ᐅ Multi-split air conditioning system in a single-family home

Hello!
We moved into our newly built single-family house in 2019, and lately, I have been seriously considering installing a multi-split air conditioning system because the last two summers were extremely challenging.

Downstairs in the living room (many patio doors, southwest-facing), the indoor temperature was almost constantly around 27°C (81°F). Upstairs in the bedrooms, it was even worse at about 28°C (82°F). All the smart advice on ventilation and external blinds eventually stopped making a difference. Once the heat was inside, we couldn’t get it out again.
Before that, we lived in an attic apartment, and I was especially looking forward to the house, but unfortunately, it’s not much cooler here either.

I am now actually prepared to invest a likely five-figure amount to enjoy the luxury of air conditioning.
I would like to brainstorm here and gather experiences, tips, and suggestions from people who may have been in a similar situation.
In my initial research, I came across multi-split air conditioning systems and am now trying to understand what kind of effort would be involved.

The standard floor plan includes a utility room, guest room, guest toilet, and living room downstairs, as well as a bedroom, bathroom, and two children’s rooms upstairs.
What should I consider? Who is best to consult? What potential (cost) traps should I watch out for?
I appreciate all input!

If you don’t already have dropped ceilings everywhere to run the cables, I would rather install oversized single split units at key locations (bedrooms, main living area). With a mechanical ventilation system with heat recovery, the cool air gradually spreads throughout the whole house. If there is no mechanical ventilation system, you will have to keep the doors open.

Option 1 is cheaper, creates less mess, and is sufficient in most cases.

I don’t have more tips yet since we are still planning this ourselves. First, we want to install photovoltaics and many other things, but for that, we need to save up first.

It really depends on which rooms need cooling to determine the most suitable option. The main cost drivers, aside from the system sizing—which should definitely be planned by a professional—are especially the piping routes. The refrigerant lines cost about 30€ per meter (approximately $32 per meter), and since you need both supply and return lines, these can significantly impact the price.

Then, of course, the manufacturer plays a role. We have a multi-split system from Daikin with four indoor units and are very satisfied with it. By the way, we also use it for heating during the transitional seasons. We consider ourselves quite fortunate that our heating installer is a certified HVAC technician first and then qualified in heating systems. So, I would recommend consulting a professional for this kind of project, even though it could theoretically be mostly installed by yourself.

They should also be able to advise you whether it’s better to install several single-split systems or if one multi-split unit would suffice. We definitely did not want four outdoor units on the house; the current one (serving three of the four rooms) is installed on the roof.

Not all indoor units are compatible with multi-split systems. Often, multiple outdoor units are more cost-effective than a single large one. Consult a professional for advice. Currently, the most attractive indoor units are Mitsubishi Diamond.

From personal experience:

- Pay attention to line lengths, as they can significantly impact costs
- Count the necessary core drillings
- Avoid condensate pumps (but this requires piping with a continuous slope)
- Choose reputable brands and quality products
- Avoid oversizing, which is a common mistake
- Single-split systems are preferable to multi-split systems, but can become expensive and require space
- The fewer exposed interior pipes, the better, as they are not very attractive
- Wi-Fi is essential
- Prioritize functionality over design
- Check the size proportions of indoor units
- Draw both indoor and outdoor units on the floor plan as a good test

Not all pipe lengths are feasible without adjustments. We had to reposition the outdoor unit and create another wall opening because the piping would have been too long from the initial location.