Mono-split or multi-split: choosing the configuration without getting the compatibility wrong
Published on 10 September 2026 · 5 min read
A multi-split gives you a clean facade and a single wall penetration, but every outdoor unit + indoor units combination must appear in the manufacturer's table. Here is how to decide and how to check.
Mono-split: one outdoor unit per indoor unit
Each room has its own outdoor unit. Advantages: maximum capacity and efficiency per room, faults stay isolated (a faulty unit does not stop the others), simple installation, lowest purchase price per kW. Drawbacks: several outdoor units on the facade or on the ground, several wall penetrations, more refrigerant pipework.
Multi-split: one outdoor unit for 2 to 5 indoor units
A single outdoor unit feeds several indoor units (wall-mounted, floor-standing, cassette or ducted units depending on the outdoor unit). Advantages: a single outdoor location, a single main wall penetration, less noise on the facade. Drawbacks: strict compatibility, capacity shared when all the units are running, an outdoor unit failure stops everything, higher price for the outdoor unit.
The rule that avoids returns: the combination table
Every multi-split outdoor unit has a table of permitted combinations: which indoor units, which capacities, how many at once, and the maximum total capacity of the indoor units (often 130 to 150% of the outdoor unit's capacity, since they do not all run at the same time). An indoor unit outside the table does not work, or works badly. At Kaisai, the M-Line outdoor units (K2OE to K5OE) take M-Line indoor units, the T-Line HE outdoor units (KKO-RTA1) take T-Line indoor units. We check every configuration before confirming the order.
Pipe runs and height differences
Every outdoor unit has a maximum total pipe run and a maximum per indoor unit, and a maximum height difference between the outdoor unit and the indoor units. Beyond that, additional refrigerant charge and loss of capacity. Note the actual lengths on the plan before choosing the outdoor unit.
When to choose what
- Two or three rooms close together, constrained facade, customer who cares about appearance: multi-split.
- Rooms far apart, intensive use of one room (main heating), tight budget: mono-splits.
- Shop or office with several zones: often a mix, cassettes or a ducted unit on a multi-split and a mono-split on the most heavily used zone.
Requesting a configuration
Send the plan with the rooms, the floor areas, the location of the outdoor unit and the approximate lengths. We reply with the outdoor unit, the compatible indoor units and the net price.