HVAC Load Calculator
Estimate the heating and cooling capacity needed for a space. This simplified Manual J calculation uses IECC climate zones for accurate regional BTU estimates, plus equipment sizing, ductwork, and energy cost projections.
Cooling base: 20 BTU/sq ft | Heating base: 30 BTU/sq ft
Load Calculation Results
Cooling Load
32,400
BTU/hr
Heating Load
46,600
BTU/hr
Total Airflow Needed
1,620
CFM
Equipment Sizing Recommendations
Air Conditioner
3.0 Ton
36,000 BTU/hr rated
Gas Furnace
50,000
BTU/hr output
Heat Pump
4.0 Ton
Handles heating & cooling
Important: Do not oversize equipment. An oversized AC or heat pump will short-cycle, wasting energy and failing to dehumidify properly. Always select the smallest unit that meets the calculated load. A professional Manual J calculation is recommended for final sizing.
Ductwork Sizing Estimate
Total CFM
1,620
Cooling BTU / 20
Main Trunk Duct
22" x 12" or 22" round
Rectangular or round
Supply Runs
10
~162 CFM each
Branch Duct Size
8" round
Per supply run
For detailed airflow calculations per room, use our CFM & Airflow Calculator.
Estimated Monthly Energy Cost
Estimates assume 8 hrs/day average run time during peak season. Actual costs vary with usage patterns, equipment efficiency (SEER/AFUE), and local utility rates.
AC Cooling
$115
/month (summer)
720 kWh
Gas Furnace Heating
$189
/month (winter)
126.3 therms
Heat Pump Heating
$210
/month (winter, electric)
1311 kWh · COP 2.5
How to Use This Calculator
Select your IECC climate zone (or find your nearest city), enter the square footage, ceiling height, and building details. The calculator uses zone-specific BTU/sq ft multipliers for both heating and cooling loads. Results include equipment sizing recommendations, ductwork estimates, and projected monthly energy costs.
Formula Used
Cooling BTU = Sq Ft x Zone Cooling Base x Height Factor x Insulation Factor x Window Factor x Sun Factor + (Occupants x 600). Heating BTU = Sq Ft x Zone Heating Base x Height Factor x Insulation Factor x Window Factor + (Occupants x 400). AC Tonnage = Cooling BTU / 12,000 (rounded up to nearest 0.5 ton). CFM = Cooling BTU / 20.
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Disclaimer
This calculator is for estimation purposes only. Results may vary based on local conditions, materials, and building codes. Always consult a licensed professional before making decisions based on these calculations. MyContractorTools is not responsible for any errors or omissions.