A ductless mini-split is a heat pump in two parts: an outdoor unit with an inverter-driven compressor, joined by a refrigerant line set to one or more indoor “heads” on a wall, ceiling or floor. It heats and cools without ductwork. Capacity is given in BTU per hour or tons, where 1 ton = 12,000 BTU/h = 3.52 kW. Since 1 January 2023, new split heat pumps must reach at least 14.3 SEER2 and 7.5 HSPF2 nationwide (10 CFR 430.32), and ENERGY STAR certification needs 15.2 SEER2, 11.0 EER2 and 7.8 HSPF2.
This article explains the parts, single- and multi-zone systems, sizing, the SEER2/EER2/HSPF2 ratings, cold-climate models, line-set limits, the move from R-410A to R-32 and R-454B, certification and permits, and what do-it-yourself kits really involve. All figures come from the documents under Sources. For a quick room estimate, use the BTU Calculator.
How a ductless mini-split works
ENERGY STAR describes the system as one or more head units mounted on an interior wall or ceiling with an accompanying unit outside: the outdoor unit extracts heat from the air, even when it is cold, and the refrigerant carries it directly to the heads; in summer the system runs in reverse as an air conditioner. The parts:
- Outdoor unit — compressor, outdoor coil, fan and controls. Mitsubishi’s MUZ-GS12NA, for example, has a DC inverter-driven twin rotary compressor and a linear expansion valve; the inverter lets the compressor run at varying speed instead of only on or off.
- Indoor heads — a coil and fan in a wall, ceiling (cassette) or floor cabinet. NEEP’s cold-climate specification lists non-ducted single-zone units by floor, wall and ceiling placement, and small “compact ducted” air handlers also exist. On the Mitsubishi pair above, the indoor unit is powered from the outdoor unit.
- Line set — two copper refrigerant lines (a smaller liquid line and a larger gas line; 1/4 in. and 3/8 in. flared for the 12,000 BTU/h Mitsubishi), the power and communication cable, and a condensate drain, which may need a small pump where gravity drainage is not possible.
Single-zone vs multi-zone
A single-zone system has one outdoor unit serving one indoor head. A multi-zone system has one larger outdoor unit serving several heads, which can be all non-ducted or a mix of ducted and non-ducted units (the categories in NEEP’s specification). For example, MRCOOL’s 5th-generation DIY multi-zone condensers serve 2 to 6 zones, from a three-zone 18,000 BTU/h unit supporting 123 ft of total line set to a six-zone 55,000 BTU/h unit supporting 221 ft. Multi-zone outdoor units carry their own limits on total and per-head piping, so the outdoor unit and each head have to be chosen together from the maker’s tables.
Sizing in BTU/h and tons
Mini-splits are sold by cooling capacity. Mitsubishi’s M-Series MUZ-GS outdoor units, for instance, come in 9,000, 12,000, 15,000, 18,000, 24,000, 30,000 and 36,000 BTU/h sizes. The conversion is fixed: NIST defines the ton of refrigeration as 12,000 BtuIT/h, 3,516.853 W.
| Capacity, BTU/h | Tons of refrigeration | Heat moved, kW |
|---|---|---|
| 6,000 | 0.5 | 1.76 |
| 9,000 | 0.75 | 2.64 |
| 12,000 | 1 | 3.52 |
| 18,000 | 1.5 | 5.28 |
| 24,000 | 2 | 7.03 |
| 30,000 | 2.5 | 8.79 |
| 36,000 | 3 | 10.55 |
The kW figures are the heat the unit moves, not the electricity it draws; see the efficiency section below. Convert other sizes with the tons to BTU/h converter.
Rule of thumb: the ENERGY STAR chart
For a single room, ENERGY STAR’s room air-conditioner chart is a reasonable first estimate. It assumes an 8 ft ceiling and is for cooling only:
| Area to be cooled, ft² (m²) | Capacity needed, BTU/h |
|---|---|
| 100 to 150 (9.3 to 13.9) | 5,000 |
| 150 to 250 (13.9 to 23.2) | 6,000 |
| 350 to 400 (32.5 to 37.2) | 9,000 |
| 450 to 550 (41.8 to 51.1) | 12,000 |
| 700 to 1,000 (65.0 to 92.9) | 18,000 |
| 1,400 to 1,500 (130.1 to 139.4) | 24,000 |
| 2,000 to 2,500 (185.8 to 232.3) | 34,000 |
ENERGY STAR’s adjustments: reduce capacity by 10% for a heavily shaded room, add 10% for a very sunny one, add 600 BTU/h for each regular occupant beyond two, and add 4,000 BTU/h in a kitchen. It warns that an oversized unit cools the room before it has removed the humidity, leaving it damp and clammy.
Why a Manual J calculation is the real answer
A per-square-foot chart cannot see insulation, windows, air leakage, orientation, ceiling height or local design temperatures, and it says nothing about the heating load, which in cold climates is often what decides the size of a heat pump. The industry method is ACCA Manual J, the Air Conditioning Contractors of America’s residential load calculation, currently the 8th Edition (ANSI/ACCA 2 Manual J – 2016). ACCA describes it as the ANSI-recognized standard for equipment sizing loads in houses, townhouses, small multi-unit buildings and manufactured homes, and says a Manual J calculation is required by national building codes and most state and local jurisdictions. ENERGY STAR’s mini-split guidance says your contractor should verify the system size with Manual J. NEEP adds that meeting its cold-climate specification does not by itself make a unit right for a house: designers should check the building loads and the equipment capacity at the design temperature.
SEER2, EER2 and HSPF2
- SEER2 — the heat removed over a cooling season in BTU divided by the electricity used in watt-hours.
- EER2 — cooling delivered per watt at one steady condition (95 °F outdoors for the federal standards), in BTU/Wh.
- HSPF2 — the heating delivered over a season in BTU (for DOE climate Region IV) divided by the electricity used in watt-hours.
- COP — heat delivered divided by electricity used at one condition, a plain ratio. A COP of 1.75 means 1.75 units of heat per unit of electricity; electric resistance heat is 1.0.
The 2023 change. In its January 2017 test-procedure rule, DOE created a new test method, Appendix M1, with new metrics SEER2, EER2 and HSPF2 that “generally have different numerical values” from SEER, EER and HSPF. Among the changes, the minimum external static pressure for testing conventional ducted systems rose from 0.10–0.20 in. w.c. (by capacity) to 0.50 in. w.c., to better represent real ductwork. The federal standards switched to the “2” metrics for equipment made from 1 January 2023, so a 2023-or-later SEER2 rating cannot be compared one-to-one with an older SEER rating. (Since 7 July 2025, ratings must use the current Appendix M1; DOE has also adopted a later Appendix M2 with new SCORE and SHORE metrics for future standards.)
Federal minimums for equipment made on or after 1 January 2023 (10 CFR 430.32(c)(5) and (6)). Heat pumps have one national level; split air conditioners have a regional split by where they are installed:
| Product class | Rest of US, SEER2 | Southeast, SEER2 | Southwest, SEER2 / EER2 | HSPF2 |
|---|---|---|---|---|
| Split heat pump | 14.3 | 14.3 | 14.3 | 7.5 |
| Split AC, under 45,000 BTU/h | 13.4 | 14.3 | 14.3 / 11.7 or 9.8 | — |
| Split AC, 45,000 BTU/h and up | 13.4 | 13.8 | 13.8 / 11.2 or 9.8 | — |
“Southeast” is Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, Puerto Rico, South Carolina, Tennessee, Texas, Virginia, the District of Columbia and the US territories; “Southwest” is Arizona, California, Nevada and New Mexico. In the Southwest the lower EER2 figure (9.8) applies to units rated 15.2 SEER2 or more.
Voluntary programs set higher bars:
| Level (split heat pump) | SEER2 | EER2 | HSPF2 | Low-temperature test |
|---|---|---|---|---|
| Federal minimum | 14.3 | — | 7.5 | — |
| ENERGY STAR | 15.2 | 11.0 | 7.8 | — |
| ENERGY STAR cold climate, non-ducted | 15.2 | — | 8.5 | COP ≥ 1.75 at 5 °F; 5 °F capacity ≥ 70% of 47 °F |
| NEEP ccASHP v4.0, non-ducted | 15 | — | 8.5 | COP ≥ 1.75 at 5 °F at maximum capacity |
A dash means that level sets no figure of its own. To estimate running cost, divide the BTU/h you need by the SEER2 or EER2 to get watts, and enter that in the Electricity Cost Calculator; it is a rough guide, because a variable-speed unit spends most of its time at part load.
Cold-climate models
Heat-pump output falls as the outdoor air gets colder, so the question for heating is how much capacity and efficiency are left on the coldest days. Two specifications address this:
- ENERGY STAR cold climate — COP at 5 °F ≥ 1.75, heating capacity at 5 °F ≥ 70% of the capacity at 47 °F, a controls verification procedure showing the unit reaches those figures under its own controls, and HSPF2 ≥ 8.5 / SEER2 ≥ 15.2 for non-ducted splits (HSPF2 ≥ 8.1 for ducted). ENERGY STAR tests down to 5 °F; the units keep working below that, but ENERGY STAR says pairing them with back-up heat is the most efficient approach for even lower temperatures.
- NEEP Cold Climate Air Source Heat Pump Specification, version 4.0 (effective 1 January 2023) — for heating in IECC climate zone 4 and colder: non-ducted HSPF2 ≥ 8.5 and SEER2 ≥ 15; ducted HSPF2 ≥ 7.7 and SEER2 ≥ 14.3; COP ≥ 1.75 at 5 °F at maximum capacity. Makers must report minimum, rated and maximum capacity and power at 47, 17 and 5 °F and at the lowest outdoor temperature they catalogue, which is the data a designer uses to match the unit to the heating load.
Look for the capacity at your local design temperature in the maker’s extended data, not just the nameplate capacity measured at 47 °F.
Line-set length, height and charge
Each outdoor unit has limits on pipe length, the height between indoor and outdoor units, and the number of bends, and it ships with refrigerant for a set length of pipe. One example, Mitsubishi’s MSZ-GS12NA / MUZ-GS12NA submittal (R-410A):
| Item | Value, US (metric) |
|---|---|
| Liquid / gas pipe size, flared | 1/4 in. (6.35 mm) / 3/8 in. (9.52 mm) |
| Maximum piping length | 65 ft (20 m) |
| Maximum height difference | 40 ft (12 m) |
| Maximum number of bends | 10 |
| Piping length covered by factory charge | 25 ft (7.5 m) |
| Factory refrigerant charge | 2 lb 9 oz (1.16 kg) |
Beyond the pre-charged 25 ft, refrigerant has to be added per foot of extra pipe. Mitsubishi’s technical data for the series also shows capacity falling as the pipe gets longer, counting each bend as 0.984 ft (0.3 m) of extra pipe. Other models and other makers have different limits, so read the submittal for the exact outdoor and indoor model numbers. On a conventional install, the line set is flared, connected, leak-tested and evacuated before the factory charge is released; Mitsubishi’s installation manual for its MSZ-A/MUZ-A series, for example, calls for a vacuum pump on the gas-side service port for more than 15 minutes before the stop valves are opened.
Refrigerants: R-410A, R-32 and R-454B
Under the AIM Act, EPA’s Technology Transitions rule limits new residential and light commercial air-conditioning and heat-pump systems, mini-splits included, to refrigerants with a global warming potential (GWP) of 700 or less. The dates, as EPA states them:
- October 2023 rule: the GWP 700 limit for these systems, starting 1 January 2025.
- December 2023 interim final rule: equipment made or imported before 1 January 2025 with a higher-GWP refrigerant could still be installed until 1 January 2026.
- May 2026 reconsideration rule (finalized 21 May 2026): removes that 1 January 2026 installation deadline for systems whose specified components were all made or imported before 1 January 2025, so such pre-2025 inventory can be installed until it runs out. Variable refrigerant flow (VRF) systems have separate dates.
| Refrigerant | GWP (EPA reference table) | Under the 700 limit? |
|---|---|---|
| R-410A | 2,088 | No |
| R-32 (HFC-32) | 675 | Yes |
| R-454B | 465 | Yes |
R-32 and R-454B are “A2L” refrigerants, the lower-flammability class in ASHRAE Standard 34, and EPA’s SNAP program lists them as acceptable in new residential air conditioners and heat pumps subject to use conditions (Copeland technical guidance). They need equipment designed for them, and servicing them calls for A2L-rated tools. Existing R-410A systems can still be repaired: EPA’s rule restricts installation of new systems, not repair of existing ones. The refrigerant is not interchangeable between these systems; use only what the nameplate states.
Installation, certification and permits
Under EPA’s Section 608 rules (40 CFR Part 82, Subpart F), anyone who attaches hoses and gauges to an appliance to measure pressure, or adds or removes refrigerant, is a technician and must be certified, and only certified technicians may buy refrigerant for stationary equipment. EPA has four certification types: Type I for small appliances, Type II for high- and very-high-pressure appliances other than small appliances, Type III for low-pressure appliances, and Universal for all of them. EPA defines a small appliance as a product fully manufactured, charged and hermetically sealed in a factory with 5 lb (2.3 kg) or less of refrigerant, such as a window air conditioner; a split system is connected in the field, so it is a Type II job. Certification does not expire.
Beyond refrigerant handling, a mini-split needs a dedicated electrical circuit, a wall penetration, a condensate drain and secure mounting for the outdoor unit. Many jurisdictions require mechanical and electrical permits for this work; requirements vary, so check with your local building department before starting.
Do-it-yourself pre-charged kits, honestly
A few makers sell mini-splits meant for homeowner installation. MRCOOL, for example, markets its DIY 5th-generation range as designed for full homeowner installation: the line set comes pre-charged with R-454B and joins with patented quick-connect valves, with no vacuum pump or special tools, and MRCOOL says the valves are tested by Intertek to UL 207 and CSA C22.2 No. 140.3. EPA’s refrigerant sales restriction does not cover equipment or components that already contain refrigerant (40 CFR 82.154(c)), so these kits are not caught by it.
What a kit does not change:
- It only deals with the refrigerant connections: routing the line set, the wall penetration, the condensate drain and mounting the outdoor unit are still done to the maker’s instructions and limits.
- The electrical circuit, disconnect and any permits follow local code.
- If the circuit ever leaks, or the system needs refrigerant recovered or added, that work needs a Section 608 Type II or Universal technician.
- Warranty terms vary by maker and may depend on registration or on how the unit was installed; read them before buying.
Sizing is still the most common mistake with any mini-split. Run the numbers in the BTU Calculator as a start, and for a whole-house or cold-climate system get a Manual J calculation.
Sources
All documents were downloaded and read on 14 October 2026. kW, ton and metric conversions are calculated with the NIST factors.
- U.S. Department of Energy, 10 CFR 430.32(c), Central air conditioners and heat pumps, eCFR current text, 2026. ecfr.gov
- U.S. Department of Energy, Energy Conservation Program: Test Procedures for Central Air Conditioners and Heat Pumps, final rule, 82 FR (5 January 2017), FR Doc. 2016-30004 (Appendix M1; SEER2, EER2, HSPF2; external static pressure). federalregister.gov; and Appendix M1 to Subpart B of Part 430, eCFR current text.
- ENERGY STAR, Heat Pump Equipment Key Product Criteria (including cold-climate requirements and metric definitions), 2026. energystar.gov
- ENERGY STAR, Ductless Heating & Cooling (mini-split guidance, Manual J, 5 °F testing) and Room Air Conditioners (sizing chart and adjustments), 2026. energystar.gov ductless, energystar.gov room AC
- Northeast Energy Efficiency Partnerships (NEEP), Cold Climate Air Source Heat Pump Specification (Version 4.0), effective 1 January 2023. neep.org
- Air Conditioning Contractors of America, Manual J Residential Load Calculation, 8th Edition (ANSI/ACCA 2 Manual J – 2016), product page, 2026. acca.org
- U.S. EPA, Technology Transitions HFC Restrictions by Sector (updated 28 August 2026), Regulatory Actions for Technology Transitions, Fact Sheet: Final Rule – Reconsideration of Certain Regulatory Requirements … Technology Transitions (May 2026), and Technology Transitions GWP Reference Table (updated 2 April 2026). epa.gov restrictions, epa.gov rules, epa.gov GWP table
- U.S. EPA, Section 608 Technician Certification, Section 608 Technician Certification Requirements and Refrigerant Sales Restriction pages, 2026; 40 CFR 82.154, eCFR current text. epa.gov 608, epa.gov sales restriction
- NIST Special Publication 811, Guide for the Use of the International System of Units, 2008 edition, Appendix B (ton of refrigeration, BtuIT/h). nist.gov (PDF)
- Mitsubishi Electric, MSZ-GS12NA & MUZ-GS12NA submittal and Outdoor Unit Technical Data, MUZ-GS series (OBD875 revised edition A); Installation manual, MSZ-A09/A12YV, MUZ-A09/A12YV(H) (SG79Y281H07). Mitsubishi Electric library
- MRCOOL, DIY 5th Generation product page, 2026. mrcool.com
- Copeland, A2L Refrigerants in Air Conditioning Applications, 2026. copeland.com
Frequently asked questions
What size mini-split do I need?
As a first estimate, ENERGY STAR’s room air-conditioner chart gives 6,000 BTU/h for 150–250 ft², 9,000 for 350–400 ft², 12,000 for 450–550 ft² and 18,000 for 700–1,000 ft², with 10% more for a very sunny room, 10% less for a shaded one, 600 BTU/h per person beyond two and 4,000 BTU/h for a kitchen. For a real installation, ENERGY STAR says the contractor should verify the size with an ACCA Manual J load calculation, which also covers the heating load.
How many BTU is a ton?
One ton of refrigeration is 12,000 BTU per hour, which NIST lists as 3,516.853 W. A 9,000 BTU/h mini-split is 0.75 ton (2.64 kW), 12,000 is 1 ton (3.52 kW), 18,000 is 1.5 tons (5.28 kW) and 24,000 is 2 tons (7.03 kW).
What is the difference between SEER and SEER2?
SEER2, EER2 and HSPF2 are the same ratios as SEER, EER and HSPF but measured with DOE’s newer test procedure, Appendix M1, which became the basis for the federal standards on 1 January 2023. DOE said the new metrics generally have different numerical values; one change was raising the minimum external static pressure for testing conventional ducted systems from 0.10–0.20 to 0.50 in. w.c. A SEER2 figure cannot be compared directly with an old SEER figure.
Do mini-splits work in very cold weather?
Cold-climate models do. ENERGY STAR’s cold-climate designation requires a COP of at least 1.75 at 5 °F and heating capacity at 5 °F of at least 70% of the capacity at 47 °F, plus HSPF2 ≥ 8.5 for non-ducted splits. The NEEP cold-climate specification (version 4.0) also requires COP ≥ 1.75 at 5 °F at maximum capacity. ENERGY STAR notes the units keep working below 5 °F but recommends pairing them with back-up heat for the coldest days.
Can I install a mini-split myself?
Some kits are sold for that. MRCOOL’s DIY line sets, for example, come pre-charged and join with quick-connect valves with no vacuum pump needed, and EPA’s refrigerant sales restriction does not cover equipment that already contains refrigerant. Anyone who attaches gauges, adds or removes refrigerant on a mini-split needs EPA Section 608 Type II or Universal certification. The electrical circuit and any permits still follow local code.