Free HVAC Calculators
Free HVAC calculators for BTU sizing, duct CFM, AC tonnage, furnace sizing, and refrigerant charge. Instant results for technicians and homeowners.
14 free calculators · No account required
HVAC BTU Requirement Calculator (Climate Zone + Annual Cost)
Calculate required structural heating and cooling loads in BTUs and Tons while conducting a side-by-side annual cost forecast comparing gas furnaces to electric heat pumps.
- ASHRAE climate zone BTU/sq ft sizing with EFLOH runtime hours
- Envelope insulation profile multipliers (1.20×, 1.00×, 0.85×)
Duct Sizing Calculator (CFM + Friction Loss)
Size round and rectangular HVAC duct systems using the ACCA Manual D equal friction equations based on CFM delivery targets and run pressure drops.
- ACCA Manual D equal friction round diameter solver
- Huebscher regression rectangular sheet metal translation
Airflow CFM Calculator (Velocity + Area)
Calculate mechanical airflow volume in CFM from round or rectangular duct area profiles utilizing anemometer velocities or Pitot tube differential pressures.
- Direct FPM or Pitot tube velocity pressure capture modes
- Rectangular and round duct cross-sectional area solver
Furnace Sizing Calculator (sq ft + insulation)
Calculate required residential furnace BTU capacity and recommended manufactured heating unit sizes using regional climate zones and structural insulation multipliers.
- ASHRAE climate zone BTU/sq ft heating factors (Zones 1–7)
- Building envelope insulation multipliers (1.20×, 1.00×, 0.85×, 0.75×)
Heat Loss Calculator (U-Value + Delta T)
Calculate mechanical building heat loss using custom multi-assembly U-value arrays, surface areas, and structural design winter delta T variables.
- Steady-state Q = U × A × ΔT transmission engine with dynamic assembly rows
- Design indoor/outdoor temperature delta with live per-assembly breakdown
AC Tonnage Calculator (Residential + Commercial)
Calculate required mechanical air conditioning capacity in BTUs and nominal Tons across residential and complex multi-load commercial property blueprints.
- Residential ASHRAE zone BTU/sq ft matrix with insulation and window multipliers
- Commercial envelope, occupant, equipment, and ventilation sensible load engine
Mini Split Sizing Calculator (Room-by-Room)
Calculate required ductless mini-split indoor head capacities zone-by-zone and derive diversified outdoor condenser structural sizing loads.
- Dynamic multi-zone room array with ASHRAE climate tier BTU/sq ft matrix
- Standard 6k–36k BTU head tier matching with optional proposed head override
HVAC Static Pressure Calculator
Calculate Total External Static Pressure (TESP) using absolute plenum values, sum optional accessory drops, and view estimated blower CFM performance drops.
- Absolute supply and return plenum TESP summation engine
- Optional filter, coil, and duct friction drop summation
Refrigerant Charge Calculator (Superheat / Subcooling)
Diagnose air conditioning R-410A charging parameters using live subcooling scales and dynamic target superheat calculation lookups.
- Superheat mode for fixed-orifice metering with dynamic target calculation
- Subcooling mode for TXV systems with manufacturer target input
Ventilation ACH Calculator
Calculate Air Changes per Hour (ACH) and required fresh ventilation CFM parameters using linear room size measurements and ASHRAE space application targets.
- Room volume solver from length, width, and ceiling height
- Live ACH and required CFM against ASHRAE space application targets
SEER / EER / SEER2 Efficiency Savings Estimator
Estimate seasonal electrical utility savings, carbon offsets, and hardware compliance status when upgrading to modern SEER2 high-efficiency air conditioners.
- SEER, SEER2, and EER mode selector with live cross-conversion helpers
- Annual kWh consumption and seasonal operating cost comparison
Ductwork Cost Estimator (Material + Labor)
Calculate accurate HVAC ductwork installation costs using linear feet takeoffs, separate accessory fittings counts, insulation wrap variables, and shop labor hours.
- Flex, sheet metal, and ductboard material cost per foot lookup tables
- Separate fittings assemblies and insulation wrap cost summation
Heat Pump Sizing & Payback Calculator
Calculate required heat pump heating capacity in tons and calculate financial payback timelines compared to legacy oil, propane, or natural gas baselines.
- Climate zone and insulation-adjusted peak heating load sizing in tons
- HSPF2 seasonal energy balance with 45% fractional load factor
Manual J Lite Load Calculator (Simplified)
Estimate residential heating and cooling peak loads along with system tonnage sizing recommendations using simplified manual-J envelope multipliers.
- Climate zone heating index and insulation-adjusted envelope load matrix
- Fenestration density and air infiltration draft load multipliers
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