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Community and Q&A

Opinions on MR Cool Universal Heat Pump

raul4817 | Posted in General Questions on

Any thoughts on the mr cool universal heat pump package.
It says it is rated to 100% of it heating capacity @ -5F.   It heats down to -22f so must have an integrated drain pan heater.   Seems like a good option to reuse existing duct work.  The price is  more manageable than the similar mitsubishi M series.  The brochure states it is a 2 stage so I guess the price point does not give the modulation you get with the mitsubishi?

I have  seen Mr cool all over the net, But is the brand OK? Is this made by midea or Gree and rebadged? What is the quality on these does anyone currently have one installed?

This unit has an option for a type of DIY quick connect precharged lineset that according to them does not need to be vacuumed. I would favor making my own flares anyway and pulling a vacuum, which is also an option as well as brazing the joints.


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  1. GBA Editor
    Brian Pontolilo | | #1

    Hey Raul.

    I have no experience or knowledge to share about the Mr Cool heat pumps, but I'm giving your post a bump, hoping for another GBA member with insights will see it.

  2. raul4817 | | #2

    Thanks Brian,

    I'm going to reach out to mr cool for some of my more technical questions. I'll post back with that info. Just curious as to the longevity of this manufacturer.


  3. Jayson Berger | | #3

    I've been considering the same unit to replace an ancient system that is dedicated to a single large room. Please post what you learn.

  4. Expert Member
    Dana Dorsett | | #4

    Raul: Do you have a model number?

    1. raul4817 | | #6

      here are the model #'s

      2 to 3 Ton 20 SEER Variable Speed MrCool Universal Central Heat Pump Split System - Upflow/Horizontal
      condenser MDUO18024036,
      air handler MDUI18024036

      both are available through ingrams and hvac direct.
      I also found it available for purchase through lowes online.


  5. raul4817 | | #5

    I called Mr Cool yesterday. Spoke with a tech support agent. I didn't get much more info than what is in the brochures. I asked specifically about the BTU modulation on these units. The rep assured me that the condenser does in fact modulate variably however he was unsure of the Min. modulation. I was also curious if the air handler would adjust cfm based on btu output? He did state that is does not communicate with the condenser, so no. Also asked the preferred method for line set, he said the pre charged, no vacuum linsets is best but You can use your own line set and flare and vacuum.
    He also said that these are so new that they are still figuring out some of the particulars, But I would think they should have a bit more data available considering the price point. I did ask how many units have actually been sold to date? Best he could tell me is that he typically gets 2 install support calls a week.
    I will continue to look into this but need to pull the trigger soon as summer is rapidly approaching. On paper this looks like a great solution for me but just wanted a little more info.
    Warranty seems good. 10years. I did ask if it is extended to homeowners self installing. And he said in my situation yes, seeing as I have all applicable permits from my village to complete this work as a homeowner.

  6. BFW577 | | #7

    Mr Cool units are rebadged Mideas. I would guess they make the universal unit as well.

    It does look interesting and has some pretty decent specs for a whole house sized unit.

    Here is all the data and documents for it.

  7. raul4817 | | #8

    Just a minor update.

    I spoke with a tech rep this morning that had a better understanding of the universal unit.

    He stated that lowest btu output is half of its rated capacity. So if set to 24k btu then 12k and 18k if set to the 36k btu output.

    Not great but the only measuring stick i have is my fujitsu 18rflcd, that modulates al the way down to 3k btu.

    The indoor unit and outdoor unit do not communicate to achieve modulation but according to him the condensor has some type of sensor that measures temperature and humidity and this in fact controls the btu output. This may be the case with other or all minisplits I'm just not that well versed to speak on it.

    Interestingly enough since is does not communicate I would be able to use a smart thermostat such as the ecobee 4 I currently use with my gas furnace.

    This seems to be the option that best suits my needs.

    I need around 30k btu for heating and 13k for cooling. And I really like the idea of being able to toggle between 24k and 36k.

    Using this with existing ducts since I dont really have the time to revamp my design right now Is also a nice touch. Not the best for efficiency but it gets me closer to net zero right now rather that waiting till I have time to actually get new ducts installed.

    My hangup was the brand itself but as bfw577 has stated it is in fact a rebadged midea. Midea seems to have a good market presence. Some could argue whether midea is a top tier brand such as Mitsubishi or fujitsu but they make a fair amount of units so the from the engineering side one would assume it's a decent product.
    If and when I pull the trigger I'll try to report back.


  8. BFW577 | | #9

    Midea are solid units. Carrier is putting their name one them. My Midea Premier came in a Carrier/Midea North America box from GA. It had both Carrier and Midea stickers in the box to put on the unit.

    I looked at the installation manual in the link I posted above and the instructions call for a 5 wire communication line between the indoor and outdoor units. They are definitely communicating with each other.

    This unit has similar specs to Mideas Premier mini split line such as full heating at -5 and cutoff at -22. It could be using the same compressor.

    1. raul4817 | | #10

      I didnt see that. I'm also guilty of not reading it thoroughly. This is what the rep told me. They are not really 100% on anything with this unit. One rep told me they had just did the product launch then everyone started working at home so they never had any formal training.

      The tech I spoke with said that flared linesets with a vacuum is the way he'd do it. Any thoughts on the precharge lines. Good or bad?

    2. fcserei | | #12

      According to MrCool:
      "Yes, the Universal system is non-communicating. It monitors line temperatures and pressures and ambient temperatures to govern the compressor operation.

      Whatever thermostat you choose will send a signal to the outdoor unit based on indoor temperatures. In other words it functions just like any other heat pump with regard to thermostat control.

      Yes, the blower motor is an X-13 type ECM rather that a variable-speed, constant volume ECM."

      " The air handler has only one speed available at a time. Any change must be done by settings internally in the air handler. The condenser has an electronic control board which monitors several different temperature sensors and adjusts the variable speed compressor to handle the load it is under."

      So the blower motor is not regulating and the connection between the units just the regular 5 wire thermostat connection.

      1. Freeness | | #31

        I'm looking at this unit too. Does this mean the air handler isn't variable in the sense that it's speed well change on the fly based on demand?

  9. jacktoth | | #11

    I am looking forward to your experience in the diy install of this unit as I want to replace my 2 ton, 20 year old Rheem Heat Pump as a diy. What is bugging me is reliability, parts and warranty as homeowner install.
    Thanks for sharing your experiences and I look forward to updates.

  10. Jaccen | | #13

    I also look forward to updates on this. Cheers!

  11. raul4817 | | #14

    Sorry for the delay. There was a delay in stock and shipping of the auxiliary heating strip from the online retailer.

    I have not been in a huge rush because we have a couple window unit keeping us relatively comfortable. But will fall approaching im actually starting my install this week.

    I reached out to my engineer to run some numbers on replacing at least my return side ducts for now. The truck is 12x8 rectangular but the branch line are simply a few joist bays with sheet metal nailed underneath.

    Im sure its not the best setup as far as efficiency and im also sick of all the crap that falls in the return side from the plaster walls. Im going to be using spiral ducts for either the branch lines or the entire return side.

    I am using a linset that I will be flaring myself seeing as I have the tools and a bit of experience. But mr cool sells a quick connect lineset.

    I'll post back hopefully buy next week with some updates


  12. raul4817 | | #15

    As of October the MR Cool universal has been running and heating the main floor(under insulated) & basement( un insulated). It has had no issues keeping the house to the 72 degree daytime setpoint and 68 night time. It ramps up around 6am and recovers reasonably.

    I couldn't tell you average temps or COP as I'm not that versed but I have a my monthly kwh usage for the past 2 months that I track with a sense device.

    October 17 - Nov 17 981 kwh
    Nov 17- Dec 17 1479kwh

    My typical kwh usage in non heating/cooling months is 500kwh +/-

    and I have a fujistu running on my better than code insulated 2nd floor so the numbers are a bit skewed

    The temps from oct to nov were above avg 50+/- at least it felt like it.
    nov-dec temps have dipped to the 30s and are closer to what winter normally looks like.

    Jan and Feb is when we will see the lowest temps and if I have to extrapolate the numbers Im thinking that my avg kwh usage will be somewhere in the 2500-3000kwh range. This is for the entire house both units.

    I have been happy so far with the heat output and have no concern with it keeping up in extreme lows, I opted for the auxiliary heat kit that was minimal in price for a bit of added insurance. The blower and available static pressure has been sufficient to function with the the original ducts that were in my house, however I did redo the return side as the old ones consisted of joist panning and were ridiculously dirty.

    Time will tell as to the quality of components but as of now its running and working.

    I did opt to purchase my own line set and flare the connections myself. Something about the pre charged diy lines didn't sit well with me. The coil is precharged and I did have to pull a vacuum on the lines individually so that added to the complexity and time invested, but I pulled a triple vacuum. This wasn't a production job so I took my time grabbed a beer and read some articles on GBA while I monitored the micron gauge.

    other Items to be noted

    The return is located on the bottom so you will need to either fabricated a base box or modify your current one.

    The provided filter is lacking so you may want to exclude it and go for something better

    outdoor unit lineset connections are tricky to say the least. I ended up kinking the 3/4" line pretty bad and had to purchase a proper hillman tubing bender to avoid damaging the second line I had to buy.

    I wasnt planning on moving over from fossil fuel just yet but because of the current net metering agreement I have in place I needed to up my yearly kwh usage to reap the benefits of my solar panels. I still have a few items to transition over, i.e Dryer, hot water heater, stove/range. But Im gonna be right in line with net zero hopefully once I do.

    Ill try to post some pics later today if anyone is interested

    Im not an installer or a GBA expert just a carpenter with an above normal IQ for technical stuff. I know just enough to be dangerous or so Ive heard.


  13. Jayson Berger | | #16

    Raul, thanks so much for sharing your experience.
    Any idea on how the actual energy consumption compares to your projections or to your old unit?

  14. raul4817 | | #17


    If I had to take a stab at it. Nov 17-DEC 17 usage was 1500 kwh

    -500kwh other non heating devices
    -200+/- fujitsu ducted

    800kwh for the mr cool. Just an educated guess. The fujitsu was off for a about 2weeks while I mixed thinset and installed durock for baths. But with that being said the mr cool was inadvertently heating the second floor since my staircase opening is quite large and as we know warm air rises.

    Tough to really compare to my old unit since it was a lennox 90% combusting unit. Ill take a look at last year's therms on my gas bill and post in a bit.

    I think a better comparison would be to the fujistu upstairs. The problem is that the sense meter has a tough time recognizing minisplits. Toasters, microwaves no problem.


  15. jacktoth | | #18

    Yes Raul thanks for the feedback. What made you avoid the pre-charged line set ? For a fairly competent novice like its seems to simplify the job.


  16. raul4817 | | #19

    So last Nov23-Dec23 total therms used was 178. Avg temp was 32f. This does include hot water, dryer and some cooking gas that runs me on average 40 therms.

    The biggest reason for not going with the pre charged lines was no way to for me to know if I had a refrigerant leak before releasing the charge from the units. Perhaps I could have bubble tested the connections but I preferred to charge with nitrogen and let it sit overnight with a gauge.

    I had also invested in in a quality flaring set, nitrogen tank, and multiple gauges including a micron as I needed all this for my fujitsu install. I found only one competent installer locally that I was comfortable installing my equipment, unfortunately the price tag was not feasible.

    As with others I found myself with a alot of free time given the pandemic so I bought some tools and had at it. I plan on switching my parents' house over to a couple ductless units at some point so that will be 4 units installed with perhaps a few more down the road so the investment for my situation made sense.

    Im not necessarily against the precharged linesets, I guess I just wanted to justify my new tools to my wife. . Im sure if you follow the torque specs you should be ok, but I think some of the other more versed members here could give you a better answer.


  17. Drew Baden | | #20

    I was considering a Mr. Cool but went with Perfect Aire just because it appeared to be the better financial deal. This will be used for around 400 square feet so it’s only a 1 ton unit. I’m not sure if you’ll find this video useful, but I hope to install this unit within the next 30 days.

  18. raul4817 | | #21


    That is a ductless unit.

    The advantage of the mr cool universal is that it uses a traditional air handler that is really kind of plug and play with your existing ductwork.

    I'm sure the efficiency takes a hit but this was my best option in my situation.
    I will be using some ductless unit at my parents' house since their current setup is baseboard radiant and no ac or ductwork. Their basement is finished and adding ductwork is not gonna be worthwhile.

    I guess its all situational as are most things in building.


    1. Eric Whetzel | | #22

      Hi, Raul. I built a Passive House in Palatine. Because of my blog, someone local who is considering a deep energy retrofit on their home contacted me about your set-up with the Mr. Cool. He's wondering if he could contact you directly to ask some questions about the system.

      If you're willing, please contact me at my email address: zewt (at) hotmail (dot) com
      so I can forward your info along to him.

      Thank you!

    2. Brian Wiley | | #23

      Hey Raul, sorry to dig up an old thread, but I was wondering if you had any new thoughts on the equipment after making it through the first six weeks of the new year. How’s it held up?

      I’m leaning heavily towards the same equipment after getting a $15k bid for a 24k-btu Daikin, so any cold weather performance insight you have would be incredibly helpful. Thanks!

      1. BFW577 | | #25

        The Mr Cool Universal is just a rebadged Gree Flexx. All the Mr Cool products are just rebaged Mideas or Grees.

  19. Deleted | | #24


  20. Brian Wiley | | #26

    Thanks, BFW. I realized that the MRCool units were Gree thanks to your earlier comment in the thread, but hadn't identified their particular model as the Flexx. I was able to look it up on NEEP, which was helpful.!/product/36396

    Specifically, I was looking for a little real-world feedback from Raul (although I'd gladly entertain any hypothetical feedback, too). He'd mentioned that he hadn't made it through the coldest part of the winter in Spokane, which has a very similar climate to Boise where I'm located.

    I had a pretty aggressive Manual J done that puts me at 21,103 Btuh heating, and 15,815 Btuh/1.32 tons cooling, and followed that up with Dana's fuel calculation in "Out with the Old, in with the New" that came in a slightly higher at 22,800 Btuh.

    In any case, I'm pretty confident that the MrCool Universal will work in terms of sizing, but was just hoping for a bit of feedback from Raul if he experienced any hiccups before I actually order equipment, especially considering that he has a nice control in that Fujitsu.

  21. Joseph_David | | #27

    While the Universal is a new product, MrCool has been around for several years at least. They're all over social media, and they've been listed on Home Depot for a while now. We had one of their mini-splits installed in our old office space. I'm not aware of any problems with it. It kept the back office really cold, I know that.

    The Universal is a variable speed inverter. This looks like it is going to be the way of the future. Bosch has one, Trane has one, I think everybody will soon. How does that stand up to an old heat pump? The heating performance is unbelievable.

    For example, the Universal is 100% capacity at -5F and 78% at -22F. This is phenomenal. Actually, that's more than phenomenal, that's impossible for previous generation technology. I don't see a lot of people talking about it, but it's a game changer. And it's not just BS. Here's an Intertek test report on their website:

    Basically, if you live anywhere that doesn't routinely get -20 days, why wouldn't you dump your gas furnace? Right now I've got a Goodman gas pack. When it goes out, I'm going to get something like the Universal. We get maybe a couple days in the teens, and that's about it. And if I don't have to have a potentially explosive gas furnace outside my house, I'm fine with getting rid of it.

    Put me on the list of wanting to hear how Raul's is working out.

  22. raul4817 | | #28


    I will post an update a little later tonight. I've been stuck at work with all the snow we saw last night.


  23. raul4817 | | #29

    Sorry for the delay. My experience so far this 1st heating season has been overall positive.

    We have had a taste of some mixed winter conditions in Chicagoland. Last week we saw consecutive below zero days and we've been hit with 36" of snow in a 2-3 week period.

    I was apprehensive and even a neighbor was apprehensive for me, but the mr cool hasn't missed a beat, neither has my fujitsu for that matter

    The kwh usage has definitely gone up with the sub zero temps but still within reason. Jan 17 thru today has me at a total kwh of 3200 all in. During the few days with highs in the low single digits I consumed around 110 kwh 15 or so is non heating. So a hair under a 100 for both units.

    Since my pv panels are under 12" of snow I will probably see an electric bill of around 300$ this month. If I was still on natural gas I would estimate this bill closer to 200$. A minimal cost for what i believe to be a greener energy source? But ill let the experts here answer that one. Even greener if my panels were not buried under snow.

    As far as longevity, time will tell. But I am very happy with the maiden voyage and can't wait to see what it can do during the summer months as it claims 19 or 20 seer.

    One thing I may not have mentioned is the capability of switching between 24k to 36k btu. I need the 36k now but I will be upgrading windows and insulating the basement so I may just be in the 24k range at some point and I will still be sized appropriately when that day comes.

    The air handler install is very similar to a standard condensing furnace so you may be able to get a competent hvac installer to install with no previous minisplit experience. There are obviously some differences that you and they should make them aware of.

    My biggest concern going into this season was whether it could keep up with harsh conditions and it has. One nice upgrade is an auxiliary heat strip that you can pair with the mr cool that gave me a little more piece of mind. So far it has not been needed. I was also glad that I could pair it with my ecobee 4 thermostat, not the case with the fujitsu.

    I found a pic of my setup that made the most sense in my situation. I hope this helps with your decision


  24. Brian Wiley | | #30

    Thanks for that update, Raul. It was super helpful.

    Somehow I got my wires crossed (I think someone on GBA previously posted about a MrCool Universal in the Pacific Northwest, perhaps) and I mistakenly thought you were in Spokane. It's even more reassuring that it's able to handle a midwest winter. I lived in Champaign for a few years, so I have a bit of insight as to how harsh those temperatures can be. I'm in Boise now, and feel like it'd handle our lowest lows easily if it can do a Chicagoland winter. Even though we're both cz5, it just doesn't stay cold for the same amount of time out here. We got 10" of snow in a day, but the next day was 42f and my neighbor was shoveling in a t-shirt.

    I'm also excited about the possibility of switching the demand. I didn't realize that you're currently running it at the 3-ton mode. Mine would only be the 2-ton, which according to MrCool's specs makes it more efficient. I do like the ability to up it if I need to as a small addition in the near future is a strong possibility.

    The other thing I like is the ability to install it myself. My longterm goal is to get my house to net zero, and PV panels will be a big part of that. I got a quote for a 2-ton Daikin that was $15,111. I get that they have different compressors, and that the MrCool isn't quite as efficient, but at the IWAE cost and doing the install myself, I can afford to get a PV system much more quickly than I would if I purchased the Daikin. Even though the MrCool wouldn't be as efficient, it's still going to be much more so than the Amana air handler from 1984 that's currently in my crawlspace.

    Speaking of install, thanks for posting those pictures. It helps to see the scale of the components. Also, I'm jealous of all that space for mechanicals. All of this is going to be squeezed into a conditioned crawlspace on my end.

  25. Venkat Y | | #32

    Hi Raul,

    Any info on the actual turn down ratio; I see earlier in the thread that a tech had mentioned 50%, but wondering what your actual experience has been for the shoulder seasons. Also, is there a constant fan mode and if so does the fan switch to a lower rpm/cfm for the constant fan mode for filtration, etc., when the compressor is off and if it does, curious how much power draw there is for this mode.

    Thanks in advance.

  26. proxybox | | #33


    Great install! I noticed on the performance charts that the universal air handler only goes to .4 in wc total external static pressure. I want to reuse my ducting but with my current setup with my furnace I measure .5. Did you measure your TESP for your ducts before swapping? Curious what your TESP was. I'm worried if I install this air handler that it'll wear the ecm motor out sooner since I'll be pushing max cfm. Ideally I was told to not go more than 70% of maximum capacity for room for overhead.


    1. user-7441979 | | #34


      You should look at the Mr. Cool Universal Series High ESP Air Handler; it is exactly what you are looking for. It appears to be the same universal air handler but with an 8 speed blower motor for up to 1” of static pressure.


      1. proxybox | | #36

        Thanks I was looking at that too but it's not available yet. I spoke to mr cool on Friday and they still don't have an ETA. Supply chain issues industry wide so I'm sure it'll be later than expected.

        Issue for me is for the local rebate. It's running out soon so I have to decide whether to pull the trigger with the low ESP model or wait for the higher one and risk losing out on the rebate. Argh!

        But this system is remarkable. Take a look at this video

        1. Expert Member
          Akos | | #37

          You can probably gain that extra bit of pressure drop by swapping out the existing filter to a larger unit. Typically a 4" filter will have less than 1/2 the pressure drop of a similar sized 1" unit.

          You can also look at the existing ducting, lot of times there are some fittings with very large EL (that is very restrictive) that can be swapped out or upsized to reduce the pressure drop even further.

          1. proxybox | | #38

            Thanks. I currently have a 4 inch Honeywell filter installed. Ducting changes is a possibility but a huge PITA. At least I have options. Appreciate the feedback.

  27. jacktoth | | #35

    Any idea when this air handler will be available.

    1. proxybox | | #39

      Spoke with ingrams too on Friday and they don't have an ETA.

  28. Brian Wiley | | #40

    Hi Proxybox,

    Just thought I’d chime in. I had the same situation, and ultimately went with the traditional AH at .4 ESP. I’m at 0.494 on my current system, and had considered the High ESP model, but the long wait time seemed too much.

    I’m pretty confident I can find the necessary reductions on static pressure by making some corrections in the current mess of ductwork. All in all, that seemed like a more direct (and ultimately more beneficial) solution than waiting for the high esp to be available.

    1. Brian Wiley | | #42

      I wanted to follow up here to share some of my experiences with install as it was a bit of a different situation than the original poster, Raul, had with his. Hopefully it'll help someone out if they're considering a Mr. Cool Universal.

      I chose the 2/3 ton model, and installed as a 2-ton in a horizontal orientation. The air handler is in a 32" tall crawlspace, so room was tight. It is possible to easily remove the blower fan to minimize the weight of the unit before taking it into the crawlspace. It's about 4 screws and a molex connector to take off. Re-installation was easy even in the confines of the cramped area of crawlspace.

      I used a pre-charged line set. The connection to the outside unit was just as difficult as others have described. I bought a 3/4" tube bender on Ebay to handle the bends, which was essential. It was $38, and I can't imagine having done the job without it, particularly because I needed to bend an oil return into the line because the outdoor unit is above the indoor unit. The instructions only explicitly call for an oil return when you're using your own line set; the pre-charged line set instructions don't call for that, but I found that curious so I called tech support. They said that you did need to bend an oil return any time the outdoor unit is higher in elevation than the inside unit regardless of which line set you're using, so plan accordingly.

      The smaller 3/8" line set was easy to bend by hand. I had a tube bender for that size, but ended up using a coffee can and bending by hand as it was easier.

      Both of the pre-charged line sets come with springs over the entire length of tubing to aid in bending. It's not readily visible because it's behind the insulation in any of the marketing literature. You can push it back out of the way for a good 6–8 feet to get a tubing bender onto the lines.

      The filter that comes with the unit is a 1' metal 'static charge' style filter, and was held in with set screws. I mention it because I couldn't find much about that part. Ultimately I added a 4" media filter, but I believe you could put a standard 1" filter in place pretty easily. The dimensions are 20.25"x19.25".

      Both the indoor and outdoor unit are super quiet compared to our previous equipment. We had a day or two where the air conditioning came on, and we could hear our neighbor's compressor 2 houses down more than we could hear the outdoor unit. We do get a bit of air handler noise through the supply ducts, which are all metal. I cut out a 4' section of the metal and replaced with flex duct pulled tightly, and we can no longer hear the handler at all in that room. There isn't any air handler noise at the return registers.

      It's also worth reiterating that the standard air handler has .4 i.w.c.. That may not be enough depending on your situation, so it'd be worth checking that out earlier than I did. I was able to redo my return duct work as part of the project to get things down to a more manageable .238 i.w.c., (it was around .5 before) but it added an extra week or more to the length of the project.

      If the ductwork wasn't part of the project and it was more of a direct swap like Raul's, I think it could have been done in 2 long days due to the tight quarters in the crawlspace.

      Overall, we've been really happy so far. While we haven't had it for more than a couple weeks, its seen both 85° days and 30° nights, and hasn't had an issue with either. I hadn't ever done any sort of hvac work, and while it took a bit of research and learning, it felt like a totally manageable project for someone with decent diy skills.

      Finally, with the duct work and all the odds and ends like tube benders, drain pans, etc, it cost just a little under $5000 for what it's worth.

      1. proxybox | | #44


        Great post! I just ordered my unit this week.

        Can you post pictures of the 3/4" tube bender you used? I'm also not willing to take the risk of bending by hand so it'll be great to see that tool.

        For the return side what did you do to reduce your static pressure by so much? I'm impressed.

        1. Brian Wiley | | #45

          Thanks! I'm glad it was helpful.

          The tube bender was from ebay. It certainly wasn't something I'd use for day-to-day stuff, but it worked well for the handful that I needed to make. There are lots of sellers of the same type; here's one example:

          As for the duct work, mine was really, really terrible—lots of hard 90° elbows, unnecessary reductions, etc. What did it for me was following Dr. Bailles Duct Design series (link below). You probably have way more experience than me, but it was really helpful in understanding the fundamentals of how the air moves. The short of it though was that bigger is generally better, both in terms of the duct size and the radius of the elbows, so I tried to keep that in mind with everything I designed. I also downloaded a copy of the Manual D to familiarize myself with the equivalent length of the types of fitting so that I could pick the least resistant type. Ultimately I embiggened (to borrow Dr. Bailles' borrowed phrase…) my return ducts to 16"x16" trunks, with a couple of 16"x8" and 14"x8" take-offs. The radius elbows were at 18" inside / 32" outside as I figured those would be the most restrictive parts that I could control. Attached is a screenshot of the design. Blue is return, green is the 4" filter, and the grey box is the AHU. I haven't begun to tackle the supply side mostly because I got better gains than I was expecting on the return side.

          I'm also happy to share some of the details on how I fabricated the elbows, but didn't want to pre-emptively go down that rabbit hole if you're not going to be doing it yourself.

          Let me know if you have any other questions that I missed.

          Duct Design Series:

          Manual D, Appendix 3 for the fittings:

          1. proxybox | | #46

            Ahh, post photos of your install. But... i understand it'll be hard to get a pic of the air handler since it's in the crawlspace.

            Can you also post a pic of the specification placard on the condenser? I wanted to see if it lists the subcooling temp. Thanks!!!

          2. Brian Wiley | | #47

            Here are some photos of the install. I only had a photo of the AHU partway through the install process, but it'll give you an idea of orientation. It was suspended so that I could slip the overflow pan underneath. The seams aren't fully taped/mastic-ed there.

            The second photo shows the spec plate on the AHU, which I thought was interesting as it makes reference to Gree parts. There were other indicators of it being rebadged, too.

            Photo 3 is for placement. The whip is extra long for when I have to move it a bit to air seal behind the unit.

            Photo 4 is how I routed the lines through the unit. On another board, I saw that someone had routed their lines through the back knockout. It wasn't for a MR COOL specifically, but it seemed applicable. People have noted that it can be difficult to bring the lines through the side knockout as it forces you to make two bends in a short span. I was able to slide the lines through the back knockout while they were still straight, then push some excess line through to make the bend, and then move it back with the 90° bend to make the connection. One thing I wish I had done before making the connection was pre-wrap that section in a Pasco tape.

            Photo 5 is the outdoor unit's plate. No specs on the temperature rating though.

          3. proxybox | | #48

            Thanks Brian! Thats a nice looking install! I hopefully will follow in your footsteps.

          4. proxybox | | #50

            Thanks for the update and description of each photo. I really like how you bent the lines from the rear for a clean look. How about just getting two short pieces of 1/2" insulation and wrap the lineset since the Mr cool is so thick? Pasco is for preventing galvanic corrosion but the insulation will prevent sweating.

            Yeah these are Gree.
            Similar but the performance specs are a little different so I'm not sure what differences there are.

            Stay warm this season!!! Are you using excess solar?

            Hmm. Can you forward the ahu nameplate picture via twitter dm? GBA reduces the resolution of your photo so it pixelates when I zoom in. I use the same handle on twitter.

            Thanks and will post when I'm done which will probably not be until the spring since I don't want to do this during the cold season even though I'm in SoCal.

        2. Brian Wiley | | #49

          It'd be great to hear about your install; post back when you've got it up and running. Good luck with the project, and let me know if you need anymore photos.

          1. Brian Wiley | | #51

            Response to comment #50

            The pasco was to protect the pipes a bit from contacting some of the parts in the back; it's pretty tight in there. I'm probably paranoid, but I just thought that years of vibration may start to wear on them. I'm sure the 1/2 inch insulation would accomplish both, and I probably need to worry more about the condensation than I was.

            I saw the subtle differences between the Gree, too. The only thing I could come up in terms of the performance differences was that maybe they're accounting for some possible differences introduced by the precharged lineset? In any case, it's nice to know what to look for in terms of parts if and when the time comes.

            So far the house has been nice and toasty. I wish I had solar, but not quite yet. Part of the motivation for going with the MR COOL was that the $10k savings over a Daikin could be used towards PV.

            I tried sending you the photo via Twitter, but it doesn't look like I can DM you until you follow me back. I'll try again later, but you might have luck right-clicking on the image and opening it in a new tab/window. I tried that and it'll let me zoom in quite a bit.

  29. Kieran973 | | #41

    When people lament the poor cold weather performance of Mr Cool ductless units, is this because they only maintain 50-66% capacity at sub-32F temps, or is it because the published cold weather specs are themselves not accurate?

    For example, the 18k btuh DIY Mr Cool ductless unit: according to the ASHP specs, it puts out 15,163 btuh at 17F and 12,357 btuh at 5F.!/product/30947

    In the real world, does it actually put out these btuh at those temps? Any reason to believe that it doesn't? Anybody with experience using these are primary heat source at those temps? I'm in climate zone 5, 99% design temp is 11F.

    1. Brian Wiley | | #43

      My guess is that those numbers are accurate—seems like risky business to lie about those ratings—but that any disappointment is due to false expectations.

      Mr. Cool does a great job marketing their stuff, but I think sometimes that creates a bit of letdown by people that don't know how to interpret the numbers.

      I don't have any direct experience with that particular unit, but I think that it'd do just fine in cz5. I'm in cz5 as well, and would feel comfortable running that as my primary heat. I'd probably keep an Envi HE 120v panel heater or two on hand for those rare, prolonged cold snaps, but otherwise wouldn't worry too much.

  30. Walter Ahlgrim | | #52


    Did you connect a separate drain line to overflow pan?

    Is there a float switch in the overflow pan to shut down the unit should both drains happen to clog up?

    Will snow clogging up your outdoor unit be an issue given your location?

    1. Brian Wiley | | #53

      Hi Walter,

      There is a separate drain line for the overflow pan with a float switch, however I may swap that out for a Rectorseal Safe-T-Switch SS2 that threads into the auxiliary outlet of the primary pan (I think thats what it's called; the one thats a bit higher than the primary outlet on the AHU). Currently I have some mineral oil poured into the existing backup drain line's trap, but I'm not sure if that's the best long term solution. If you—or anyone else—has any thoughts on if that's good enough, i'd love to hear them.

      The condensate pump has a safety switch as well thats wired as 'normally open' that runs to a small alarm in our laundry room. If it turns on, I know I've got an issue. I may wire that in series with the float switch later so that it kills the power to the unit, but for now that's the safety system.

      As for the snow, Boise averages less than 20" per year. Even our worst 'once in a generation' winters are below 40" between November and February. It's elevated a little more than 4" off the concrete pads, which seems to be the norm around here.

  31. WI_Northwoods | | #54

    Hi all, I’ve been looking at the Mr Cool Universal since Feb. ‘21 and finally purchased from Home Depot in Aug. ‘21. Delivered in Sept. ‘21 and finally installed 12/1/21. I purchased the 35ft precharged lineset and did all the electrical work myself. I needed to hire a contractor to switch out the old electric furnace unit and connect the Universal Air Handler to existing ductwork which cost me $1145 for 11 hours labor and materials.
    Originally I was quoted $14k for a Mitsubishi multi-split to be installed, but after looking at the MrCool Universal, this seemed like quite a savings compared to what the HVAC installer wanted to sell me.
    The install was fairly straightforward but I forgot to measure the access hole to my crawlspace, and I am glad I did. When the Mr Cool air handler arrived and we tried to maneuver it into the crawl space, it was too big. After looking at the unit for a while, I decided to take it apart, down to a single panel with the horizontal drain pan and A-coil remaining in tact. The fan unit and electrics all came out in a single unit. If I had measured beforehand, I might not have bought it knowing it was too large to fit through my crawlspace opening. After we got the parts down into the crawlspace, I put it back together with a few dozen Philip’s screws. As I was waiting for the installers schedule to swap out the air handler on Dec. 1, I worked on the outside condenser unit and wiring using 8-2 UF-B for outdoor lines and 6-2 romex for the air handler. I overwired the 2-ton install specs in case I ever want to flip the dipswitches to 3-ton, I’ll have the needed wiring for that capacity in place should I want or need 3 -ton. I also installed the 8kw heat strip coils, which was only another $120. After is was all connected I checked the lines with soapy water and had a tiny microbubble leak at one connector. After running it for 24 hours, I shut it down and rechecked all the connections on the precharged lineset and there were no leaks or bubbles with the soapy water.
    I figured I'd post some pictures to show and give folks an idea of a horizontal install in a crawl space.
    Feel free to share your thoughts or questions. I’m happy to tell about my DIY installation of the MrCool Universal.

  32. kns306 | | #55

    Newbie here to the forum. I am glad I found this site and the shared experiences here, hoping to get some feedback from the folks here.

    Have an old (1983) house in CT with original to house oil burner and 15yr old AC. Looking to replace both with heat pump. Initial quotes I have gotten from HVAC companies are in $15k range for a 16Seer 4ton unit. Which seems excessive because I know the units are not more than $5-6k.

    Looking at the Mr.Cool 4-5Ton 18 Seer unit as a DIY project to replace the furnace and wanted to get an opinion if anyone has explored the new unit. I really like this unit for what it offers just unsure if any experience with that air handler. So it was nice to see the images above.

    How well does this unit handle zoned dampers (Have a honeywell zone control board) I am assuming it just wires right up to the controller. I am not completely new to electrical but the HVAC wiring pieces are where I am most concerned. I am hoping to tackle this project in the spring as I am getting tired of paying $600+ a month in oil.

    1. Expert Member
      Akos | | #58

      If you have oil fill up data, I would run through the calculations here to size your system:

      It is pretty unlikely that your real heat load is near 4Tons.

    2. Brian Wiley | | #61

      One thing thats worth reiterating from earlier in the thread is to make sure that your duct work isn't exceeding the static pressure limits of the air handler. I believe most ducted ASHPs tend to have lower available static pressure, which would be important in a retrofit situation like yours where you can't design the duct work to the unit's specs. Most manufacturers also make a high-ESP air handler, but I'm not sure that Mr Cool's high-ESP AH unit is available yet.

  33. Kieran973 | | #56

    Not sure where in CT you’re located, but if price is the main reason you’re looking at the Mr Cool DIY, I would encourage you to keep talking to Mitsubishi or Fujitsu installers until you find one with more reasonable pricing. In my experience, the smaller hvac companies (like 1-2 people) sometimes offer better pricing, and as long as you have your unit installed by any licensed hvac contractor, you get the 10 year warranty. The main reason I would go that route is that the Mitsubishi and Fujitsu units have significantly better COP specs at winter temps than the Mr Cool units. For example, my Fujitsu ductless wall units have a COP of around 5 at 47F (pretty much the average temp during the nine month heating season for
    September to May), whereas the Mr Cool has a COP of around 3. For me, that translated into long term electricity savings that would wipe out whatever up front savings there would be on the initial install of a DIY Mr Cool.

    1. kns306 | | #57

      Thanks for the note, I have not looked at Mitsubishi or Fujitsu at all. I have central air so expecting to stay with that, might add ductless to the upstairs bedrooms and get rid of that zone from the main system eventually.

      Im located in Fairfield county so that carries its own "Fairfield Tax" because of the assumed ability of everyone to pay up. (Literally couldnt afford my house here today, got lucky buying a few years back)

      Ill see if Fairfield or Fujitsu have a central system. Also got a quote for a Trane XR16 heat pump unit which was more reasonable so lets see.

      1. Kieran973 | | #59

        Mitsubishi and Fujitsu make ducted units that do both heating and cooling. It's just an air handler connected by the line set to the outdoor condenser - you can connect it to your existing ductwork and it will replace both your furnace and AC. Here is the 4 ton Fujitsu:!/product/33978

        Not sure how big your house is, but 4-5 tons might be oversized. Others on this site will tell you to do a Manual J (heat loss analysis) to properly size the equipment. With heat pumps, oversizing can drastically reduce efficiency. For reference, my two-story, 1800 sq ft house is leaky (it's 100 years old), has OK insulation, and has a total heat load of around 30,000 btu/h at 11F (the temperature it stays above 99% of the hours in a year).

        I'm also in Fairfield County. Check out Chillie Willie - he specializes in Fujitsu units. You might also call Air Professional Associates - they're in Westchester, but they also work in Fairfield.

        1. Freeness | | #60

          Your explanation is super helpful. I'm trying to understand COP. In that link, the 17 degree COP is rated 2.28. I'm pretty sure the Mr Cool is 1.94, so if I understand correctly, it would take 18% more electricity to get the same amount of heat? If that's correct it makes sense but I don't get the charts min and max COP numbers as they look reversed to my untrained eye. I also don't get how the Mr C 100% BTU claim at 5 degrees vs the Fujistu's 83% number impacts any of running costs.

      2. BFW577 | | #62

        CT resident here as well. Have you looked into the rebates that energize CT has for heat pumps? It looks like its $1500 per ton now so a 4 ton unit would be eligible for a $6k rebate. A neighbor said they recently got $6K towards a $10k 4 ton system that cost her a little over $4k out of pocket. You have to use a contractor to get the rebate as its not valid for self installs.

        1. kns306 | | #66

          Do you have a reference for which contractor he used, the HVAC contractor I got is not listed with energize CT and for some reason the other HVAC quote I got only has the $500 per ton rebate not the rest of it.

          Would appreciate any help.

          1. BFW577 | | #68

            I'll see if I could find out. I would contact energize CT and they might be able to help recommend someone that deals with the rebates. Maybe they have a authorized contractor directory on the website?

  34. Kieran973 | | #63

    Yeah, COP is basically just output divided by input - in this case, units of heat produced divided by units of electricity consumed.

    My underslept mind says 34% at 17F (2.28 - 1.94). But the most important COP to look at is not at winter lows (17F, 5F, -5F) that only last for a few hours or days, but winter averages. 46F is the average temp in Fairfield County from September to May, so the COP at 47F rating will give you a decent ballpark from which to estimate total electric usage in a heating season. For example, if it takes 20,000 kWh to heat a house from Sep-May with electric resistance baseboard heat, and electric resistance heat has a COP of 1 (efficiency of 100%), then a heat pump with a COP of 5 at 47F should be expected to use around 4,000 kWh to heat that same house during the Sep-May heating season.

    The more important metric to look at with winter lows is the heat pump’s max btu output at those temps. Since the 99% temp here is 11F (the temp it stays above 99% of hours), then you need to 1.) figure out your whole house heat load at 11F and then 2.) see if the max output in the specs at 11F is capable of meeting that. They don’t give specs for 11F, but since 11F is exactly halfway between 5 and 17F, you can just average the max output ratings at 5F and 17F to get a sense of what the output at 11F should be. At my 11F heat load of 30,000 btu/h, most of the 3 ton Mitsubishi and Fujitsu units would be oversized. I heat my house with two ductless Fujitsu wall units (one 15K btu and one 9K btu), so put together they’re a “2 ton” system. Their combined total output at 11F is about 37,000 btu/h so even they are slightly oversized for my heat load.

    1. BFW577 | | #67

      This is spot on advice for CT. You really shouldn't worry about the extreme cold cop's at 5 and 17 since we spend such little time of the year in them. Get a unit that has good performance at 47.

      I have been using 2 12k Gree Sapphires I bought at Home Depot for $1200 each and self installed the last 2 years. At their minimiium output at 47 where they spend a huge chunk of their time they have a cop of 5.42. The cold weather capacity and cop,'s are good and they handled the recent single digit cold fine. They also have excellent low speed cooling/dry mode efficiency using only 80 watts for a cop of 10.42. I use the dry mode and have a low cooling load as I live on the coast.!/product/25406

      Kieran973- How long have you been using the mini splits for heat in CT? I highly recommend an electricity monitor to track the usage. Its really eye opening to see how efficient and little electricity they use. I have 3 years of data so far. January was a cold month and both my units used a total 673 kwh. I have solar with enough net metered electricity to get me through winter but that would have cost me around $150 if I bought it from Eversource. People with heat pumps in CT saw huge savings this winter compared to oil and propane.

      Definitely install an energy monitor if you don't already have one. Its so cool to see all the data.

      1. Kieran973 | | #69

        Cool. Yeah, I’ve been meaning to get an energy monitor for them, just haven’t got around to it. What’s the best kind?

      2. Nick Defabrizio | | #70

        The Gree Sapphires are very efficient units. I have a Gree at my dad's summer house and it works fine. I have two Fujitsu low temp units in northern NJ (zone 5) and they have no trouble heating our house on the coldest winter days (they did well even at -10F).

        It is great that you could install the Gree units yourself, but most people won't have the tools to do the lines. Was it difficult? Otherwise, HVAC install prices are skyrocketing. This is why the MrCool DIY units are so attractive and why they are selling thousands. I am getting quotes of $5k for install of a single head Fujitsu for my basement (versus $1500 for the DIY). From a purely dollars and cents basis, the electricity savings will not cover the "cost of funds" (i.e., interest on a loan or lost investment income) on the $3,500 differential. Maybe it is better to put that $3,500 into air sealing (or a donation to Habitat for insulating low income homes) ?

        By the way, MrCool is not the only DIY mini split. Blue Ridge also is DIY-probably the same units as MrCool. Also, there is the Perfect Aire DIY brand. They seem to have slightly better performance numbers than the current MrCool line of DIY. For instance the 18kbtu single head Perfect Aire unit has an HSPF of 11.6 and the 24kbtu multi head DIY unit compares favorably with the Fujitsu 24k multi units. I know that MrCool recently AHRI tested another generation of DIY units (with a "C" designation) that will come out sometime in the future and those numbers seem close to the Perfect Aire units. So maybe Perfect Aire is one generation ahead. I heard by the way that they are Media units, not Gree, but who knows.....

        1. Brian Wiley | | #71

          Nick, I believe you’re right about the minisplits being Midea, but I think it depends on the line. My understanding is that the Mr Cool Universal is a rebadged Gree Flexx.

  35. Freeness | | #64

    That all makes sense. Not sure I made the best decision after learning about COP and I'm trying to see what I can do to mitigate.

    At what temp/cop does a HP cost more to run than a traditional 80% efficiency gas baseboard hot water heating system? I know electric vs gas rates make it impossible to know exactly, but I'm trying to figure out a decent guesstimate.

    I replaced an old, dying AC only unit with a HP. It was only slightly more than an AC only unit and I figured bonus of it could run my heat instead of my older, but perfectly working gas fired hot water baseboard heat. In December 2021 my gas/electric bill was a 20% lower than my December 2020 bill using the HP for heat but my January 2022 bill was nearly double my January 2021 bill. January was much colder and I suspect the Dec bill used an estimated meter reading. I know that's a very inexact measuring stick as I'm not taking temp or cost of power differentials into account.

    I tried to figure out all the therms and such to really compare but the math was beyond my skills.

    1. kns306 | | #65

      So exactly for this reason I am planning to supplement my HP with a pellet stove/wood burning stove.

      We are in a big house, but only about 2800 sqft of that is heated by the main heating system the remaining space in lower level (finished but only has gym, spare office and such) is baseboard electric. The issue we run into is the main area (see picture) has 20ft ceilings and is open to dining room, family room and kitchen. So this 1500 sqft of space is our main use and is heated from 7AM to 9PM so the high ceilings take a toll. This is why we need the 4 ton system, my oil boiler right now is 185000 BTUs at 80% AFUE

      Right now we only heat 2 bedrooms at night (600 sq ft) and in summer months that goes up to cooling 3 bedrooms (800 sq ft).

      Plan is to heat the main area with fireplace insert when its too cold to supplement heat pump, both the bedrooms that get heated in the winter have oil radiators for supplemental heat that work well so that will continue to supplement heating.

      Appreciate any feedback or input.

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