Adding a second AC unit to a house typically costs $3,500-$15,000, depending on system type, cooling capacity, ductwork, and electrical work. A ductless mini-split is often less expensive when cooling a separate room or addition, while a second central system can cost more if it needs new ducts.
| Item | Low | Average | High | Notes |
|---|---|---|---|---|
| Second central AC system | $6,000 | $10,000 | $16,000 | New equipment and typical installation |
| Single-zone mini-split | $3,500 | $5,500 | $8,500 | One indoor head and outdoor unit |
| Multi-zone mini-split | $7,000 | $11,000 | $17,000 | Multiple rooms or indoor heads |
| New ductwork, if needed | $2,000 | $4,500 | $8,000 | Varies with access and run length |
What a second AC system costs by type
A second central air-conditioning system generally costs $6,000-$16,000 installed, with a typical project around $10,000. That range assumes a 2- to 3-ton unit, standard-efficiency equipment, a straightforward equipment location, and limited duct modifications. New duct runs, panel upgrades, or difficult access can push the total higher.
A single-zone mini-split commonly costs $3,500-$8,500, while a multi-zone system often runs $7,000-$17,000. The mini-split price generally includes equipment, basic installation, and a standard refrigerant line run. For a small addition without ducts, a mini-split is often the lower-cost way to add independent cooling.
Assumptions: Typical U.S. contractor pricing, standard equipment, normal access, and no major structural or electrical upgrades.
Where the central AC installation quote goes
For a typical second central system costing about $10,000, equipment and labor make up most of the quote. Ask whether the estimate includes a load calculation, thermostat, condensate drainage, startup testing, and disposal of any removed equipment.
| Quote item | Typical cost | Pricing basis | What changes it |
|---|---|---|---|
| Condenser and indoor coil | $2,500-$5,500 | Equipment package | Capacity, efficiency, and brand tier |
| Installation labor | $1,800-$4,000 | About $75-$150 per hour | Access, crew size, and system complexity |
| Ductwork and air balancing | $500-$4,500 | About $15-$35 per linear ft | New runs, returns, and attic access |
| Electrical, drain, thermostat | $400-$1,800 | Per project | Panel capacity and wiring distance |
| Permit and disposal | $150-$700 | Per project | Local fees and old-unit removal |
Separate labor and materials in the written quote so added wiring, ductwork, or permit charges are visible.
How tonnage, duct length, and electrical capacity change the price
Capacity should be based on a room-by-room load calculation, not simply the size of the existing unit. A roughly 1.5-ton system may suit a modest, well-insulated addition, while a 3-ton system may be needed for a larger or sun-exposed area. Oversizing can increase equipment cost and contribute to short cycling and uneven humidity.
Adding more than 20-30 feet of duct from the air handler, or serving multiple rooms with long branches, can add roughly $500-$2,500 or more. A home with a full electrical panel may also need a new circuit or panel work, adding $500-$3,000. Confirm that the quote includes both the cooling load and the home’s electrical capacity.
How long installation takes and what labor covers
A straightforward mini-split installation may take 6-10 hours; a central system with limited duct changes often takes 1-2 days. Projects that require new duct trunks, a platform, extensive wiring, or difficult attic work may take 2-4 days. Labor pricing reflects setup, refrigerant-line work, drainage, electrical connections, commissioning, and cleanup.
Ask whether the crew will test airflow and refrigerant charge, and whether the quoted labor includes inspection corrections. Unexpected access or code work can add both labor hours and a return visit.
Central air versus ductless cooling for a new zone
A second central system is useful when several rooms need cooling and a separate duct network can be installed economically. It can cost $6,000-$16,000 before major duct expansion. A ductless system avoids new supply ducts, but each indoor head and the required line-set route affect the quote; extra indoor heads often add $1,500-$3,500 each.
Extending the existing system may appear cheaper, but it can leave the original equipment undersized or deliver weak airflow. A contractor should check capacity and duct static pressure before quoting an extension. Compare a properly sized independent system with a verified extension, not just the lowest initial number.
How location shifts second-unit AC prices
Quotes in high-cost coastal metros and dense cities can be 10%-25% above a national middle estimate because of labor rates, permits, and access constraints. Smaller markets may come in 5%-15% below that baseline, although limited contractor availability or long travel distances can erase the difference.
Seasonal demand also matters. Emergency work during a heat wave can carry a 10%-20% premium, while scheduling a nonurgent installation during a contractor’s slower period may produce more flexible pricing. Local permit charges vary; confirm whether the contractor obtains the permit and includes its fee.
Which choices can lower the second-unit AC bill
Keep the project focused on the rooms that need separate cooling, and avoid adding unused zones or premium controls unless they solve a specific problem. Get at least three itemized bids using the same capacity assumptions, efficiency level, and scope. Compare warranties, startup testing, and duct or electrical allowances as well as the total.
Prepare clear access to the attic, equipment pad, and electrical panel, and ask whether minor site work can be completed before installation. Do not skip a load calculation or required permits to cut the estimate. Reducing unnecessary duct runs and equipment upgrades is safer than reducing system capacity or installation quality.