HVAC Heat Load BTU Calculator

HVAC Heat Load BTU Calculator helps HVAC technicians, engineers, and contractors calculate accurate cooling and heating loads. Calculate accurate cooling and heating loads using a simplified ACCA Manual J methodology based on room dimensions, insulation levels, window types, and ASHRAE climate zones — the industry standard for professional air conditioning system sizing.

LOAD CALCULATION MODES:
Cooling Mode — Calculate BTU/h cooling requirement for air conditioning
Heating Mode — Calculate BTU/h heating requirement for furnace and heat pump sizing
Automatic Tonnage Conversion — Get AC tonnage (0.5 to 5+ tons) from load results
CFM Requirement — Airflow from the supply-air temperature difference, around 400 CFM per ton

ROOM PARAMETERS:
Room Dimensions — Enter length, width, and ceiling height
Exterior Walls — Count how many of the room's walls face outdoors
Insulation Levels — Poor, Average, Good, or Excellent, mapped to assembly U-factors
Window Types — Single Pane, Double Pane, Triple Pane, Low-E, with U-factor and SHGC
Window Orientation — North, East, South, West or mixed exposure for solar gain
Floor Type — Over conditioned space, over crawlspace/garage, or slab on grade
Climate Zones — 5 zones with ASHRAE design temperatures, overridable by hand
Duct Location — Add duct gain/loss when the ducts run through unconditioned space
Occupant Load — Sensible and latent heat from building occupants

COMPONENT BREAKDOWN:
Wall conduction load
Window conduction and SHGC-based solar gain, shown separately
Ceiling and roof heat gain
Floor and slab-perimeter load
Infiltration load from envelope tightness
Occupant sensible and latent heat
Duct gain/loss in unconditioned space
Sensible and latent totals, tonnage, airflow and BTU/h per sq ft

OPTIONAL PRO UPGRADE — $2.99 ONE-TIME IN-APP PURCHASE
The following features require a separate one-time in-app purchase. They are not required to use the calculator:
• Unlimited saved calculation history
• PDF export of results
• Dark theme
• Ad-free experience

WHY HVAC PROS USE THIS CALCULATOR:
Faster Manual J estimates than spreadsheets or online calculators
Accurate BTU sizing prevents oversized/undersized systems
Reduces callbacks from incorrect system selection
Quick cooling load checks on service calls
ASHRAE-compliant Manual J methodology for commercial work
Improves customer confidence with detailed technical reports

PERFECT FOR:
HVAC design engineers sizing air conditioning systems
HVAC field technicians quick-checking load requirements
AC contractors preparing accurate equipment bids
HVAC apprentices learning Manual J methodology
Building maintenance engineers planning replacements
Residential and commercial HVAC system sizing
Energy auditors estimating cooling needs

Based on ACCA Manual J design methodology: assembly U-factors, SHGC-based solar gain, ASHRAE design conditions, and no arbitrary safety padding.

Part of HVACTools Suite — the professional HVAC technician app for field calculations, refrigeration diagnostics, and air conditioning system design.

Recent changes:
Added a link to TradeTools — the one-app version of this calculator and 61 more, for HVAC, electrical, plumbing, fire protection, solar and carpentry. Nothing else changed.