Please help w/Mini-Split choice

[MstrCarpenter]

I was wondering if anyone has a little time to review/confirm a Mitsubishi 3 head system I have in a shopping cart. My Manual J calculations put the total BTU's about right. The 28' x 38' second floor addition will utilize the existing boiler with F.H.W. baseboard if/when necessary. The project is in S.E. NH.

25,000 BTU 20 SEER Mitsubishi Tri Zone Mini Split Heat Pump System 6+9+12
Model: MXZ-3C24NA3 / MSZ-GL06 / MSZ-GL09 / MSZ-GL12 ID: 8093
Heat Pump Condenser 1 x 25,000 BTU Mult Zone Condenser
Zone 1 1 x 6,000 BTU Wall Mounted Mitsubishi Mini Split GS Series - Air Handler
Zone 2 1 x 9,000 BTU Wall Mount
Zone 3 1 x 12,000 BTU Wall Mount

Specifically, I can't seem to find a good reason for the different (newer?) model 6k wall unit. Are they better? Should I try to get them in the 9 and 12K flavors?

The price point seems to be good at $4k. Package comes with 3 remotes. I've already ordered the line sets, wall mount, wiring, ect.(less than $1k). They should be here today; I have to get them installed on Monday to beat the insulation crew.

Obviously this isn't my primary occupation, but I've installed a few (shy of a dozen) mini-splits with no issues after several years. This is my first multi-head install. BTW, no license req'd. in NH.

[blackhat]

Not sure what you are looking for?  Does your job require a 6,9 and 12 k heads?  Make sure you land the different size heads on the correct outlets at the condenser. IIRC, the 12k heads can only go on one set of valves. Maybe 2 (maybe). Check the condensing unit literature carefully for that info.

[MstrCarpenter]

Thanks Blackhat. I checked the cart again tonight; all 3 indoor wall units have been upgraded (?) to the newer GS series. That was what I was concerned about, and the supplier really didn't know what the difference was. He was sure they looked different though.
 Here's what I found.

"The GS model is Mitsubishi Electric's most flexible indoor solution with a wide range of sizes from six to 24K BTU/H, as well as as a Powerful Mode for rapidly cooling or heating a space to the desired temperature. In addition, there's Swing Mode, which can move air throughout the room like an oscillating fan, and Econo Cool, which adjusts the amount of air directed toward occupants based on the air-outlet temperature."

Sounds like an upgrade to me. And yes, one of the line set ports is larger than needed, 1/4+1/2 vs, 1/4+3/8 for the other two. I think I have a 1/2 x 3/8 flare ordered. I'll just have to remember to bring a short piece of 1/2" O.D. tube.

Which brings me to another question; I'll be over the (condenser pre-charged) 92' of line set by about 10'. Manual says add 1.08 oz./5'. But I'm assuming that is with a 1/2" suction line (for a larger BTU wall unit). I've got 40' of 3/8" not 1/2" on an inverter compressor. How much do I need to add, if any?

[blackhat]

Maybe 1 1/2 oz and let the inverter and receiver manage any difference.  At that percent of total charge it’s not critical.