Product Overview
Page ___________ of ______________
Form C-HU - Page 7
ENGINEERING DATA (cont’d)
TERMS, ABBREVIATIONS AND FORMULAS
Following is a list of terms, abbreviations and formulas to assist in specifying the correct
size hydronic heating equipment for a specic application. All terms and abbreviations
apply to both steam and hot water heating unless otherwise noted.
ATR Air Temperature Rise - The difference between the Entering Air Temperature (EAT) and the Leaving
Air Temperature (LAT) due to the amount of heat added.
BTUH British Thermal Units per Hour - The common measure of heating output or capacity.
CFM Cubic Feet per Minute - The volume of air moved through the heater.
COND Condensate - The amount of water that results from removing heat from steam, measured in Pounds
per Hour (lb/hr) - steam heat only.
EAT Entering Air Temperature - The temperature of the air just before it passes through the heat
exchanger.
EDR Equivalent Direct Radiation - A measure of heat output measured in square feet - steam heat only.
EWT Entering Water Temperature - The temperature of the water as it enters the heat exchanger - hot
water heat only.
FPM Feet Per Minute - The measure of the velocity of air as it leaves the heater.
GPM Gallons Per Minute - The measure of the ow of water that passes through the heat exchanger - hot
water heat only.
L Latent heat of steam - steam heat only.
LAT Leaving Air Temperature - The temperature of the heated air just after it passes through the heat
exchanger.
LWT Leaving Water Temperature - The temperature of the water as it leaves the heat exchanger - hot water
heat only.
MBH One thousand BTUH
PSI Pounds per Square Inch - The measure of the pressure of steam in pipes - steam heat only.
RPM Rotations Per Minute - The number of rotations the fan will make in one minute.
WPD Water Pressure Drop - The resistance to the ow of water through a system created by friction between
the water and piping - hot water heat only.
WTD Water Temperature Drop - The difference between the Entering Water Temperature (EWT) and the
Leaving Water Temperature (LWT) due to the amount of heat removed - hot water heat only.
ATR = BTUH ÷ (CFM x 1.08)
LAT = EAT + BTUH ÷ (CFM x 1.08)
GPM = BTUH ÷ (WTD x 500)
WTD = BTUH ÷ (GPM x 500)
COND = BTUH ÷ L
COND = EDR ÷ 4
EDR = BTUH ÷ 240 (at 2 psi only)