Mini split(s) - How many BTUs for a bus?

belfert · October 02, 2025, 07:40:35 AM

My 1995 Dina has three 15K BTU rooftop A/C units. I have one in the rear bunk area, and two in the front living/kitchen area. The two up front can barely keep up on a 90+ degree day. One of the front A/C units appears to have lost its refrigerant. We were struggling to keep the front area at 85 degrees with only one working A/C unit.

The 1999 I want to use a mini-split. How many BTUs would I realistically need? 36K BTU seems like a lot, but 36K BTU is less than the 45K BTU in my 1995. Now, I understand that rooftop A/C units can be very inefficient so a mini-split can be smaller. My 1,300 square foot house only has a 30K BTU central A/C system. I saw a video tour of a Van Hool double decker conversion recently. They said they have an 18,000 BTU mini-split. That seems quite small to me.

luvrbus · October 02, 2025, 10:07:23 AM

It depends on the location, glass and insulation in a bus ,they shouldn't be that hard to cool when parked in the shade, here in AZ with the heat mini splits struggle I know a owners that has 3 -9000 btu mini splits he went with 9000 btu because they are 110v he put one roof top back on for faster cool downs once it cools down he does ok with 2 running in a 40 ft bus parked, Ac units cannot keep up when driving a bus down the road ,just stop and think the dash air on a automobile is around 27k btu on high fan.My friend Kenny went with 3 of the new inverter type (like a mini) 13,500 roof tops on his Prevost they do a good job here in AZ.He went that way to get away with losing bay space bay for the condenser and fan plus the lines routing for the mini's he loves his new units they are quite too, He is like me he doesn't like the looks of the cassette hanging on a wall inside the bus, I don't like those in a house either my daughter has 2 in her house lol they look like something in motel room to me

belfert · October 02, 2025, 10:23:05 AM

I am always in the sun. No shade where I go. My 1995 only has the three rooftops for road air. It works okay most of the time.

The 1999 has working road air. The issue is all the space it takes up, plus the ductwork is in the overhead luggage racks. I also read it can cost a ton of money to keep it working.

Dave5Cs · October 03, 2025, 07:27:13 AM

This summer we put a Furrion chill 18K on the roof in the LR Kit area and with the 13.5 in the Bedroom Houghton rec pro the Bus stays very nice even in 109 degree that it was this year. I don't care about the looks of the roof tops and I too don't care for the ones inside hanging off the wall. The ones we have are very quit. About 45 to 50 at full speed and lower at low speed. The Furrion even has a Turbo cool the really cranks it up fast if needed.

luvrbus · October 03, 2025, 08:49:04 AM

Quote from: Dave5Cs on October 03, 2025, 07:27:13 AM
This summer we put a Furrion chill 18K on the roof in the LR Kit area and with the 13.5 in the Bedroom Houghton rec pro the Bus stays very nice even in 109 degree that it was this year. I don't care about the looks of the roof tops and I too don't care for the ones inside hanging off the wall. The ones we have are very quit. About 45 to 50 at full speed and lower at low speed. The Furrion even has a Turbo cool the really cranks it up fast if needed.

belfert · October 03, 2025, 01:36:52 PM

The Chill Cubes are nice units, but I really want heat pumps. I have an Atwood rooftop unit that makes all kinds of wind noise when driving regardless if running, or not.

The debate on mini-split vs rooftops could go on forever. The folks who have mini splits in their RVs really like them.

luvrbus · October 03, 2025, 03:57:14 PM

Attwood AC units are just a downgraded Dometic AC I had one that didn't last 2 years,your AC is choice no one can make that call for you.You can duct 3 roof tops and they are quite I had 3 Colemans 15,000 btu with heat pumps on my Country Coach you barley hear those run , what I didn't like was the heat pumps were worthless below 30 degree but I had floor heat along with the Aqua Hot so I seldom used the heat pump
The coldest were in was -5 and the floor heat was my choice when plug to power ,it never made a sound and kept you very warm. If I buy another RV it will have floor heat.In our Eagle we had 3 Cruise/Air they were quite with vibrable speed fans only thing I didn't like was the price of those units

epretot · October 05, 2025, 03:09:28 AM

I have two 18k heads in the bus. One on the back wall and one over the windshield.

I'm in the direct sun and it gets very uncomfortable at times. The windows are the issue.

Also, the head in the back is oversized. I probably should have done 24 and 12. It causes the humidity to climb as a result if the small space.

3 heads would be great but didn't have a place for it.

If I had it to do over I would double the btus

luvrbus · October 05, 2025, 06:36:50 AM

Quote from: epretot on October 05, 2025, 03:09:28 AM
I have two 18k heads in the bus. One on the back wall and one over the windshield.

I'm in the direct sun and it gets very uncomfortable at times. The windows are the issue.

Also, the head in the back is oversized. I probably should have done 24 and 12. It causes the humidity to climb as a result if the small space.

3 heads would be great but didn't have a place for it.

If I had it to do over I would double the btus

That is some good information for Belfert ,I have always said when you see the mini splits offered from the big boy converters and motor home somebody has figured it out and that won't happen till the mini splits are manufactured for RV and mobile use.I know Taylor tried it on a few if her entrainer buses a few years ago but running a 100,000 mile a year they didn't hold up and she went back to 5 roof mounts on her buses ,the tubing on those are paper thin, where do get service for 1 in bus here no AC Co. will work on a mini in bus we tried for a friend calling a dozen places

Jim Blackwood · October 06, 2025, 06:28:10 AM

I've discovered I have a very close friend who spent his career in the HVAC industry, often designing custom systems with multiple units and his son went into the business as well and is still active. He has volunteered to take a look at my sketches and specs for the system I want to build and then pass it along to his son for evaluation and recommendations. If both of them need more expertise they know where to find it.

I talked with Ed about the system I want. The key is finding 3 high efficiency soft start compressors with about a 18k btu capacity that run on 110v. The next step is designing a suction side manifold that will guarantee correct oiling for each compressor and not starve any of the three for oil. Ed is familiar with such manifold designs.

So now I need to sit my butt down and write up the specs as completely as I can manage to do, and once I pull this one off I will have a system that makes use of all the original OTR parts with a few more bits for stationary operation. Should end up being an absolute killer system if it all works out as intended, and not terribly expensive to install. Not putting warts on the roof will be a plus I think.

Jim

luvrbus · October 06, 2025, 06:53:10 AM

Air conditioning is all the same you circulate the freon and it absorbs the heat inside and dumps it outside ,you just figure out the most effective way to do it that works for you

belfert · October 06, 2025, 08:36:17 AM

My bus has sort of a shelf above the engine in the back. Could I place a mini split in there and bring air in from the side and exhaust air out the side? Would this work while in motion?

luvrbus · October 06, 2025, 10:03:30 AM

Quote from: belfert on October 06, 2025, 08:36:17 AM
My bus has sort of a shelf above the engine in the back. Could I place a mini split in there and bring air in from the side and exhaust air out the side? Would this work while in motion?

Are saying install the condenser inside the bus and pipe fresh air to it % they need all the fresh air they can get to keep from building up high head pressure and shutting off

Jim Blackwood · October 06, 2025, 11:41:45 AM

Systems can be simple or complex. For example the OTR 102 system has one condenser, one compressor, and four evaporators. It can run any of the 3 smaller evaporators while powering the main one, or none of them except the main one. Simple solenoid valves control the flow and the compressor cranks out enough freon for about 13 tons of cooling in total as I understand it. The use of smaller compressors and valving to direct the freon to the smaller evaporators should allow satisfactory cooling for stationary use. That's my plan anyway, we will see how well I am able to implement it.

Jim

belfert · October 06, 2025, 12:29:01 PM

Quote from: luvrbus on October 06, 2025, 10:03:30 AM
Are saying install the condenser inside the bus and pipe fresh air to it % they need all the fresh air they can get to keep from building up high head pressure and shutting off

Yes, not really any different than placing it in a luggage bay like some do. Also not much different than drawing air through for for generator in a luggage bay. The Dina has limited luggage bay space due to being 43 feet versus 45 feet, plus the short wheelbase. I would prefer not to take up a luggage bay. I would build a box for it with some sort of gasketed doors to work on it. The side and back wall of the bus would have large vents for airflow.

I realized the one reason not to do this is how hot it gets back there. I chose not to put my LifePo4 batteries back there due to the heat. I built an insulated wall with gasketed door to try to keep that heat out of the rest of the coach.