Steam distributing coils are also referred to as non-freeze steam coils, tube-within-a-tube, and IDT (inner distributing tube).  They are designed for low temperature applications with entering air temperatures of 40 degrees or less.  Steam distributing coils utilize a common header and do not have any return bends. The tubes are a tube-within-a-tube design where there is a perforated inner distributing tube encased in an outer tube.  The steam flows through the inner tube and condenses.  It then “drains” to the outer tube and then flows back to the header and comes out the return connection on the header.  This design will help protect the condensate from freezing as it returns back to the header.

Commercial Coils offers steam distributing coils for many different applications, utilizing a host of different material options and metal thicknesses, for just about any type of environment.

Steam Distributing Coil Specifications

Primary Surface

Round seamless copper tubes are mechanically expanded into the fin collars of the secondary surface. The mechanical expansion provides a permanent metal-to-metal bond for efficient heat transfer. The 5/8″ O.D. inner steam distributing tubes are centered in teh outer condensing tube (1-1/8″ O.D.). The inner tube has proportionally spaced directional steam jet orifices that direct the condensate flow to the outlet.

Tube Size Options:

1-1/8″ O.D. x .035″ wall thickness standard with optional wall thickness of (.049). Centerlines are 3.0″ in the tube face and one row is the only option.
5/8″ O.D. outer with 3/8″ O.D. inner steam distributing tube

Secondary Surface

Corrugated plate type fin that is die-formed. Fin collars are full-drawn to provide accurate control of fin spacing and maximum contact with tubes.
Fin Material Options:

Aluminum fin thickness of .010 inch standard with optional (.008). Optional copper fin thicknesses available are (.006) (.008) and (.010). Fins per inch available 6 through 14.


Seamless copper with die-formed holes that provide a parallel surface to the coil tube for strong brazing joints.


Red Brass Schedule 40 male pipe thread (MPT) is standard with optional copper female pipe thread (FPT) available. Maximum fin length of 120 inches with same end connections. Fin length over 120 inches is recommended to have steam supplied at both ends (Type 9NOD). Any fin height over 48 inches will have two supplies and two returns.


Using 16-gauge minimum thickness material, 1 1/2″ flanges are die-formed to permit easy stacking and mounting. Intermediate tube supports are supplied on coils over 44″ fin length with an additional support every 42″ multiple thereafter.
Casing Material Options:

Full G-90 galvanized steel standard with optional stainless, aluminum and copper.

Testing & Performance

All coil assemblies are leak tested under water at 315 PSIG air. Standard construction is suitable for 50 PSIG steam pressure. Heavier wall, high pressure construction available up to 100 PSIG.

PERFORMANCE IS CERTIFIED under ARI Standard 410. All coil performance ratings are according to Commercial Coils, Inc.’s ARI certified selection software.