Mitsubishi Hyper-Heat FX 18,000 BTU
#2 in 18,000 BTUFull review
Mitsubishi’s flagship cold-climate system: it makes more than its rated heat at 5 °F and keeps heating to −22 °F. For a home that relies on it as the main heat through a cold winter.
The Mitsubishi Hyper-Heat FX 18,000 BTU and the ACiQ Extreme Heat 18,000 BTU are evenly matched, rated 4.7 and 4.7. The Mitsubishi Hyper-Heat FX 18,000 BTU leads on efficiency. The ACiQ Extreme Heat 18,000 BTU wins on noise.
ACiQ Extreme Heat 18,000 BTU
#3 in 18,000 BTUFull review
ACiQ’s cold-climate line, sold online, keeps most of its rated heat at 5 °F, heats to −22 °F and gets a 12-year compressor warranty once registered. A certified technician has to install it.
Prices were last checked October 21, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Which should you buy?
- Choose the Mitsubishi Hyper-Heat FX 18,000 BTU for efficiency (11.1 HSPF2, 25.5 SEER2, COP 2.06 at 5 °F vs 11 HSPF2, 21.4 SEER2, COP 1.92 at 5 °F).
- Choose the ACiQ Extreme Heat 18,000 BTU for noise (indoor unit from 19.5 dB(A) vs indoor unit from 27 dB(A)).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every 18,000 BTU mini-split; a clear win is highlighted. How we rank explains each one.
| Factor weight | Mitsubishi Hyper-Heat FX 18,000 BTU | ACiQ Extreme Heat 18,000 BTU |
|---|---|---|
| Overall rating | 4.7/5 | 4.7/5 |
| Cold weather 40% | 100 keeps 139% of its heat at 5 °F, heats down to -22 °F | 100 keeps 100% of its heat at 5 °F, heats down to -22 °F |
| Efficiency 30% | 88 11.1 HSPF2, 25.5 SEER2, COP 2.06 at 5 °F | 72 11 HSPF2, 21.4 SEER2, COP 1.92 at 5 °F |
| Warranty 20% | 100 10-year compressor, 10-year parts | 100 12-year compressor, 7-year parts |
| Noise 10% | 62 indoor unit from 27 dB(A) | 98 indoor unit from 19.5 dB(A) |
Specifications
| Mitsubishi Hyper-Heat FX 18,000 BTU | ACiQ Extreme Heat 18,000 BTU | |
|---|---|---|
| Capacity (certified) | ||
| Size (nominal) | 18,000 BTU | 18,000 BTU |
| Cooling at 95 °F | 17,200 Btu/h | 18,000 Btu/h |
| Heating at 47 °F | 17,000 Btu/h | 18,000 Btu/h |
| Heating at 17 °F (max) | 28,200 Btu/h | 19,200 Btu/h |
| Heating at 5 °F (max) | 23,600 Btu/h | 18,000 Btu/h |
| Heat kept at 5 °F | 139% | 100% |
| Efficiency (certified) | ||
| HSPF2 (Region IV) | 11.1 | 11 |
| SEER2 | 25.5 | 21.4 |
| EER2 | 13.1 | 12.5 |
| COP at 5 °F | 2.06 | 1.92 |
| ENERGY STAR | ENERGY STAR Cold Climate | ENERGY STAR Cold Climate |
| AHRI certificate | 215611128 | 216032336 |
| Operating range | ||
| Heats down to | -22 °F | -22 °F |
| Cooling range | 14 to 115 °F | -22 to 122 °F |
| Installation | ||
| Installed by | Professional (sold through installers) | Professional (sold through installers) |
| Line set connection | Flare fittings (vacuum pump needed) | Flare fittings (vacuum pump needed) |
| Line set | up to 100 ft | up to 98.4 ft |
| Voltage | 230 V | 230 V |
| Refrigerant | R-454B | R-454B |
| Indoor unit | MSZ-FX18NL | ACIQ-18W-HH-MD |
| Outdoor unit | MUZ-FX18NLHZ | ACIQ-18ZPL-HP230C |
| Build | ||
| Indoor noise | 27–45 dB(A) | 19.5–49.5 dB(A) |
| Outdoor noise | 52 dB(A) | 59 dB(A) |
| Wi-Fi | Built in | Optional module |
| Weight | indoor 31.4 lb / outdoor 119 lb | indoor 27.3 lb / outdoor 99.9 lb |
| Warranty | 10 yr compressor, 10 yr parts | 12 yr compressor, 7 yr parts |
| Warranty with DIY install | No, a licensed installer is required | No, a licensed installer is required |
| Released | 2025-02 | - |