Zone count, BTU sizing, line-set length and installed cost for a ductless mini-split.
Estimates are planning aids, not a professional quote. Double-check quantities and product coverage — and any local code or permit requirements — before you buy.
⚠ In most U.S. states, only an EPA 608-certified technician may open a sealed refrigerant circuit. Pre-charged quick-connect line sets (the ones priced here) are the DIY-legal path — they never need brazing or a vacuum pump as long as the run fits a standard kit length.
| HVAC | $3,051–$4,127 |
| Total | $3,051–$4,127 |
Excludes tools, delivery, tax and permit fees. Labor not included — this is a DIY materials estimate.
These are affiliate links: we may earn a commission if you buy through them, at no extra cost to you. It never changes what the calculator recommends — the shopping list comes from your dimensions, not from what pays.
About this calculator
Enter the square footage you're heating or cooling and how many independently controlled zones you want, and the Mini Split Calculator sizes each indoor head in BTU, rounds it to a standard capacity tier, and works out whether one shared outdoor condenser or a dedicated unit per zone fits your setup better. It also sizes the pre-charged line-set kit each head needs, stepped to the fixed lengths those kits actually come in.
Ductless systems are a refrigerant-side install, not a duct-and-vent one, so the takeoff here is different from anything else on the site — wall sleeves, line-set cover, condensate routing and the outdoor disconnect a code-compliant install requires. Toggle between wall, ceiling-cassette or floor-console heads and between a shared multi-zone condenser and one dedicated unit per zone to see how each choice moves the cost.
Step by step
A step-by-step walkthrough to go with your plan above. Follow the product instructions and any local code or permit requirements as you work.
Use the calculator to size BTU per zone from the room's area, insulation and sun exposure, and decide between a shared multi-zone condenser or one dedicated condenser per head. Getting this right up front avoids buying an undersized head that short-cycles or an oversized one that never dehumidifies properly.
Mount the indoor head high on an interior wall clear of doors and furniture, and set the condenser location where it has clearance for airflow and service access. Keep the line-set run as short and direct as the routing allows — every extra foot adds cost and a small efficiency loss.
Drill a sleeved, slightly downward-sloping hole through the wall behind the head's mounting plate so any condensation drains outward, not back into the wall cavity. Seal the sleeve with foam and a wall cap once the lines are through.
Hang the head on its mounting plate and set the condenser on its pad or bracket, using a level on both — an out-of-level condenser wears its compressor unevenly over time. Leave slack in the line set for service loops at each end.
Route the insulated line set and condensate tubing from the head to the condenser, then torque each flare fitting to the manufacturer's exact spec with a calibrated torque wrench. This single step is the most common source of refrigerant leaks on DIY installs, so don't eyeball it.
Land the communication cable between head and condenser, and have a licensed electrician run the dedicated circuit and mount the code-required disconnect within sight of the outdoor unit. Don't energize the system until the disconnect and circuit have passed inspection.
Snap line-set cover over the exposed exterior portion of the run and route the condensate line to a safe discharge point away from foundations and walkways. This is also when you'd caulk and touch up the wall cap on the interior side.
Follow the manufacturer's startup sequence, confirm the compressor pulls the expected amp draw with a multimeter, and let the system run through a full heating and cooling cycle before calling it done. Check every flare fitting again after 24 hours — a slow leak often shows up as a faint hiss or oily residue at the joint.
Equip the job
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Interior & Finishing
Answers
A rough planning rule is 20 BTU per square foot at average insulation and an 8 ft ceiling, adjusted up for poor insulation or heavy sun and down for good insulation or shade. A 400 sq ft room at average conditions lands around 8,000 BTU, which rounds up to a 9,000 BTU head. This calculator runs that math per zone and rounds each zone to the nearest standard head size — 9,000, 12,000, 18,000, 24,000, 30,000 or 36,000 BTU — since that's what's actually sold.
A multi-zone condenser runs several heads (typically up to five) off one outdoor unit and one electrical circuit, which usually costs less overall and takes less exterior space. The tradeoff is that all connected heads share the same total capacity, so if one zone is pulling hard the others get less. A dedicated single-zone condenser per head costs more up front but gives every zone full independent capacity — a better fit if one room (like a home gym or a sunroom) runs very differently from the rest.
Mounting the indoor head, running a pre-charged quick-connect line set through a wall sleeve, and setting the outdoor condenser on a pad are all within reach for an experienced DIYer, and pre-charged kits are specifically designed to skip the brazing and vacuum-pump steps. What you generally can't do without an EPA 608 certification is open a sealed refrigerant circuit — so if your run is longer than a standard kit and needs a field-brazed extension, that portion needs a licensed technician even on an otherwise DIY job.
Pre-charged quick-connect kits come in fixed lengths, commonly 16, 25, 35, 50 and 65 feet, and this calculator steps your entered run up to the next available size since that's what you actually buy. Most manufacturers cap a single pre-charged run around 65 to 100 feet one-way; longer runs need extra refrigerant charge and a field connection, which pushes the job past what a quick-connect kit alone can do.
Most condensers run on a dedicated 208/230V circuit sized to the unit's nameplate, plus a disconnect switch mounted within sight of the outdoor unit — both of which are electrical-code requirements in nearly every jurisdiction, and most local codes also require the circuit to be inspected. Unless you're comfortable pulling a permit and running new circuit wiring yourself, that part of the job is usually worth hiring out even on an otherwise DIY install.