Mitsubishi 18,000 BTU R454B Ceiling Cassette Heat Pump System
The SUZ-AA18NL-U1 and SLZ-AF18NL-U1 form the top of Mitsubishi's single-zone R454B cassette range at 18,000 BTU/h cooling and 20,000 BTU/h heating at 47°F, and they are the only pairing in the family built on the taller outdoor chassis. That larger cabinet buys something no other size in this line offers: 100 ft. of maximum line set length and a 50 ft. height difference, versus 65 ft. and 40 ft. on the smaller units. For a rooftop condenser over a two-story building, or a long run around a warehouse wall to reach an interior room, that is often the deciding specification. Rated 17.5 SEER2 with a 9.6 HSPF2 and ENERGY STAR certified, the system ships with the SLP-18FAU grille and the MHK2 kumo touch wireless wall thermostat already included.
Is an 18,000 BTU Ceiling Cassette System the Right Size?
A one-and-a-half ton cassette generally covers conditioned areas in the 700 to 1,000 square foot range, and it is the last stop before a project needs either a multi-zone system or ducted equipment. It suits genuinely open floor plans and rooms where the load is driven by people and equipment rather than envelope — a full training room, a busy restaurant dining area, a fitness studio, or a server-adjacent office. With 475 CFM at high fan and 300 CFM at low, the SLZ-AF18NL-U1 moves noticeably more air than any other cassette in the family, though it also runs louder at 32 to 43 dB(A), which is worth weighing in a quiet space.
Because this is the largest single-zone option here, oversizing is a real risk rather than a theoretical one. A cassette that is too big satisfies the thermostat before it removes moisture, leaving a cool, clammy room and a compressor that never settles into efficient part-load operation. It modulates down to 5,300 BTU/h, but that floor is higher than the smaller units'. Where the load calculation lands between two sizes, or where several rooms need separate control, a multi-zone arrangement usually performs better than one large cassette.
Ideal for: Open-plan offices, restaurant dining rooms and bars, fitness studios and gyms, large training rooms, retail sales floors, community and fellowship halls, warehouse offices, and any room where the outdoor unit must sit far from the ceiling location.
Need more capacity? This is the largest single-zone cassette in the SLZ-AF line. For greater total capacity or independent control of multiple rooms, see the multi zone mini split heat pump systems or the full ductless mini split complete systems selection.
Recommended applications are general guidelines only. Actual system requirements depend on insulation, window area, ceiling height, occupancy, internal heat gain, and local design temperatures. Request free sizing assistance, contact Budget Heating, or call 813-885-7999.
What's Included
| Outdoor Heat Pump | SUZ-AA18NL-U1 — 18,000 BTU/h Inverter Heat Pump Condenser |
|---|---|
| Indoor Unit | SLZ-AF18NL-U1 Four-Way Ceiling-Recessed Cassette |
| Cassette Grille | SLP-18FAU Architectural Grille — Included |
| Controller | MHK2 kumo touch RedLink Wireless Wall Thermostat — Included |
| Application | Single-Zone Ductless Ceiling Cassette Heat Pump System |
| Refrigerant | R454B (A2L, Low GWP) |
| Cooling / Heating | 18,000 BTU/h Cooling — 20,000 BTU/h Heating at 47°F |
| Efficiency | 17.5 SEER2 / 12.0 EER2 / 9.6 HSPF2 — ENERGY STAR Certified |
| Electrical | 208/230V, Single Phase, 60 Hz — MCA 25A, MOCP 42A |
| Line Set Connections | 1/4 in. Liquid × 1/2 in. Gas, Flared |
| Maximum Line Length | 100 ft. with 50 ft. Maximum Height Difference |
| Manufacturer Warranty | 10 Years |
The 18,000 BTU package is the outlier of the group in ways that affect the job estimate. The outdoor unit stands 34-7/16 in. tall and weighs 115 lb., so plan the pad, lifting, and clearances accordingly rather than reusing the layout from a smaller cassette install. Minimum circuit ampacity jumps to 25A with a 42A maximum overcurrent protection, which usually means a dedicated 30A circuit. In exchange you get the longest permitted piping run in the line at 100 ft. with 50 ft. of vertical separation — the reason this size gets specified on jobs where the smaller units simply will not reach. As with every SKU in this family, the SLP-18FAU grille and the MHK2 wireless wall thermostat are included rather than quoted separately. Line set, control wire, and disconnect are field-supplied. A2L-qualified, EPA 608 certified installation is required.
Outdoor Unit & Ceiling Cassette Features
SUZ-AA18NL-U1 Outdoor Heat Pump
- 18,000 BTU/h rated cooling with a 5,300 BTU/h minimum from the inverter-driven compressor
- 100 ft. maximum refrigerant line length and 50 ft. maximum height difference — the longest in this line
- 20,000 BTU/h heating at 47°F with a 21,800 BTU/h maximum and a 3.1 COP
- 13,200 BTU/h of heating still delivered at 17°F outdoor ambient with a 2.7 COP
- ENERGY STAR certified at 17.5 SEER2 and 12.0 EER2 with a 9.6 HSPF2
- Taller 33-1/16 in. × 13 in. × 34-7/16 in. cabinet weighing 115 lb. with a larger condenser coil
- 2,193 CFM cooling and 1,949 CFM heating airflow through the outdoor coil
- 54 dB(A) cooling and 55 dB(A) heating sound pressure level
- 25A minimum circuit ampacity and 42A maximum overcurrent protection on 208/230V single-phase
- Cooling to 23°F ambient, or 0°F with the optional wind baffle, and heating operation to -4°F
SLZ-AF18NL-U1 Four-Way Ceiling Cassette
- Highest airflow in the SLZ-AF family at 300, 420, and 475 CFM across three fan speeds
- Covers wide open-plan areas from one ceiling position where a smaller cassette would leave dead corners
- 32 to 43 dB(A) sound pressure range, matched to occupied commercial rather than sleeping spaces
- Four independently driven vanes producing 72 selectable airflow patterns
- Vanes can be individually closed to protect a bar top, a workstation, or a treatment table from direct throw
- Fits the same 2 ft. × 2 ft. ceiling grid opening at 22-7/16 in. square and 8-3/16 in. deep
- SLP-18FAU grille included, so the ceiling finishes out on the same visit the cassette is hung
- MHK2 kumo touch wireless thermostat included for wall-mounted control and 7-day scheduling
- Integral condensate lift pump raising drainage up to 33 in. above the unit
- 31 lb. chassis identical in footprint to the smaller cassettes, keeping ceiling coordination consistent
Specifications & Manuals
Verify the 25A minimum circuit ampacity, the taller outdoor cabinet dimensions, and the additional refrigerant charge required beyond 25 ft. of piping in the SUZ documentation before finalizing the electrical and line set scope. SLZ literature covers ceiling opening layout, grille installation, and drain lift routing.
Frequently Asked Questions
How far apart can the outdoor unit and cassette be on this system?
Up to 100 ft. of refrigerant piping with a 50 ft. maximum height difference. That is the longest run in this cassette family — the 9,000 through 15,000 BTU units are limited to 65 ft. and 40 ft.
Is the 18,000 BTU outdoor unit the same cabinet as the smaller models?
No. The SUZ-AA18NL-U1 uses a taller chassis at 33-1/16 in. wide, 13 in. deep, and 34-7/16 in. high, weighing 115 lb. compared to 81 lb. on the compact cabinet. Plan the pad and clearances for the larger unit.
Do I need extra refrigerant for a long line run?
Yes, beyond 25 ft. Additional R454B is calculated at roughly 1.08 oz. per 5 ft. of piping over 25 ft., reaching about 16.2 oz. at the full 100 ft. run. The exact table is in the SUZ technical specifications.
Why is the SEER2 lower here than on the 15,000 BTU system?
Larger single-zone inverters generally rate slightly lower seasonally because the compressor's minimum output is a bigger share of the load. At 17.5 SEER2 and 9.6 HSPF2 this system is still ENERGY STAR certified, and its EER2 of 12.0 matches the 15,000 BTU pairing at peak conditions.
How loud is the cassette compared to the smaller sizes?
32 dB(A) on low and 43 dB(A) at high fan, against 25 to 31 dB(A) on the 9,000 BTU unit. It moves 475 CFM at high speed, so it suits occupied commercial rooms better than bedrooms.
Would two smaller cassettes be better than one 18,000 BTU unit?
Often, yes — if the space is divided into rooms that need independent setpoints, or if the load calculation lands near the middle of two sizes. A multi zone heat pump system gives separate control per room and better part-load behavior than one oversized cassette.
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