HVAC Load Calculator
Estimate heating and cooling load with Manual J-style inputs for a quick HVAC sizing check.
This is a quick HVAC load estimate, not a full Manual J report.
Results
This is a quick HVAC load estimate, not a full Manual J report.
How to use this calculator
- 01Choose dimensions or known floor area.
- 02Enter area, ceiling height, climate, insulation, sun exposure, windows, air leakage, occupants, and space type.
- 03Choose the furnace AFUE used for the input BTU estimate.
- 04Read the cooling load, heating load, AC tons, recommended ranges, and furnace input/output BTU.
For a simpler room-level estimate, use the BTU Calculator.
For one ductless room or zone, use the Mini Split Size Calculator to estimate a common single-zone BTU size.
Understanding the math
Cooling starts with a normal area load rate and adjusts for ceiling height, climate, insulation, sun, windows, air leakage, space type, and extra occupants. Heating uses a climate-based load rate, then adjusts for ceiling height, insulation, windows, air leakage, and space type.
cooling load = area x cooling base rate x factors + occupants heating load = area x heating base rate x factors AC tons = cooling BTU/hr / 12,000 furnace input BTU = heating output BTU / AFUE
Use the AC Tonnage Calculator when you only need cooling tons, and use the Furnace Size Calculator when you only need furnace input/output BTU.
If you only need heating envelope loss for a room, zone, or house, use the Heat Loss Calculator.
After load sizing, airflow and duct checks can be handled with the CFM Calculator and Duct Size Calculator.
HVAC load quick reference
Use these ranges as a rough check. Real heating and cooling loads can move outside the table when local weather, insulation, glass area, air leakage, or duct conditions are unusual.
| Space | Area | Cooling guide | Heating guide |
|---|---|---|---|
| Small room / zone | 150–300 sq ft | 18–25 BTU/hr per sq ft | 30–45 BTU/hr per sq ft |
| Bedroom or office | 300–600 sq ft | 18–28 BTU/hr per sq ft | 30–50 BTU/hr per sq ft |
| Living room / open area | 600–1,200 sq ft | 20–30 BTU/hr per sq ft | 35–55 BTU/hr per sq ft |
| Small home | 1,200–1,800 sq ft | 18–28 BTU/hr per sq ft | 35–60 BTU/hr per sq ft |
| Average home | 1,800–2,400 sq ft | 18–30 BTU/hr per sq ft | 35–60 BTU/hr per sq ft |
| Large home | 2,400–3,200 sq ft | 18–32 BTU/hr per sq ft | 35–65 BTU/hr per sq ft |
Frequently asked questions
What is a Manual J calculation?
Manual J is a residential HVAC load calculation method used to estimate heating and cooling loads for equipment sizing.
How to do a Manual J calculation?
A full Manual J uses detailed room areas, insulation, windows, orientation, air leakage, duct losses, and local design temperatures. This calculator is only a quick planning estimate.
Can I do my own Manual J calculation?
You can make a rough estimate yourself, but a full Manual J uses detailed room-by-room inputs, insulation values, window data, air leakage, duct losses, and local design temperatures. For final equipment sizing, proper software or an HVAC professional may be needed.
How to calculate HVAC load?
A quick estimate starts with area or volume, then adjusts for climate, insulation, windows, sun, air leakage, occupants, and space type. This calculator estimates both heating and cooling loads.
Can I use this calculator with metric measurements?
Yes. Use the Imperial / Metric toggle. Inputs, results, and reference values follow the active unit system where applicable.
Related calculators
AC Tonnage Calculator
Convert cooling load into AC tons and a nominal air conditioner size.
Furnace Size Calculator
Estimate furnace input BTU from heating load, climate, insulation, and AFUE.
BTU Calculator
Estimate room-level heating or cooling BTU/hr from size and room conditions.
CFM Calculator
Estimate room airflow from ACH or duct airflow from velocity.
Duct Size Calculator
Estimate round and rectangular duct sizes from airflow and target velocity.