To install a rooftop AC on your school bus conversion seems intimidating at first. It’s actually pretty straightforward once you take time to read through the installation instructions for your upper unit and ceiling assembly. Familiarize yourself with those instructions, and check out our process below. This should get you well prepared and confident for the job!
An important note before we start. This post is all about how we installed a Dometic Rooftop AC unit on our skoolie school bus conversion. Now that we have lived in the bus for over 8 months, we wish we had installed a mini-split system. Here’s why:
- It’s quieter. The rooftop unit is LOUD. We like to host dinner guests (who are the very people we most often run the AC for), and the loudness is pretty annoying when you’re trying to have conversation.
- Our unit cools the back studio of our bus really well. But the front area…not so much. We thought this may be because we have so many exposed windows (we are insulated really well). BUT we’ve read accounts from other skoolies that said their mini-split systems cool their buses well, even with a lot of window exposure like us. So now we have a sneaky suspicion that a mini-split might have worked better for cooling our space. (Our bus is 35ft long with 198 sq ft of space. More on our specs here.)
So, given that information, if you are still dead set on a rooftop A/C unit, here is our post to help you navigate the installation process! Read on!
Rooftop A/C Installation Required Tools & Equipment:
- Angle Grinder
- Power Drill
- Measuring tape
- Piece of cardboard to create template
- 2x4s cut into 1×2 boards
- 1-inch or larger L brackets
- Self-tapping, sheet metal screws
- AC Top Unit (this is the exact model we used)
- AC Ceiling Assembly (Non-Ducted) (this is the exact model we used)
Full disclosure guys, some links on here are affiliate links meaning we may get a commission if you buy something or take an action after clicking. As an Amazon Associate we earn from qualifying purchases. Not much, but something. This is really important – we only link to products we actually used in our conversion.
Cut the Ceiling Hole
- Make a cardboard template of the exact size opening your unit will need. These exact dimensions will be given in your upper unit installation instructions. We have a 13,500 BTU Dometic Unit, which requires 14.24 x 14.25 inches. Make a pencil-sized hole in the exact center of the template.
- Decide the location of your unit. Tip: We found that the rear vent of the unit pushes out A LOT more air than the front and side vents. Keep this in mind when choosing the location of your unit.
- From the roof of your bus, measure from the side ribs to find the exact center midline of the roof. You’ll see in the video that I measured from the inside first, which was a mistake. Measure from the roof.
- Drill a hole at the exact center, place the template on the roof and hold it in place with a pencil or bolt inserted through both. Mark around the template with pencil or sharpie.
- Use the angle grinder to cut the hole.
Build the inside support mount
- Build an H-shaped mount to fit directly underneath the hole. The inside square of the mount should match the dimensions of your ceiling hole. We can’t give you exact dimensions of the longer edges of the mount, because the distance between every set of bus ceiling ribs is different. You can see the shape of the mount in our video. Build a mount of the same shape, making the long pieces match the dimensions of your bus in order to fit snug between the ribs on either side of your ceiling hole.
- Secure the mount to the ribs using L-brackets and self-tapping screws for sheet metal. You will have to drill the holes for the screws first, even though they are self-tappers.
Place upper unit on roof
- Get the upper unit up to your roof. We took it from front of the bus, we’ve also seen others pull it up with a ladder. Either way, be careful!
- Position the unit directly over the hole, with someone below checking that it is correctly in position.
Secure the inside metal framework
When we say “inside framework” we are not talking about the ceiling assembly. We are referring to the metal framework of the upper AC unit that holds it from the inside. This “metal framework” comes in the box with the upper unit itself (the ceiling assembly is purchased separately from the upper unit).
This is where the instructions for your particular upper unit are really going to come into play. For our unit, it was very straightforward. The unit came with the inside gear metal framework and a set of 4 long bolts. We:
- Positioned the metal framework directly below the upper unit
- Slid the bolts through the metal framework and to the corresponding holes in the upper unit.
This is where our video ends. We didn’t install the ceiling assembly until much later, so that will be put into a separate video. We understand that you might be doing the entire process right now, though! So here is the skinny on how we installed the ceiling assembly.
Install the ceiling assembly
Note: In the video we say we are going to use a ducted ceiling assembly. That was our original plan, but we realized that created a ducted system in our bus ceiling was going to be a serious amount of work. So we ended up going with the non-ducted ceiling assembly for our unit.
Second note: Again, this is really where you need to follow the exact instructions of your unit/ceiling assembly before all else.
This is how it went for us:
- Bring the 120V power supply electrical line (12 gauge) into the metal framework, per the instructions for our ceiling unit. To do this, we had to drill a .75 inch hole in the front section of the bracket to run the line through and then bring it into the framework. We didn’t hook up the supply ourselves; we left this for our electrician to do.
- Cut the separator foam that comes with the ceiling unit. The amount that is cut depends on the amount of inches from the metal framework to the top of your mount (your unit’s installation instructions will have exact recommendations for how much to cut). Tip: Keep the leftover foam! We ended up using our leftovers in other parts of the conversion.
- Your ceiling assembly will come with a set of screws. Match to the corresponding holes in the metal framework and screw that assembly in place! Feel around the edges of the foam separator to make sure it forms a complete seal between the air intake and outtake.
- Later on, our electrician hooked up the power supply and we were able to crank that thing on for the first time!
How do we power our rooftop AC?
The Art We There Yet bus is proudly solar powered. But our battery bank is definitely not sufficient to crank up and run an AC unit. Nope!
Our AC unit requires at least a 3500 generator. We have a 3500 Powerhorse Inverter Generator which does the job like a champ. We can run the AC for at least 8 hours on one tank of gas (which runs around $16 depending on gas prices).
The power supply line for the AC is completely separate from the 120V system that runs our lights and appliances in the bus. Essentially, a 120V power supply is run directly to the AC unit, which the electrician set up to convert into its own 15 amp plug. We can plug this directly into the generator. Or we can run an extension from it to the grid.
Tip: If you run an extension from your A/C to the grid and you plug into any normal household socket, prepare to trip a breaker. If you can run the extension to a socket specially rated for higher electrical draw – such as many sockets in garages – this is better.
Curious about how our electrical is set up? We lay out those details here.