HVAC Calculator is an app that performs many calculations that are useful to have available for anyone working with or have interest in HVAC and energy use in buildings. The app performs many of the calculations that you never remember the formulas for when you need them for quick calculations, for example in a meeting or out on the construction site. Many of the calculations can also be a bit difficult to calculate with a normal calculator. Now you can perform these calculations easily on your iPhone/iPad. The app is universal, so you only have to buy it once to use it on both iPhone and iPad. The app helps you calculate all this and more: -SFP from measured/design fan power and airflow -SFP at reduced airflow for VAV ventilation -SFP at design conditions or maximum performance for VAV ventilation -Temperature efficiency of heat recovery -Temperature after heat recovery unit (HRU) in air handling unit (AHU) -Temperature of exhaust air from air handling unit after heat recovery -Actual temperature efficiency of heat recovery when the exhaust temperature is limited to minimum 5°C for reuse as frost free garage ventilation -Air velocity in ducts with known dimensions and airflow -Maximum airflow in a duct with dimensions and maximum air velocity as specified requirements -Dimensions of rectangular and circular spiral ducts for specified air flow and velocity requirements -Pressure drop in Pa/m for rectangular and circular spiral ducts -Equivalent diameters for rectangular ducts -Hydraulic diameter for rectangular ducts