Space Heating Equipment - Trap

The best trap will depend on the type of space heating application.

Trap Requirements - Constant Pressure

Unit Heaters and Air Handling Units
Pipe Coils
Finned Radiators

The steam traps that best suit constant pressure applications:

conserve energy by operating reliably over a long period of time
resist wear
can withstand hydraulic shock
provide abrupt, periodic discharge to purge condensate and air from the system
have the ability to handle dirt

The first two conditions are overriding. If the trap does not fulfill these requirements well, it should not be considered for these applications.

For unit heaters and air handling units, an inverted bucket (IB) with a large vent is recommended regardless of the pressure. A float and thermostatic (F&T) trap is a reasonable alternative within pressure/temperature limitations.

	Characteristic	Inverted Bucket	F&T	Disc	Thermostatic	Differential Controller
A	Method of Operation	Intermittent	Continuous	Intermittent	Intermittent	Continuous
B	Energy Conservation (Time in Service)	Excellent	Good	Poor	Fair	Excellent
C	Resists Wear	Excellent	Good	Poor	Fair	Excellent
D	Resists Corrosion	Excellent	Good	Excellent	Good	Excellent
E	Resists Hydraulic Shock	Excellent	Poor	Excellent	Poor	Excellent
F	Vents Air and CO₂ at Steam Temperature	Yes	No	No	No	Yes
G	Vents Air at Very Low Pressure (1/4 psig)(.02 bar)	Poor	Excellent	NR	Good	Excellent
H	Handles Start-up Air Loads	Fair	Excellent	Poor	Excellent	Excellent
I	Operates Against Back Pressure	Excellent	Excellent	Poor	Excellent	Excellent
J	Resists Damage from Freezing	Good	Poor	Good	Good	Good
K	Can Purge System	Excellent	Fair	Excellent	Good	Excellent
L	Performs on Very Light Loads	Excellent	Excellent	Poor	Excellent	Excellent
M	Responds to Slugs of Condensate	Immediate	Immediate	Delayed	Delayed	Immediate
N	Handles Dirt	Excellent	Poor	Poor	Fair	Excellent
O	Comparative Physical Size	Large	Large	Small	Small	Large
P	Handles "Flash Steam"	Fair	Poor	Poor	Poor	Excellent
Q	Mechanical Failure (Open -- Closed)	Open	Closed	Open	Open, Closed	Open


First Choice				Alternative				Overriding condition

In addition, many finned radiators and pipe coils are installed in metal fascia panels or hung on the wall. These cases have another requirement:

Comparatively small physical size

An IB with a large vent is the primary recommendation for finned radiators and multiple pipe coils. Thermostatic or radiator traps provide a reasonable alternative in most cases. On single pipe coils, use IB traps with thermic bucket vents when quick heating is required. Otherwise, use a standard IB trap.

Trap Requirements - Modulating Pressure

Steam traps that best suit modulating pressure applications:

conserve energy by operating reliably over a long period of time
resist wear
vent non-condensables at very low pressure (1/4 psi/.02 bar)
can discharge start-up air loads
perform well with very light loads

On variable pressure service, the F&T trap is the first choice, up to its pressure/temperature limitations. An IB with a large vent is a reasonable alternative, except on air handling units with a pressure of less than 30 psig (2 bar). In that instance, an IB with thermic bucket is a better second choice.