A quick tonnage estimate from floor area, climate and insulation. Use it to check a quote, not to buy equipment.
3.0 tons2,000 sq ft, mixed climate, average insulation18 BTU per sq ft × 2,000 sq ft × 1.00, rounded to the nearest half ton. Two same-size houses on one street can differ by a full ton.
The short answer
A 2,000 sq ft house in a mixed climate with average insulation needs about 3 tons of cooling (36,000 BTU per hour), with a likely range of 2.5 to 3.5 tons.
Use this to check a quote. The real answer comes from an ACCA Manual J load calculation. If a contractor quotes 5 tons and this says 3, ask why before you sign.
Check the size
Floor area, climate and insulation. Use the result to check a quote. Nothing is emailed.
This is not a Manual J. Do not buy equipment on it. HyreHVAC does not size or install systems. Ceiling height, glass and orientation are invisible here.
Why do the square-foot rule and Manual J disagree?
How far each input moves the calculated load, against a mixed-climate, average-insulation baseline.HyreHVAC calculation from this tool’s own numbers.
The square-foot rule uses one input: floor area. ACCA Manual J uses dozens, including which way the house faces, windows, shade, insulation, air leaks, ceiling height, duct location, and the people and appliances inside.
So two houses of the same size on the same street can land a full ton apart. The rule of thumb cannot see why. That is why it gives a range, not an answer.
HyreHVAC analysis: look at the insulation (envelope) setting in the calculator. Moving it from “poor” to “excellent” changes the result by 45%. That is more than the whole gap between the hottest and coldest US climate zones.
If one dropdown can outweigh all of climate, a one-input method cannot size a system. That is the case for Manual J, made from inside the rule of thumb.
How many square feet does each AC size cover?
Tons
BTU per hour
Floor area by rule of thumb, mixed climate
Typical home
1.5
18,000
about 1,000 sq ft
Apartment, small bungalow, or one zone
2.0
24,000
about 1,330 sq ft
Small to mid-size house
2.5
30,000
about 1,670 sq ft
Mid-size house
3.0
36,000
about 2,000 sq ft
The most common home size
3.5
42,000
about 2,330 sq ft
Larger house, or an average one in a hot climate
4.0
48,000
about 2,670 sq ft
Large house
5.0
60,000
about 3,330 sq ft
Large house, and about the biggest single home system
One ton is 12,000 BTU per hour. Floor areas assume 18 BTU per square foot and average insulation.
Above about 5 tons, most homes do better with two systems or zoning than with one very large unit. One big system for the whole house is also the setup most likely to short-cycle.
What goes wrong when an AC is too big?
Problem
Why it happens
What you notice
Damp air
The AC hits the set temperature and shuts off before it runs long enough to pull out moisture
The house feels cold and clammy. The most common complaint, and the hardest to fix later
Starting is the hardest thing a compressor does, and short cycling means more starts
It fails sooner than expected
Higher price
More tons cost more, and may need duct or electrical upgrades a right-size unit would not
You paid more for a worse result
No gain on the hottest day
Extra capacity does nothing once the heat load is met
The margin you paid for is never used
Why “go bigger to be safe” is the wrong instinct for cooling: the extra margin works against you.
Between 31% and 48% of installed systems are oversized, per DOE’s review of field studies. Slightly undersized is the smaller mistake. It runs longer, dries the air better, and falls short only on the hottest days.
How does your climate change the answer?
Cooling degree days by state, 2020: weighted by population, from each surveyed household’s own location.HyreHVAC calculation from EIA RECS 2020 microdata.
The climate setting squeezes a huge range into five choices. The map shows the real spread in cooling degree days: single digits in Alaska, over 4,000 on the Gulf Coast and in Hawaii.
That matters in two ways. A BTU-per-square-foot figure from a national article may be several zones away from yours. And 82.0% of US homes have ducts, but that share varies a lot by region.
In the Pacific states, where homes rarely needed cooling, many houses have no ducts at all. There the question is which kind of system, not what size.
HyreHVAC analysis: if your house has no ducts, this calculator may not fit your question. Ductless mini-splits sized room by room are usually the realistic option. See the best mini-splits.
What should you do with this number?
Use it to test a quote, not to buy equipment
If a contractor quotes 5 tons and this says 3, talk about that gap before you sign. If the quote is within half a ton, this tool has told you all it can.
Ask for the Manual J report
A load calculation is a document. If one was done, it can be printed. “We sized it like the old one” is a common answer, and it copies the last installer’s mistake.
Check that the ducts were measured too
Leaky ducts are the most common fault DOE found: 90-100% of systems tested needed sealing or repair. A right-size AC on leaky ducts still underperforms.
Do not size from the old unit
The old unit may have been too big. The house may have new insulation or windows since. Copying the old size locks in the mistake for another 15 to 20 years.
This tool ignores ceiling height
It works per square foot of floor. A room with a vaulted ceiling holds more air and usually more glass than its floor area suggests.
It also ignores which way the house faces
West-facing windows drive the afternoon peak harder than almost anything else. Manual J counts them. A square-foot rule cannot.
The part most sizing advice leaves out
Is Manual J enough to size an AC?
No. Manual J is the first of three ACCA manuals. The other two, Manual S and Manual D, are where a correct load still turns into the wrong system.
ACCA publishes Manual J: Residential Load Calculation, 8th edition, with the ANSI designation ANSI/ACCA 2 Manual J - 2016. ACCA states: “A proper load calculation, performed in accordance with the Manual J 8th Edition procedure, is required by national building codes and most state and local jurisdictions.”
Manual J establishes the heating and cooling load of the dwelling. It answers one question: how much heat this house gains and loses on a typical hot or cold design day where you live. It names no equipment and says nothing about ducts.
Manual S: Residential Equipment Selection selects equipment against the Manual J load at the design conditions. This step turns a load in BTU per hour into a model number. It takes judgment, because the load almost never lands on a size you can buy.
Manual D: Residential Duct Systems sizes the duct system to deliver the airflow the equipment needs. A unit rated to move a set amount of air will not do it through ducts designed for something else.
HyreHVAC analysis: homeowners ask for the Manual J because it is a report they can hold. Nobody can see whether Manual S was done.
Manual D is the one almost nobody asks about, yet duct problems showed up in 90-100% of systems DOE’s review covered. If you ask for one extra thing, ask about the ducts.
Building codes are adopted locally. Whether your town requires a Manual J, and in what form, is a question for your local building department.
What happens when a sizing step is skipped?
The right-hand column is the useful one. It shows what you inherit when a step was skipped, often noticed years later.
Document
What it produces
How you can tell it was done
What its absence means
Manual JANSI/ACCA 2 Manual J - 2016
A heating and a cooling load for this house, in BTU per hour, at the design conditions for its location
A report of several pages that names the design temperatures and lists room-by-room assumptions
The size came from floor area, the old unit, or a guess. Every future replacement that copies it inherits the error
Manual SEquipment selection
A specific equipment pairing chosen against that load, not against the tonnage on the box
The proposal names the indoor and outdoor models together, with capacity at a stated outdoor temperature
Size was picked from the box tonnage. Nobody chose the moisture-removal capacity, which is why the house ends up cold and clammy
Manual DDuct design
Duct sizes and a layout that deliver the airflow the new equipment needs
A static pressure reading in the survey notes, and duct sizes on the drawing instead of “reuse existing”
The new unit inherits the old ducts. Low airflow shows up in more than 50% of systems, and it can send liquid refrigerant back to the compressor
None of the threeThe common case
Nothing. A tonnage and a price
It is fast. A quote over the phone cannot include any of them
You are buying the last installer’s guess with a new warranty. It may be fine. Nobody knows
How each ACCA manual shows up in paperwork you can ask to see.
HyreHVAC analysis: every item in the third column is a document or a measurement, not a promise. “We size everything properly” cannot be checked. A static pressure reading in inches of water column can.
Why does AC size come in half-ton steps?
Because that is how home equipment is made. Every load lands between two sizes, and someone has to choose which way to round.
Illustrative: four example loads rounded up to the nearest half-ton size you can buy. These are not real houses. The chart shows the size of the step between product sizes.HyreHVAC arithmetic on the standard half-ton sizes. Illustrative only.
A ton of cooling is 12,000 BTU per hour. Home units come in half-ton steps: 18,000, 24,000, 30,000, 36,000, 42,000, 48,000 and 60,000 BTU per hour. There is nothing in between.
HyreHVAC calculation: the chart rounds four example loads up to the next size. Depending only on where the load falls, that adds 1% to 12% of capacity. A 38,200 load becomes a 3.5-ton unit, 10% bigger. A 43,500 load becomes 4 tons, also 10% bigger.
So rounding is a real decision. Manual S makes it against the load and the maker’s performance tables. In cooling, the unit that runs longer removes more moisture, so rounding down is often the better choice.
What to ask: if a quote is a full ton above this calculator, ask which way the selection rounded and why.
A good answer points to the load report: a humid climate, lots of west-facing glass, a leaky house.
“We always go a bit bigger to be safe” is the habit DOE links to 31% to 48% of systems being oversized.
What do the terms on a load calculation mean?
A Manual J report is easy to read once you know six terms. They also help you tell a real report from software output nobody checked.
Design conditions
The outdoor temperatures the calculation sizes for. Not the record high or low, but a level exceeded only a few hours a year. Sizing for the record buys capacity you use for a handful of hours and pay for in every other hour.
The heat carried by moisture: from people, cooking, showers and humid outdoor air. Removing it lets you feel comfortable at a higher setting. A thermostat cannot see it, which is why an oversized AC can satisfy the thermostat and leave the house clammy.
Sensible heat ratio
The sensible load divided by the total load. A low ratio means a humid climate or a moist house, so the equipment must be chosen for moisture removal, not just tons. Manual S weighs this. A square-foot rule cannot.
Block load and room load
The block load is the whole house at once. Room loads are each room on its own. Equipment is chosen on the block load; ducts are sized on room loads. A report with only a block figure has not given Manual D what it needs.
The tonnage on the box. It is a rating at one set of test conditions, not what the unit delivers on your hottest day. Manual S uses the maker’s expanded performance tables instead.
Does the size belong to the outdoor unit?
No. A home system’s rating belongs to a specific pairing of outdoor unit, indoor coil and air handler. One question on a quote checks it.
A certified rating belongs to a specific combination of outdoor unit, indoor coil and, where present, air handler or furnace. Each certified combination carries its own AHRI Reference Number.
An outdoor unit on its own does not carry a certified SEER2. A quote that names only a condenser model number has not yet told you what the system is rated at.
The regulation itself is written in the same terms: 10 CFR 430.32(c)(6)(ii) speaks of an outdoor unit "that has a certified combination", not of an outdoor unit rating.
HyreHVAC analysis: two quotes with the same outdoor unit at the same price are not always the same system. With different indoor coils they are different certified pairings with different ratings. One may not be certified at all. Capacity moves along with efficiency.
What to ask: ask for the AHRI Reference Number of the proposed pairing, and for the indoor model number next to the outdoor one. A quote with an outdoor model but no indoor model has not yet named a system.
What we could not check: The AHRI page returned 403 to automated retrieval on that date. The matched-system rule is taken from 10 CFR 430.32(c)(6)(ii) and 10 CFR 429.16, which we read directly. AHRI material describes it the same way.
The rule few people mention
Can an AC be illegal to install where you live?
Yes, in the Southeast and Southwest. There the federal efficiency minimum applies on the day the unit is installed in your house, not the day it was made.
Federal minimum SEER2 by product class, for equipment made on or after January 1, 2023. These are legal floors, not targets. Most certified equipment sits well above them.HyreHVAC presentation of the table at 10 CFR 430.32(c)(5) and (c)(6). Retrieved from the eCFR content API, 2026-09-05.
DOE says that in the North the standards are enforced by date of manufacture. In the Southeast and Southwest they are enforced by date of installation.
The Southeast is Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, Puerto Rico, South Carolina, Tennessee, Texas, Virginia, the District of Columbia and the US territories. The Southwest is Arizona, California, Nevada and New Mexico.
10 CFR 430.32(c)(5) and (c)(6) says: “Any model of outdoor unit that has a certified combination with a rating below the applicable standard level(s) for a region cannot be installed in that region.”
The same rule adds: “The least-efficient combination of each basic model, which for single-split-system air conditioners with a single-stage or two-stage compressor (including space-constrained and small-duct high-velocity systems) must be a coil-only combination, must comply with the applicable standard.”
HyreHVAC analysis: that second sentence is stricter than it looks. Compliance is judged on the worst certified pairing of the model.
So an outdoor unit that meets the minimum with a good coil can still be barred, because a weaker pairing of the same model falls short.
The number on your quote is not the number the rule checks.
Older stock built to the national minimum is legal to install in the North and not in the Southeast or Southwest. The install is the regulated act, so the risk lands on the homeowner, not the seller.
What to do: in either region, get the certified SEER2 of the exact pairing in writing before install. DOE publishes an address and a telephone number for reporting an air conditioner it believes was installed in breach of a regional standard. Email EnergyEfficiencyEnforcement@doe.gov or call 202-287-6997.
A minimum says what may be sold, not what is worth buying.
Split-system air conditioners, under 45,000 Btu/hr
14.3 SEER2
14.3 SEER2
11.7, or 9.8 where the certified SEER2 is 15.2 or higher
Split-system air conditioners, 45,000 Btu/hr and over
13.8 SEER2
13.8 SEER2
11.2, or 9.8 where the certified SEER2 is 15.2 or higher
Single-package air conditioners
No regional standard
10.6 SEER2
None
Minimums for split-system and single-package air conditioners installed on or after January 1, 2023 in the Southeast or Southwest, from 10 CFR 430.32(c)(5) and (c)(6).
The Southwest adds a second test. EER2 is measured at 95°F outdoors, so it asks how the unit performs when it is hot. The EER2 bar drops once certified SEER2 reaches 15.2. Heat pumps have no regional standard; only the national minimums apply to them.
What should you ask for before you sign?
You do not need to know HVAC to ask these. Each is a document or a measurement that either exists or does not.
Ask for the Manual J report, not just the tonnage
The report names its design conditions and lists room-by-room assumptions. If it was done, it can be printed. Ask before you sign.
Ask what design temperatures were used
One number for cooling, one for heating. It tells you whether the calculation used your location or a software default. A few degrees off changes the whole result.
Ask for the measured static pressure
A number, taken with a pressure gauge (manometer) on the current system. It is the reading most likely to reveal a duct problem. 90-100% of systems in DOE’s review needed duct work. “The ducts looked fine” is not a measurement.
Ask for the indoor model number as well as the outdoor one
A certified rating belongs to the pairing. A quote that lists only the outdoor unit has priced half a system.
Ask which way the size was rounded, and why
Loads rarely land on a size you can buy. A good answer comes from the load report. “Bigger is safer” is the answer that leads to a clammy house.
Ask for moisture-removal (latent) capacity at your design condition
It is in the maker’s performance tables. It decides whether the house feels comfortable or just cold. In a humid climate it matters more than the tonnage.
Do not accept “same as the old one” as a method
The old unit may have been too big, and the house may have new insulation or windows. Copying the old nameplate locks in an old guess.
Do not accept a size quoted over the phone
No load calculation happened on that call. A phone quote is a price for a system nobody has specified.
What can this AC sizing tool not do?
These are real blind spots, not a disclaimer. The calculator cannot see any of them.
It cannot see the shape of the house
It knows only floor area. A long narrow house and a compact square one of the same size have different wall area, so different loads.
It cannot see the windows
Window area, glass type and direction are among the biggest parts of a real load. West-facing glass drives the afternoon peak hardest. This tool asks about none of it.
It cannot split temperature load from moisture load
It gives one number. A real calculation gives two, and choosing equipment needs both. In a humid climate, the moisture half often decides the right unit.
It cannot tell whether your ducts can carry the result
Delivering the capacity is a duct question. A right-size unit on small ducts underperforms in a way that looks like a sizing error.
It cannot check whether the unit is legal where you live
It does not know your location. In the Southeast and Southwest, the regional minimum is checked at install against the worst certified pairing of the model.
It has no prices in it
HyreHVAC does not install, service or sell HVAC equipment, and holds no data on quotes, invoices or finished jobs. Nothing here is a price we observed. That is also why these tools can tell you to keep the system you have.
It cannot say you need a new system
If your AC cools the house, has no fault and costs what it always has, a sizing figure is no reason to replace it. “Keep what you own” is an allowed answer.
Questions this calculator answers
What size air conditioner do I need?
About 16 to 22 BTU per square foot, depending on climate and insulation. A 2,000 sq ft house in a mixed climate with average insulation lands near 3 tons. Treat that as a starting point. A Manual J load calculation gives the real size.
What is a ton of cooling?
12,000 BTU per hour. Home systems usually range from 1.5 to 5 tons, sold in half-ton steps.
Why does everyone say to get a Manual J?
Because floor area is only one input. ACCA Manual J also counts which way the house faces, window area and type, shade, insulation, air leaks, ceiling height, and the people and appliances inside.
Is it better to buy a bigger AC to be safe?
No. An oversized AC turns on and off too often and leaves the air damp. Slightly undersized is the smaller mistake: it runs longer, dries the air better, and falls short only on the hottest few days.
Can I use this calculator to buy equipment?
No. Use it to see whether a contractor’s size is in the right range. Buy on a Manual J report for your house.
Regional Standards Enforcement (US Department of Energy, Office of the General Counsel, retrieved 2026-09-05. Enforcement by manufacture date in the North and by install date in the Southeast and Southwest.)
Manual J: Residential Load Calculation (Air Conditioning Contractors of America, retrieved 2026-09-05. The ANSI/ACCA 2 Manual J - 2016 designation and ACCA’s statement on building codes.)
How to use the AHRI directory (Air-Conditioning, Heating, and Refrigeration Institute, retrieved 2026-09-05. Returned 403 to automated retrieval. The matched-system rule is taken from 10 CFR 430.32(c)(6)(ii) and 10 CFR 429.16.)