top of page

MRCOOL DIY Multi-Zone Mini Split | Barndominium Install

Updated: Dec 19, 2023

Part 1| Preparing the Barndominium

This all about the MRCOOL mini split system. We will go through the entire install and testing in my barndominium. I will also be giving my honest opinion about the system. We have the 48k mini split system. It does five different zones of heating and cooling. With our kit, we recieved three 9k heads and one 12K head. For step one I'm going to move the unit to where I want it. I want to keep mine pretty hidden so I'm going to put in on the back side of my barndominium.

Zoned Cooling and Heating

I started by pouring a 36x24x4 inch concrete pad to set the condenser unit on. I used five bags of quikrete. The concrete pad will allow me to bolt it down so wind won't blow it over or anything like that. You will need quite a few 2x4s, a level, a circular saw to cut your forms, some screws, and a gun to put your forms together. I needed to dig out some rock to create a flat surface. Then I got my forms all flattened out and set. Keep in mind that your condenser has to be off the wall a certain distance so make sure to check that it is the correct distance away. This will vary based on your condenser and where you live. So we made a 24x36 box out of 2x4s and made sure it was level on the ground. It is a good idea to put in a couple stakes to hold it in place. I used compacted gravel underneath to set the frame on. We then mixed up some concrete and poured it in the frame. Once everything is poured, you can smooth it off and then let it dry.


When you are using a unit like this, you need to make sure that the it is up off the

ground because when you use it as a heat pump in the winter, there is a lot of condensation that needs somewhere to run off. To do that I built concrete pillars. I used 2x10s to create a frame that was 22.5x6 and I screwed in some anchors to tie this concrete to that slab.


You can also just buy stands but I couldn't find a good stand for what I wanted. I then measured out where the anchor bolts should go, stuck those in, and let it dry. I roped in some teammates to help me lift the unit onto the concrete stands I created. It can be tough trying to get all the anchor bolts to match up but if your measurements are correct it should eventually fit right in there. Once you have it on the stand, you can bolt it down.




Part 2 | Installing in the Barndominium

One of the biggest things that we encounter with a barndominium is figuring out how to handle the HVAC system. Mini split systems have really come a long way just in the last couple years. I have two conventional HVAC systems that serve the downstairs and upstairs of the house part of my barndominium, however my business has grown and I now have a 40x56 garage that has a storm shelter, a canning kitchen, and now a design office. It’s very important that we have AC in there. I already have in-floor heat that I put in when we originally built the house, but I've partnered with MRCOOL and I'm going to try out the mini split system for some AC and additional heat.


The reason I like MRCOOL and I went to them is because they are a DIY friendly company. The unit that I'm using is a 48k condenser. It has two fans. The other thing that's great about it is that I can have up to five heads on it. I got three 9k units and also one 12K unit. You can get these on the MRCOOL website. Just go to the website and put all of your information in and they will send you all of the stuff that you need. I'm getting a pre-charged line set so all I have to do is make the connection from the line set to the condenser. These units also come with the electrical connections done inside and your wire that runs back to the condenser where it pulls power from. They recommend having power run to your condenser. Mine took a 40 amp circuit.


One thing you need to think about with mini splits is the condensation that comes off of them. They are designed with a tube that you run back with your power so that you can hook up and bring outside. Another cool thing about these is that they act as heat pumps so in the winter, in addition to my in-floor heating, I can get heat out of these in the. One thing about when this condenser is acting as a heat pump, the condensation is going underneath the system. They also sent me white line set covers that match my siding. If yours don’t match you can just paint them. I’m installing the system on the back side of my house so that you won’t be able to see when you drive up and down the driveway.

Mini-split systems are known for their energy efficiency

We are going to go ahead and mount our indoor unit. Step one to mounting our indoor unit is to put up the mounting plate. The Mr Cool units come with a template. It’s pretty self-explanatory but can help you ensure that you do everything correctly. I am mounting this in a post frame structure so I first need to figure out where my eight foot on center column is because I don't want to run into it. Everywhere I have a row of screws is a girt, which is a 2x6 that I can fasten the indoor unit to. So I used the template they provided by cutting the holes in the card board where I needed them and then making my markings so I’m ready to cut. I also used a laser level to get my markings perfectly level. My plate will be able to get mounted but the problem is that I have a three-quarter inch gap behind it on one side due to the siding. I'm going to take a piece of wood and build that out so that the bracket has something solid to sit against and hold onto. Once we do that we can mount this plate and keep on moving forward.


I start drilling my hole but before I drill all the way through, I make sure to go look out there to make sure I don't land on a rib or anything. Once I cut a hole through all of our spray foam insulation and out to the outside I'll go ahead bend our pipe that is coming off of our unit. We have to put a sleeve through the hole and spray foam on the outside to protect everywhere and seal it all up.


To bend the line set you just grab it at the bottom and then slowly rotate it up so it's facing straight out. Your condensation line will go on the outside and it gets taped to the bottom. Then it all gets hooked up on the outside of the house. I'm going to use electrical tape to lightly tape those together so they go through the hole nice and easy. When I put the sleeve through the hole I have to go outside to cut off the excess, then I’ll spray any remaining space with spray foam and put the cap on . That sleeve is what everything runs through including our electrical line which is already pre-wired to the unit.

Mini-split systems are relatively easy to install, especially compared to traditional ducted HVAC systems

Before I put the cap on, I'm going to put a bead silicone outside so when I put the cap on it has a good seal. Once you have that done, it's time to slide everything through. You want to make sure the drain line is on the bottom so it can be bent and come down at an angle. I first put the electrical line through, followed by the portion we taped together earlier. I get that mounted and then go back outside to spray foam and fill in any gaps.


I'm going to have to bend my line set down and then use the line set covers to hide it. The line sets are pre-charged so all I have to do is mount all of my covers, get it over to my condenser, hook my line set in, and then wire it. This system makes it really easy to understand everything you need to. We are now ready to set up number two which is in our canning kitchen. For this one I'm going to have to make an access plate to make sure I can check the connections when I need to. I'm going to mount it much the same and then I’ll run it down and out. The drain pipe is going to go into the drain system.

 This zoning can help you save energy by only cooling or heating the spaces that are in use

Once again I will stick my power cord through the hole first and then I'll pull the line set out and stick that through. Since it is an inside wall, it is going to be a little bit of a pain but I do have a 20x14 basement that I can run this down and out to the I-joists to the outside. The line set comes with a gas and a liquid line and they have caps on, a gray cap and a blue cap. The caps make it really easy to match them up with the condenser. My BTU heads are different sizes, one is 12000 BTUs and then my other is 9000 BTUs. The manual says to mount the largest BTU heads at the bottom. You’ll want to hook up your line sets from the unit inside before you hook them up to the condenser. Make sure you match blue to blue and gray to gray. We need to take the protective colored caps off and then connect those to the corresponding one. Start by hand tightening and then you want to get your wrenches on there and tighten some more. You need to move pretty quickly because you don’t want a large amount of gas escaping.


After you get them tightened, it’s best to leave them exposed because once you get this all hooked up to your condenser, you’ll want to do a leak test to make sure there's nothing leaking. If you are working with an exterior wall your condensate line can just go right outside and drain there but with inside walls it is different. In our canning kitchen we decided to run our condensation line down into the PVC that goes to our drain. Running your lines from interior walls will be different for every layout of a home. You have to do what works for you and your home.


Once you have all your stuff run out to the exterior, you can now make sure everything is all sealed up. I used spray foam to fill everything and then I took a layer of putty to fill any gaps. I also put a bead of silicone around the outside of the caps. You then can get all of your line set covers put on so everything can be neat and tidy. We have three out of our four units hooked up to our condenser so that is enough that I can power this thing on. It says you have to have two-thirds of the load hooked up in order to run it which I now have. We have so much information about the mini split system, we decided to make three parts. So next we'll cover the electrical install and testing of the units.


Part 3 | Barndominium DIY Reveal + Electrical

This is part three of our MRCOOL mini split installation series. This time we’re going to cover the electrical, the startup, and the testing. The first thing I have to do is run power from my breaker box and in my opinion, for my house, we only need a disconnect outside to cut power to this unit. We don’t need disconnects on each of the units inside. If we were doing something more commercial, it might be better to have a disconnect on each individual unit. If you're not familiar with electricity you should leave that to somebody that is more familiar but I feel quite confident to wire this up so I'm going to do it. I need a minimum of a 40 amp breaker. I have that and the proper size of wire, I just need to install that in my box. I'm going to run it up into my attic, across, drop it down in the wall by the compressor, then out of a disconnect which I’m going to put right up here.


My disconnect is right by the condenser which is good because it is required that it is within eyesight. The disconnect box is going to mount on the wall. It has a little piece that you can just pull out to kill the power. If it’s up, you know it's turned off, but if it is down, it is on. That is so if you want to work on your unit outside you can just pull this out. It makes everything safe.


It’s also very important to have the appropriate size breaker. I have a Square D box so I have a Square D breaker. You’ll also need a whip which is just a pre-made conduit with the proper size wires in it. It’ll go from the disconnect to the condenser unit. The whip can be cut down if it's too long and it comes with a couple different ends. One end to go to the disconnect box and one to go into the actual unit. I'm going to take my wire and I'm going to run it from my main box to where the location of my breaker box is going to be.


So this is my main panel and I have it all uncovered. Then I have this trough up above it and a two inch nipple that goes up in the attic space. I'm going to use the nipple to take my line up into the attic and down to where I want it. I also need to put in another conduit from the trough, down to the main panel so that I can have space to bring my breaker wire all the way down. Once you get that conduit put in, you can get up in the attic and feed your line through to where it can easily reach the main panel. There might be some insulation in the way so you’ll have to pull that out. It is legal to run Romex covered wire as long as the space is less than two feet. I stripped it in my trough and then continued to run it down. Once I ran it down I tucked my wires away from the panel so there was no chance that they could flip over and hit anything that they were not supposed to. I wait until the very end to hook these up because that way I can assure myself there's no power going into this line while I'm working on it. Once I get everything hooked up I come back in here and do my final connection.


I now need to drill a hole in the attic to run my wire down. Once I get the wire out to where I need it, I will coil it up the excess and store it up here so if I ever have an issue or I need to cut some wire off I have some extra. Next I'll tidy up the attic and put wire staples in it where I need to. Once we've our power line running all the way down, I go outside and mount my disconnect switch. To mount it, I'll drill a hole in the wall and then put a piece of conduit on the back to run my wire through and I'll put that through the wall. Then I can run the wire right into the box. When mounting the box I’ll use sealing clay around the conduit to make sure it's all sealed and secured. I can screw it in and then hook it all up and fill the rest of the hole with spray foam. Once we are good on this end I can then work my way back to the main panel securing the wire.

Mini-split systems come in various capacities and configurations

On the back of this piece, it shows you the line and load. My two hot wires coming from my box will go to the lines and my two hot wires from the condenser will go to the load. Next I’ll hook my wires up to the unit. We have line one, line two, and the ground. Next I'll hook them up in a disconnect. Now I just need to hook all my air handlers up. They are all nice and labeled on the condenser and they match up with the corresponding wires. There's also ground terminals back behind for your grounds. After that I just follow the line back, secure it back to the electrical box, and hook it up there.


Once we have everything hooked up and secure, we can go through and start opening lines and testing them. I go back inside to the main panel and make sure everything is hooked up and then go through and open up all the valves. After I do that and work through the checklist provided in the book, we can start testing this thing. Each one of these heads or units on the wall has a USB controller that will need to be installed. There's an app on your smartphone that you can use to run them. To install it, you pull the front of the unit up and then in that lid there is a spot where you can plug that USB in.

Mini-splits can provide both cooling and heating, ensuring year-round comfort in your barndominium

When it comes time to open and test the valves. You will want to open every valve you are using including the king valves. You then can turn the power on and check every head to make sure they're heating and cooling and check all the connections for leaks. You can do this testing by using a spray bottle with soapy water. If you see bubbles you know there is a leak.


Now that we have tested all of our units we can go ahead and wrap all of the joints with the sound deadening material. It's almost like a really thick, sticky rubber membrane. Once the connections are wrapped I can get them all sealed up, insulated, and put our cover on.

They require minimal structural modifications

Now it's time to test the individual units and see how they're working. The first step is to use the remote to turn it on. I'm going to turn it to the cooling mode and let it run for 10-15 minutes. I turned it on to the lowest temperature and put it on turbo mode. In that 10-15 minutes I will make sure everything's operating fine and then I'm going to respray my connection points to make sure I still have no leaks. You always want to check again because it will gain a little bit more pressure as the system starts running. Keep in mind that in the cooling mode, the condensation comes from the indoor unit. So you’ll want to check the condensation lines to make sure they're draining properly. You’ll need to look for the condensation running through the line and coming out to the proper draining spot. Once that is done, you want to turn it to heating and check that. Mine took about three minutes to change from cooling to heating. For heating you just want to make sure that hot air is coming out of your unit and that the condensation is coming out underneath the condenser.


The excess line set outside by your unit might need to be tidied up. The manual says you need to lay those horizontally but I called my contact at MRCOOL and they said that there is no problem doing it vertically. In my situation it worked a little bit better to coil vertically so that's what we did.

Mini-split systems are known for their quiet operation

I've had this installed for a couple weeks and I wanted to give my initial thoughts. So far I haven't had to use it on the heating cycle, just on the cooling. Based on that, it has performed above my expectations. The indoor units as well as the outside unit are very quiet which has pleasantly surprised me. It also seems to be doing very well at keeping our spaces cool. I've even been running it a little bit in the large part of the garage and it was able to cool that big space. So far, I am very happy with how it runs.


Next I want to touch on the installation process. I thought that the instructions were really well written and I feel like they were easy to follow. I would say that the most difficult part for somebody to do would be the electrical and that basically just comes down to whether you have the experience or not. In the manual it specifically says to have a qualified, certified electrician do the main electrical hookup. Every person needs to know what their limitations are, so if you aren't capable of doing that then you should definitely shouldn't do it. Overall I feel like this is a very doable installation for somebody with some DIY experience.


I would definitely recommend a MRCOOL Mini Split to somebody that is looking for a DIY option. I would say for somebody that has the time you could easily do this installation in two days. All things considered, I am very happy with the MRCOOL Mini Split System.


Thank you,

MR Post Frame








bottom of page