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Free HVAC Load Calculator

HVAC Load Calculator

Estimate how much heating and cooling a space needs before sizing the equipment. Enter the area, climate zone, and building-envelope details to estimate cooling and heating loads in BTU/hr and an estimated tonnage using a simplified approach based on Manual J concepts. Results update as you enter your information. No signup, no email.

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Estimate Your HVAC Load with Arrivy

Enter the area to condition, climate zone, and envelope details such as insulation, sun exposure, windows, doors, and occupants. The estimated cooling and heating loads update as you work, along with the estimated tonnage.

The space

Simplified Manual J estimate for a single zone.

Area to condition

ft²

Ceiling height

Climate zone

Envelope

Insulation

Sun exposure

Windows

Exterior doors

Occupants

Kitchen

Recommended cooling size

0 tons

Cooling

Heating

Ft² / ton

Cooling load (BTU/hr)

Cooling load

Heating load

Cooling tons

Rounded size

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Why Oversizing Is the Mistake to Avoid

A larger HVAC system isn’t automatically better. An oversized system can reach the thermostat setting before it runs long enough to remove enough humidity, leading to short cycling and less consistent comfort. Frequent cycling can also increase wear and energy use.

Proper equipment sizing starts with the home’s heating and cooling loads rather than simply choosing the largest available equipment. This calculator helps estimate the required size so you can use the result as a starting point when evaluating equipment options.

How the Estimate Works

A full Manual J accounts for detailed building assemblies, windows, orientation, infiltration, ventilation, duct loads, and other factors. This simplified calculator focuses on the major drivers so you can use the result as a preliminary sizing check.

1. Start with area and climate. The conditioned area and local design conditions provide a starting point for estimating heating and cooling demand.
2. Adjust for the building envelope Insulation, ceiling height, and sun exposure affect how much heating or cooling the space needs.
3. Account for windows, doors, and internal gains. Window and door characteristics, occupants, lighting, appliances, and other internal gains can affect the heating and cooling loads.
4. Estimate the cooling load. The estimated cooling demand is expressed in BTU/hr and converted to an estimated equipment tonnage for preliminary sizing.
5. Estimate the heating load separately. Heating demand is estimated separately using the area's heating conditions and other inputs. In colder climates, the heating load may determine the required equipment capacity.

What Drive the Load

A load calculation typically includes:

Area & climate zone

The conditioned area and local climate are the two biggest starting points for estimating heating and cooling demand.

Insulation & air sealing

A well-insulated, tightly sealed building generally loses and gains less heat than one with a poorly insulated envelope.

Sun exposure

Solar gain through exposed windows can increase the cooling load, especially on sunny orientations.

Windows & doors

Window area, glazing, and exterior doors affect how much heat enters or leaves the conditioned space.

Occupants & kitchen

People and cooking equipment contribute internal heat that the HVAC system must handle.

Ceiling height

Higher ceilings increase the volume of air that needs to be conditioned and can affect the estimated load.

Frequently Asked Questions

This is a simplified estimate based on several of the same factors considered in Manual J, including area, climate, building-envelope characteristics, windows, and internal gains. It does not model every building component, window orientation, infiltration path, ventilation load, duct load, or other detail included in a full ACCA Manual J calculation. Use it as a preliminary sizing check, not as a substitute for a professional load calculation.

There is no reliable single tons-per-square-foot rule for every home. Climate, insulation, windows, air sealing, sun exposure, ceiling height, and other building characteristics can significantly change the required capacity. Square footage is a useful starting point, but a proper load calculation is more reliable than choosing equipment from a rule of thumb.

A preliminary load estimate can differ from a contractor's equipment recommendation because the contractor may be accounting for building details that this simplified calculator does not capture. If the difference is significant, ask the contractor to explain the sizing and, where appropriate, provide the results of a full Manual J calculation.

It depends on the climate and equipment. In many warmer climates, cooling demand can determine the required capacity. In colder climates, heating demand may be the larger load and can influence equipment sizing. This calculator shows both so you can compare the estimated heating and cooling requirements.

Conditioned area and climate are important starting points, but insulation and air sealing, windows, solar exposure, ceiling height, doors, and internal heat gains can all affect the result. That's why a load calculation considers more than square footage alone.

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