A mini split is a heat pump with no ducts, unless it’s a cooling-only model. An outdoor unit moves heat through refrigerant lines to a head in the room, and each head holds its own temperature. That suits a house with no ducts, electric baseboard heat or one problem room. It’s a harder case to make in a home with sound ducts and a gas furnace with years left in it.
This guide runs in the order most people need it: what you’d be buying, whether a mini split system fits your house, what it costs to run, then care and repairs. Each section links to the full page, with the worked numbers. The Last Furnace sells and installs nothing.
What a mini split is
Federal rules put mini splits in the same family as central heat pumps: the definition in 10 CFR 430.2 covers both, and the same federal minimum for split heat pumps, 14.3 SEER2 and 7.5 HSPF2, sits behind both. So the real comparison is ductless against ducted, and our page on how a mini split differs from a central heat pump sets it out. Three terms cause most of the confusion in quotes:
- Cooling-only. Not a heat pump. If you want heat, the quote and the sheet must both say heat pump.
- Single-zone and multi-zone. One outdoor unit with one head, or with several. A single-zone rating doesn’t carry over to a multi-zone system, so ask for the rating of yours.
- Ducted mini split. Mini split equipment with a concealed indoor unit and short ducts, so “mini split” doesn’t always mean ductless.
Does one fit your house?
Your ducts decide most of this. Our mini split vs central air comparison works it through:
| Your house | Usually leans toward |
|---|---|
| Sound ducts, and the old AC has failed | Central air, or a ducted heat pump |
| Radiators or baseboard, no ducts | Mini split |
| One hot room, an addition, a room over the garage | Keep what you have and add one mini split |
| Leaky ducts in a hot attic | Price a duct repair against a mini split |
| Many small rooms with doors usually closed | Central air, or concealed ducted heads |
| Wildfire smoke or allergies are a main concern | Central air, with a filter your system can take |
| A gas furnace you want to keep | Central air, or a mini split for summer and mild days |
Cooling bills alone rarely settle it. In that page’s worked example, a 20 SEER2 multi-zone system beats a 14.3 SEER2 central system with 15% duct loss by about $117 a year (our arithmetic on an assumed 20 million Btu of cooling a year, at 18.16 cents per kWh, EIA’s preliminary US average for August 2026). That rarely pays for ripping out central air that works. No published duct-loss figure describes your ducts either, so ask for a duct leakage test.
One room or the whole house?
Some mini splits can heat a whole house if the house suits them. A Building America case study of eight new, high-performance Massachusetts homes concluded they can work well in many houses, but those were tight new homes, so don’t carry the result over to a drafty older one. Three questions decide it:
- How does each room without a head get heat with its door shut?
- What heats the house on the coldest day? A British Columbia field study says ductless units typically have no backup coil, so a whole-house plan needs enough capacity or a second heat source.
- What can the unit deliver at your design temperature? Rated capacity isn’t winter capacity. One Mitsubishi sheet (2023, an example, not a pick) lists 14,690 Btu/h at 5°F against a maximum of 21,000 at 47°F. Our cold-weather guide explains why.
For one room, the mini split size calculator estimates the cooling and heating load and checks a unit’s own numbers. It doesn’t replace a load calculation. Bigger isn’t automatically better: a 2016 Massachusetts and Rhode Island evaluation found units averaged about 2.6 times the Manual J cooling load, which its authors suggest may reflect sizing for heat.
What it costs to run
Metered mini splits in northern US climates have averaged about 1,700 to 2,050 kWh a year for heating and about 200 to 250 kWh for cooling, per unit, in studies for Efficiency Maine in 2024 and 2026 and for NEEA in the Northwest. At 18.16 cents, that’s roughly $340 to $420 a year (our arithmetic). None of this is a national average, and in one Maine study nearly 40% of units used under 1,000 kWh a year for heating and nearly 25% used over 3,000.
How much of the house the unit really heats matters more than its size, and cooling can run far higher in the South. The mini split electricity calculator estimates your own yearly kWh and cost, with heating and cooling kept apart.
When a furnace is the better call
At US average prices, a heat pump of either type needs a seasonal COP of about 3.55 to match a 95% gas furnace on running cost, and about 2.99 to match an 80% one. That’s our arithmetic on the same summer electricity price and EIA’s $14.77 per Mcf of gas (first quarter of 2026) and 1,036 Btu per cubic foot.
The studies above averaged seasonal COPs of 2.57 to 3.15, which is no promise for your home. At those COPs and prices, a 95% furnace costs less to run than the heat pump, and an 80% furnace can go either way. Oil and propane differ: the line is about 1.01 against an 85% oil furnace and 1.60 against 90% propane, on EIA’s oil and propane prices for 26 October 2026, excluding tax.
Local prices move this a lot: against a 95% gas furnace, the line is about 2.69 in Georgia and 5.92 in Michigan. Keeping your furnace is a sound decision. Our heat pump vs furnace guide shows where each one wins, and the gas furnace calculator runs your own bills. For oil, propane or electric heat, use the heat pump savings calculator.
Rebates can change the layout
The federal credit is gone: 25C doesn’t apply to property placed in service after 31 December 2025. State and utility money remains, and its rules can shape the design. Efficiency Maine’s claim form, dated 2 October 2026, pays rebates on single-zone units on its list, while multi-zone units earn none, though their capacity counts toward its sizing test. So one outdoor unit with three heads can earn nothing there, where three single-zone units might. That’s one program, and 2026 offers can change on 31 December, so start at our rebates and rules hub before you settle on a layout. The program decides what qualifies.
Looking after one
Most of the job is filters. Most manuals we read say every two weeks of regular use and a few say monthly, so follow yours. Our guide on how to clean a mini split has the steps and a table of who does what.
Stop at filters, the case and a clear outdoor unit unless your manual gives you more. Popular guides show owners spraying the coil, but Mitsubishi’s European MSZ-EF manual says never to try washing the inside. Our heat pump maintenance guide covers the technician’s side.
When something goes wrong
- Water from the head. Usually condensate that isn’t reaching the drain, from a blocked line, a frozen coil or a poor pitch. Turn it off, catch the water and follow our page on a mini split leaking water. Water under the outdoor unit in heating season is normally fine.
- Weak or no cooling. Set Cool several degrees below the room, clean the filter and clear the outdoor unit. Then our mini split not cooling guide adds a thermometer test and the mode conflict that can leave one head idle on a multi-zone system.
- Weak or no heat. Heat pump not heating has a section on ductless units.
- Anything else. Use the symptom chart.
Your side ends at the remote, the filter and clear airflow. Ice on the coil or copper lines, an error code that stays, a breaker that trips more than once, or a burning smell means turn it off and call. “Low refrigerant” means a leak, and handling refrigerant takes EPA Section 608 certification, so be wary of a top-up with no leak search.
What to get in writing
- That the system is a heat pump, with exact outdoor and indoor model numbers.
- A room-by-room load calculation, and which rooms get no head.
- The maker’s capacity at your design temperature, from the sheet.
- What heats the house on the coldest days.
- The maker’s MCA and MOCP, and who does the electrical work.
- Who pulls the permit. If you’re not sure one applies, ask the local building department.
This page is general information, not professional, tax or legal advice. Your own unit’s manual overrides anything here.
Sources checked on 4 November 2026.
