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Gary Hatt
August 1, 2023
206 views

Cooling Options for a Bus Conversion

This month I am in the Midland, Texas area.  The daytime temperatures get up to as much as 111° F during the daytime.  For most people that is hot, and it is especially hot in a metal-enclosed bus conversion that is like a tin can.  

I lived in the Dallas area for ten years back in the 80s, so the heat does not bother me much if the humidity is not too high.  In the Midland and Dallas areas, the humidity is generally pretty low, so I can tolerate the heat. But I am not a fan of high humidity because of my allergies and asthma. 

Being inside a bus can make things much more uncomfortable than in a well-insulated house with 4” to 6” thick well-insulated walls. In a house, built especially with double-pane windows and a decent air conditioning system, you can keep it very comfortable inside even when the temperatures outside exceed 100° F.  

But in a bus, it can get very hot, very fast, especially on a hot sunny day.  Being inside a bus in the hot summer feels like being in an oven unless you have some very good insulation such as EHP or some other high-end product. 

Over-the-road passenger buses are built with extremely good factory air conditioning.  With a typical bus, you can run the over-the-road air conditioning and keep it a comfortable 72° F throughout the inside of the bus all day and all night even with ambient temperatures above 100° in places like Houston, Miami, or Las Vegas.  You can’t beat over-the-road air conditioning in a bus when traveling down the road on a hot summer day.  Of course, most new buses have double-pane tinted windows, and that too makes a huge difference.

Passenger buses generally remain idling when passengers are loading or unloading, or even when just sitting in one place when it is hot outside, mainly to keep the air conditioner running. On the other hand, most converted bus owners, when parked, shut down the engine, and with no engine, there is no over-the-road air conditioning.  Because of that, unfortunately, many people remove the factory-installed air-conditioning to reclaim the space for something else, not realizing that they will never be able to even come close to what they had with factory air.

I had one bus with the factory air conditioning and two buses without it.  I much preferred driving the bus with the factory air conditioning on hot summer days.  In just a few minutes, you can cool down the entire inside of the bus.  One of the drawbacks of the over-the-road air conditioning is that it is a bit noisy outside and it also blows dust on a dirt road all over the place.  

This is not a problem when the bus was in passenger service as they mostly parked on paved surfaces such as at bus terminals or parking lots.  But when converted into a motorhome, many people drive on gravel roads in RV parks or when boondocking stirring up the dust. 

That being said, most people remove the factory air and install either roof air conditioners or lately mini-split units with the head of the unit on a wall inside the bus and the compressor mounted somewhere outside the bus where it can exhaust the heat outside.  

The three roof air units on my current 40’ Eagle bus, each being 15,000 BTU units, do a very good job at keeping the inside of the bus comfortable even when temperatures soar over 100° F.  The one drawback is that they are a bit noisy unless they are as ducted as many higher-end conversions are.  Mine unfortunately are not ducted, and talking on the phone with all of them running can be challenging. 

When ducted, the noisy roof air conditioners are muffled by a second lowered ceiling a few inches down from the roof itself where the ducts and wiring are run.  This way, the noise from the blower unit is muffled making the inside of the bus much quieter. 

Roof air units take up the least amount of space and are the easiest to change out if and when they fail, which seldom happens with these units anyway.  They usually last about 15 to 20 years until they must be replaced, at which time, they can be swapped out for a new unit in about an hour.

Basement units are the ultimate and are often found in high-end coaches.  This type of unit keeps the noise in the bay of the bus and out of the living area. They force cool air up through ducts into the living space in the bus and the warm air is passed back down through the floor back to the unit.  This requires one or two large holes in the floor to pass the ductwork through.  

These units are the ultimate as it keeps all of the noise out of the living area.  This type of unit is the most expensive option, and they also take up a lot of bay space, which is a bit of a drawback for a bus conversion.  But those that have them, love them.

Jerry Work’s Note: The problem is the company that made most of these “CruiseAir” units is no longer in business, so parts and repairs are a big problem.  A company in Florida has just started making a drop-in replacement but they are so new to the market we know little about longevity or performance over time.  I will let you know more about these as we learn more.

Mini-splits have become all the rage lately.  They have the condenser unit mounted outside of the bus or better yet, in a bay under the bus in a clean environment, and Freon passes via tubing from the condenser up into the living area of the bus to a blower unit mounted on a wall facing the living area.  

People love these units as they have a low amp draw, and if you have sufficient solar wattage and lithium battery amp hours, you can run these without a generator or being plugged into an external power source. However, they do not have nearly the cooling capacity of the units previously mentioned and they would be hard-pressed to keep the inside of your bus comfortable on a hot day in south Texas, where I am now.  But for milder climates, they work just fine and will heat and cool the inside of a bus very comfortably, and many of them, extremely quietly. A huge advantage.

The other disadvantage of the mini-split units is that the compressor needs to be mounted outside of the living quarters and many people hang them on brackets on the rear of a bus or on hangers under the bus.  Both locations are bad as all the road grime, salt, dirt, dust, snow, and everything else gets kicked up by the tires and get sucked into the condenser unit.  A roof air unit on the other hand is on the roof far away from the dust and dirt.

Many people are beginning to discover that these systems fail prematurely if used on a bus conversion unless extra care is taken to clean them regularly, and even then, they tend to die prematurely due to the environment they are subject to.  

Mounting anything under a bus is the worst thing you can do, especially behind the rear tires, and especially anything that has an electric motor, as they get caked with dust road dirt, and mud on a rainy day and the next thing you know is that they are overheating and they quit working, usually when you need them the most.

So those are your choices for air conditioning in a bus.  One of these systems will be ideal for your situation and budget, depending on where you live and where and when you plan to travel.  Unless you are using your bus as an entertainer coach, with several bunks, you do not need to have five or six air conditioners on the roof.  Three roof air conditioners are generally sufficient for a 40’ or 45’ bus without slides, and two mini-split units will keep your bus comfortable when the temperature remains below 100° outside, but nothing like the other units previously mentioned.

One thing you need to be cognizant of is that if you buy a roof air conditioner with a heat pump, as I did once, it will shut down when it gets around 107° outside, so if you plan to drive through Vegas or Houston on a hot summer day, you may be very uncomfortable. I learned that the hard way.  However, as long as you do not travel where it is not excessively hot, you will be fine with one of these heat-pump units and they also do a decent job of heating the inside of your bus as well.

Entertainer Coach with five (count them) roof air conditioners.

At the other end of the spectrum, if you travel in cold climates, many heat pumps stop heating when the ambient temperature drops below 40° F.  So, if you plan to travel in very hot or moderately cold climates, be sure to check the specifications of the unit you are interested in or alternatively, plan on using an alternate heating system in very cold weather.

When I lived in my bus where the temperatures would become extremely hot during the day, I found that if I started my A/C units early in the morning, before it began getting hot outside, then it stays cooler throughout the day inside.  You are cooling the mass of everything inside the bus to start with, so it holds in the cooler air longer in the day.  

Another thing that people can do that do not have sufficient A/C in a bus, is to close off part of the bus during the hottest times of the day.  So maybe you only cool the driver’s area when you are driving, by hanging an insulated curtain behind the cockpit.  Once you are stopped for the day, you may pull the curtain across to keep the heat out of the main part of the bus, because everyone knows, the windshield can radiate more heat than any other window in the bus so the cockpit area can get very hot.

When you are ready to go to bed, you may close off the bedroom, with a door or curtain, to ensure all the cool air from the A/C unit is concentrated in that one room so you can sleep better.

You can also install insulated drapes inside all windows to keep the heat out in the summer.  Many folks that live up north in the winter use insulated drapes to cover all windows to keep the heat in.  You can also park in the shade if possible or get an outside windshield cover to keep the sun off the windshield.  I have an outside windshield cover, electric curtains inside my front windows, and a curtain I hang inside the curtains.  This combination keeps out most of the heat when I am facing the sun during the day.

Awnings are also a big help.  I have a 22’ awning on the curbside of my bus.  I will usually put it out far enough to keep the hot sun off the windows, and on a really hot day, I put it out even further to keep the sun off the side of my bus above the floor line.  This makes a big difference too.

On the street side of the bus, I have a long awning that covers all of the windows on my bus with the exception of the bedroom.  I have not put them on the bedroom windows at least yet, as that is a small room so the A/C in there is able to keep up even on the hottest day.  Of course, if you can park under a tree or any place you can get shade, that can drop the temperature of your bus down several degrees and that is free. 


Another option is to run a fan or several fans inside your bus to keep the air moving.  I have a 23” box fan that I sometimes place on the floor in the doorway to my bedroom, to force the cold air from that room into the main part of the bus. As I said earlier, the A/C works very well in there, so why not force some of that cold air into the main living area of the bus during the day?  I even do this when it is not overly hot outside, as by running the rear roof air in conjunction with a fan, I do not always have to run the front A/C units, so it keeps it quieter up front in the main living/office area.

If you live in a dry climate, another very good option is to buy a TurboKool (evaporative cooler) unit for your roof.  If you have solar and lithium batteries, this is a great solution.  This unit draws very little amperage (2.2A – 4.6A at 12V) and will reduce the temperature of the inside of your bus significantly on a hot summer day.

The only drawback to these units is that they drink a lot of water, and they must be plumbed into your fresh water system. But if you have that, these units work great and can drop the inside temperature of a bus or house by 20 – 30° F, with very little power consumption. This is generally sufficient to make it comfortable inside. Again, the huge advantage is that this unit runs on your house batteries. 

TurboKool rooftop unit. It mounts in the same 14” square hole as an air conditioner.

Here is a video on TurboKool you may enjoy.

Whatever cooling system or method you choose, it may or may be sufficient to keep your bus comfortable on the inside, and “comfortable” is defined differently for all people.  Some people think 85° F is comfortable in the summer, whereas some people are not comfortable when it is over 72° inside a bus.  

One must take into consideration where they plan to travel and at what times of the year.  Many people travel north in the summer and south in the winter, so this is not an issue for them.  But for those that must deal with extreme temperature changes, I hope this helps you to choose the best option or combination of options noted above for your bus conversion lifestyle.

Article written by Gary Hatt

Since July 2012, Gary Hatt has been the Publisher of Bus Conversion Magazine. Gary does most of his own work on his bus with the help of mechanic friends. He has owned tents, truck campers, travel trailers, and stick-n-staple motor-homes until he bought his first bus in 1997 which was a 1972 MCI MC-7 Combo. When he had a chance to buy a 1983 MCI MC-9 Log Cabin bus with larger windows he jumped at the chance. On Thanksgiving of 2014, Gary bought a 1967 Model 08 Eagle and has since been living and traveling full time in that.

You may reach Gary Hatt at
Gary@BusConversionMagazine.com

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