Do any of you have a mini-split to help your main AC keep rooms cold?

We have two units, a downstairs and upstairs. The downstairs is solid as a rock, keeps everything at 70-72 all summer long, doesn't matter how hot it gets.

The upstairs unit is a POS. We keep it at 70 and it'll warm up to 74-75 at the thermostat. In the back bedrooms, it's like 85 and terrible. Could be a ducting issue, or maybe a sunrise/sunset issue since the back bedrooms get the full afternoon sun. There is a game room with the AC return, closed off from the rest of the house by french doors and it has a hallway that leads to a bathroom and the two hot back bedrooms. If I installed a mini-split in the game room, would it help keep everything up there cooler?

Behind the french doors, the gameroom/bathroom/two bedrooms is probably 750 sqft and is hot.

All AC units were replaced in 2016, we moved in to the house in 2019 and we don't know what was done.

If you put a mini split in the Game Room it would definitely help keep the upstairs cooler during the Summer months.

Attic temps??,do you have attic fans?

I have helped install about 2 dozen mini split systems. They are by far more efficient and economical than standard AC systems. If I was to build a house now, I would mini splits through out the house. They have new systems that run multiple heads off one condenser.

Go up in the attic and count the number of ducts you see, and then count the number of vents you have in the house. My neighbor's house was built in 2016 and he just moved in last November. They have a great room (kitchen/dining/living) that wouldn't get cool. Turned out there was a vent that was covered by the drywall on the ceiling since the house was built.

Our house in San Antonio had 2 HVAC units. One for upstairs and one for the main floor. The builder had the ducts strapped tightly up against the roof sheathing, not sure if that was standard practice or if they just forgot to lower them after they blew in the attic insulation. Once I cut the straps and suspended them further away from the roof my upstairs rooms were much better.

I wouldn't spend any additional money on equipment until you figure out why the upstairs unit is not cooling properly. There are a tremendous amount of variables missing to give a proper answer. IE, is the unit properly sized, is there suffient insulation, the color of the roof, heat gain/loss, manual j calcs, shading co-efficient of windows, building materials blah blah blah.....Is the unit properly charged (ie refrigerant), is a txv acting up.. whatever it may be.... I'll give whomever installed the units the benefit of the doubt that they were installed correctly; sized correctly, etc.... So i'd start there before sinking any real money into an supplemental system....a few hundred service call may be more well spent than a few thousand dollar supplement unit.....

Now- back to ductless splits, Yeah, they're excellent, very easy to install, and very low maintenance. I'm a big fan of them.... and yes, as someone else said, you can run multiple evaporators (the thing that blows air and hangs inside your house) off one condensing unit (the thing outside). The largest residential system (in terms of number of evaps) I've seen had 5 evaps off 1 condensing unit....if you get into commercial applications with products like the City Multi systems, you can do much more.

Just .02 from a guy who used to do hvac.

if you wanna pm me more details, i'd be happy to put it around my head.....would be helpfup to first know the total square footage of the entire house, the 1st / 2nd floor, and the size (tonnage) of the units.... ie, the first floor is 5 tons, and the 2nd floor is 2.5 tons.... if you dont know the size of the units, if you go outside to the condensing units.....most brands will have a multible of 12 in the model number...... 12,000 btu = 1 ton..... so a 24 in the model number is a 2 ton.... a 36 is a 3 ton.....60 is a 5 ton, etc etc.... (and that was keyword MOST brands) oh, and 6's, not just 12....so 18 would be 1.5..... 30 would be 2.5......etc

I had a similar problem at my house. On AC unit cools half my downstairs and all my upstairs. Upstairs was 10+° warmer in the summer. My local AC company found dampers that were installed and mostly closed. That helped some. Then I had them put in a 2 zone system and it basically fixed my problem. I was debating a ductless unit as well and am glad I didn’t. The air handler that made the 2 zone system was about $2k installed.

Thank you all for the input. Lot's to consider here. My MIL has the mini-split system, new all crated up, so there would be no cost there. I was just wondering before I put this giant thing on my wall if it would really make a difference. I'm not sure how powerful these things are or if it's just a glorified window unit. I feel like a lot of heat is coming from the attic, I probably need to have more insulation blown in this winter.

Just make sure its sized correctly for what your wanting it to cool. And believe me its not a glorified window unit. Uses 1/10 of the energy and so much for profficient.

I have a 36k BTU mini split with 3 12K heads that cools a 900 sq/ft addition plus one added in our kitchen/great room to assist the ducted A/C when we have 20+ guests for holidays/parties. Unit is super efficient and quiet. These units are heat pumps and one of the 12K heads kept around 700 sq/ft great room toasty during the deep freeze event this past February.

You mentioned the hot issue being behind french doors. I had a similar problem in 2 bedrooms. The occupants slept with their doors closed. My problem was I needed return air vents in those rooms. The closed doors were causing pressure in the rooms which kept air from entering well.