What Is a Radiator Coil?
“Radiator coil” is a common name for the hot water or steam heating coils that actually do the heating inside an air handler, unit heater or rooftop unit—the same coils HVAC engineers call hot water coils or steam coils. Whichever name you use, the job is the same: hot water or steam runs through the coil, and air moving across it picks up the heat before being distributed into the space.
Hot Water vs. Steam Coils
Both heat air by circulating a hot medium through a tube-and-fin coil, but the medium changes the design:
| Type | Construction | Typical Conditions |
|---|---|---|
| Hot Water | 1–3 rows of tubes | Water enters around 180°F, air enters at 40–65°F |
| Standard Steam | Single-tube, typically 5/8″ tubes | Used when entering air is above 40°F; casing is pitched to drain condensate |
| Non-Freeze Steam | Dual-tube (tube inside a tube) | Inner steam tube keeps outer condensate from freezing in cold entering air |
Steam coils need to be specially circuited for steam rather than water, even though the supply and return connections look the same as a hot water coil—so a straight swap between the two isn’t usually possible without re-checking the design.
Custom Replacement Radiator Coils
When a hot water or steam heating coil needs replacing, Mainstream builds exact-match custom heating coils rather than a close-enough catalog part. A Mainstream representative can field-measure the existing coil, and standard or custom tube, fin and material options are available for new installations or retrofits, with expedited delivery when a project can’t wait.