HVAC Load Calculator (Cooling And Heating Estimate)
This is a rule-of-thumb load estimate, not a replacement for ACCA Manual J. Use it to sanity-check an existing system, size a rough budget, or catch an obviously oversized proposal — then run a full Manual J before you sell the equipment.
Home Details
Base BTU per square foot.
600 BTU added per person beyond two.
900 BTU added per window.
Estimated cooling load
64,700 BTU/h
Cooling capacity
5.4 tons
Round to the nearest available equipment size
Estimated heating load
71,170 BTU/h
Square feet per ton
371
Cross-check against local norms
Design airflow
2,157 CFM
At 400 CFM per ton
What This Estimate Is Good For
Three honest uses: checking whether an existing system is wildly oversized or undersized, giving a homeowner a budget range on the phone before you schedule a survey, and catching a competitor's proposal that jumps two tons above what the house could plausibly need.
What it cannot do is account for duct location, infiltration measured by blower door, window orientation and shading coefficients, or internal gains from a kitchen that runs all day. Those are exactly the variables that separate a comfortable system from a callback, and they only come out of a full load calculation.
Sizing Rules Worth Remembering
Round to the nearest half ton, and when the number falls between sizes, prefer the smaller unit in humid climates and the larger in dry ones. A slightly undersized system runs longer and dehumidifies better; a slightly oversized one short cycles and leaves the house clammy.
This is a rule-of-thumb estimate for preliminary discussion only. Perform an ACCA Manual J load calculation before specifying, quoting, or installing equipment.
Frequently Asked Questions
- Is this a Manual J calculation?
- No. ACCA Manual J is a room-by-room calculation using construction assemblies, orientation, infiltration testing, and local design temperatures. This tool is a square-foot estimate for sanity-checking an existing system or a proposal. Sell equipment on a Manual J, not on this.
- How many square feet per ton of air conditioning?
- Between roughly 400 and 700 square feet per ton depending on climate, insulation, and window area. A tight new build in a mild climate can exceed 700; a leaky older home in a hot climate can fall below 400. Any shop quoting a single national figure is guessing.
- Why is an oversized system a problem?
- It satisfies the thermostat before it removes humidity, short cycles, wears components faster, and leaves the house cold and clammy. Oversizing is the most common residential design error, and it usually traces back to a rule of thumb applied without a load calculation.
- What does the heating estimate assume?
- It scales the cooling load by a climate-dependent heating factor. Heating loads are far more sensitive to design temperature and envelope tightness than cooling loads, so treat the heating number as the rougher of the two.
Stop Rebuilding These Numbers By Hand
JobOpsPro keeps your rates, price book, estimates, and job costing in one system — $25 per user per month, every module included.