Free HVAC Load Size Calculator
HVAC Load Size Calculator
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.
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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.
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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
Know Your True Load Cost
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Everything else a load calculator operation needs — same engine, load calculator-tuned:
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