HVAC Calculator Suite

Field & design engineering tools

    Heat Load Calculator

    Estimate cooling load in BTU/hr, kW and Tons of Refrigeration (TR) from room size, sun exposure, occupancy and equipment load.

    Heat load
    -BTU/hr
    In kilowatts
    -kW
    In tons (TR)
    -TR
    Formula: Base load = Area × BTU/sqft factor; +600 BTU per occupant beyond 2; + equipment (W × 3.412). Field estimate — use full ASHRAE load calc for critical/large projects.

    CFM (Airflow) Calculator

    Convert cooling load to required supply air volume in CFM.

    CFM (rule of thumb)
    -CFM
    CFM (ΔT based)
    -CFM
    Rule of thumb: CFM = TR × 400. ΔT method: CFM = (TR × 12000) / (1.08 × ΔT).

    Air Change per Hour (ACH) Calculator

    Calculate how many times air is replaced in a space per hour.

    Air changes per hour
    -ACH
    ACH = (CFM × 60) / Room volume. Typical: offices 6-10, hospitals OT 20-25, kitchens 15-20.

    Duct Size Calculator (Round)

    Find round duct diameter from required airflow and design velocity.

    Duct diameter
    -inches
    Cross-section area
    -sq ft
    Area = CFM / Velocity. Diameter = √(4 × Area × 144 / π). Supply duct typical velocity: 700-1200 FPM.

    Duct Velocity Calculator

    Find air velocity inside a rectangular duct from airflow and duct dimensions.

    Velocity
    -FPM
    Velocity (FPM) = CFM / [(W × H)/144].

    Pipe Size Calculator

    Find required chilled/condenser water pipe diameter from flow rate and velocity.

    Pipe internal diameter
    -inches
    GPM = 2.448 × V(ft/s) × d²(in²) → d = √(GPM / (2.448 × V)). Typical chilled water velocity: 4-8 ft/s.

    Pump Head Calculator

    Estimate total dynamic head (TDH) for pump selection.

    Total dynamic head
    -ft
    TDH = Static lift + (Friction rate × Equivalent length / 100). Add fittings into equivalent length.

    Chilled Water Flow Calculator

    Find required chilled water flow rate (GPM) for a given cooling load and design ΔT.

    Chilled water flow
    -GPM
    GPM = (TR × 24) / ΔT. At standard ΔT=10°F this equals 2.4 GPM/Ton.

    Cooling Tower Calculator

    Estimate cooling tower tonnage, range and approach from water flow and temperatures.

    Tower tonnage
    -TR
    Range
    -°F
    Approach
    -°F
    TR = (GPM × ΔT) / 24 (ΔT = hot − cold). Range = Hot − Cold. Approach = Cold − Wet bulb.

    Static Pressure Calculator

    Sum duct friction and fitting losses to find total system static pressure.

    Total static pressure
    -in.wc
    Total SP = (Friction rate × Length/100) + Fittings loss + Grille/diffuser loss.

    ESP (External Static Pressure) Calculator

    Find static pressure available for ductwork after internal AHU/FCU component losses.

    Available ESP
    -in.wc
    ESP available = Total fan static − (Filter + Coil + Other internal losses).

    Refrigerant Charge Calculator

    Estimate approximate refrigerant charge for split/ductable units including extra pipe length.

    Base charge
    -kg
    Extra charge
    -kg
    Total charge
    -kg
    Base charge = Tons × factor(kg/TR). Extra = max(0, Actual−Standard length) × g/m rate. Always confirm against OEM data.

    Psychrometric Calculator

    Estimate wet bulb temperature and dew point from dry bulb temperature and relative humidity.

    Wet bulb temp
    -°C
    Dew point
    -°C
    Wet bulb via Stull's approximation; dew point via Magnus formula. Accurate within ±0.3°C for 5-40°C, 5-95% RH.

    Fresh Air Calculator

    Calculate required outdoor fresh air quantity based on occupancy.

    Required fresh air
    -CFM
    Fresh Air CFM = Occupants × CFM/person (ASHRAE 62.1 guidance bands). Check local code for minimums.

    Expansion Tank Calculator

    Size a hydronic expansion tank from system water volume and expected water expansion.

    Required tank volume
    -litres
    Ve = System volume × Expansion%. Vt = Ve / (1 − Pi/Pf). Typical expansion: ~3% for 10→82°C heating water.
    HVAC Engineering Calculator Suite — field estimation tools. Verify critical designs against ASHRAE/SMACNA standards and local codes.