Sizing a mini split for an RV

[Steve from Socal]

I want to get rid of the roof mount AC units on my 5th wheel.

The area is divided into a main area kitchen, living etc and bedroom/bath. The main area is roughly 25X12X8' with the slides extended. The bedroom/bath is 15X10X7' slide out.

There are two 15K BTU roof mount AC units both ducted into a central plenum one unit keeps the camper cool under "most" conditions.

The on-line specs for two zone mini's show 18K BTU able to cool up to 850 Sq Ft? Is an 18K two zone the right choice?

 

[PoorUB]

At a glace I would say the 18K should do it. but you are removing 30K and I wonder how well insulated a RV really is, so I question the sizing. Maybe 24K would be better? But I really have no idea.

How well did the two units cool the space in hot weather when they worked properly? Did they run all the time? Half of the time?

 

[dcg9381]

The on-line specs for two zone mini's show 18K BTU able to cool up to 850 Sq Ft? Is an 18K two zone the right choice?

Those specs probably don't take into account the "great" insulation common to most RVs. The roof top ducted units aren't that great because the ducts typically run along what's left of roof insulation.

And the splits are pretty directional. Might not be a big deal in Kansas, but a 5th wheel with a single AC would fry here in Texas front to rear.

Typically RVs only have 120V available, so how many BTU can you get on 20A?

 

[Steve from Socal]

The RV is well insulated for an RV R-25 roof and floor, R-15 walls. This is not wired as a standard RV, I have the original 50 amp RV plug and a 50 amp 240 plug and panel for electric stove, water heater and Mini?

The mini would be a two zone so one wall unit in the bed and one in the main. A 9K in the bedrom and 12K main? The roof tops are not known to be that efficient and the plenum is kind of a good/bad overall. I would not discount a 24K unit but, I have heard not to oversize these by too much?

 

[thunderalley3]

No real advice as I am not an AC guy but I would look at the new AXIOM 5th wheels as they are using mini splits in them from the factory. We were at an RV show and went through a couple of them that had factory mini splits.
This may give you some guidance on size and ideas for mounting the unit etc.

 

[PoorUB]

The RV is well insulated for an RV R-25 roof and floor, R-15 walls. This is not wired as a standard RV, I have the original 50 amp RV plug and a 50 amp 240 plug and panel for electric stove, water heater and Mini?

The mini would be a two zone so one wall unit in the bed and one in the main. A 9K in the bedrom and 12K main? The roof tops are not known to be that efficient and the plenum is kind of a good/bad overall. I would not discount a 24K unit but, I have heard not to oversize these by too much?

With that much insulation the 18K would probably do just fine. The 9k and 12K seems reasonable. You should look closely at specs and you can often over size the indoor heads by 125% You might be able to put an 18K head in the main part and a 6K in the bedroom. Granted on wide open you will only get what the outdoor unit will put out.

As for over sizing, pretty much all mini splits are inverter units and ramp down pretty far. Depending on the brand they might ramp down to 4K BTU, so it is pretty much impossible to over size one. A few years back for the brands I sold a 12K or an 18k would both ramp down to 4K.

 

[dcg9381]

The RV is well insulated for an RV R-25 roof and floor, R-15 walls. This is not wired as a standard RV, I have the original 50 amp RV plug and a 50 amp 240 plug and panel for electric stove, water heater and Mini?

That's amazing insulation for an RV. You've got 240V power in it... Go for it. 9k/12k should work just fine. You really can't get this too wrong with the way modern mini-spits work and they're certainly better than the roof top units in terms of efficiency. Climate matters though, I'd probably do 12k/12k in Texas minimum.

If you're going to heat with these, watch their low temp performance. Nothing eats propane faster than an RV in winter!

You may find it's easier (and more cost effective) to do two separate units over a dual-head deal.

 

[Steve from Socal]

That's amazing insulation for an RV. You've got 240V power in it... Go for it. 9k/12k should work just fine. You really can't get this too wrong with the way modern mini-spits work and they're certainly better than the roof top units in terms of efficiency. Climate matters though, I'd probably do 12k/12k in Texas minimum.

If you're going to heat with these, watch their low temp performance. Nothing eats propane faster than an RV in winter!

You may find it's easier (and more cost effective) to do two separate units over a dual-head deal.

This is an older premimum 5th wheel designed for ful time living in both cold and hot weather. It gets about as hot in central Kansas as Texas, mid 90's to 100 teens with moderate humidity. We do get much colder winters, as far as heat, a heat pump mini and a couple of electric space heaters would be more than enough. I have keeped the inside at 65+ in the low teens with space heaters alone. There is no propane in this, I removed all the gas equipment and went ellectric hence the 240 service.