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.
The ACiQ Extreme Heat 18,000 BTU is the better mini-split overall, rated 4.7 to 3.6. The ACiQ Extreme Heat 18,000 BTU leads on cold weather, noise and efficiency.
Mitsubishi GX 18,000 BTU
#14 in 18,000 BTUFull review
Mitsubishi’s standard line, quiet and efficient, for milder winters: it loses a good share of its heat in deep cold and stops heating at −5 °F.
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 ACiQ Extreme Heat 18,000 BTU for cold weather (keeps 100% of its heat at 5 °F, heats down to -22 °F vs keeps 70% of its heat at 5 °F, heats down to -5 °F), noise (indoor unit from 19.5 dB(A) vs indoor unit from 28 dB(A)) and efficiency (11 HSPF2, 21.4 SEER2, COP 1.92 at 5 °F vs 10.3 HSPF2, 22.5 SEER2, COP 1.80 at 5 °F).
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 | ACiQ Extreme Heat 18,000 BTU | Mitsubishi GX 18,000 BTU |
|---|---|---|
| Overall rating | 4.7/5 | 3.6/5 |
| Cold weather 40% | 100 keeps 100% of its heat at 5 °F, heats down to -22 °F | 39 keeps 70% of its heat at 5 °F, heats down to -5 °F |
| Efficiency 30% | 72 11 HSPF2, 21.4 SEER2, COP 1.92 at 5 °F | 59 10.3 HSPF2, 22.5 SEER2, COP 1.80 at 5 °F |
| Warranty 20% | 100 12-year compressor, 7-year parts | 100 10-year compressor, 10-year parts |
| Noise 10% | 98 indoor unit from 19.5 dB(A) | 57 indoor unit from 28 dB(A) |
Specifications
| ACiQ Extreme Heat 18,000 BTU | Mitsubishi GX 18,000 BTU | |
|---|---|---|
| Capacity (certified) | ||
| Size (nominal) | 18,000 BTU | 18,000 BTU |
| Cooling at 95 °F | 18,000 Btu/h | 18,000 Btu/h |
| Heating at 47 °F | 18,000 Btu/h | 21,600 Btu/h |
| Heating at 17 °F (max) | 19,200 Btu/h | 18,200 Btu/h |
| Heating at 5 °F (max) | 18,000 Btu/h | 15,200 Btu/h |
| Heat kept at 5 °F | 100% | 70% |
| Efficiency (certified) | ||
| HSPF2 (Region IV) | 11 | 10.3 |
| SEER2 | 21.4 | 22.5 |
| EER2 | 12.5 | 14.1 |
| COP at 5 °F | 1.92 | 1.80 |
| ENERGY STAR | ENERGY STAR Cold Climate | ENERGY STAR Cold Climate |
| AHRI certificate | 216032336 | 215862736 |
| Operating range | ||
| Heats down to | -22 °F | -5 °F |
| Cooling range | -22 to 122 °F | 14 to 115 °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 98.4 ft | up to 100 ft |
| Voltage | 230 V | 230 V |
| Refrigerant | R-454B | R-454B |
| Indoor unit | ACIQ-18W-HH-MD | MSZ-GX18NL |
| Outdoor unit | ACIQ-18ZPL-HP230C | MUZ-GX18NL |
| Build | ||
| Indoor noise | 19.5–49.5 dB(A) | 28–49 dB(A) |
| Outdoor noise | 59 dB(A) | 54 dB(A) |
| Wi-Fi | Optional module | Built in |
| Weight | indoor 27.3 lb / outdoor 99.9 lb | indoor 37 lb / outdoor 116 lb |
| Warranty | 12 yr compressor, 7 yr parts | 10 yr compressor, 10 yr parts |
| Warranty with DIY install | No, a licensed installer is required | No, a licensed installer is required |
| Released | - | 2025-02 |