HVAC Tools

HVAC Load Calculator

Calculate HVAC system sizing, duct requirements, and equipment costs. Manual J compliant calculations for proper system design.

HVAC Load Calculation

System Requirements

Cooling BTU 0
Heating BTU 0
Airflow Required 0
Main Duct Size 0
Return Duct Size 0
Equipment Cost $0
Installation Cost $0

BTU Guidelines

Cooling: 20-30 BTU/sq ft

Heating: 30-40 BTU/sq ft

Add 10% for high ceilings

Add 10% for poor insulation

Duct Sizing Rules

  • 400 CFM per ton cooling
  • 0.1" WC pressure drop per 100 ft
  • Return duct = 75% of supply
  • Seal all duct joints

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HVAC Load Calculator for Construction Projects

Proper HVAC system sizing is critical for energy efficiency, comfort, and equipment longevity. Our free HVAC calculator performs Manual J compliant calculations to determine accurate heating and cooling loads for residential and commercial buildings.

Manual J Load Calculations

Manual J is the industry standard for calculating HVAC loads:

  • Heat Transfer: Through walls, windows, doors, and roofs
  • Air Leakage: Infiltration through cracks and openings
  • Internal Loads: People, appliances, lighting, and equipment
  • Solar Gain: Heat from sunlight through windows
  • Building Orientation: Direction buildings face affects solar loading

BTU Sizing Guidelines

General BTU requirements by climate and building type:

  • Mild Climates (South): 20-25 BTU per square foot cooling
  • Moderate Climates: 25-30 BTU per square foot cooling
  • Cold Climates (North): 30-35 BTU per square foot cooling
  • Heating: 30-40 BTU per square foot (varies by fuel type)
  • Commercial Buildings: Higher loads due to occupancy and equipment

Duct System Design

Proper duct sizing ensures efficient air distribution:

  • Airflow Calculation: 400 CFM per ton of cooling capacity
  • Friction Rate: 0.1 inches water column per 100 feet
  • Supply Ducts: Sized for total airflow requirement
  • Return Ducts: Sized for 75% of supply airflow
  • Branch Ducts: Reduce size as airflow decreases

HVAC System Types

Choose the right system for your application:

  • Split Systems: Separate indoor/outdoor units, most common
  • Packaged Units: All components in one unit, for rooftops
  • Heat Pumps: Provide both heating and cooling
  • Ductless Systems: No ductwork required, zone control
  • Variable Speed: Precise temperature control, energy efficient

Energy Efficiency Considerations

SEER and AFUE ratings determine energy efficiency:

  • SEER: Seasonal Energy Efficiency Ratio (cooling)
  • AFUE: Annual Fuel Utilization Efficiency (heating)
  • HSPF: Heating Seasonal Performance Factor (heat pumps)
  • Proper Sizing: Right-sized systems are most efficient
  • Maintenance: Regular filter changes and tune-ups

HVAC FAQ

How many BTU do I need for my home?

Calculate BTU by multiplying square footage by 20-30 BTU for cooling, 30-40 BTU for heating. Add factors for ceiling height (10% for 9+ feet), insulation quality, window area, and climate. Use Manual J calculation for accurate sizing. Oversized systems waste energy and don't dehumidify properly.

How do I size HVAC ducts?

Duct sizing requires calculating total CFM (400 CFM per ton) and maintaining proper pressure drop (0.1 inch WC per 100 feet). Use a ductulator or ACCA Manual D for proper sizing. Supply ducts carry conditioned air, return ducts bring air back. Seal all joints and insulate ducts in unconditioned spaces.

What's Manual J and why is it important?

Manual J is the industry standard for calculating HVAC loads, published by ACCA. It considers all heat transfer paths, infiltration, internal loads, and solar gain for accurate system sizing. Proper Manual J calculations prevent oversized systems that waste energy and undersized systems that can't maintain comfort.

How often should I replace my HVAC system?

HVAC systems typically last 15-20 years with proper maintenance. Signs of replacement include rising energy bills, frequent repairs, uneven heating/cooling, and age over 15 years. New high-efficiency systems can pay for themselves through energy savings. Always get multiple quotes and check SEER ratings.

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