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Community and Q&A

Inverter-Driven Window Unit AC

bfw577 | Posted in General Questions on

This looks like an interesting new design for a window ac. They claim it is inverter driven and uses 35 percent less power than a regular window unit and was awarded an energy star 2020 most efficient award. They also claim its 9 times quieter than a regular windo unit. Would be awesome if they can make one that also heats. It also appears you can get a much more airtight seal since the window is practically closed. You can also still fully open the window with the unit in place. It must screw into the sill.

Wonder if these will take off? Considering how many window units are out there these could have huge impact on lowering energy use.

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  1. iced98lx | | #1

    Been seeing this on my facebook feed as well.. Unfortunately a lot of double hung windows rely on both sashes being completely closed to seal so this still going to let air and noise in the joint, but it is a nice step forward in terms of technology used I think. Damage to window frames will looks mandatory as you noted since the window can open it must be screwed in.

    Wonder when we'll see a small two piece where the lineset + external power is flexible enough to be put through a small hole and plugged into the interior unit, which then plugs into a wall with 120v. Pre charged, extra lineset coiled in the exterior unit with the instructions being to put them directly across the wall from one another to avoid a long line set. They're basically there with this design but have removed the challenge of users touching the lineset (a great idea whenever possible obviously). I think for the more hard core DIYer sealing a 1 inch hole and mounting something on both sides of a wall is a step up from even this solution since most windows only seal their best closed.

    1. _jt | | #8

      There is something like that ... Rollicool mini split. But the performance and reviews weren't great. Especially since the manual was short and didn't cover condensate drains.

  2. Debra_Ann | | #2

    It looks pretty impressive - particularly the sound level (only 40-45 dBa). They are under production right now, with the first units due to become available in April. They come with an adjustable platform to fully support the unit even when the window is open. And they include a dense foam board to insulate the small areas that are still open when the window is mostly closed between the interior and exterior units.

    I would really love it if they could design it to heat, as well. Then we could easily install the units ourselves without the excessive prices that HVAC companies are charging for mini splits. In my area, installing a Mitsubishi mini split costs between $6,500 and $8,000 - yikes!

  3. Expert Member
    Dana Dorsett | | #3

    Any idea if it is using hydrocarbon rather than HFC refrigerant?

    1. Debra_Ann | | #4

      I read through all the information I could find, and didn't see any mention of hydrocarbon (or what refrigerant was used).

      1. Expert Member
        Dana Dorsett | | #5

        Hit the "SPECIFICATIONS" tab. Six lines down it indicates R32 (an HFC refrigerant):,000-BTU-U-Shaped-Window-Air-Conditioner

        That's too bad, but not surprising.

        Several recent vintage Asian refrigerator & window AC designs are using combinations of hydrocarbons as the refrigerant, which have a much lower environmental impact than HFCs but are flammable, and thus a hazard in the event of a leak.

        In the US there is a 150 gram limit to the total refrigerant weight when using HC refrigerants- most home refrigerators can make it under that spec, many/most window AC units don't (but hope springs eternal, eh? :-) )

  4. bfw577 | | #6

    Found this production photo. The compressor looks exactly like a Toshiba/Midea mini split compressor. It is also interesting that the front coil is curved similar to a wall mount mini split. It also has a air vane that sweeps just like a mini split.

    Maybe this might spawn small really cheap window style mini splits. Seems all its missing is a 4way valve and you could have heat. It also doesn't look to difficult to slim the part that the window closes on down. The refrigerant lines look very small. Doesnt seem to hard to notch the bottom of the window or something to provide for the lines. If you could fully close the window and have an airtight seal that would be a game changer.

  5. 730d | | #7

    You could build it into the wall. Make a window jamb wide and tall enuff .
    Mount the unit premanently in an insulated rectanguler frame. Leave it in year round ?

    1. Expert Member
      NICK KEENAN | | #9

      That sort of installation is really common in motels. Units provide both heating and cooling. It's the cheapest way to give each room independent thermostat control.

      It can also be set up to vent outdoor air.

  6. bfw577 | | #10

    So I emailed Midea what the modulation range was for the 8k unit . The Midea rep said engineering said the btu range is around 2k-8k btu. Thats pretty impressive and I bet most small bedrooms may only have a 2k cooling load. Compared to the millions of window units that overcool running at max speed these will be great if they catch on. Midea also confirmed there is no start up surge. I also saw on Facebook that Midea posted their engineers are working on a unit that heats.

    I just preordered a 8k unit for $279 and will report back when I recieve it in April.

    1. Debra_Ann | | #11

      I asked them about the modulation range for the 12k unit. It only goes down to 6k. As for the cooling load for a small bedroom, our Manual J has our 120 square foot bedrooms at only 550 btu each - at most. And we're not building a Passive house, either. But I'm glad to hear they are working on a unit that will also heat, too.

      1. bfw577 | | #12

        Here was there response when I asked about the BTU and wattage range of the compressors on Facebook. I also asked if there would be a submittal sheet like a mini split. They claim there will be one out soon.

        "All 3 units can modulate down to 2k BTU. We are verifying the wattage at the low end to make sure we report the correct values, but it follows the trend that Brian mentioned for the mini-split. Stay tuned!"

        1. Debra_Ann | | #13

          Hmm... So they aren't providing the same information to everyone who asks. That's disconcerting.

          1. bfw577 | | #14

            It seems when you email them it's just a customer service rep that gets their information from engineering. Here is the follow up response directly from engineering.

            We have confirmed that the units will modulate down to 2k BTU. At that condition the units will pull roughly 120W.

            Based on the algorithm we use (that closely follows our mini-split algorithm) it is more common for the units to spend time operating slightly above that 2k level. For the respective 8k/10k/12k units the consumption at that capacity is around 147W/171W/190W. Let us know if you have any other questions!

  7. bfw577 | | #15

    Looks like Midea is trying to get a waiver from the DOE on its window ac testing for this unit. The current rating is done at a full load and does not account for its variable speed capacity.

    Its interesting in the docket that Pacific Gas and Electric is fighting against the change in the comments section.

    This document announces receipt of and publishes a petition for waiver from GD Midea Air Conditioning Equipment Co. LTD. (“Midea”), which seeks an exemption from the U.S. Department of Energy (“DOE”) test procedure when determining the efficiency of listed room air conditioner basic models. Midea seeks to use an alternate test procedure to address issues involved in testing the basic models listed in its petition. According to Midea, the current DOE test procedure for room air conditioners, which provides for testing at full-load performance only, does not take into account the benefits of room air conditioners that use variable-speed compressors (“variable-speed room air conditioners”), with their part-load performance characteristics, and misrepresents their actual energy consumption. Midea requests that DOE permit Midea to test the basic models listed.

  8. bfw577 | | #16

    Has anyone purchased one of these units? I saw some people on Facebook that had the plug in killawatts on them showing them using only 120 watts at low speed.

    1. raeyn | | #25

      @BFW577, sorry to bug you but I’ve been trying to get info on this for nearly two months now and you seem to understand this better than almost anyone from the info you shared. I’m not a builder/contractor, just a user and I’m trying to get my head around how it works. I can’t get a straight answer and when I called Midea, the phone reps didn’t have any info.

      I actually purchased the 8K BTU version but it was lost/stolen while being shipped here. I can’t get it replaced for a few months but the 10K BTU is available much sooner. I actually wanted to get this 10K BTU size because we plan to move soon and I feel it would be a much more versatile size. Our bedroom is moderate size on a west facing wall so gets direct afternoon sun. On a traditional unit, 8k BTU is probably about right but we need it to cool the bedroom and the hallway/bathroom/adjacent room too (we leave the door open). I know that on a standard window AC, if you buy too large a unit, it won’t cool properly as it cycles off before it actually cools. Should I be OK with the 10K BTU on this new type of unit since it works like a mini-split?

  9. willymo | | #17


  10. type2 | | #18

    I installed the 8,000 btu on Saturday 6/6/20 in our upstairs 269 sq ft bedroom. I can confirm via IotaWatt that it does modulate. I left it set at 68* over night and from what I can tell at full throttle it's running about 450 - 500 watts and at the lowest it's running about 140 - 200 watts.

    The attachment shows a wattage of 216 but there is a 30 watt phantom draw from the TV, Xbox and Switch. So right about 186 watts. Keep in mind this screen shot is only that - a quick snippet in time. The power consumption bounces up and down constantly so it is hard to say it draws exactly X amount of energy at a certain setting.

  11. type2 | | #19

    Here is a graph from last night 6/7/20 at 9:00 pm up through when I type this 6/8/20 at 6:48 am CST. You can see the initial spike from the compressor turning on then the modulation. I was hoping this compressor would have a "soft start" but I guess not.

    1. bfw577 | | #20

      Looks exactly like the modulation on my 12k Midea Mini Split. Those spikes are the inverter ramping up to push the refrigerant oil through the system. At low modulation the oil doesn't flow very well so the software ramps up the inverter briefly every 15 mins or so.

      I contacted Midea and they said it can modulate down to 1600 btus. These seems like they would be extremely energy efficient in small bedrooms. Regular window units only run at max speed and usually use like 3 to 4 times the wattage.

  12. type2 | | #21

    I am happy with the cooling capacity and power usage of this unit so far. It vibrates a bit which makes contact with my window and results in a very audible vibration. Because you can't put the window all the way down there are several inches on each side of the window where you simply can't block the sunlight or views from outside. I ended up putting a piece of cardboard the entire width of the window which helped to squeeze up against the U part of the unit and this mostly eliminated the vibration noise.

    I also have a problem with the fitment and air gaps. The bottom under the unit has a long strip where the unit rests on the bracket. I had to plug it up with rubber foam from the local hardware store. Same with the sides. Oh, and where the window drops in between the unit, I had to place foam there but that is common with all window AC units.

    From the outside, you see a hodge podge of different pieces of foam blocks and rubber foam trying to plug every hole as well as a large piece of cardboard. Not exactly classy but it gets the job done.

    I like the design of the Soleus Air but it is pricey.

    What I would like to see is this exact Midea unit (with a heat option) BUT cut the damn thing in half and have it mount just like a mini-mini-split ™℠®©. Mount the compressor outside and mount the head unit inside. That would make it perfect. Include a 2 foot tube that goes through the wall like the DIY Mr. Cool unit and coil the tube inside the outdoor compressor unit in case there is extra slack. Keep the inside power cord just like it is. That way no need for special wiring. And them mount this little sucker wherever you want.

    Maybe this winter if I get some free time I'll take a look inside the unit and see if that can be accomplished.

    Edit: I looked up the Soleus Air for comparison and the specs are not very impressive. For the 8,000 BTU unit (Model No. WS3-08E-201) it operates at 667 watts with a CEER rating of 12.0. Link:

    1. raeyn | | #24

      I totally agree that would be the absolute ideal setup. We tried a similar idea by ForestAir two years ago and it was awful. It was loud, inefficient, and worst of all, quit cooling after 3 weeks. It’s expensive too. But the idea was sound. We have a “real” mini split now in our main living area and I simply can’t believe how incredible it is. I had no idea it would work so well and be so quiet. Even the outdoor compressor is crazy quiet. Install wasn’t simple but we’re not in a typical location either. But if a company like Midea would do this, it would transform the market.

      ForestAir made a window mount for the outdoor compressor. Midea could do the same. It means no obstruction of the view at all. They could also do a window pass through like Freidrich made for the short lived DIY mini-split that they only sold for about 18 months several years ago now. It was an insulated piece about 3-4” high that had a space for the hoses to pass through and you closed the window down on it, kind of like what you get with a portable AC (except much better made and insulated).

  13. bfw577 | | #22

    My sister lives in VT and efficiency VT now has a $250 rebate on these units. The 8k unit is $339 on Amazon so you could get it for $89.

  14. raeyn | | #23

    Hi! I’m not a contractor or builder and I’m trying to get more info on this unit and kind of “get my head” around how it works.

    It seems to me that because it will modulate with a similar algorithm as their mini-split units, that if I purchase one size larger, it wouldn’t make any difference. It will run at the speed that it needs to run to cool the space. Am I understanding this correctly? I know mini-split inverter units work this way. We would like to get the 10K BTU unit because we’re going to be moving soon and we’d rather have a more versatile size. It’s in a bedroom on a west facing wall so gets a lot of afternoon sun and we leave the door open because it needs to cool that whole back part of the apartment. Since it modulates down, am I correct that it won’t have the issue that cheaper/traditional type window units have where if the unit size is too large for the room it’s in, it simply won’t cool effectively because it cuts off after a short time and never gets all the humidity out? Am I understanding it correctly? Is there any reason the 10k BTU wouldn’t work since they all modulate down to 2k or thereabouts? Thanks so much in advance! I really appreciate any input.

    1. Expert Member
      Peter Engle | | #26

      The problem with getting a grossly oversized unit is that even at its minimum modulation, it can still be too big. 2k BTU is still a lot for a bedroom. A bedroom in a well-insulated house only needs about 500 BTU in most locations. So it will still cycle on and off. However, if you leave the bedroom door open and the unit is trying to cool the "whole back part of the apartment," this adds to the load, and the 2k minimum might be OK. The only way to really tell is to run a quick room-by-room Manual J calculation to see what the loads are likely to be.

      1. Expert Member
        Dana Dorsett | | #27

        >" A bedroom in a well-insulated house only needs about 500 BTU in most locations. "

        A bit of a stretch, mayhaps?

        It doesn't take a huge amount of unshaded west-facing code-min window to blow by that tiny number.

        >"It seems to me that because it will modulate with a similar algorithm as their mini-split units, that if I purchase one size larger, it wouldn’t make any difference. It will run at the speed that it needs to run to cool the space. Am I understanding this correctly?"


        The gist of Peter's message is true- modulation ranges are not infinite, and larger units usually have a higher minimum modulated output. Very few bedrooms with insulated roof/attic and low-E windows (or low-E storms over single panes) would have a design cooling load anywhere near 10,000 BTU/hr. A "typical" number for a ~250 square foot bedroom with an average glazing/floor ratio would be closer to 2000 BTU/hr, with many exceptions on both sides of that. The minimum-modulated output level of a given mini-split or other modulating air conditioner (independent of it's max capacity) will be more important for comfort than the maximum capacity. When it's modulating both the temperature and humidity will usually be steadier than when cycling the compressor & or blower on/off.

        Don't guess, run a or calculation on the bedroom in question, using aggressive rather than conservative assumptions on R-values, air tightness, etc.

        1. raeyn | | #28

          OK, I think I get what you’re saying now. If you get a larger unit that won’t modulate down as far as you need, then you have too big a unit for your space.

          However, with these units, the engineers have said (according to post #12 on this thread) that all three units modulate down to 2K. I think this has been substantiated by other users, though I’m not quite sure on that. This is why I thought that, for this particular design, it’s OK if I purchased a little oversized because it can still modulate down to whatever it needs but would still have the overhead for more power if needed.

          I did take your advice and ran the calculations with multiple R values on both site (we live in an apartment and I’m unsure of the actual building specs). This actually made very little overall difference in the final numbers. What made the most difference was the number of electronic items in the room. I tried to add them as accurately as possible and it made a big difference in cooling needed. is showing between 7400BTU and 8400BTU depending on R values and some fluctuation in electronic devices. It drops with no added devices at all. I found all that very interesting. I did my best to make it accurate (I did the bedroom on the second floor of a three story condo setup on since we have apartments above/below us and I tried to make the insulation and build type as close to what we have as possible.

          Thanks so much for taking the time to share. I really appreciate it!

  15. tonybluegoat | | #29

    I have two of these units mounted in through the wall of a 650 square foot portable building. They are almost silent in a normal living atmosphere. They cool extremely well. I've had them for over a year in East Texas heat. I'm a big fan. I have used lots of window AC units. These are better than anything else I've use by a mile.

  16. Robert Opaluch | | #30

    If you are interested in a small, "two holes through the wall" system that looks elegant, and I think is about $2,000 US, check out their brochure or web site:

    Ephoca has a range of units either 120VAC or 240. The problem is you have to order it from Italy at the moment, so shipping charge is outrageous. They apparently are doing a trial in CO now. Hopefully available in the near future.

    1. Expert Member
      MALCOLM TAYLOR | | #32


      Those look great!

  17. _jt | | #31

    Midea has a heat pump inverter window AC now. Not U shaped and outside temperature range is pretty bad (40 deg F) - but it's a start!,000-btu-cooling-inverter-window-air-conditioner.product.100849391.html

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