Sizing the systems
Central air conditioner installation cost
A 3.5 ton system at mid efficiency runs about $9,800 installed in ductwork that already exists — roughly $2,800 a ton — and about $17,300 in a house that has no ducts. But a price for central air means nothing until you know what size it is for, and most replacement quotes simply match whatever was there before. Work the size out from your house below, then type the tonnage from your quote and see what the difference is costing you.
Written and edited by Pablo Ruiz Quintero
Last reviewed 2026-09-17 · Nothing you type leaves your browser
What are you cooling?
A price for central air means nothing until you know what size it is for. So this works out the size first, from the house, and then prices it — which is the order a quote should follow and often does not.
Heated and cooled floor area. Leave out the garage and an unconditioned basement.
Above 8 ft there is more air to cool, and the load rises with it.
Washington DC, Nashville, Kansas City, Portland
Two speeds, so it spends most of its life on the low one — which is quieter and, more to the point, actually removes humidity instead of just dropping the temperature.
Insulated walls and attic to the standard of its decade. The baseline these figures assume.
Around 15% of floor area, double glazed.
Some sun on the house for part of the day.
Each person adds about 600 BTU/h. It matters less than everything above it.
Replacing a system in existing ducts and putting one into a house that never had them are different jobs.
Optional, and the most useful box on this page. Type what the contractor wrote and we price the difference.
Used only to pick a regional labour rate. It stays in your browser.
Installed
$9,767
3.5 tons · 42,000 BTU/h · $2,791 a ton
$7,205 to $13,610 depending on who you ask
Screening load 3–3.75 tons, so the nearest size actually manufactured is 3.5 — 4 per cent over the mid load, against the 15 per cent Manual S allows.
Where the money goes
- Equipment and fitting$8,967
- Pad, disconnect and whip$450
- Permit and inspection$350
Only the labour half moves with where you live — the equipment costs much the same in every state, which is why a national “average price” is less useful than it sounds.
What each efficiency tier costs, on this house
Same size, same ducts, same day’s work. Only the box changes.
Shopping list
- Condenser and coil, 3.5 tons, 15.2 SEER2
42,000 BTU/h of cooling · two stage · equivalent to about 15.9 on the pre-2023 SEER scale1 system - Pad, disconnect and whip
Almost always included, occasionally not. Worth reading the quote for.$450 - Permit and inspection
Required nearly everywhere for equipment replacement, and the item most often left off a cheap quote.$350
What it costs
National average. Condenser, evaporator coil, refrigerant lines, commissioning and disposal of the old unit, in ductwork that already exists. Repairs to the existing ducts, asbestos work and any structural change are separate.
$2,791 a ton — the figure to compare quotes on, because a total means nothing without the size beside it. If there are no ducts, price a mini split against this before committing, and see the BTU calculator for the sizing on its own.
Worth knowing
- 3.5 tons — 42,000 BTU/h — at mid efficiency, about $9,767 installed. That is $2,791 a ton, which is the number to compare quotes on: a price for the whole job tells you nothing until you know what size it is for.
- SEER2 is not SEER. The scale changed in January 2023 and it is measured against more static pressure, so the same machine loses about 4.5 per cent of its number without changing at all — 15.2 SEER2 is roughly 15.9 on the old scale. Any comparison with a brochure printed before 2023 is comparing two different measurements, and almost nobody says so.
- This is a screening figure, not a Manual J. A real load calculation works room by room from the actual construction, orientation, glazing and infiltration, and it routinely lands 20 to 30 per cent away from any per-square-foot rule. Use this to judge a quote and to set a budget; get a Manual J before you buy.
On this page — 7 sections
- 01What central air actually costs installed
- 02Why the size is the price, and why the quote in your hand may be wrong
- 03SEER2, and the scale change almost nobody mentions
- 04The cheapest legal unit is not the same in every state
- 05Why two quotes for the same job are thousands apart
- 06Ducts or no ducts, which is two different jobs
- 07What goes wrong
What central air actually costs installed
The short version
- About $9,800 for a 3.5 ton system at mid efficiency in existing ducts — roughly $2,800 a ton.
- Compare per ton, never in total. Two totals for different sizes are not comparable, and quotes rarely lead with the size.
- No ducts doubles it. Add about $7,500, and price a mini split against it before you commit.
- Oversizing costs twice. You pay for tons you do not need, and the house ends up cold and humid.
Every published price for this job is quoted as a range several thousand dollars wide, and the reason is not regional variation. It is that the same phrase — “central air installed” — covers four different jobs.
$8,150
3.5 tons, minimum efficiency
In ducts that already exist
$9,800
3.5 tons, mid efficiency
Two stage — the sensible default
$13,700
3.5 tons, premium
Variable speed, same capacity
$17,300
The same, with new ducts
The ductwork roughly doubles the job
Four prices, one house, one amount of cooling. The capacity is identical in all four and the bill varies by more than double. That is the whole reason a national average price is nearly useless — it is an average across four questions nobody asked you.
installed cost = tons × price per ton × efficiency factor + ductwork + extras
- tons
- from the load, not from the old unit and not from the floor area alone
- price per ton
- about $1,500 to $3,000 installed, of which roughly half is labour
- efficiency factor
- 1.0 at the legal minimum, 1.22 at mid, 1.75 at premium
- extras
- permit, pad, disconnect, line set, thermostat, any electrical work
Worked through — 3.5 tons at $2,100 a ton, times 1.22 for two-stage, is about $8,970, plus $800 of permit and pad — $9,770. Only the labour half of the per-ton figure moves with where you live.
MaterialsEstimator, HVAC equipment and installation price survey · checked 2026-09-16
Why the size is the price, and why the quote in your hand may be wrong
A ton is 12,000 BTU per hour of cooling. It is not a weight — the name comes from how much heat melting a ton of ice absorbs in a day — and it is the unit the entire price is built on.
So the first question is how many. And here is the thing nobody selling you a system has any incentive to say: most replacement quotes simply match whatever was there before, and whatever was there before was probably oversized, because the same shortcut was taken fifteen years ago.
Which is why the most useful box in the calculator above is the optional one: type the tonnage from your quote and it prices the difference. A system a ton larger than the house needs is roughly $2,800 of equipment bought to make the house less comfortable.
What this page cannot do is a Manual J. A real load calculation works room by room from the actual construction, orientation, glazing specification and measured infiltration, and it lands 20 to 30 per cent away from any per-square-foot rule often enough that no web page should pretend otherwise. Use this to judge a quote and to set a budget. Get a Manual J before you sign.
Air Conditioning Contractors of America, ACCA Manual S, Residential Equipment Selection · checked 2026-09-16
SEER2, and the scale change almost nobody mentions
Efficiency is the variable that moves this price most and moves the cooling not at all. Every tier in the calculator delivers the same BTU; they differ in what it costs to run and what it costs to buy.
And there is a trap in comparing them. SEER2 replaced SEER in January 2023, and they are not the same scale. The new test is run at higher external static pressure — closer to what real ductwork imposes — so an unchanged machine scores about 4.5 per cent lower. A 15.2 SEER2 unit is roughly 15.9 on the old scale. If you are weighing a quote against a brochure or a review written before 2023, you are comparing two different measurements, and the newer one will look worse for no reason.
| Tier | SEER2 | Old SEER | Price factor | What you are buying |
|---|---|---|---|---|
| Minimum efficiency | 13.4 | 14.0 | ×1 | The cheapest unit that is legal where you live, and in the South the legal minimum is higher than this. One speed: it is either running flat out or it is off. |
| Mid efficiency | 15.2 | 15.9 | ×1.22 | Two speeds, so it spends most of its life on the low one — which is quieter and, more to the point, actually removes humidity instead of just dropping the temperature. |
| High efficiency | 17 | 17.8 | ×1.45 | Where the payback arithmetic starts to get hard outside the hot South. Worth checking against your own cooling hours before you sign. |
| Premium, variable speed | 20 | 20.9 | ×1.75 | Modulates continuously instead of cycling. The comfort difference is real and the energy payback rarely is; buy it for the humidity control and the silence, not for the bill. |
US Department of Energy, Central air conditioner and heat pump energy conservation standards (SEER2 / HSPF2, effective January 2023) · checked 2026-09-17
The cheapest legal unit is not the same in every state
Since 2023 the federal minimum efficiency for a split system under 45,000 BTU differs by region: 13.4 SEER2 in the North and 14.3 in the South and Southwest. It is one of very few places in construction where what you are allowed to buy depends on your address.
Two practical consequences. First, a price you read from someone in another state may be for equipment you cannot legally install. Second, in the South the rule is enforced at the point of installation rather than at the point of sale, which is why remaining northern-spec stock occasionally turns up in a cheap southern quote.
That is not automatically a bad buy and it is not automatically a scam. But it is a thing to know you are being offered, and the calculator flags it when the tier you have picked is below the minimum for the zone you have chosen.
US Department of Energy, Central air conditioner and heat pump energy conservation standards (SEER2 / HSPF2, effective January 2023) · checked 2026-09-17
Why two quotes for the same job are thousands apart
Three reasons, in this order of size. They are for different tonnages. They are for different efficiency tiers. And one of them has left something off.
Ask every contractor for these, in writing
- Tonnage, and what load calculation it came from. 'The same as the old one' is not a load calculation.
- SEER2 rating, and the AHRI certificate number for the matched combination — the rating only applies to the certified pair.
- Whether the indoor evaporator coil is being replaced. A new condenser on an old coil loses efficiency and usually the warranty.
- Whether the refrigerant line set is being reused, flushed or replaced.
- Whether the permit and inspection are included. This is the item most often missing from the cheapest quote.
- Pad, disconnect and whip — almost always included, occasionally not.
- Any electrical work: a larger unit may need a bigger breaker, and an old panel may have no room.
- What happens to the old unit, and whether refrigerant recovery and disposal are in the price.
- The labour warranty separately from the manufacturer's parts warranty. They are not the same and the second is worthless without the first.
| Item | Typical | Why it moves |
|---|---|---|
| New refrigerant line set | $600–2,000 | R-410A and R-454B lines are not interchangeable with old R-22 pipe, and a system changing refrigerant needs the lines flushed or replaced. |
| Pad, disconnect and whip | $250–800 | Almost always included, occasionally not. Worth reading the quote for. |
| Smart thermostat | $150–500 | A variable speed system needs a communicating thermostat and will not modulate without one. |
| Permit and inspection | $150–900 | Required nearly everywhere for equipment replacement, and the item most often left off a cheap quote. |
| Electrical upgrade | $400–2,200 | A larger unit than the old one may need a bigger breaker and cable, and an old panel may not have room. |
Ducts or no ducts, which is two different jobs
Replacing a system in ductwork that already exists is a one-day job for two people. Putting central air into a house that has never had it is a week, and it involves carpentry, ceilings and losing a cupboard.
Both are sold as “central air installation” and the published price ranges average the two. That single ambiguity is most of the width you see quoted anywhere.
| Central air in new ductwork | Ductless mini split | |
|---|---|---|
| This house, installed | About $17,300 | Depends on zones — usually less |
| Building work | Trunks, returns, a dropped ceiling or a lost closet | A 3 in hole per indoor head |
| Zoning | One thermostat unless you pay for dampers | Every head is its own zone, included |
| Efficiency loss in ducts | Typically 20–30% in an unconditioned attic | None — there are no ducts |
| Appearance indoors | Registers only | A visible head on the wall in each room |
| If ducts already exist | Much the cheaper answer | Rarely worth it |
What goes wrong
01Matching the size of the old unit
It is the default on nearly every replacement quote, and it assumes the last installer did a load calculation. Usually nobody did — the shortcut has been repeating itself for decades, and the house may also have new windows and insulation since.
Instead — Screen the load from the house as it is now, then ask for a Manual J. If the honest answer is a size smaller, that is money back and a more comfortable house.
02Buying bigger 'to be safe'
Cooling capacity is not a safety margin. A bigger unit hits the setpoint before it has removed any humidity, leaves the house cold and clammy, and short-cycles its compressor to an early death.
Instead — Size to the load and let Manual S's 15 per cent take care of the rounding. If you want margin, spend it on two stages, which run longer at lower output.
03Comparing quote totals
Two totals for different tonnages and different efficiency tiers are not comparable at all, and the front page of a quote rarely says either.
Instead — Convert every quote to dollars per ton at a stated SEER2. The spread usually collapses, and what is left is the itemisation.
04Comparing a SEER2 rating against a SEER one
They are different tests. The same machine scores about 4.5 per cent lower under SEER2, so anything written before 2023 flatters itself against a current quote.
Instead — Check which scale each number is on before comparing. If a brochure just says 'SEER', it is almost certainly the old scale.
05New condenser on the old indoor coil
Efficiency ratings apply to a matched, AHRI-certified pair. A mismatched system delivers well under its label and most manufacturers will not honour the warranty on it.
Instead — Replace the coil at the same time and ask for the AHRI certificate number. It is also the cheapest moment to do it, because the system is already open.
06Assuming the permit is included
Equipment replacement needs a permit nearly everywhere, and it is the single item most often missing from the cheapest quote. An unpermitted install can surface at resale.
Instead — Ask explicitly, in writing, and treat a contractor who prefers to skip it as having told you something important.
07Paying for high efficiency in a cold climate
The payback depends on cooling hours. The same upgrade that repays itself in Houston will not in Minneapolis, because the machine barely runs.
Instead — Take the mid tier for the two-stage humidity control, which is a comfort benefit you get everywhere, and put the difference into insulation or duct sealing.
08Ignoring the ducts
Ductwork in an unconditioned attic loses a fifth to a third of the cooling it carries. You buy a bigger system to overcome a problem that costs far less to fix directly.
Instead — Have the ducts checked and sealed before the equipment is sized. It can drop you a half-ton size, which pays for a good part of the sealing.
- 01Measure the conditioned areaHeated and cooled floor area only. Leave out the garage and any unconditioned basement, because you are not paying to cool them.
- 02Work out the load before looking at any priceClimate zone, insulation, glazing and shading. A price per ton is meaningless until you know how many tons.
- 03Check the size against what is there nowIf the old unit was oversized — most were — matching it repeats the mistake for another fifteen years.
- 04Pick an efficiency tier on your own climateThe payback on high efficiency depends on cooling hours. The same upgrade is sensible in Houston and never repays in Minneapolis.
- 05Check the legal minimum where you liveThe South and Southwest require more than the North, so the cheapest legal unit is not the same everywhere.
- 06Add the items quotes leave offPermit, pad, disconnect, line set and any electrical work. These are what make two quotes for the same equipment differ by thousands.
- 07Compare quotes per ton, not in totalTwo totals are not comparable if they are for different sizes, and they usually are.
The BTU calculator does the sizing on its own, for cooling and heating together, without the pricing — including what a furnace has to deliver alongside it.
Just need the size?- Ton
- A unit of cooling capacity, not weight: 12,000 BTU per hour. It comes from how much heat melting a ton of ice absorbs in a day, which is why the number looks arbitrary.
- SEER2
- Seasonal Energy Efficiency Ratio, 2023 revision. Cooling delivered over a season divided by the electricity to deliver it. Higher is cheaper to run and more expensive to buy.
- SEER
- The pre-2023 scale. It is not interchangeable with SEER2 — the new test uses higher external static pressure, so the same machine scores about 4.5 per cent lower without changing at all.
- Manual J
- The room-by-room load calculation that says how much cooling a house actually needs. It is the only honest basis for sizing, and it is skipped on most replacements.
- Manual S
- The rule for choosing equipment against that load. It allows exceeding the calculated load by up to 15 per cent — above that is not margin, it is a design fault.
- Condenser
- The outdoor unit: compressor, coil and fan. It is the expensive half and the one people mean when they say the air conditioner died.
- Evaporator coil
- The indoor coil, usually sitting on the furnace. It has to be matched to the condenser — a new condenser on an old coil loses much of the efficiency you paid for, and often the warranty.
- Line set
- The pair of insulated copper lines between outdoor and indoor units. R-410A and the newer R-454B will not run in pipe that carried R-22 without flushing or replacement.
- Short cycling
- Switching on and off too frequently. It is what an oversized unit does, and it wears the compressor while leaving the house humid.
- Latent capacity
- The part of the work that removes moisture rather than temperature. It only happens while the unit is running, which is exactly what an oversized one does not do for long.
- Single, two stage, variable speed
- How many speeds the compressor has. One speed is all or nothing; variable speed modulates continuously and runs longer at lower output, which is what actually dries the air.
- AHRI matched
- A combination of outdoor unit, indoor coil and air handler certified together. The rated efficiency only applies to the matched set, so a mixed system does not deliver its label.
Common questions
- How much does it cost to install central air conditioning?
- About $9,800 for a 3.5 ton system at mid efficiency in ductwork that already exists — roughly $2,800 a ton, in a range from about $7,000 to $14,000 depending on the contractor and the region. Putting central air into a house that has never had ducts is a different job: add about $7,500 for the ductwork, which roughly doubles it.
- What size air conditioner do I need for my house?
- An 1,800 ft² house in the mixed middle of the country screens at about 3.5 tons, and the same house in Houston at 4. But square footage alone is the weakest possible basis: insulation, glazing and shading move the answer by a quarter each way. The calculator above takes all four, and it still only produces a range to judge a quote against — the number you buy on should come from a Manual J.
- How much does central air cost per ton?
- Around $2,300 a ton at minimum efficiency and $2,800 at mid, installed in existing ducts. Per-ton is the figure to compare quotes on, because two totals for different sizes are not comparable and contractors rarely put the size on the front page.
- Is a higher SEER2 worth the money?
- Going from 13.4 to 20 SEER2 adds about $5,500 to a 3.5 ton job whose cooling capacity has not changed by a single BTU. Whether that returns depends entirely on cooling hours: in the hot South it can pay back inside its life, and in the North it will not. Buy the mid tier for the humidity control that two stages give you, which is a comfort argument rather than an energy one and a much better one.
- What is the difference between SEER and SEER2?
- SEER2 replaced SEER in January 2023 and they are different measurements, not different numbers for the same thing. The new test runs at higher external static pressure — closer to real ductwork — so the same machine scores about 4.5 per cent lower. A 15.2 SEER2 unit is roughly 15.9 on the old scale. Any comparison against a pre-2023 brochure is comparing two different tests.
- What is the minimum SEER2 I am allowed to install?
- 13.4 SEER2 in the North and 14.3 in the South and Southwest, for split systems under 45,000 BTU. It is one of the few places in construction where the cheapest thing you can legally buy depends on your address, and it catches people comparing a quote from out of state.
- Is it bad to get an air conditioner that is too big?
- Yes, and worse than getting one slightly too small. A big unit hits the thermostat setting quickly and switches off, and moisture removal only happens while it is running — so the house ends up cold and clammy. It also short-cycles, which wears the compressor. Manual S allows equipment to exceed the calculated load by 15 per cent; beyond that it is a fault, not a safety margin.
- Why are two quotes for the same job thousands apart?
- Usually three things, in this order: they are for different sizes, they are for different efficiency tiers, and one of them has left out the permit, the pad, the line set or the electrical work. Ask each contractor for tonnage, SEER2, and an itemised list including the permit — permit and inspection is the item most often missing from the cheap one.
- Do I have to replace the indoor coil too?
- Almost always, and a quote that does not is worth questioning. The rated efficiency applies to a matched pair certified together; a new condenser on a mismatched old coil delivers well under its label, and most manufacturers will not honour the warranty. It is also the one moment when replacing the coil is cheap, because the system is already open.
- How long does a central air conditioner last?
- Fifteen to twenty years in a temperate climate and closer to twelve on the Gulf coast, where it runs most of the year. An oversized unit lands at the bottom of that range because short cycling is what wears a compressor, so the sizing decision is also a lifespan decision.
- Is a heat pump cheaper than central air?
- The equipment is more expensive per ton, but it heats as well as cools, so it replaces two machines with one. If the furnace is also near the end of its life the comparison changes completely, and in most of the country a modern heat pump now heats well below freezing. Price both before deciding, on the same house.
- Can I install central air in a house with no ductwork?
- Yes, and it roughly doubles the price — about $7,500 for the ducts on top of the system. It also costs space: trunks and returns have to run somewhere, usually through closets or a dropped ceiling. In a house with no ducts, price a ductless mini split against it first; it is frequently both cheaper and less invasive.
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About the author
Pablo Ruiz Quintero — Editor
Editor of MaterialsEstimator. Decides which documents count as a source, what every default value is, and where the line sits between what the reader parses and what the engines compute.
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