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Using a Window AC Unit In a Skoolie | Air Conditioning Options For a School Bus Conversion

With our future travels bringing us to National Parks like Death Valley and Arches, having AC is a must. We are from Washington after all and consider the mid 70s to be hot.

We did a lot of thinking about which option we should go with and where we would even put it. We went with a fairly unconventional route and chose to use a window AC unit and retrofit it to be installed without a window.

We're happy with our choice and love how well hidden it is. Most AC options require some tacky looking white box hanging around somewhere or taking up roof space. Ours does neither!


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Why We Chose A Window AC Unit

The biggest reason we chose a window unit is because we can hide it away inside as opposed to having it awkwardly stand out on the outside. We also loved the price tag it came with! We bought ours at Lowe's for round $160, which was cheaper than some of the other popular options. Here is a Frigidaire window AC unit that would work great for the setup we did.

With the spray foam insulation we put in, we're pretty confident that we will be able to keep our indoor temperature reasonable in the heat. Our biggest worry is about the bedroom (in the back of the bus) getting too hot since sleeping in a hot room is rather uncomfortable. So that's where we decided to put our AC unit.

The AC unit we bought is 5,000 BTU and says it is good for rooms up to 150 square feet. Our bus is a bit bigger than that, but I think we'll be fine between the AC and spray foam insulation.

Other AC Options

There are, of course, other options to choose from for your AC setup. I'm going to share with you the two most common options we've seen with their pros and cons. While we found that these options wouldn't work for our build, they could certainly work for you.

Mini Split

heating and cooling mini split for school bus conversion
Here is an example of a mini split. The top unit is installed inside, and the bottom unit is installed outside.

This is the option we origianlly thought we were going to go with. It seemed like everyone was using one and so we assumed it was the best way to go.

By no means is it a bad option! It just wasn't right for us.

One of the reasons we didn't want to use a mini split is because so much of the setup has to be outside and is overall bigger. We don't like the idea of having extra bulk hanging off our bus if we can avoid it.

Another reason we didn't choose the mini split is because it would have been a bit overkill for our space. Our bus is the size of one small room, which a window unit could handle easily. The mini splits are rated to cover much bigger areas than we need.

Mini splits do heating as well as cooling. For our skoolie build, we will have a mini wood stove. So this makes the heating ability of the mini split useless for us.

And of course, we don't have a huge budget for this build so the high price came into consideration. Of the few options I'm discussing, this was the most expensive.

RV Roof Top AC Unit

Another option we've seen used a lot is an RV AC unit that is installed on the roof.

Right away we were opposed to this option because it would take up our precious roof space. Between our 12' deck and the solar panels we are going to add, there just wasn't enough room to accommodate an AC like this.

Also, we are running our electrical system to be 120 volts. Most RV AC units like this are only 12 volt, which wouldn't work for our system.

As far as price goes, it is more expensive than the window unit but cheaper than the mini split.

If you have the roof space available and a 12 volt electrical system, then this could be a great option for you.

How We Got The Window Unit To Work Inside

Like I mentioned before, we chose to have our AC unit in the bedroom in the back of the bus. This area serves a few functions so let me explain the layout to you.

The back two feet of the bus is storage space. The bottom half is only accessible from the back hatch and we call the space the garage.

plywood walls storage cabinet in a school bus from the back hatch.
This the "garage" in the back of the bus. It is about 2' tall, 2' deep, and 8' wide.

The top half is closet space that is only accessible from the bedroom. This is also where the AC unit is installed, though it isn't installed yet in this picture.

I am laying on top of the garage and inside the bedroom cabinets.

We put the AC up as high as we could so we don't take up too much of our closet space.

Since AC units create condensation, we needed a way for the water to drain. Normally, this type of unit is hanging out a window so the water is free to spill out the back. With our unit being installed completely inside, this water would start seeping into our walls.

Matthew's solution was to attach a leftover Pex plumbing elbow and some Pex tubing to the unit to create a drain pipe. This pipe then sticks out the back of the bus to drain freely.

pex tubing water drain for condensation off a window AC unit in a school bus conversion skoolie bedroom
This is the view under the AC where we attached a water drain.

We also needed a way to vent out the hot air. Since this is a window unit, the hot air normally just blows out the backside of the unit pushing it outside. There is about a foot of space from the back of the AC unit to the back of the bus where we have an air vent. We built a tunnel out of 1/4" plywood to direct all the hot air from the back of the AC unit to the air vent. We then sealed all the gaps with either spray foam or caulk.

The air vent that we bought was about (dimensions). We used an angle grinder to cut the hole out for the vent to fit in. Then we used construction adhesive to secure the vent in place from the inside. To make sure everything is water tight, we used caulk to seal the gaps on the outside.

skoolie roof raise with roof top deck and ac vent on back side.
This is the air vent for the AC on the outside. It's way up there! We'll paint over it when the weather clears up again

This is the beginning of the process of making the air tunnel to direct the hot air outside. We used 1/4" plywood and 2x2s to make it. The pieces were all small enough that we could use scraps, which is always nice.

window AC unit retrofit into a school bus conversion with hot air vent tunnel
We attached a 2X2 to the platform that the AC is resting on. These are the supports for the sides of the air tunnel we built. In the back, you can see one side has already been attached.

plywood box for AC unit in school bus conversion
Now this side is attached. We also screwed in another piece of plywood on top to enclose the tunnel.

We also did some work to help the AC unit look better in our room. A white box in the middle of our mahogany cabinetry would look pretty out of place.

We used a hammered bronze colored spray paint to redesign the look of the unit. We only painted the front panel since that is all that will ever show. This panel came off easily after undoing a few screws. We didn't paint the control panel since we didn't want to cover up the settings, but we are going to try putting a tint over it to make it stand out less.

To make sure that the spray paint would stick, we sanded all the surfaces lightly to create a slight texture for the spray paint to grip onto. In any little spot that we missed, the paint struggles a bit to stick properly.

The result is pretty cool and looks much better in the room.

How AC Works

For the record, I had no idea how AC worked until earlier this week when I asked Matthew about it in preparation for this blog. A crash course from Matthew and a couple YouTube videos later, I now feel comfortable enough talking about how air-conditioning works.

That being said, I'm no expert on the subject yet. If you're interested in an in-depth explanation on how AC units work, check out this blog from the Home Air Guides. They did a great job explaining the process and you'll learn much more from them than you would from me.

If you want the short and simple Kaitlynn interpretation of how a window AC unit works, then here you go.

Inside the AC unit, there is a metal coil full of coolant winding around. When the AC turns on, it sucks up air from the room and runs the air over these cooling coils which absorb the heat. This cools the air before pushing it out the front and into your room. When the coils absorb the heat, it produces condensation. This helps to dehumidify the room as well as cool it.

The hot air that is created during the process is pushed out the back to keep it from recirculating through the room.

There is a lot more to it than that, but that was enough information for me to feel somewhat knowledgeable.

Knowing how your AC unit works, even just a little bit, can help you make the best choices when setting it up. If we didn't know about the condensation produced from the AC, we wouldn't have made a drain pipe which could have resulted in water damage.

Keeping It Cool

It feels really weird and unnecessary to be installing the AC unit when its December. In fact, I wish we were installing a wood stove right about now!

But it is another thing we can check off the list of things to do. Now that we have that out of the way, we can move on to building the cabinetry around it.

We saved the bedroom for last because we are going to put the most amount of design work into this room. Now that we have acquired a few skills with a router and some nifty wood working techniques, we feel more comfortable attempting to build our design.

Our goal is to make the room match this cabinet door, which will be the centerpiece of the room.

piano front board cabinet door in School bus conversion and air conditioning unit in bedroom
Look at that inlay! And there's pearls in it!

This door is actually the front board from an upright piano that is over 100 years old. A few years ago, Matthew saved this piece from a piano that was about to be thrown away and held onto it waiting for an opportunity to use it. That opportunity is finally here. I absolutely love this piece and am excited to have it installed soon.

The best part is that it is just as functional as it is beautiful since it works as a door for our cabinet!


If you have any questions about our AC setup, we'd love to connect! Fill out a contact form on the bottom of the page or write a comment right here, and we'll be sure to get back to you with an answer.

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Meet the Author


Hey! I'm Kaitlynn, a lover of the outdoors and all things travel. I quit my job to travel full-time with my husband, Matthew, in our skoolie. 

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Matt & Kate

Project 63 

Bringing you travel information and inspiration as we travel to all 63 National Parks.

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