ᐅ Is a split air conditioning system sufficient for cooling three rooms?

Hello everyone,
we recently installed a photovoltaic system on the roof of our older house (built in 1959). This system is intended not only to reduce our electricity consumption but also to cost-effectively power other electrical devices. Specifically, I am interested in an air conditioning system for our upper floor. During hot summer nights, temperatures sometimes reach 27–29°C (81–84°F), making it almost unbearable to sleep. My attempts to use portable air conditioners (monoblocks) have not been very successful. I was already aware that such a monoblock is not an ideal solution. That is why I now want to install a split air conditioning system.

Currently, I am researching how many indoor units I will need. My plan is as follows:
I would install one air conditioning unit in the hallway, hoping that if the doors to the bedrooms and both children’s rooms remain open and the unit runs all day (when there is enough sunlight), the rooms will be sufficiently cooled in the evening and at night.

What do you think? Will this plan work, or should I actually install an air conditioning unit in all three rooms?

The plan works; the open doors allow for even cooling.
For insurance reasons, I would have a professional company handle this.
Close the door to the staircase, otherwise the cool air will disappear downstairs.

Is 12,000 BTU enough, or should I rather go for 18,000 BTU?

Nida35a schrieb:

Close the door to the staircase, otherwise the cold air will flow downwards.

Or maybe size it large enough so that the cold air can also move downwards if needed.

I wouldn’t consider it guaranteed that this will work. You shouldn’t overestimate the air exchange. The question is also how well your walls and masonry retain cold/heat.

But: just give it a try. If it’s not enough, you’ll simply need additional equipment.

In our previous apartment, we had an 18k BTU split air conditioner. It was able to cool the entire apartment with the doors open. Approximately 75m² (800 sq ft). In your case, be sure to close the door to the staircase leading down, because cold air is heavier and will mostly "fall" down the stairs.