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Installing my own minisplit heat pump

Matthew_Salkeld | Posted in General Questions on

I am installing a mini-split heat pump for my small house that is heated with electric baseboard heaters. It should require two air handler heads, one per floor, the floor concept is quite open so maybe 9,000 BTU/hr upstairs and 12,000 BTU/hr downstairs.

I think there are systems for sale on Amazon with precharged line sets.  Has anyone tried this, or hired a refrig mechanic to make the final connections? Is it worth the effort compared to hiring it all out?

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  1. RussMill | | #1

    Finehomebuilding had an article, justin fink installed one in his garage. Look on their website

  2. Patrick_OSullivan | | #2

    While I've not done this myself, I'm of the opinion that anything is worth doing yourself if you (1) want to and (2) have evidence based confidence that you can do it reasonably well.

    (1) is sometimes a tricky one to decide because "want" is often relative to how much you *don't want* to pay someone else to do it.
    (2) is still subjective but at a certain point you realize that nothing is magic and can somewhat objectively assess your ability to complete a certain task.

    That being said, you didn't mention doing a load calculation for this space, which is something that should be done to deploy the appropriate capacity.

  3. Birdo | | #3

    About to do the same. With you in spirit.

  4. aunsafe2015 | | #4

    There's a website called Garage Journal (hope I'm allowed to post that here--if not, Mods feel free to delete this post) that has a forum similar to this one with an HVAC section. A number of folks there have done DIY mini split installs. There are units with precharged linesets (MrCool DIY) that believe it or not do need pressure testing or vacuum pulling (in fact, b/c the linesets themselves are precharged, you affirmatively should not do those things). A number of folks are reasonably happy with those units although I do not believe they have very good low temp heating capacity. Other folks have DIY installed Mitsubishi/Fujitsu/etc., but for those you would need to do a lot of research to make sure you know what you are doing, plus spend hundreds of dollars on tools (vacuum pump, flaring tool, nitrogen tank + regulator, pressure gauges, etc.).

    Another thing to be aware of is EPA 608 certification requirements. I'm not sure if that applies to things like MrCool DIY, but I'm pretty sure for at least the Mitsubishi/Fujitsu options you technically need to be EPA certified to complete the installation (i.e., connect gauges and other equipment to refrigerant lines, release the refrigerant, etc.).

  5. WPmichael | | #5

    The only gotcha of DIY is the electrical portion (generally 220V ) and then evacuating the linesets, you need a vacuum pump ( not cheap $200+ ) and gauge to make sure the lines are dry. If you don't get this right the unit will not work properly. I am not a pro, I am sure one of the pros will correct me if I am not right....

  6. kjmass1 | | #6

    Considering the high cost I paid for someone to install 4 heads and not really satisfied with the craftsmanship, I'm certain I could have done a better job myself and would have no problem buying all the necessary tools needed. You could always sell them off on craigslist and get most of your money back. I wasn't messing around going 30' up on a ladder though.

    For short runs, especially a DIY kit, I think it makes sense. Or buy Fujitsu/Mitsu online and forgo the warranty, and have someone do the refrigerant work. Don't expect any tech to be able to service a MrCool though outside of charging it.

  7. Expert Member
    Akos | | #7

    Doing the install with an HVAC tech for vacuum and leak check is the easiest for a one off. Just make sure you have somebody lined up to do it before you start. The tech wanted $450 to purge and leak check 3 mini splits.

    For power, there are some 120V versions, but low temp heating performance is limited. If your basement is unfinished and have easy access to your panel, pulling a permit and installing the 240V power feed is fairly quick.

    The biggest issue I've had with these is drain lines. Don't ever use the corrugated stuff they send in a kit, they are trouble. Stick to poly irrigation pipe and fittings and watch the slope.

  8. Trevor_Lambert | | #8

    Be very careful with the equipment selection. All of the pre-charged models I've seen are poor performing at low temperatures. You don't mention your climate zone, so maybe that is not a big concern. They all are on the lower end of efficiency as well, but that might be offset by the savings. Make sure look at the detailed specs at temperatures you are likely to see in your area.

  9. Expert Member
    Dana Dorsett | | #9

    Patrick OSullivan has it right: Before embarking on any project like this it's important to get an accurate handle on the cooling and heating loads. Most DIY units use simpler-cheaper compressors that crap out on capacity at sometimes surprisingly moderate outdoor temperatures. I'm not aware of any DIY mini-splits on the market using "hyper-heating" technology (as alluded to by Aun Safe in response #4.)

    Getting an EPA certification for handling refrigerants properly takes a bit of study, but there isn't any rocket science to it, and the acquired knowledge is valuable to have. R410A is an extremely powerful greenhouse gas (~2000x CO2 @ 100 years), and just one or two screw-ups can do a surprising amount of damage. There are a number of online EPA 608 certification online study guides (including practice tests) out there, and the fee for taking the test isn't enormous. eg:

  10. Matthew_Salkeld | | #10

    Thank you everyone. I am in a very cold climate, Ottawa, Canada (design temperature -25 c) so I want the best performing, highest HSPF and to maintain heating capacity at very cold temperatures. It sounds like I will have to go with Fujitsu or Mitsubishi in that case.

    Side note - in my modelling work I discovered that the HSPF rating does not properly represent or credit the heat pump's heating capacity at cold temperatures. HSPF is tested at +8.3 C, and can cause units to rate lower that have the best cold weather performance.

    1. Expert Member
      Dana Dorsett | | #11

      >"I am in a very cold climate, Ottawa, Canada (design temperature -25 c) so I want the best performing, highest HSPF and to maintain heating capacity at very cold temperatures. It sounds like I will have to go with Fujitsu or Mitsubishi in that case."

      The ACCA data lists the the 99% outside design temperature for Ottawa as -8F/-22C:

      But yes, if using it as a primary heat source it needs to be a hyper-heating type, preferably with a pan heater for managing defrost ice build up.

      There are several other companies other than Fujitsu & Mitsubishi with that technology. LG has a pretty good 3/4 ton through 1.5 ton series that are specified down to -25C, Midea & Gree both have models specified down to -30C.

      Many of the dozens of heat pumps listed on NEEP's cold climate heat pump database have a specified output at -25C or colder, but you'll have to look up the extended temperature capacity from the manufacturers' documentation, since NEEP only lists max capacity down to -15C/+5F. So with heat load calculations in hand start the initial search here:!/

      For a quick guesstimate, at -25C most will still deliver ~75% of the max output at -15C. Take note of the description of how the pan heater is operated too- if it doesn't have a description it may not have one, which becomes a monitoring and manual de-icing issue when contemplating weeks/months of operation at temps well below 0C.

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