HVAC
Ductless mini-split and multi-zone heat pump install field guide
Set the indoor heads, run and flare the lineset to torque, evacuate deep, add charge for the line over the factory length, and prove every zone drains and runs.
Direct answer
A ductless mini-split is an inverter heat pump split into an outdoor condensing unit and one or more indoor heads joined by a refrigerant lineset, with no ductwork. Connect the heads with flared, torqued joints, evacuate to about 500 microns, add charge for lineset over the factory length, and slope the condensate so it drains.
Key takeaways
- Mini-splits are flared and torqued, never brazed; use a 45-degree HVAC flare, and the flare is the number one leak source.
- Evacuate to about 500 microns and prove it holds with a decay test before opening the service valves.
- Slope the condensate drain by gravity at a minimum of about 1/4 inch per foot; add a float switch on any pump.
- Factory charge often covers 25 feet of lineset per port; add refrigerant per foot beyond that, then verify by subcooling or superheat.
- Size each head to its room load so connected heads fit the condenser total; oversizing kills inverter modulation and causes short-cycling.
What a ductless mini-split is, and where it beats a ducted system
A ductless mini-split is an inverter-driven heat pump split into an outdoor condensing unit and one or more indoor heads, joined by a small refrigerant lineset and control wiring, with no ductwork between them. The head sits in the conditioned space and blows directly into the room. The refrigerant runs to it, not air through a duct, so the losses and the leakage of a duct system are simply not there.
Where it earns its place is the retrofit and the zone. A house with no ducts, an addition, a finished attic, a garage shop, a room the central system never reached: that is the mini-split's home turf, because you skip the cost and the destruction of running duct. Each head is its own zone with its own setpoint, so you heat the bedroom and leave the spare room alone instead of conditioning the whole envelope to satisfy one thermostat.
The install shares its physics with the ducted split system, and the ducted split guide covers the parts that overlap, the matched pair, the evacuation, the charge by subcooling and superheat. The difference that drives this guide is the connections. A mini-split is flared, not brazed, and the heads drain condensate where they hang, which is where most of the callbacks come from.
The indoor head types and where each one fits
Four indoor styles cover almost everything, and picking the right one for the room is half the install quality. The wall-mounted head is the default: cheapest, easiest to service, the filter pulls out behind the front panel, and it hangs high on an exterior or interior wall blowing down and across the room. It is what goes in most bedrooms and living rooms.
The ceiling cassette recesses flush into a dropped ceiling and throws air four ways from the center, which suits a square open room or a space where a wall head would look wrong or short-throw a long room. The ceiling-concealed or short-duct head hides in a soffit or above the ceiling and feeds a few short duct runs to grilles, so you get the look of central air over two or three small rooms off one head. The floor or console unit sits low on the wall where a baseboard or radiator used to be, blows up, and fits a room with knee walls, big glass, or no wall height to spare.
Match the head to the room before the equipment is ordered. A wall head fighting a long, narrow room throws short and the far end never conditions, and that is a layout mistake the charge and the airflow cannot fix.
| Head type | Where it fits |
|---|---|
| Wall-mounted | Most rooms; cheapest, easiest filter and service access |
| Ceiling cassette | Square open rooms, dropped ceilings, four-way throw |
| Ceiling-concealed / short-duct | Two or three small rooms off one head, hidden look |
| Floor / console | Knee walls, large glass, low wall height, baseboard replacement |
Single zone vs multi-zone: one condenser, how many heads?
A single-zone system is one outdoor unit feeding one indoor head, matched and rated as a pair. A multi-zone system is one outdoor unit feeding several heads, each its own zone with its own remote and setpoint, which is the layout that lets you condition four rooms off one condenser on the wall.
The number of heads a condenser carries is set by the model, not by a rule of thumb, and the manufacturer's data is the only place to read it. Common multi-zone outdoor units run two to five heads, and some lines reach eight or nine when the architecture allows it. The catch most people miss is total capacity. The condenser has a rated total, and the heads you hang have to add up under that total with the manufacturer's connection ratio, or you oversize the heads against the compressor and the system short-cycles and never modulates right.
Sizing the heads is where multi-zone goes wrong. The temptation is to hang the biggest head in every room. Size each head to its room load and confirm the combined connected capacity falls in the range the outdoor unit allows, because an oversized head on an inverter loses the part-load efficiency that is the whole reason you bought it.
On a multi-zone the refrigerant has to split from one outdoor unit out to several heads, and there are two ways the manufacturers do it. Some condensers have a header with a dedicated set of ports, so each head runs its own lineset straight back to the outdoor unit. Others route a single main lineset to a branch box, a distribution box that sits in the ceiling or the attic and splits the refrigerant out to the individual heads from there. The branch box is not optional where the model calls for it, and it is brand-specific.
A condenser is rated to work with particular branch boxes, and you cannot mix a box from one line onto another manufacturer's outdoor unit. Some lines build the distribution smarts into the heads and use simple refrigerant splitters instead of a box, which is how a few systems reach a high head count. The branch box buys flexibility worth having: leave a port capped and add a head to that room later without replacing the outdoor unit, as long as the connected capacity still fits. Plan the box location for service access, because when a zone faults the diagnostics often live at the box.
| Item | Single zone | Multi-zone |
|---|---|---|
| Heads per condenser | One | Two to five typical, more on some lines |
| Distribution | One lineset, head to unit | Lineset per head, often a branch box |
| Zoning | One setpoint | Independent setpoint per head |
| Capacity check | Matched pair | Connected heads must fit the condenser total |
The inverter compressor and what variable speed buys you
The compressor in a mini-split is inverter-driven, which means it modulates its speed instead of cycling full-on and full-off the way a single-stage compressor does. It ramps up to pull the room to setpoint, then throttles down and holds a low, steady output that matches the room's actual heat loss. That part-load running is where the efficiency lives, and it is why mini-splits post the SEER2 and HSPF2 numbers they do.
Variable speed changes the install in two practical ways. There is no hard start, no big inrush slamming the contactor every cycle, so the electrical demand is gentler and the comfort is steadier with smaller temperature swings. And the system spends most of its life at low speed, which is exactly why oversizing hurts. An oversized head or an oversized condenser cannot turn down far enough, so it cycles like a single-stage unit and throws away the modulation you paid for.
Size to the load, not above it. The inverter rewards a tight match between the equipment and the room. The old habit of padding the capacity for a safety margin works against an inverter system, because the margin becomes time spent short-cycling at the bottom of the modulation range.
Cold-climate hyper-heat, defrost, and the base-pan heater
Cold-climate or hyper-heat mini-splits are built to keep putting out heat when the outdoor air is well below freezing, where an ordinary heat pump has given up. The published numbers on these lines show rated heating continuing down to around minus 13 to minus 22 degrees F, depending on the model, with the capacity tapering as it gets colder. That is what makes a ductless heat pump a real primary heat source in a cold climate instead of a shoulder-season helper.
Defrost comes with the territory. Running in heat, the outdoor coil drops below freezing and frost builds on it, so the control periodically reverses to cooling for a few minutes to melt the frost, with the outdoor fan off. During defrost the head will pause its warm air, which is normal and not a fault. A unit that ices solid and never clears has a defrost control, sensor, or charge problem.
In snow country the outdoor unit needs help the ducted condenser rarely gets. Mount it on a stand or wall bracket high enough to clear the seasonal snow line so meltwater and snow do not pack the coil. Cold-climate units commonly include a base-pan heater that keeps defrost meltwater from refreezing in the bottom of the unit and lifting it off the mounts. Confirm the model has it, or wire in the accessory, where the unit runs through hard winters.
Mounting the head: location, throw, level, and the slope to the drain
The head goes where its air reaches the room and where the lineset and drain can leave the building cleanly. On a wall head that usually means high on an outside wall near the corner, with the throw aimed down the length of the room, and with the clearances the manual gives above and to the sides so the unit can pull return air across the coil. Crowd it under a soffit or against a ceiling and it starves and short-cycles.
Mount the wall plate dead solid and to the manufacturer's clearances, because the head hangs off it and a loose plate buzzes and sags. Here is the detail that separates a clean install from a leaker. The head is set very slightly low toward the condensate side so water runs to the drain port, not back into the unit. A head hung dead level, or worse tilted away from the drain, holds water in the pan and pushes it out the front to drip down the wall. The slope is small, just enough that the pan drains to the fitting, and you check it with a level on the chassis before you commit the lineset.
Plan the hole before the head goes up. The lineset, the drain, and the comms wire all leave through one penetration behind the head, pitched down to the outside, so the bundle drops away from the unit and water cannot track back inside.
Why is my mini-split head leaking water?
A mini-split head leaks water for one of two reasons almost every time: it was not sloped to drain, or the drain itself is blocked or pumping uphill and failing. The head pulls moisture out of the air in cooling, that water collects in the pan, and it leaves by gravity down a small drain line bundled with the lineset. Get the slope right and keep the line clear and the head stays dry for years. Miss either one and it drips down the wall, which is the single most common ductless callback.
Gravity is the drain you want. A continuous downward slope from the head to the outside, commonly held at a minimum of about 1/4 inch per foot, lets the pan empty with nothing to fail. Keep the line the same diameter the whole way, no dips, no traps that hold water and grow biofilm, no upward runs. Most leaking heads on a year-old system are not a bad unit, they are a flat or back-pitched drain line that finally clogged.
Where gravity will not work, a basement head below the drain, a wall where the line cannot fall, you add a condensate pump. Treat the pump as the last resort it is, because it is one more thing that fails, and when it fails the pan overflows. Wire a float switch into the pump or the control circuit so a failed pump or a backed-up drain shuts the head off before the water finds the floor, the same insurance the ducted attic air handler gets.
Do you braze or flare a mini-split?
You flare a mini-split, you do not braze it. The lineset connects to the indoor head and to the outdoor unit's service valves with flared joints and flare nuts, a mechanical seal you make with a flaring tool and a torque wrench. No torch touches a standard mini-split connection, which is one of the things that makes the install approachable and also one of the things that gets done badly.
The flare exists because the equipment is built for it. The head and the service valves come with flare fittings, and the field side of the lineset gets flared to match, then torqued to the value for the line size. This is different from the ducted split system, where the lineset is brazed to the coil and the condenser. If you do braze a joint on a mini-split, extending a lineset, repairing a kink, the rules from the ducted side apply: flow dry nitrogen through the line while you braze so you do not scale the inside of the copper, and the split-system install guide covers that technique and the evacuation that follows.
Because the connection is mechanical, the quality is entirely in the flare and the torque. A brazed joint either flows or it does not. A flare can look finished and still weep, which is why the flare gets its own section below. It is where the leaks come from.
The flare is the number one leak source: prep and torque it right
Most mini-split leaks are at the flare, and most bad flares come from poor prep, not a bad tool. The sequence is not negotiable. Cut the tube square with a tubing cutter, deburr and ream the inside edge so no chips or burr ride into the seat, slide the flare nut on before you flare it, then make a clean 45-degree flare with a flaring tool. Use the 45-degree HVAC flare, not the 37-degree automotive angle, and inspect the flare face for cracks, scoring, or an off-center cone before you assemble it.
Then torque it, do not gut-feel it. Hand-start the nut to seat it square, then bring it to the value for the line size with a calibrated torque wrench. Under-torque and the seat does not seal and it weeps slowly, the leak that drains the charge over a season. Over-torque and you crush the flare seat or split the cone, which is a leak you made trying to prevent one. The torque ranges below are common figures across brands, but the install manual for the unit is the authority, so set the wrench to the manual's number for that model.
A drop of refrigerant oil on the seat and threads, where the manual allows it, helps the nut pull up evenly to torque without galling. Soap the flares at pressure test and watch them. A flare that bubbles at test is cheap to fix now and expensive to find after the wall is closed.
| Flare / line size | Common torque range (verify the manual) |
|---|---|
| 1/4 in (liquid) | Roughly 10 to 18 ft-lb |
| 3/8 in (suction) | Roughly 22 to 30 ft-lb |
| 1/2 in | Roughly 36 to 45 ft-lb |
| Authority | The manufacturer install manual sets the exact value |
Lineset length, vertical lift, and the line-hide cover
The lineset is a small insulated suction line and a bare liquid line running from each head to the outdoor unit or branch box. Size it to the connection on the head and the manufacturer's tables, not to whatever roll is on the truck, and route it with as few tight bends as you can, because every elbow adds equivalent length and a kink chokes the line for good.
Every system has a maximum total lineset length and a maximum vertical separation between the indoor and outdoor units, and on a multi-zone there is often a limit on the longest single run and on the total across all heads. The numbers are model-specific and live in the install manual. Common single-zone allowances run in the neighborhood of 50 to 100 feet of total line with several tens of feet of lift, and the higher reaches need the larger line sizes the manual specifies. Exceed the lift or the length and you starve the far head or fail to return oil to the compressor.
Oil return is the quiet failure on a tall riser. The refrigerant carries the compressor's oil around the loop, and on a long vertical rise the gas can lose the speed it needs to drag oil up. Where the manual calls for a trap on the suction riser at intervals, you install it. Skip it on a tall lift and the compressor slowly runs itself dry, which the data plate will not warn you about.
Outside, the lineset, the drain, and the comms wire run together down the wall, and they get a lineset cover, the rigid line-hide channel, rather than the foam-and-tape job that chalks and falls apart in a couple of seasons of sun. The cover protects the insulation from UV, keeps the drain pitched, hides the bundle, and gives a finished look that is the difference between a professional install and a homeowner special. Run it plumb and level, with the fittings at the corners, and seal the top where it meets the head penetration.
The penetration through the wall is where water and air get into the structure if you let them. Sleeve the hole, pitch the sleeve slightly down to the outside so any water in the line cover drains out and not in, and seal both sides against air, water, and pests. An open or back-pitched penetration is a path for humid air into the wall cavity and for condensate to track back inside and rot the sheathing behind a head that looks dry. The drain inside the cover still has to fall continuously, so the cover run cannot create a dip that holds water.
How do you evacuate and charge a mini-split?
The outdoor unit ships with a factory charge sized for a set lineset length, and the work is to evacuate the lines and the heads, then release that charge and add for any line beyond the rated length. Single-zone units are commonly pre-charged for the first 25 feet of lineset per port, some for 15, and over that length you add refrigerant per foot by the manual's number for the line size. The factory charge lives in the condenser behind the closed service valves the whole time.
Evacuate before you ever open those valves. Connect the vacuum pump to the service port, pull the system and the lineset down to about 500 microns on a micron gauge, and prove it holds with a decay test before you release the charge. The deep vacuum boils off the moisture and air that would otherwise acid up the oil and ice the metering device. Pull through removed valve cores with vacuum-rated hoses, the same as the ducted side, and the split-system and charging guides cover the core tools and the standing decay test in depth. Never purge the lines with refrigerant to skip the vacuum, that vents refrigerant and leaves moisture behind.
Only after the vacuum holds do you open the service valves and let the factory charge into the system, then weigh in the per-foot adder for the extra line. With the system running, confirm the charge against the data plate, which on a TXV system means subcooling and on a fixed-orifice means superheat. The refrigerant charging guide walks both numbers and how to read them. Do not set a mini-split charge by pressure alone.
| Step | Target (verify the manual) |
|---|---|
| Factory pre-charge good for | Often 25 ft of lineset per port, some 15 ft |
| Adder over rated length | Refrigerant per foot, by line size, from the manual |
| Evacuation | About 500 microns, then a decay test |
| Charge verification | Subcooling (TXV) or superheat, against the data plate |
The disconnect, the circuit, and the communication wiring
The outdoor unit runs on a dedicated circuit sized off the nameplate, with a disconnecting means within sight of the unit so a tech can kill power standing at it. HVAC equipment falls under NEC Article 440, and the nameplate sets the electrical limits, not a guess from the tonnage. Read the minimum circuit ampacity to size the conductors and the maximum overcurrent protection to pick the breaker, and never fuse above the maximum overcurrent protection, which defeats the unit's protection.
Most residential mini-splits power the outdoor unit only, and the indoor heads draw their power from the outdoor unit over the connecting cable, so the head does not get its own circuit. That is one of the things that makes the install clean, but it means the connecting cable between head and unit carries both power and the communication signal, and it has to be the right cable landed right. Confirm whether your model powers the heads from the outdoor unit or separately, because lines differ.
From the disconnect to the unit runs a flexible whip into the connection. Land the line voltage on the marked terminals, torque the lugs, and keep the line-voltage and the comms conductors separated where the manual requires it so the power side does not induce noise on the data side.
The head and the outdoor unit talk to each other over the communication wire in the connecting cable, and a miswire here is the fault that stops a system that otherwise looks installed. The boards exchange a signal so the outdoor unit knows which head is calling and how hard to run, and on a multi-zone the address of each head matters so the right zone gets the capacity. Land the comms by the wiring diagram on the unit, terminal for terminal, not by the color you expect, because the color conventions vary by brand and the diagram is the only authority.
Many systems are polarity-sensitive and address-sensitive, so terminal 1 on the head goes to terminal 1 on the unit, terminal 2 to 2, and the ground to ground, every head matched to its port. Cross two terminals or swap a head's address on a multi-zone and you get a communication error and a system that will not start, or a head that runs the wrong zone's call. Torque the terminal screws and tug-test every conductor, because a comms wire that backs out of the terminal throws an intermittent no-communication fault that is miserable to chase after the cover is on. A communicating bus does not tolerate the loose connection a line-voltage circuit shrugs off.
Commissioning: prove every zone heats, cools, and drains
Commissioning is where the install gets proven, and on a multi-zone you prove every zone, not just the one nearest the door. With the vacuum held and the service valves opened and the charge set, power it up and run each head in cooling and in heating, one at a time and then together, and confirm each one actually delivers conditioned air to its room and responds to its own remote.
Work the numbers in order. Confirm the charge by subcooling or superheat against the data plate. Take the supply and return air temperatures at each head and confirm a reasonable split across the coil. Clamp the outdoor unit's amps and compare to the nameplate. On a heat pump run it through heating and watch a defrost cycle behave. The charging guide covers the subcool and superheat method that backs the charge.
Then test the condensate, which is the step that gets skipped and the one that comes back. Pour water into each head's drain pan, or run the head in cooling long enough to make condensate, and watch the water leave the building at the outside end of the drain. A head that does not drain on the test bench will not drain in August. Set up the controls and the app last, hand the owner a working remote for each zone, and write down every reading as the baseline.
The controls: remote, app, and the central controller
Most mini-split zones come with a handheld infrared remote, and on a multi-zone each head has its own, so the owner controls each room separately. That is the basic case and it works, but it is also where owners get confused, because a stack of identical remotes for different rooms is easy to mix up. Label them to the room at handoff.
A wifi adapter and the manufacturer's app put the zones on a phone and add scheduling, away setpoints, and fault alerts, and most lines either include the adapter or sell it as a clip-in accessory. Confirm the adapter is on the unit's compatible list, because a third-party adapter that half-works generates support calls. For a whole-house multi-zone, a wired central controller or a wall thermostat that ties to all the heads gives one place to manage the system and a familiar interface for an owner who does not want a remote per room.
Set the controls up at commissioning, not as an afterthought from the truck. Confirm each zone responds, confirm the app sees each head as the right room, and confirm any central controller addresses the heads correctly, which ties back to the addressing you set on the comms wiring.
A2L refrigerants on new mini-splits
New mini-splits ship with A2L refrigerants, commonly R-32 and R-454B, which are mildly flammable, and that changes a few things on the install. Equipment built and sold after the 2025 transition uses these instead of R-410A, so most new ductless installs are A2L now whether the owner knows it or not. Mildly flammable does not mean it lights easily. An A2L burns slowly, needs a high concentration in air, and takes a strong ignition source, far more than a fuel gas.
What the install has to respect is charge limits by room size. The listing standards cap how much refrigerant can serve a given floor area so a worst-case leak cannot reach a flammable concentration, and on a small room with a larger head that limit is a real constraint, sometimes requiring a minimum room area or a leak-detection and mitigation feature. The head, the smallest enclosed space on the system, is where that calculation bites.
The handling rules carry over with additions. You still need EPA Section 608 certification to handle the refrigerant, and you keep open flame away from a charged A2L circuit. Where you braze a joint, flow nitrogen and clear the area of ignition sources first. Follow the manufacturer's A2L-specific instructions, which are not optional on this equipment, and the split-system guide covers A2L handling in more detail by topic.
Keeping it running after turnover
A ductless install hands the owner a system that mostly maintains itself, with one easy job and three that need a tech. The easy one is the head filter. The wall-head filter lifts out behind the front panel, rinses in the sink, dries, and snaps back, and it is the single thing that keeps the head moving air. A clogged filter chokes airflow, drops capacity, and ices the coil, and it is the first thing to check when a head quits cooling. Show the owner where it is and how often to clean it.
The tech jobs are the coil, the drain, and the blower wheel. The outdoor coil mats with cottonwood, grass, and dust and gets rinsed gently, not blasted. The condensate drain gets flushed before the cooling season so it never has the chance to clog and overflow. And the blower wheel inside the head, the squirrel-cage that throws the air, grows a film of mold and dust over a few years that a filter never catches, and it has to be pulled and deep-cleaned periodically. A head that smells musty and blows weak has a fouled wheel, and that is the maintenance that gets neglected because it takes a real teardown.
The charge should not need touching. A flared system that was torqued right and evacuated deep does not consume refrigerant. If it is low next year, a flare or a joint leaked, and the fix is to find it, not to top it off every spring.
Where the mini-split ends and VRF begins
The mini-split is the small end of the same family of technology that scales up to VRF, variable refrigerant flow, on commercial buildings. A multi-zone mini-split feeding four or five heads off one inverter condenser is doing in miniature what a VRF system does for a whole office floor, a single outdoor unit modulating refrigerant out to many indoor units, each its own zone.
The line between them is size, the number of indoor units, and the control sophistication. VRF systems run dozens of indoor units, use larger branch distribution, and on heat-recovery versions can heat one zone while cooling another off the same loop by moving heat between them, which a typical residential multi-zone cannot do. The refrigerant, the flared or brazed connections, the evacuation, the charge by length, and the commissioning discipline are the same skills, scaled up.
If you can install and commission a multi-zone mini-split cleanly, you have the foundation for VRF, and the commercial VRF guide covers the larger system by topic. The habits that matter, the flare and torque, the deep vacuum, the per-foot charge, the comms addressing, the condensate proof, carry straight across.
What to document
The commissioning record proves the system was installed right and gives the next tech a baseline to measure against, and on a multi-zone it has to be per zone, because the heads run independently and fail independently. Capture the readings and the install details for each head, because a number with no zone and no context cannot be reproduced.
| Per zone / head | What to record |
|---|---|
| Zone and head type | Room served and the head style installed |
| Lineset length and lift | Routed length and vertical separation for the run |
| Condensate method | Gravity slope or pump, and the drain test result |
| Charge | Factory charge plus the per-foot adder, by weight |
| Flare torque | Value used against the manual for each line size |
| Vacuum achieved | Microns reached and the decay test result |
| Test run | Cooling, heating, and the temperature split per zone |
| Amps and controls | Outdoor unit amps and each zone's control confirmed |
Common mistakes
- Making a sloppy flare or skipping the torque wrench, so the joint weeps the charge over a season.
- Over-torquing the flare nut and crushing the seat, making the leak you were trying to prevent.
- Hanging the head dead level or back-pitched so it holds water and drips down the wall.
- Running a flat or back-pitched condensate line, or pumping uphill with no float switch backup.
- Adding no per-foot charge for lineset over the factory-rated length, so the system runs low.
- Miswiring the head-to-condenser communication, or swapping a head's address on a multi-zone.
- Opening the service valves before the vacuum holds, leaving moisture and air in the system.
- Oversizing the heads against the condenser total, so the inverter cannot modulate and short-cycles.
- Leaving the site without pouring water through each head's drain to prove it actually empties.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The manufacturer's installation instructions govern this work, and on a mini-split that is even more true than on a ducted system. The manual sets the flare torque, the lineset length and lift limits, the factory charge and the per-foot adder, the required vacuum, the branch-box compatibility, the comms wiring, and the head clearances. Where general guidance and the install manual disagree, the manual wins, because the equipment is listed to it.
AHRI certifies the matched outdoor and indoor combination and the rating it carries, and the AHRI directory is where you confirm the pair and the multi-zone combination. Refrigerant handling, recovery, and the ban on venting fall under EPA Section 608. The electrical side follows the adopted electrical code, with HVAC equipment under NEC Article 440, the disconnect within sight, conductors sized to the minimum circuit ampacity, and overcurrent at or below the maximum overcurrent protection. The mechanical code, the IMC in many jurisdictions, covers the condensate, the clearances, and the equipment access.
The energy code and the efficiency rating, SEER2 and HSPF2 on current equipment, depend on the system being sized and charged the way it was rated. A2L equipment follows the equipment listing and the manufacturer's A2L instructions for charge limits by room size and leak detection. Article and section numbers shift between code cycles and the refrigerant rules keep moving, so confirm the adopted editions and the current refrigerant regulations against the jurisdiction and the manufacturer before you rely on a specific number.
Units and terms
Ductless work carries its own vocabulary, and the same part goes by a few names across a data plate, a manual, and a quote.
The indoor head is also called the indoor unit, the air handler, or the evaporator, depending on the source. The outdoor unit is the condenser or condensing unit. A multi-zone outdoor unit feeding several heads is sometimes called a multi-split. The branch box is the distribution box that splits refrigerant to the heads. Capacity is rated in BTU per hour and in tons, where 12,000 BTU per hour is one ton. Efficiency reads as SEER2 for cooling and HSPF2 for heating. Vacuum is read in microns, where 500 microns is the common evacuation target. Flare torque is given in foot-pounds or newton-meters.
- Indoor head
- The indoor unit that hangs in the room; also called the air handler or evaporator
- Single zone / multi-zone
- One condenser feeding one head, versus one condenser feeding several independent heads
- Branch box
- The distribution box on some multi-zone systems that splits refrigerant out to each head
- Inverter
- The variable-speed compressor that modulates output instead of cycling full on and off
- Flare
- The 45-degree mechanical refrigerant connection torqued to spec; the primary leak source
- Micron
- Vacuum unit; about 500 microns is the common evacuation target before opening the valves
- SEER2 / HSPF2
- Current cooling and heating efficiency ratings for the equipment
- A2L
- The mildly flammable low-GWP refrigerant class, such as R-32 and R-454B
FAQ
What is a ductless mini-split?
A ductless mini-split is a heat pump with an outdoor condensing unit and one or more indoor heads connected by a refrigerant lineset instead of ductwork. Each head conditions its own room as a separate zone, which makes the system a strong fit for retrofits, additions, and rooms a central duct system never reached.
Single zone vs multi-zone mini-split: what is the difference?
A single-zone mini-split is one outdoor unit feeding one indoor head. A multi-zone is one outdoor unit feeding several heads, each its own zone with its own setpoint, often through a branch box. Multi-zone heads must add up under the condenser's rated total capacity, so size each head to its room, not oversize.
Do you braze or flare a mini-split?
You flare a mini-split, not braze it. The lineset connects to the head and the outdoor service valves with flared joints torqued to spec, no torch required on a standard install. If you do braze a joint, such as extending a line, flow dry nitrogen through the copper to keep scale from plugging the metering device.
Why is my mini-split head leaking water?
A mini-split head leaks water because it was hung level or back-pitched instead of sloped to the drain, or because the condensate line is flat, clogged, or pumping uphill and failing. Water that cannot drain overflows the pan and the fan pushes it out the front. Slope the head to the drain and keep the line clear and falling.
How much refrigerant do you add for a long mini-split lineset?
The outdoor unit is pre-charged for a set length, often the first 25 feet per port, and you add refrigerant per foot beyond that by weight. The install manual gives the per-foot adder for the line size and refrigerant. Add it after the vacuum holds and the valves are open, then verify the charge by subcooling or superheat.
How many indoor heads can one mini-split condenser run?
It depends on the model. Many multi-zone outdoor units carry two to five heads, and some lines reach eight or nine with the right branch-box or splitter architecture. The hard limit is total capacity: the connected heads must add up under the condenser's rated total, so confirm the count and the capacity in the manual.
Do mini-splits work in cold weather below freezing?
Cold-climate or hyper-heat mini-splits keep producing heat well below freezing, with rated heating on many models continuing down to around minus 13 to minus 22 degrees F, capacity tapering as it gets colder. They run a defrost cycle to clear coil frost, and in snow country need a stand and often a base-pan heater.
What torque do mini-split flare nuts need?
Flare torque runs by line size, commonly around 10 to 18 ft-lb for 1/4 inch and 22 to 30 ft-lb for 3/8 inch, but the install manual sets the exact value for the model. Use a calibrated torque wrench. Under-torque weeps the charge, and over-torque crushes the flare seat and makes the leak you meant to prevent.
Do you need a condensate pump for a mini-split?
Only when gravity will not drain the head, such as a basement unit below the drain point. Gravity drainage at about 1/4 inch per foot is the first choice because nothing fails. Where you must pump, treat it as a last resort and wire a float switch so a failed pump shuts the head off before water overflows the pan.
How deep a vacuum does a mini-split need?
Pull a mini-split to about 500 microns on a micron gauge and prove it holds with a decay test before you open the service valves and release the factory charge. The deep vacuum removes moisture and air that would acid up the oil and ice the metering device. Pull through removed valve cores with vacuum-rated hoses.
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