General Formulae:
Face Area Square Feet = (FH x FL) / 144
View face area charts for tube size
Cooling/Heating:
Total Capacity (BTU/hr) = 4.5 x CFM x (H_{ewb} – H_{₁wb})
Sensible Capacity (Btu/hr) = 1.08 x CFM x (T_{1}db – Tedb)
Latent Capacity (Btu/hr) = 0.68 x CFM x (Grains H_{2}O removed per lb. air)
Sensible Heat Ratio = Sensible Heat / Total Heat
Lb per hr H_{2}0 Removed = 4.5 x CFM x Grains H_{2}0 removed per lb. air7000
Water Coils:
Fluid Velocity (feet per second) = (TC x GPM) / (Number of Feeds)
Tube OD  Tube Wall  TC 

5/8″ 


1/2″ 


3/8″ 


*Cooling: Total Capacity (Btu/hr) = 500 x GPM x (T_{1w}T_{ew})
*Heating: Total Capacity (Btu/hr) = 500 x GPM x (T_{ew}T_{1w})
*Assumes use of water (no glycol solution)
Steam Coils:
Lbs condensate per hour = BTU per hr of coil / *Latent heat of steam
*Assumes saturated steam
Steam pressure (psig) 
Latent Heat 

2 
966 
5 
961 
10 
953 
50 
912 
100 
881 
Symbol 
Description 

FH 
Fin height (inches) 
FL 
Fin length (inches) 
CFM 
Cubic feet per minute airflow 
H_{ewb} 
Enthalpy (total heat content) of air at entering wet bulb 
H_{wb} 
Enthalpy of air at leaving wet bulb 
T_{1db} 
Leaving air dry bulb temperature 
T_{edb} 
Entering air dry bulb temperature 
GPM 
Gallons per minute of cooling or heating water 
T_{ew} 
Entering water temperature 
T_{1w} 
Leaving water temperature 
Useful Coil Conversion Factors
To Obtain 
Multiply 
By 

BTU 
Kilo Calories 
3.9683 
BTU 
Watts 
3.41214 
BTU/lb 
kJ/Kg 
0.43 
Centimeters 
Inches 
2.54 
CFM 
Cubic Meters Per Hour 
0.5886 
Cubic Feet 
1 Liter 
0.035 
Cubic Feet Per Minute 
Liters Per Second 
2.1189 
Cubic Feet Per Minute 
Cubic Meters Per Minute 
35.31 
Cubic Meters 
1 Cubic Foot 
0.0283 
Cubic Meters Per Hour 
CFM 
1.699 
Cubic Meters Per Hour 
Liters Per Second 
3.57 
Degrees Celsius 
Degrees Fahrenheit 

Feet 
Meters 
3.281 
Feet Per Minute 
Meters Per Hour 
0.05468 
Feet Per Minute 
Meters Per Second 
196.85 
Feet Per Second 
Meters Per Second 
3.28 
Fins Per Millimeter 
Fins Per Inch Spacing 
25.4 
Gallons (U.K.) (IMP) 
1 Gallon (U.S.) 
0.8327 
Gallons (U.K.) (IMP) 
1 Liter 
0.21997 
Gallons (U.K.)/Minute 
Liters Per Second 
13.198 
Gallons (U.S.) 
1 Gallon (U.K.) (IMP) 
1.2 
Gallons (U.S.) 
1 Liter 
0.2642 
Gallons (U.S.)/Minute 
Liters Per Second 
15.85 
GPM (U.S.) 
GPM Water Flow (U.K.) (IMP) 
1.2 
Horse Power 
Kilowatts (kW) 
1.341 
Inches 
Meters 
39.37 
Inches Mercury 
Pa or N/m² 
0.004 
Inches of Mercury 
kPa 
0.296 
Inches of Water Gauge 
Feet of Water Gauge (Water Pressure Drop) 
12 
Inches WG 
Kilo Pascals (kPa) 
4.015 
Kilo Calories Per Hour 
BTU Per Hour 
0.251034 
Kilo Calories Per Hour 
Watts 
0.8598 
Kilo Pascal 
Feet of Water Gauge (Water Pressure Drop) 
2.99 
Kilo Pascal 
PSI (Pounds Per Square Inch) 
6.895 
Kilo Pascals (kPa) 
Inches of Water Gauge (Air Pressure) 
0.24908 
Kilo Pascals (kPa) 
1 Meter Water Gauge 
9.804 