Enter your space area, ceiling height, climate region, and key factors like insulation grade, sun exposure, and window tightness to calculate the right HVAC system size for your space. You'll get the recommended BTU capacity and tonnage so you avoid buying an oversized or undersized unit.
Recommended HVAC Capacity
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Calculated Cooling Load
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Recommended Tonnage
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Base Area Load
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Occupant & Equipment Load
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An HVAC load calculation determines how many BTUs per hour your heating or cooling system needs to maintain comfortable indoor temperatures. Getting it right prevents oversizing (which wastes energy, causes humidity issues, and short-cycles the unit) and undersizing (which can't keep up on extreme days). A proper load calculation is the foundation of any efficient HVAC installation.
A common rule of thumb is 20–25 BTU per square foot, but this varies significantly based on climate zone, ceiling height, insulation quality, sun exposure, and other factors. For example, a well-insulated home in a mild climate may need only 15–18 BTU/sqft, while a poorly insulated space in a hot region could need 30+ BTU/sqft. This calculator applies all those adjustments automatically.
One ton of HVAC capacity equals 12,000 BTU/hr of cooling. A 2-ton unit delivers 24,000 BTU/hr, a 3-ton unit delivers 36,000 BTU/hr, and so on. Residential systems typically range from 1.5 to 5 tons. Your recommended tonnage is simply your required BTU/hr divided by 12,000.
The US is divided into climate zones by ASHRAE. Zone 1 (Red) covers hot/humid areas like South Florida. Zone 2 (Orange) is hot/dry like Arizona. Zone 3 (Yellow) covers mixed climates like Tennessee. Zone 4 (Green) includes mixed-cool areas like the Pacific Northwest and much of the Mid-Atlantic. Zone 5 (Blue) covers cold climates like the Midwest and New England. You can look up your exact zone on the ASHRAE or DOE climate map.
Absolutely. Insulation is one of the biggest factors in heat gain and loss. An extremely well-insulated home can need 30–40% fewer BTUs than a poorly insulated one of the same size. Upgrading insulation before buying an HVAC unit is often the most cost-effective way to reduce equipment size and long-term energy costs.
South- and west-facing rooms with large windows receive substantial solar heat gain, which increases cooling load. A space with strong direct sun exposure can require significantly more cooling capacity than a shaded or interior room of equal size. This calculator adds a solar gain factor based on your selected sun exposure level.
Common signs of an oversized AC include: the unit cycles on and off frequently (short-cycling), indoor humidity stays high even when it's running, some rooms feel cold while others stay warm, and energy bills are higher than expected. An oversized system cools too fast before properly dehumidifying the air, leading to clammy, uncomfortable conditions.
Yes. Kitchens generate significant heat from cooking appliances and should add approximately 4,000 BTU/hr to the cooling load. Glass sunrooms are extremely heat-intensive due to all-around solar exposure and can require up to 2–3× more BTUs per square foot than a standard insulated room. This calculator accounts for both factors.