Reference

Reference tables

The factors and typical values the calculators use, on their own pages so you can look them up without a calculator.

  • BTU per square foot table by climate zone

    Cooling and heating loads per square foot for DOE zones 1 to 7, design temperatures, degree days, adjustment factors and the ENERGY STAR room AC chart.

  • HVAC efficiency ratings

    SEER2, EER2, HSPF2, COP, AFUE and UEF in one table, with the 2023 conversions, federal minimums and the running-cost formulas.

  • Duct size chart

    CFM capacity of round ducts from 4 to 24 in by friction rate and velocity, rectangular equivalents, velocity limits and fitting lengths.

  • Fuel energy content and cost per million BTU

    EIA energy content of every heating fuel, default prices and efficiencies, and what a million BTU of delivered heat costs with each.

  • Ventilation and exhaust minimums

    ASHRAE 62.2 fresh-air rates, IRC and HVI rules for bathroom fans and range hoods, makeup air, air change targets and humidity guidance.

  • HVAC unit conversions

    BTU, watts, tons, therms, MBH, boiler horsepower, CFM, m³/h, inches of water, pascals, GPM and temperature conversions.