MRCOOL DIY 4th Gen 18,000 BTU vs MRCOOL DIY 5th Gen 18,000 BTU
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Quick take: The MRCOOL DIY 5th Gen 18,000 BTU replaced the MRCOOL DIY 4th Gen 18,000 BTU, which is discontinued; the MRCOOL DIY 4th Gen 18,000 BTU is the more efficient unit (22.7 SEER2).
| Spec | MRCOOL DIY 4th Gen 18,000 BTU | MRCOOL DIY 5th Gen 18,000 BTU |
|---|---|---|
| Price | $2,200 | $2,609 |
| Rating | 4.9★ (10) | — |
| Type | Single-Zone DIY | Single-Zone DIY |
| Capacity | 18k BTU | 18k BTU |
| Coverage | ~750 sq ft | ~700 sq ft |
| SEER2 (cooling) | 22.7 | 22.5 |
| HSPF2 (heating) | 9.8 | 11.5 |
| Low-Ambient Heating | to -13°F | to -13°F |
| Max heat at 5°F (NEEP) | 11,700 BTU | 12,800 BTU |
| Heat kept at 5°F | 65% of rated | 71% of rated |
| Refrigerant | R-410A | R-454B |
| Zones | Single zone | Single zone |
| Voltage | 230V | 230V |
| WiFi Control | Built-in | Built-in |
| Install | Same precharged 25-ft quick-connect lineset as the 12k — hang, connect, torque, open valves, no vacuum pump. The difference is power: it needs a dedicated 208/230V circuit (30A breaker territory), so budget for an electrician or a subpanel run if you don't have 240V nearby. | Precharged 25-ft R-454B Quick Connect lineset (1/4" x 1/2"), no vacuum pump, same as the rest of the DIY line. Power is a dedicated 208/230V circuit; MRCOOL's spec sheet lists an 18A minimum circuit ampacity and 20A maximum fuse, so a 20A double-pole breaker covers it. The condenser is about 93 lb, a two-person carry if stairs are involved. Seal the wall penetration with putty or silicone, not expanding foam: the air handler's R-454B leak sensor can read curing foam as a leak. |
| Warranty | 7-year compressor / 5-year parts with online registration (limited lifetime compressor promo when registered) | 7-year compressor / 5-year parts with registration (MRCOOL DIY Direct also offers an optional lifetime-compressor upgrade) |
Pros & cons
MRCOOL DIY 4th Gen 18,000 BTU
- ✓Precharged 25-ft quick-connect lineset installs without vacuum pump or HVAC tools
- ✓Energy Star certified, so it's eligible for many utility rebate programs
- ✓Rated heating down to -13°F keeps it useful as primary heat in most climates
- ✓Variable-speed inverter compressor is quiet and sips power at part load
- ✓Frequent Costco/retail clearance deals well under list price
- ✗Needs a dedicated 208/230V circuit — electricians quote $300-800 if you don't have one
- ✗Same control-board failure pattern reported across the DIY series
- ✗R-410A refrigerant is on its way out; 5th Gen R-454B replaced it
- ✗MRCOOL support is email/photo-driven and owners report multi-week waits on parts
MRCOOL DIY 5th Gen 18,000 BTU
- ✓11.5 HSPF2 on the certified pairing, up from 9.8 on the 4th Gen
- ✓Holds 12,800 BTU at 5°F at a 2.44 COP, the best 5°F efficiency of any MRCOOL DIY unit
- ✓20A maximum fuse on a 208/230V circuit, a lighter electrical requirement than most 1.5-ton units
- ✓Energy Star certified and NEEP cold-climate listed, which is what most heat-pump rebate programs check
- ✗Still needs a 240V circuit and disconnect, which is the most common surprise cost for DIY buyers
- ✗About $400 more than the 4th Gen 18k's typical price
- ✗Cooling efficiency didn't improve (22.5 SEER2 vs 22.7)
- ✗Too new for any long-term owner history, so reliability past the first couple of years is unknown
- ✗No interchangeability with 4th Gen linesets, couplers, or boards