What size air conditioner does my home need?
Choosing the right size air conditioner is one of the most important decisions in a cooling project, and one of the easiest to get wrong. An AC that is too small will run constantly and never quite cool your home, while one that is too big cools too fast, short-cycles, and leaves the air clammy.
Online rules of thumb based on square footage are a starting point, but they ignore the factors that really drive cooling load in a Metro Vancouver or Fraser Valley home, such as insulation quality, window count, and sun exposure.
At HeatLand, we size every system with a proper load calculation. Here is how AC sizing actually works and why guessing costs you comfort and money.
How AC Size Is Measured
Air conditioner capacity is measured in tons and BTUs per hour. One ton of cooling equals 12,000 BTU per hour, so a common two-ton unit removes 24,000 BTU of heat each hour. The bigger the number, the more heat the system can pull from your home.
More capacity is not automatically better. The goal is to match the unit’s output to your home’s actual heat gain so it runs in long, steady cycles. Those longer cycles are what let the system dehumidify properly and hold a comfortable, even temperature.
A rough starting estimate is around 20 BTU per square foot of living space, which would put a 1,500 square foot home near 30,000 BTU, or 2.5 tons. Treat that only as a ballpark. The real answer depends on the specific characteristics of your home, which is why a load calculation matters far more than any simple formula.
What a Proper Load Calculation Includes
The industry standard for sizing is a Manual J load calculation. Rather than relying on floor area alone, it accounts for the many factors that determine how much heat your home actually gains on a hot day.
Those factors include insulation levels in walls and attic, the number, size, and orientation of windows, ceiling height, air leakage, local climate data, shading from trees or neighbouring buildings, and even how many people typically occupy the home. A well-insulated, shaded home needs far less cooling than a leaky home with large west-facing windows of the same square footage.
A licensed HeatLand technician gathers these details during an in-home assessment and runs the calculation to pinpoint the right capacity. This is the difference between a system that quietly keeps you comfortable and one that struggles or wastes energy. Sizing by guesswork is the single most common cause of comfort complaints we see.
The Cost of Getting Size Wrong
An undersized air conditioner cannot keep up on the hottest days. It runs nonstop, drives up your energy bill, wears out faster, and still leaves your home warmer than you want. Homeowners often assume the unit is broken when it is simply too small for the load.
An oversized unit is just as problematic. It cools the air quickly, then shuts off before it has run long enough to remove humidity, so your home feels cold and clammy at the same time. These short on-off cycles stress the compressor, waste electricity, and shorten equipment life.
Right-sizing avoids both problems and delivers steady comfort, better humidity control, lower bills, and longer equipment life. Because so much rides on the number, sizing should never be a guess or a match to the old unit that may itself have been wrong. Let a licensed professional run the calculation.
Quick Checklist
- Gather your home’s square footage and ceiling heights
- Note insulation levels in walls and attic
- Count windows and their direction of exposure
- Identify shading from trees or nearby buildings
- Request a Manual J load calculation, not a square-footage guess
- Have a licensed technician confirm final capacity
| Home Size (approx.) | Rough BTU Estimate | Approx. Tonnage |
|---|---|---|
| 1,000 sq ft | ~20,000 BTU | ~1.5 tons |
| 1,500 sq ft | ~30,000 BTU | ~2.5 tons |
| 2,000 sq ft | ~40,000 BTU | ~3 tons |
| 2,500 sq ft | ~50,000 BTU | ~4 tons |
Frequently Asked Questions
Can I size an AC by square footage alone?
Square footage gives only a rough ballpark. Two homes of identical size can need very different cooling capacity depending on insulation, windows, sun exposure, and air leakage. A Manual J load calculation accounts for all of these, which is why it is the accurate method. Sizing by area alone often leads to an oversized or undersized system.
What happens if my AC is too big?
An oversized AC cools the air quickly, then shuts off before running long enough to remove humidity. The result is a home that feels cold and clammy, plus frequent short cycling that wastes energy and wears out the compressor. Proper sizing produces longer, steadier cycles that control both temperature and humidity.
Should I just match my old unit’s size?
Not necessarily. Your old unit may have been sized incorrectly, and your home may have changed with new windows, insulation, or additions. Always confirm with a fresh load calculation rather than copying the old capacity. A licensed technician can tell you whether the previous size was right for your home.
How long does a load calculation take?
A technician can typically complete the in-home assessment and calculation during a single visit, gathering measurements and details about insulation, windows, and orientation. The result is a precise capacity recommendation tailored to your home. It is a small step that prevents the comfort and cost problems that come from a wrongly sized system.
Reviewed by the HeatLand Heating & Cooling team — licensed HVAC contractor serving Metro Vancouver & the Fraser Valley since 1999. This article is for general guidance only. If you smell gas, suspect a carbon monoxide leak, or are unsure about any electrical or gas component, stop troubleshooting immediately and call a licensed technician or 911.