Central Air Installation Cost for a Home Without Ductwork

Updated September 2026 · Home Project Resources

In a house with no ducts, the central air installation cost is mostly carpentry, sheet metal and drywall, not air conditioning equipment. The condenser and the air handler are the predictable part. Finding a legal, sane path for supply and return air through a finished house, framing the chases, cutting the openings and putting the walls back is where the hours go, and it is why two bids on the same house can be so far apart.

That gives you a clear job before you talk to anyone. Walk the house and find the air paths. Stacked closets, a chase behind a plumbing wall, an unfinished basement ceiling, a full attic over the top floor, a knee wall in a cape. Whatever paths exist decide which of the three retrofit routes below is realistic, and the route decides the number.

Updated September 2026

A note on numbers. No dollar figures on this page, on purpose. Equipment, sheet metal labor, drywall and finish carpentry are priced completely differently in every market, and in a retrofit the scope varies more than anything else does. What you get instead is the three routes, the load calculation you should insist on, the complete line item list, and the mid job surprises that are legitimate versus the ones that are not.

The wall repair is a real line item, and it is the one most often left out. Chases, soffits, register openings and access panels all mean cut drywall or cut plaster. Total up the openings and get your sheets, tape and compound from our free Drywall Calculator, then make every bidder state in writing whether patch, texture and paint are theirs or yours.

Three ways to get cool air through a house with no ducts

Nobody route is right for every house. The wrong answer is picking the route by preference and then forcing the house to accept it. A contractor who walks in and says "mini splits" or "we can duct anything" before opening a single closet door has not looked.

There is a hybrid worth knowing about too: a small ducted air handler in an attic or a dropped ceiling serving just the bedrooms, plus a single ducted or ductless unit for the main living area. In a two story house with a finished basement and no attic, that combination often beats fighting the whole house with one system.

What a central air installation cost estimate covers when there are no ducts

Line by line, here is what a complete quote includes. Print it and check it against every bid.

1. Load calculation, done room by room, not a rule of thumb off square footage.
2. Equipment selection matched to that load: condenser, coil or air handler, model numbers and capacity.
3. Duct design, meaning trunk and branch sizes, the CFM going to each room, and the return path.
4. Chase and soffit framing, listed by location, so you know exactly where the house changes shape.
5. Duct material and insulation, with the R value of any duct in an unconditioned attic stated.
6. Duct sealing with mastic or approved tape, and ideally a leakage test result at the end.
7. Supply registers and return grilles, counted, with sizes.
8. Refrigerant line set, length, routing, and how it penetrates the building envelope.
9. Condensate, meaning a primary drain, a secondary drain or pan with a float switch, and a pump if gravity does not work.
10. Electrical, meaning the disconnect, the whip, the circuit, and an honest answer about whether the panel has capacity.
11. Thermostat and controls, including any zoning dampers and their wiring.
12. Structural work, since notching or drilling joists has rules and sometimes needs a header or a support.
13. Drywall and plaster repair, texture and paint, or a clear exclusion.
14. Permit, inspection and load calc submission, plus who pulls it.
15. Startup and commissioning: refrigerant charge verified by weight, static pressure measured, airflow balanced room by room.
16. Warranty, split into equipment, parts and labor with each term written out.

Line 15 is the one that separates a system that works from a system that merely runs. A retrofit duct system almost always has higher static pressure than a new build system, and a contractor who does not measure it hands you a system that cannot deliver its rated capacity.

Insist on a Manual J, not a rule of thumb

The old "one ton per 500 square feet" habit produces oversized systems, and oversizing is worse than undersizing in a humid climate. An oversized unit satisfies the thermostat fast, shuts off before it has removed moisture, and leaves you with a cold clammy house that short cycles all summer.

A proper load calculation, called Manual J, uses the actual house: orientation, window area and type, wall and attic insulation levels, infiltration, ceiling heights and the number of people. Then Manual S selects equipment that matches the load, and Manual D sizes the ducts to deliver the required airflow to each room.

Three numbers to ask for by name:

• Total sensible and latent load, in BTU per hour, for cooling.
• Room by room CFM, so you can see whether the back bedroom is actually getting air.
• Design external static pressure, and the measured value at commissioning.

For airflow, a conventional system is designed around roughly 400 CFM per ton. High velocity systems intentionally run less air at a colder supply temperature, in the neighborhood of 250 to 350 CFM per ton, which is exactly why their tubing can be so small. Different design, different physics, both valid.

While the house is being evaluated, get the attic checked. Adding insulation before sizing can drop the load enough to change the equipment selection, and it keeps paying afterward. See how to insulate an attic for what that job involves.

Worked example: a 1,600 square foot two story with radiators

This is the classic case. Built in 1948, hot water radiators, plaster walls, a full unfinished basement, and a low attic over the second floor with about 30 inches of clearance at the peak.

Step 1. Walk the paths. The basement ceiling is open, so first floor supplies are easy from below. The attic is tight but accessible, so second floor supplies can drop from above through small chases in closet corners. There is no chase connecting basement to attic except a boxed in chimney and a plumbing wall.

Step 2. Load calculation. The Manual J comes back at roughly 26,000 BTU per hour of sensible cooling load, which lands on a 2.5 ton system rather than the 3.5 tons the square footage rule of thumb would have suggested.

Step 3. Pick the route. Two options make sense. One air handler in the basement serving the first floor, one in the attic serving the second, sized separately. Or a single high velocity system with the air handler in the attic and tubing fished down interior walls.

Step 4. Count the openings. Two systems means two condensers on pads, two line sets, two condensate paths, two electrical circuits and two thermostats, but almost no new chases. The high velocity route means one system, but about 16 to 20 small outlets at roughly 40 CFM each, and a fished tube to every one of them.

Step 5. Count the returns. This is where retrofits fail. A 2.5 ton system moving 1,000 CFM needs return grilles large enough that face velocity stays low, or the whole house whistles and the coil ices. Two central returns, one per floor, in a hallway ceiling, usually beats trying to return through a single undersized grille.

Step 6. Price the repair scope separately. Twelve register openings, two return grille openings, two closet chases and four plaster patches where tubing crossed a wall. That is a real drywall and plaster day or two, and in a plaster house it is skilled work, not filler.

Step 7. Decide. In this house the two system approach usually wins on comfort and on repair scope, and the high velocity approach usually wins on preserving plaster and trim. Both are legitimate. Ask each bidder to price the same house both ways if they do both.

Where the ducts can actually go

Search for these paths before anyone quotes. If none of them exist, you have your answer already.

• Stacked closets, one above the other, are the best retrofit chase in any house.
• Boxed in soffits along a hallway ceiling can carry a trunk without touching any room.
• Unfinished basement ceilings feed first floor floor registers with almost no repair work.
• Full attics feed top floor ceiling registers the same way.
• Knee wall spaces in capes and story and a half houses carry ducts, but only if the duct stays inside the insulated envelope or gets serious insulation of its own.
• An abandoned chimney chase is sometimes usable, subject to code, condition and whether anything is still venting into it.
• Furred out corners in a bedroom, framed and drywalled, are the last resort. They work, and they are visible forever.

Anything running through unconditioned space needs insulated duct and airtight sealing, or you cool the attic and pay for the privilege. Duct leakage in an attic is one of the most expensive invisible defects in a retrofit.

What legitimately drives the estimate up mid job

The real ones:

• The planned chase turns out to contain a stack, wiring or a structural post.
• Knob and tube wiring shows up in a wall the tubing has to cross, and it has to be dealt with first.
• Old pipe insulation or old flooring adhesive requires testing before demolition in a house of that vintage.
• The electrical panel has no spare capacity, so a subpanel or a service upgrade gets added.
• Plaster keys break well beyond the cut line, so a small patch becomes a whole ceiling.
• The load calculation comes back higher than the walkthrough guess because of a big west facing window wall.
• Balancing shows one bedroom starved, so a branch gets resized after the fact.

And the ones to challenge: a change order for "extra duct" on a job that was quoted without a duct design, any request to skip the permit, and a proposal to reuse an old gravity furnace's octopus ductwork without testing whether it can carry cooling airflow. Old gravity ducts were sized for slow warm air, not for cooling CFM, and reusing them is a case by case engineering question, not a freebie.

If a bidder wants to sell you a full system replacement conversation instead, read HVAC replacement first so you know what that scope should look like. And if you are weighing heating and cooling together, heat pump installation is worth pricing at the same time, because the duct work is identical and doing it once is far cheaper than doing it twice.

Comparing bids on a ductless house

If one bid is far below the others, go down the column and find the empty cells. In retrofits, the missing item is almost always the wall repair or the return air plan, and both of them come back to you later either as a bill or as a system that never quite works.

Once the system is in, the maintenance and failure patterns are the same as any other central system. Our guide to air conditioning repair covers what breaks, what a real diagnosis measures, and what belongs on a repair invoice. For a straight equipment swap in a house that already has ducts, see air conditioner installation instead, since that is a different job with a different cost structure.

Frequently asked questions

Is it cheaper to add central air or install mini splits in a house with no ducts?

It depends entirely on the duct paths. If the house has a full attic, an open basement or stacked closets, a ducted system is often competitive and gives you one thermostat and a single filter. If there is no path at all, mini splits avoid the framing and repair scope, which is usually the bigger half of a retrofit.

Can I add central air to a house with radiators and keep the radiators?

Yes, and it is common. The cooling system is completely separate: its own air handler, ducts, condenser and thermostat, with the boiler and radiators left alone. It does mean two systems to maintain, and it means the duct work has to find paths that were never planned for it.

Do I need a permit to add central air?

Almost always, because it involves refrigerant lines, electrical work and often structural modifications for chases. Many jurisdictions also want the load calculation submitted with the application. Check your local rules early with our guide on whether you need a permit, since permit requirements can affect which route is practical.

How many tons of air conditioning do I need?

You need whatever the Manual J says, which in an older, leakier house with big windows may be more than the square footage rule suggests, and in a tightened, well insulated house is usually less. Ask for the report. Oversizing causes short cycling and poor humidity control, so bigger is not safer.

Will retrofit ductwork ruin my ceilings?

It changes them somewhere, and honest planning means deciding where. Soffits in a hallway, a furred corner in a closet or a dropped section in a stairwell are the usual sacrifices. High velocity systems minimize this because their tubing fits in existing cavities, which is exactly why old house owners choose them.

How long does a no duct retrofit take?

Plan on multiple days to a couple of weeks depending on route and repair scope. Equipment set and line sets go fast. Fishing tubing, framing chases, cutting openings and then patching, texturing and painting is the part that stretches, especially in plaster. For the patch work itself, how to patch drywall covers what good repair looks like so you can judge the finish.

What is the single most overlooked item in these quotes?

Return air. Supply registers get counted carefully and returns get treated as an afterthought, and then the system runs at high static pressure, moves less air than it was designed for, and freezes the coil on the hottest afternoon of the year. Ask for the return grille sizes and locations in writing, every time.