Sizing · independent publisher, not a contractor
What size AC does a Los Angeles home need?
The size of an AC in tons should come from a Manual J load calculation of your house; the LA price guides pair roughly 600 square feet with each ton, so an 1,800 sq ft home starts near 3 tons, but Valley heat, windows and insulation can move that by a ton either way.
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- Why two houses the same size need different ACs
- Key takeaways
- Tons, BTUs and what the numbers mean
- The rule of thumb and its limits
- Why your part of LA changes the answer
- What pushes the size up or down
- What each size costs in Los Angeles
- What goes wrong with the wrong size
- What to have ready for the contractor
- When two quotes give different sizes
- Sizing a heat pump or mini-split
- The ducts have to match the size
Why two houses the same size need different ACs
Picture two 1,800 sq ft houses. One sits a mile from the beach in Santa Monica; the other faces west in Woodland Hills with single-pane windows. The floor-area rule gives both 3 tons. The weather does not agree:
That is why a size has to be calculated for the house, not read off a chart.
Key takeaways
In short
- 600 sq ft per ton is a budgeting start, not a size.
- The same house can need different sizes on the coast and in the Valley.
- Ask every quote for the Manual J result.
- Fix insulation, shading and duct leaks first; they can lower the size you buy.
Tons, BTUs and what the numbers mean
AC capacity is sold in tons. One ton of cooling is 12,000 BTU per hour, so a 3-ton system removes about 36,000 BTU of heat an hour at its rated conditions. Residential split systems commonly come in half-ton steps up to 5 tons.
| Size | Capacity | Floor area on the LA guides' rule of thumb |
|---|---|---|
| 2 ton | 24,000 BTU/h | ~1,200 sq ft |
| 2.5 ton | 30,000 BTU/h | ~1,500 sq ft |
| 3 ton | 36,000 BTU/h | ~1,800 sq ft |
| 3.5 ton | 42,000 BTU/h | ~2,100 sq ft |
| 4 ton | 48,000 BTU/h | ~2,400 sq ft |
| 5 ton | 60,000 BTU/h | ~3,000 sq ft |
The 600 sq ft per ton pairing is the one the two LA price guides that print sizes use (Reliable Heating and Air; Cold Cloud). It is a budgeting starting point, not a size.
The rule of thumb and its limits
Generic guides online quote anything from about 500 to 600 square feet per ton, which for an 1,800 sq ft house means 3 to 3.6 tons before anyone has looked at the windows. The spread itself tells you the rule is not a calculation.
The Department of Energy lists oversizing alongside improper charging and leaky ducts as installation problems that "result in efficiency losses, occupant discomfort, and shortened equipment life" (DOE FEMP). The industry method that prevents it is ACCA Manual J.
What a Manual J actually counts
Room by room: floor area, ceiling height, wall and attic insulation, window area and direction, shading, air leakage, duct location, how many people live there and the local design temperature. HyreHVAC explains what a Manual J load calculation measures.
Why your part of LA changes the answer
| Station | Days ≥ 90 °F | Days ≥ 100 °F | Cooling degree days |
|---|---|---|---|
| LAX | 4.8 | 0.2 | 720 |
| Long Beach airport | 23.3 | 1.9 | 1,166 |
| Downtown LA (USC) | 25.6 | 1.8 | 1,296 |
| Burbank airport | 53.9 | 7.2 | 1,481 |
| Woodland Hills | 115.3 | 35.6 | 1,819 |
NOAA NCEI U.S. Climate Normals 1991–2020, retrieved 2026-09-29.
A coastal house can often take less than the floor-area rule suggests. A Valley house with west-facing glass and a hot attic may need more. Our estimator applies a half-ton shift for coast and Valley as a labelled rule of thumb; a Manual J replaces it.
What pushes the size up or down
| Factor | Pushes size | What you can do about it |
|---|---|---|
| West- or south-facing glass | Up | Shades, low-e film or awnings |
| Little attic insulation | Up | Add insulation before sizing |
| Leaky ducts in a hot attic | Up | Seal ducts; Title 24 may require it anyway |
| High or vaulted ceilings | Up | Count the volume, not just floor area |
| Coastal marine layer | Down | Size for your station, not the Valley |
| Mature shade trees | Down | Note it on the prep sheet |
| New double-pane windows | Down | Tell the contractor the window type |
Fix the house before you size the AC
Insulation, shading and duct sealing done before the load calculation can lower the size you buy. A smaller system costs less up front; LA sources print a 3-ton central AC at $8,000–$16,000 against $9,500–$19,000 for 4 tons.
What each size costs in Los Angeles
Each step up in size raises the installed price, so an extra half-ton "to be safe" is not free. See the full tonnage table with heat pump prices and sources.
What goes wrong with the wrong size
Too small
- Runs flat out through a heat wave.
- Never reaches the setpoint on the hottest afternoons.
- Most common when a coastal-sized unit goes into a Valley house.
Too large
- Cools fast, shuts off, repeats (short cycling).
- Leaves humidity behind and rooms uneven.
- DOE: performs "less efficiently and effectively" than a properly sized unit.
More on the second case: problems an oversized AC causes.
What to have ready for the contractor
- Floor area and ceiling heights, room by room if you can.
- Window sizes and directions, and whether they are single or double pane.
- Attic insulation depth, if you can see it safely.
- The old unit's model plate, so the contractor can see its size.
- Rooms that run hot or cold today, and when.
The sizing preparation tool turns these into a one-page sheet to hand over, and HyreHVAC's AC sizing calculator shows how the inputs move a result.
When two quotes give different sizes
Different sizes on two quotes are common. One contractor matches the old unit; another runs a calculation. Ask each:
- What size did you calculate, and can I see the Manual J summary?
- Which design temperature and window areas did you use?
- Did you allow for duct leakage, and will the ducts be sealed?
A contractor who cannot say how the size was worked out is guessing. Record the answers in the quote tool.
Sizing a heat pump or mini-split
A heat pump is sized like an AC for the cooling load, then checked against the heating load. In most of Los Angeles the summer load is the larger one, so the cooling calculation usually decides the size.
A mini-split is sized room by room: each head for its own room's load, then the outdoor unit for the heads it serves. See single-zone vs multi-zone.
The ducts have to match the size
A bigger unit pushes more air. If the ducts were sized for the old unit, a larger new one can be noisy and still underperform.
ENERGY STAR estimates 20 to 30 percent of air in a typical duct system is lost to leaks (ENERGY STAR), so sealing ducts can do as much for comfort as adding capacity.
Sources
- NOAA NCEI, U.S. Climate Normals 1991–2020, annual/seasonal (stations USW00023174, USW00093134, USW00023152, USC00049785) (retrieved 2026-09-29)
- US Department of Energy, "Energy Saver Guide: Tips on Saving Money and Energy at Home" (2022) (retrieved 2026-10-18)
- US DOE Federal Energy Management Program, "Purchasing Energy-Efficient Residential Central Air Conditioners" (retrieved 2026-10-18)
- Reliable Heating and Air (Woodland Hills), AC installation cost in LA and Ventura County (retrieved 2026-09-29)
- Cold Cloud (Glendale), central air cost in Los Angeles (retrieved 2026-09-29)
Questions
What size AC do I need for a 1,500 sq ft house in Los Angeles?
On the LA price guides' 600 sq ft per ton rule, about 2.5 tons. A coastal house may need less and a Valley house with west-facing glass more. Only a Manual J load calculation gives the right size.
What size AC do I need for a 2,000 sq ft house?
The 600 sq ft per ton starting point gives about 3.5 tons. Insulation, windows, shade and where in LA the house sits can move that by half a ton or more in either direction.
How many square feet does a ton of AC cool?
The LA price guides pair about 600 square feet with each ton. Generic national guides use anything from about 500 to 600, which shows it is a rule of thumb, not a calculation.
Is a bigger AC better?
No. An oversized AC short-cycles, removes less humidity and leaves rooms uneven. DOE says an oversized unit performs less efficiently and effectively than a properly sized one.
What is a Manual J?
ACCA Manual J is the industry method for calculating a house's heating and cooling load room by room, from insulation, windows, orientation, air leakage and local weather. It replaces the floor-area rule of thumb.
Should I just replace my AC with the same size?
Not without checking. Insulation, windows or duct sealing may have changed the load since the old unit went in, and the old unit may never have been sized correctly. Ask for a load calculation.
Does a Valley house need a bigger AC than a coastal one?
Usually. On NOAA normals Woodland Hills averages 115.3 days a year at 90 °F or above against 4.8 at LAX, and about 2.5 times the cooling degree days.
How much does each extra ton cost?
It varies by source, but the published LA band for central AC runs $8,000–$16,000 at 3 tons and $9,500–$19,000 at 4 tons. See the tonnage table on the cost guide.
Can I size a mini-split the same way?
Each head should be sized for its own room's load, then the outdoor unit matched to the heads. A Manual J done room by room gives those numbers.
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