Cassettefrom $1,312
How do you plan a MRCOOL multi-zone with ceiling cassettes?
Short answer: Go room by room: put a cassette only where there is attic above, size each room at 6K to 18K, then pick the outdoor unit for the rooms that run at the same time on the worst day. Check that every line set stays under 75 ft and the total stays under the limit for your outdoor unit. Complete cassette multi-zone systems start from $4,633 for two rooms (prices as of November 2026).
Planning a multi-zone with ceiling cassettes takes a little more homework than an all-wall system, because the attic decides as much as the floor plan. This guide walks through the planning, room by room, for 2- to 6-room DIY 5th Gen systems.
What does a cassette multi-zone include, and what does it cost?
A 5th Gen multi-zone has one outdoor unit and one indoor unit per room, each on its own pre-charged Quick Connect line set. With cassette systems, the indoor units are OuttaSight one-way cassettes, 6K to 18K.
Our 2- and 3-room systems let you pick a line set length per room. Systems with 4 to 6 rooms come with a 16 ft line set per room, and you order longer sets separately.
| Rooms | All cassettes, from | All wall units, from |
|---|---|---|
| 2 | $4,633 | $2,923 |
| 3 | $6,172 | $3,607 |
| 4 | $8,256 | $4,836 |
| 5 | $10,238 | $5,963 |
| 6 | $12,462 | $7,332 |
At six rooms, an all-cassette house costs about $5,130 more than all wall units. That gap is the main reason to mix the two.
Which rooms suit a cassette?
The test for each room is simple: can you get above the ceiling, and is the wall space worth keeping clear? Here is how the usual rooms shake out.
| Room | Cassette? | Why |
|---|---|---|
| Kitchen on the top floor | Often yes | Cabinets and windows use up the walls, and the attic is right above |
| Living room on the top floor | Often yes | Keeps the white box off the TV wall; size it at 12K or 18K |
| Bedrooms under an attic | Yes | Easy access above, and 6K to 12K covers most bedrooms |
| Finished basement | Maybe | The ceiling is the floor framing of the room above; works best before the drywall goes up |
| First floor room under a second floor | Usually no | No attic to work from; a wall unit is far simpler |
| Room needing more than 18K | No | Cassettes stop at 18K; use a wall unit up to 24K |
Size every room with our sizing guide before you assign a unit type. If you're still on the fence about a cassette for a given room, our cassette vs wall unit comparison covers that decision in detail.
Can you mix cassettes and wall units on one outdoor unit?
Many cassette plans end up this way, with cassettes in the living spaces and wall units in rooms where a wall unit is easy. Because the parts are sold separately, you can build it yourself: a multi-zone outdoor unit from $1,555, OuttaSight cassettes from $1,312, wall air handlers from $457, and a line set for each room.
Before you order a mixed setup, confirm the exact combination for that outdoor unit on the multi-zone spec page. A typical 4-room ranch plan might look like this:
- Living room and kitchen, open plan: 18K cassette.
- Primary bedroom: 9K cassette.
- Second bedroom: 6K wall unit.
- Home office: 6K wall unit.
That adds up to 39K of indoor units, which fits a 36K outdoor unit with BTU sharing, as the next section explains.
Next: How does one outdoor unit share capacity when every room runs?
Which outdoor unit should you pick?
The 5th Gen outdoor units are 18K (2 to 3 rooms), 27K (2 to 4), 36K (2 to 5), 48K (2 to 6) and 55K (2 to 6). The 18K takes indoor units up to 12K only, so any 18K cassette in your plan rules it out.
Your indoor units can add up to more than the outdoor unit. Three 12K bedroom cassettes on a 27K outdoor unit make 36K of indoor units. When one or two rooms run, each gets its full 12K; when all three run hard on the hottest night, the 27K is shared and each gets about 9K. Nothing breaks. The rooms just take longer to reach the setpoint.
So size the outdoor unit for the rooms you run at the same time on the hottest or coldest day. In the ranch plan above, if the living room and the bedrooms rarely peak at the same hour, 36K works. If they all peak together, go to the 48K.
Watch for the basic idea of one outdoor unit feeding several rooms, then sketch your own line set runs from that one spot.
How do you plan the line set runs through the attic?
Cassette runs are longer than they look on the floor plan, because the line set goes up into the attic, across it, and back down or out the wall to the outdoor unit. Measure the real path with a tape, including the rise and the drop.
- Each room: 75 ft maximum.
- All rooms together: 172 ft on the 3-room outdoor unit, 221 ft on the 4- to 6-room units. For a 2-room plan, check the manual.
- Height difference between any two indoor units: 24 ft maximum.
- Stock lengths: 16, 25, 35 and 50 ft. A coupler kit ($425 for 6K to 18K units) joins two sets for 66 or 75 ft.
A 4-room attic plan with runs of 35, 35, 25 and 16 ft totals 111 ft, comfortably inside 221 ft. Pre-charged line sets can't be cut, so pick the next size up and coil the extra where the manual allows. Longer pre-charged line sets cost from $264 for 25 ft, $502 for 35 ft and $587 for 50 ft.
Useful if one cassette room sits at the far end of the house and its run needs more than 50 ft.
Next: What is the order of work for installing each cassette?
What if your plan doesn't fit the usual pattern?
What if I want cassettes in every room?
It works if every room has attic above it, and it looks the cleanest. Budget for it honestly: six cassette rooms start from $12,462, against $7,332 for six wall rooms.
What if one cassette is upstairs and a wall unit is in the basement?
Measure the height between them. More than 24 ft between the lowest and highest indoor unit won't work on one outdoor unit, so that room needs its own single zone.
What if the attic runs past the 221 ft total?
Move the outdoor unit closer to the middle of the house, or split the house into two systems. A single zone, like the 18K single zone cassette at $3,418, can take the farthest room off the multi-zone.
What if winters here drop below −13°F?
The 5th Gen multi-zone keeps heating down to −13°F outside. Below that, keep a backup heat source or size up, and call us for cold-climate sizing.
What should you do next?
Draw your floor plan, mark which rooms have attic above, and size each one. Then measure each line set path and add up the total before you choose the outdoor unit. Our 5th Gen ceiling cassette guide has the sizes and prices for each cassette.
Once you have the list, call +1 (844) 999-9725, Monday to Friday, 9 AM to 5 PM EST, or text it to 302-385-6142, and we'll help you settle on the outdoor unit and the mix of cassettes and wall units. You can browse complete systems in the ceiling cassette collection.
