Sizing the systems
Window AC cost
A 350 sq ft room takes an 8,000 BTU window unit: about $320 for the unit, $475 bracketed and fitted by a handyman, and about $72 a year to run in a mixed climate. The size comes from the room — the ENERGY STAR chart, corrected for sun, people and a kitchen — and the size decides whether the outlet can carry it: on a circuit shared with the room's lights the code allows a plug-in unit 7.5 A, so a 12,000 BTU unit for 500 sq ft wants its own circuit ($955), and from 15,000 BTU the unit needs a 230 V outlet. This sizes the unit, checks the circuit, and prices window, inverter, through-the-wall and portable side by side for ten summers.
Written and edited by Pablo Ruiz Quintero
Last reviewed 2026-09-24 · Nothing you type leaves your browser
Window AC cost calculator
The room, the unit, and the outlet it plugs into
The room sets the BTU; the BTU sets the price and the amps; the amps decide whether the outlet that is there can carry it.
The space the unit cools, with open doorways.
No adjustment.
600 BTU each past two.
No.
For the running cost. Washington DC, Nashville, Kansas City, Portland
Sits in a double-hung window on a bracket, with side panels. The cheapest cooling per BTU there is.
The room's ordinary outlets and lights on one 15 A circuit. The code allows a plug-in AC half of it: 7.5 A.
Rooms of this size.
A handyman.
Used only to pick a regional labour rate. It stays in your browser.
8,000 BTU window unit, installed
$475
8,000 BTU needed · 115 V, 6.3 A · about $72 a year to run
The outlet can carry it
About 6.3 A, within the 7.5 A the code allows on a regular outlet on a shared circuit. Straight into the wall — not an extension cord or a power strip.
Sized to the room
350 sq ft → 8,000 BTU → a 8,000 unit.
An oversized unit cools the air in minutes and switches off before it has pulled the moisture out, and the room ends up cold and clammy; an undersized one runs all afternoon and never catches up. The ENERGY STAR chart, corrected for sun, people and a kitchen, is the size that does both jobs.
This room, four ways to cool it
Installed, then ten summers of electricity in zone 4.
What it costs
- 8,000 BTU window unit
115 V, about 6.3 A running, CEER 11. Sits in a double-hung window on a bracket, with side panels. The cheapest cooling per BTU there is.$320 - Support bracket
A support bracket under the unit, bearing on the wall, not the sill.$45 - Fitting it
Fitting the unit in the window, the bracket, side panels, foam seal and a lock for the sash.$110
What it costs
National average. One 8,000 BTU window unit for a 350 sq ft room. Not included: a new window, repairs to the sill or siding, or removal of an old unit.
A whole house is sized on the BTU calculator; the ductless alternative that heats as well, on the mini split page.
Worth knowing
- 350 sq ft is 8,000 BTU on the ENERGY STAR chart: 8,000 BTU, so a 8,000 BTU unit. Bigger is not better — an oversized unit cools the air in minutes and shuts off before it has taken the moisture out, and the room feels cold and clammy.
- At about 6.3 A, a 8,000 BTU window unit is within the 7.5 A the code allows on a regular outlet on a shared circuit. Plug it straight into the wall: not into an extension cord or a power strip.
- Running it: about 436 kWh a year in climate zone 4 — 72 dollars at 16.5¢ a kWh — at a CEER of 11. An inverter window unit would run for about $53.
- A handyman fits it for about $110: a bracket bearing on the wall rather than the sill, the side panels, foam in the gap and a lock so the sash cannot be raised from outside. It is a two-person lift over about 10,000 BTU.
On this page — 5 sections
Sized to the room
The short version
- 350 sq ft: 8,000 BTU, $475 installed, $365 fitted yourself.
- About $72 a year to run in a mixed climate.
- On a shared circuit the unit may draw 7.5 A. A 12,000 BTU unit does not fit.
- From 15,000 BTU: a 230 V outlet on its own circuit.
The unit’s price is set by its BTU, and its BTU should be set by the room: 8,000 for 350 square feet on the ENERGY STAR chart, 12,000 for 500, 18,000 for 900 — less for a shaded room, more for a sunny one, a kitchen or a room full of people. The temptation is to buy the next size up. An oversized unit brings the air to temperature in minutes and switches off before it has taken the water out of it, and the room is cold and clammy; the right size runs long enough to dry the air as it cools it.
$325
150 sq ft, 5,000 BTU
Installed
$475
350 sq ft, 8,000 BTU
Installed
$955
500 sq ft, 12,000 BTU
With its own circuit
$1,305
900 sq ft, 18,000 BTU
With a 230 V circuit
U.S. EPA ENERGY STAR, Room air conditioners — sizing chart and combined energy efficiency ratio (CEER) · checked 2026-09-24
Plugged into a circuit that can carry it
A plug-in air conditioner is limited by the circuit it plugs into. The code allows it half of a circuit that also runs the room’s lights and other outlets — 7.5 amps on the usual 15-amp bedroom circuit — and 80% of a circuit it has to itself. An 8,000 BTU unit draws about 6.3 amps and fits; a 12,000 BTU unit draws about 9.5 and does not, which is why the breaker trips the first hot evening someone vacuums. From about 15,000 BTU the units are made for a 230-volt outlet on a double breaker, with a plug that does not fit a household outlet at all.
| Shared bedroom circuit | Its own circuit | |
|---|---|---|
| Allowed for the AC, 15 A circuit | 7.5 A | 12 A |
| 8,000 BTU, about 6.3 A | Fits | Fits |
| 12,000 BTU, about 9.5 A | Does not — $955 with a new circuit | Fits — $605 |
| 18,000 BTU | 230 V only | 230 V only |
| Extension cord | Never | Never |
National Fire Protection Association, NFPA 70, National Electrical Code, Article 440 Part VII — Room air conditioners (440.62) · checked 2026-09-24
Window, inverter, wall or portable
The same cooling can be bought four ways. A plain window unit is the cheapest per BTU there is. An inverter unit, often U-shaped so the window closes into it, costs about half as much again and runs for a third less and far more quietly — the one for a bedroom. A through-the-wall unit leaves the window free and pays for its opening once. A portable unit needs no installing and is the dearest to run.
| 350 sq ft, 8,000 BTU, zone 4 | CEER | Installed | A year | Lasts |
|---|---|---|---|---|
| Window unit | 11 | $475 | $72 | 10 yr |
| Inverter window unit (U-shaped) | 15 | $619 | $53 | 12 yr |
| Through-the-wall unit | 10 | $1,446 | $79 | 12 yr |
| Portable unit | 7 | $734 | $113 | 7 yr |
The portable’s higher draw pushes it past a shared circuit here, so its figure includes a new one.
MaterialsEstimator, Window, through-the-wall and portable air conditioner price survey · checked 2026-09-24
Fitting it
Before it goes in
- The room measured and the size read off the chart, not rounded up.
- What else is on the outlet's breaker, from the panel.
- Past 7.5 A on a shared circuit, or 15,000 BTU, the circuit first.
- A bracket bearing on the wall below the window.
- Two people for anything over about 10,000 BTU.
- A slight tilt outward, side panels, foam in the gap, and a sash lock.
- Plugged straight into the wall — no cord, no strip.
What goes wrong
01Buying the next size up
It cools fast, switches off early, and leaves the room damp.
Instead — The chart's size, corrected for sun, people and a kitchen.
02A 12,000 BTU unit on the bedroom circuit
It draws more than the 7.5 A the code allows on a shared circuit; the breaker trips.
Instead — Its own circuit, or a smaller unit.
03An extension cord
Most are too light for the current and heat up at the plug.
Instead — Straight into a wall outlet that can carry it.
04No bracket
The sill and the sash carry 70 lb leaning outward.
Instead — A bracket bearing on the wall.
05Level, or tilted in
Condensate runs back onto the sill and down the inside wall.
Instead — A slight fall to the outside.
06A portable to save money
It is $113 a year to run the same room a window unit cools for $72.
Instead — A window unit wherever a window allows it.
- 01Measure the roomLength times width, and add any space it opens onto without a door.
- 02Read the chartThe ENERGY STAR size for that area, then 10% for sun or shade, 600 BTU per extra person, 4,000 for a kitchen.
- 03Pick the kindA window unit for most rooms; inverter for bedrooms and bills; through-the-wall to keep the window; portable only where nothing else fits.
- 04Check the circuitFind what else is on the outlet's breaker. Shared, the AC may draw half of it; alone, 80%. From 15,000 BTU it needs 230 V.
- 05Fit it properlyA bracket on the wall, side panels, foam, a sash lock. Two people over about 10,000 BTU.
- 06Price the summersBTU divided by CEER is the watts; the calculator runs them through your climate's cooling hours.
A mini split heats and cools, is quieter and more efficient, and frees the window. The mini split page prices it zone by zone.
For a room lived in all year- BTU
- British thermal units per hour: how much heat the unit removes. Room units run from 5,000 to about 24,000.
- CEER
- Combined energy efficiency ratio: BTU per watt, including standby. The number on the yellow label that sets the bill.
- Inverter unit
- A room AC with a variable-speed compressor that slows down instead of cycling off. Quieter and a third cheaper to run.
- U-shaped window unit
- A window unit shaped so the sash closes into its middle, putting the compressor outside the glass. Much quieter.
- Through-the-wall unit
- A room AC that slides into a sleeve set in an exterior wall, leaving the window free.
- Portable unit
- A room AC on wheels with an exhaust hose to a window kit. Needs no installing; the least efficient.
- Dedicated circuit
- A circuit from the panel that serves only one outlet. A plug-in AC may use 80% of it.
- Shared circuit
- A circuit that also feeds the room's lights and other outlets. A plug-in AC may use only 50% of it.
- 230 V receptacle
- The larger outlet, with differently shaped pins, that big room units plug into, on a double breaker.
- Support bracket
- A bracket under the outside half of a window unit, bearing on the wall, so the sill does not carry the weight.
- Short cycling
- An oversized unit reaching the set temperature fast and switching off before it has dried the air.
Common questions
- How much does a window AC cost?
- About $320 for an 8,000 BTU window unit — the size for a 350 sq ft room — and $475 with a bracket and a handyman to fit it, or $365 if you fit it yourself. Units run from about $170 for 5,000 BTU to $880 for 24,000. An inverter unit of the same size is $619 installed.
- How much does it cost to install a window air conditioner?
- About $110 for a handyman to fit it — the unit set level with a slight tilt out, a bracket on the wall, the side panels, foam and a sash lock — plus about $45 for the bracket. If the outlet cannot carry it, a new circuit is $350 for 115 V or $450 for 230 V. A through-the-wall unit's first opening is about $800 of carpentry.
- What size window AC do I need?
- The ENERGY STAR chart: 5,000 BTU up to 150 sq ft, 6,000 BTU up to 250 sq ft, 7,000 BTU up to 300 sq ft, 8,000 BTU up to 350 sq ft, 9,000 BTU up to 400 sq ft, 10,000 BTU up to 450 sq ft, 12,000 BTU up to 550 sq ft, 14,000 BTU up to 700 sq ft, and up to 24,000 for 1,500 sq ft. Take 10% off for a heavily shaded room, add 10% for a very sunny one, 600 BTU for each regular occupant past two and 4,000 for a kitchen. Bigger is worse: an oversized unit leaves the room cold and damp.
- Does a window AC need its own circuit?
- Often. The code lets a plug-in air conditioner use half of a circuit that also feeds lights and outlets — 7.5 A on a 15 A bedroom circuit — and 80% of one it has to itself. An 8,000 BTU unit at about 6.3 A fits a shared circuit; a 12,000 BTU unit at about 9.5 A does not, which is why the 500 sq ft room is $955 with a new circuit and $605 where one already exists.
- Which window ACs need 230 volts?
- Most units from about 15,000 BTU up, for rooms of 600 sq ft and more. They have a different plug and need a 230 V receptacle on a double breaker — $450 if there is none. The 900 sq ft room here takes an 18,000 BTU unit: $1,305 with the circuit.
- How much does it cost to run a window AC?
- About $72 a year for an 8,000 BTU unit in a mixed climate — 436 kWh at 16.5¢ — and about $144 in a hot one. The watts are the BTU divided by the CEER on the label; an inverter unit at CEER 15 runs the same room for about $53.
- Window, through-the-wall or portable?
- Window: $475 installed, cheapest per BTU. Inverter window: $619, quieter and cheaper to run. Through-the-wall: $1,446 the first time, because an opening is cut and framed, and it keeps the window free. Portable: $734 with no installing, and the dearest to run — it pulls hot air in to replace what it blows out.
- How much is a through-the-wall air conditioner installed?
- About $1,446 for an 8,000 BTU unit in a new opening: the unit and sleeve, and about $800 to cut the wall, put a header in, set the sleeve and finish the siding and drywall. Replacing one in an existing sleeve is the price of the unit.
- Can I install a window AC myself?
- Yes, and most people do: $365 for the unit and a bracket. Two people over about 10,000 BTU, because it is 60 to 80 lb held out of a window. Tilt it slightly outward so condensate drains outside, support it on a bracket rather than the sill, and plug it straight into the wall.
- Is a mini split better than a window unit?
- It is quieter, more efficient, heats as well as cools, and leaves the window free — and it costs several times as much installed. For one room used a few months a year, a window unit is hard to beat; for a room lived in year-round, a mini split pays its way.
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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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