit/furnace thing and discovered a lot of leaks. Purchased duct tape at home depot and patched many of them. Also, placed saran wrap under most vents on first and second floor. Keep door closed on third floor and lower window blinds to avoid light and heat during the day. Problem solved! 3rd floor is a lot cooler. Haven’t used window unit yet.

    • What was the saran wrap intended for?

      • The saran wrap prevented the air from going onto the first and second floors, which were cold enough. By having fewer open vents (and just closing a vent doesn’t seal it well), it forced the air to the third floor.

        Oh.. and it hides the stench of the dead body in the duct.

        • Emmaleigh504


        • I would not recommend completly sealing off lower floor ducts.I tried this. It worked great for about a week untill my central airconditioner compresser froze. I turned off the air, let everything thaw out, and it worked again for another few days untill it froze up again. I had to remove the tape from the first floor ducts and the problem stopped.

  • I have one of those to cool my apartment. It’s loud and large, but it works great to cool the place. I have a dual-hose type so you don’t have to drain it.

  • Do you have a properly vented attic? If not, you probably have 150 degree temps in your attic that transfers into your 2nd story. Not even the most efficient AC can take care of that.

  • 78-80?! eesh, i keep mine on 69-71

  • We have one on our upper floor. Problem I am having is that the waste heat is ejected through a long duct that itself serves to heat the room, so even though it blows cold air big time, the heat from the duct offsets it. Need to figure out how to insulate it.

    • Yes – the duct issue was one of the primary complaints on all the reviews – plus the noise.

      Thanks for all the thoughts so far. A couple of other facts

      – The actual HVAC unit is in the basement, so the air just has a long long way to go to the 3rd floor, and the air return a long way to get back.

      – I have had it serviced regularly, so leaks shouldn’t be a problem. I’ve asked several HVAC guys for solutions but no one really has any.

      – I did put plastic wrap under some of the air vents last year, but it looked like some mildew was starting around the edges, so maybe not a good idea.

      – I bought a bracket thing so I might be able to figure out how to stick the window unit in a front window where the intense sun and roof heat won’t seep in around it.

      – and yes, I am an AC whimp! I have to bring leggings, socks and a sweater if I go to a movie in the summer.

      • Are the 3rd floor vents running through your attic? What temperature is your attic? Do you have vaulted ceilings and your ducts are running within inches of your roof?

        If you don’t have vaulted ceilings, buy and install an attic fan and insulate the HVAC pipes in the attic to prevent heat loss. Lowering the temperature of your attic will increase the life of your roof and lower the heat load on the upstairs bedrooms.

        I second the “a properly designed system should not do this”.

        If your regular technicians are servicing your AC system and not solving this problem, then you need to fire them. Call Argent if you haven’t already. They’re pretty good.

        Just some thoughts.

  • I have central air with the air handler and thermostat on the first floor. To get and keep the third floor cool with the vents closed on the first floor i had to set the thermostat at 68, i.e. the first floor was an ice box. Then I went to window units on my third floor. Cool bedrooms hot bathroom and hallway. Finally two years ago I had a new A\C zone added for the third floor w\its own thermostat on the third floor. HEAVEN. I wish I had done this a long time ago.

  • Reading some of these solutions make me laugh.

    1. Closing wall/floor vents isn’t going to reduce your electricity bill. The units are still producing the same amount of chilled or heated air, you are just blocking the end flow.

    2. Unless you know how your system is zoned, then putting saran wrap over vents on seperate floors is either the placebo effect (you “think” its doing something when in reality it isn’t), or your HVAC system is so old that your entire house is a single zone, which hasn’t been done on 3 story houses in a couple decades.

    Here are two solutions that will actually work. They will work independantly, but work best together.

    1. Make sure your attic is properly insulated, and I am not talking about a layer of haphazardly thrown down fiberglass. I mean getting your attic up to an R-35-R-40 with a foot of blown in spray cotton/denim or cellulose (about a 1.25 per sq/ft installed) or if you are feeling frisky, some spray foam (about 2.75 per sq/ft installed).

    2. Install a white roof. If you have the typical DC rowhouse roof, its a flat black torch-down asphalt roof that is either black, or if you are lucky, silver. If its black, your roof is just absorbing the sun, heating your third floor like an oven making it impossible for your HVAC to keep up. White will reflect about 90% of the sun. The surface temp differential in direct sun from a black to white roof can be anywhere from 50-100 degrees. Its a no brainer.

    Google white epdm membrane. It sells for about ~1/sqft and you can just lay it down over your existing roof.

    Or, Lowes sells a rubberized heavy white roof coating paint that you can paint on your roof.

    You need to solve the problem of why your 3rd floor is so hot. Not simply try to treat the symptoms.

    • Thanks but

      1. The goal of closing vents is not to reduce the bill but to force more air up to the 3rd floor – you’re saying that doesn’t happen?

      2. How do I tell if my system is a single zone or not? There is only one thermostat – on the third floor. The house was renovated around 1990 – before I bought it.

      3. I’m not feeling frisky enough to tear down any ceilings right now to check the insulation.

      4. The roof is already painted white – a roof guy checked it and said it was good for low heat absorption.

      It isn’t that the 3rd floor is terribly hot – it isn’t. I’m just trying to get it a little cooler without freezing me on the lower 2 floors.

      • pablo .raw

        Like I said in an earlier comment, there are many things that could be wrong and we are all trying to guess :D.
        You say your unit is serviced regularly, that is different to say that there are leaks in the ducts that take the air up; what if some of that air is not being delivered to the third floor? Also, is that the same HVAC unit when you bought the house? Newer HVAC units are much more efficient, look for Energy Star Seer 13 or 14.

      • You have a single zone system. They continue to be installed in America even to today, despite the previous poster’s comments. They’re more expensive, because it’s more components.

        One solution would be to move your Thermostat to the 3rd floor. However, you’ll have the reverse problem in the winter that you do now.

        Closing the vents on the lower floors is the only real solution. The major question is whether the 3rd floor pipes are somehow partially blocked or whether your fan isn’t strong enough to push air fast enough up to the 3rd floor.

  • The location of the return vent on the top floor of your multiple level row house is important for proper air circulation.

    Hot air rises naturally and this is dramatically evident in a row house with multiple levels.

    What is needed and critical is that the return vent be located properly and at the highest point possible; on the ceiling of the top floor above the stairs is good.

    The return draws air back down to the air handler which cools and recirculates the air throughout the house.

    As a previous commenter wrote, an attic vent that allows for air flow within the attic and there not to be an oven of an attic with static hot air will also facilitate the cooling of the living areas of the levels below.

  • I have a similar situation to the OP, actually. I live in a 3bd apartment in the master bedroom, which has lots of windows. The central a/c doesn’t cool it much in this hot weather, so I have a portable air conditioner that I use to supplement it. It works really terrifically, and I’m so glad to have it! I actually bought it last year when the building I was in kept having the a/c break for weeks and weeks at a time.

    The model I bought was from Home Depot, and it doesn’t need to have any water emptied. I think it cost about $300, which was a pretty big investment, but SO worth it in the summer!

    HOWEVER – it’s loud, and pretty directional. I really think the OP should just turn the thermostat down and wear a sweatshirt in order to save the tenants the added annoyance of the noise (I can’t watch TV in the same room as my portable unit because it’s so loud). 76 is not an unreasonably low temperature for the tenants to request – I know I’d request 70, so perhaps OP should count themselves lucky!

    • This is pretty much us, too. Our master bedroom faces west and it’s easily 82 in there by 6pm–even with the insulation we had blown in last fall (for about $1k/800 sq ft, for the guy below who asked). Part of the problem is that the ceiling in the room was raised to almost 12 feet, so we only have a couple of inches of insulation in the attic above.

      Also, the vents are stupidly placed and no matter how we close vents and an in-duct lever, we just can’t get the room cool. We only run the portable AC unit at night because I cannot sleep in 82F, even with a fan going. It works, but it is very loud, and I don’t think it would cool our entire upstairs.

      We are debating a split-system unit to heat and cool the upstairs, since we have issues with both depending on the season. They’re not that expensive–definitely far less than a second zone traditional AC unit.

  • Insulation is cheap, and incredibly effective. Or get a duct blaster test to determine if you’ve got a severe disconnect behind a wall. the “cool roof” theory isn’t that strong around here….maybe if we lived in the sunbelt.

    Pop two access panels on the high/low sides of the ceiling and dense pack blown insulation into the space. You will also probably feel more uniformity in temperature during the winter months.

    Portable units don’t ever work well IMO

  • I have NOT read all the responses and am just giving my experience.

    I bought one of these units (Everstar – BTU – yea, it’s gottem) from Home Depot for about $400 a few years ago when my mom – from a cool, non-humid climate – was visiting me for an extended vacation a few years ago. That was my impulse.

    Since then, I have used it faithfully in my upstairs room that I use as an office, where the computer is located and where I spend most of my day.

    Yes, I have to keep an eye on the drain pot (not a technical term). On super humid days (like we are having presently), it fills about every two hours. Fortunately, I have a window that drains into the birdbath positioned for this purpose. At night, depending on the forecast, I either turn it off or turn it to “fan” to avoid this interruption.

    Additionally, I use four window mounted exhaust fans: two in the bedroom, one in the living room and one in the kitchen. I rent, so permanent installation of anything is not a choice. My upstairs stays at a tolerable 86 during the day and drops to the mid-70s at night. I can live with that.

    Back to to A/C. It’s my little R2D2, which it resembles. I thought it was a true extravagance when I bought it, but I gotta tell you, of all my appliances – including the microwave – this is the one that has made every day a little bit better.

  • I, too, live in a DC rowhouse where the second floor gets little to no air circulation…I have been speaking with my HVAC guy about possible options. He mentioned the register fans that someone else has already mentioned. He also suggested trying Mitsubishi’s Mr. Slim… It’s different from a window unit because it is mounted on the inside of your home, high on a wall (the wall must be an outside wall to the house because the device connects to a different part that must be outside) and they are supposedly more efficient and less of an eye sore, although they are more expensive than window units, largely for those reasons. Has anyone tried using one of these? Also, with regards to putting in a second A/C unit for the upstairs, he recognized the space limitation in the DC rowhouses. He suggested putting another unit on my roof, since my roof is flat. He warned me that there would need to be all kinds of permits required to do this, including a permit to get the crane necessary to lift the unit to the roof. Has anyone ever considered this, as well?

    • He’s talking about a split system; they’re used all over the world, literally, except for the US. Personally, I think they’re great: if you only need AC in one room, you just turn that one on. You basically would be creating a second zone by installing it. You can get them with up to four separate blowers, so you could have an individual blower in each of your upstairs rooms. Some even do heating and AC. I have no idea about permits required, though.

      • Dress, have you received any cost estimates for a split system? Is there an HVAC person you can recommend for this type of work? Have you tried using register fans first? Is it worth exploring that option?

        • Sorry, I haven’t looked into it beyond checking prices for the split system alone on the internet–no idea what the installation would cost or who could do it. We haven’t tried register fans, largely because it wouldn’t help due to the really stupidly placed registers.

  • Many people have suggested installing insulation and an attic fan. Any recommendations on who could perform this work? I know installing installation could be a DIY but the attic fan seems to require a bit more skill and I have 0 DIY skills.

  • I commented on exactly the same issue a few weeks ago on POP. There are lots of options depending on your criteria and budget. Best temporary solution is to use a 3rd floor window unit. If you rebalance your ducts minimizing air flow to the thermostat location it will cause your main unit to run constantly and boost your electric bill by more than the cost of running a window unit.

  • i have been using a portable unit in addition to my central ac for two years now. 7000 btu, got it from target. it does not need to be emptied, it works off evaporation. it reads commercial cool on the front. i like it cold and this did the trick. good luck.

  • I had my AC condenser moved from the ground level to the roof 2 years ago. I live in a 2 story rowhouse. The contractor told me they needed a crane to move it to the roof—not true. The condenser weighs 50 pounds. They tied a rope around it and carried it up a ladder.

  • I’ve used a portable A/C, but in a basement rather than on the third floor. It’s not great, but better than nothing. For us, it was one of few viable options as the windows were small, oddly shaped and oddly placed (and we didn’t want to block any). A few things to note:

    1. Portable units work best in small spaces. The bigger the space, the more BTU’s you need and the less well it will work.

    2. The unit is big and bulky.

    3. The unit has an exhaust hose that has to connect to a window. The shorter the hose length, the more efficient the cooling (because as somebody else noted, the hose loses heat back to the room).

    4. The unit has to be either continuously drained, or (depending on humidity & how much you run it) the reservoir emptied once to several times a day. If you run the drain hose into a bucket with the best of intentions of emptying it periodically, it WILL overflow and make a mess.

    It may cost more, but in the long run a mini split (ductless) system may be a better option. This is what we’re investigating for our basement apartment.

  • I bought a large portable LG unit from Overstock about a year ago and it’s served me well. It cost me about $350 (including free shipping) and its served me well.

  • Also, make sure that you have enough power for a large unit. I recently had to install and extra panel/power supply to run my AC upstairs to my portable unit. They suck up a lot of juice!

Comments are closed.