Looking for expedited fan arrays and coils for critical applications? Contact Us
Looking for expedited fan arrays and coils for critical applications? Contact Us
Steam coils are a common heat source in an air handler and provide heating for commercial and industrial buildings. Similar to a hot water coil, the supply and return connections are the same on these coils. Despite this similarity, steam is very different than hot water, and steam coils are specially built for and circuited for steam.
There are two types of steam coils used in commercial and industrial applications: standard steam coils and non-freeze (steam distributing) coils. Standard coils have a single-tube contraction, while non-freeze coils have a dual-tube construction.
Standard coils are made with 5/8” tubes, and the tube thickness differs based on the application and steam pressure. They are used when entering air temperatures are above 40ºF. It’s recommended to pitch the casing on almost all steam coils to remove the condensate.
In a non-freeze steam coil, a tube is set inside another tube. The steam on the inner tube prevents the condensate in the outer tube from freezing. Coils were initially designed to distribute steam evenly along their length and to eliminate any dead spots on the coil. Because of this, the coils were not as likely to freeze, so they became known as “non-freeze”, which is mostly accurate. In reality, any coil can freeze under certain conditions, but this design is what needs to be used when the entering air is under 40ºF.
We have both Standard Steam and Non-Freeze Steam Coils with optimized tube sizes for ideal steam distribution.
Off-the-shelf steam coils are built to a grid of standard face sizes, row depths and fin spacings. If your air handler was built around one of those sizes, a standard coil is the fastest and cheapest route, and for a straightforward swap in a common cabinet it is usually the right answer.
The catch is that most air handlers in service were not built around a catalogue. Casings get modified, coil pockets get shimmed, connections get relocated. A coil that is a quarter of an inch too deep does not go in — and a standard coil that almost fits costs more in installation labour and downtime than the price difference ever saved.
A custom coil is field-measured: face dimensions, casing depth, connection size and position, tube and fin material, and the header orientation the pocket will actually accept. We can quote from a model number, or a Mainstream representative can measure the coil in place. The result drops into the existing opening without modifying the unit.
Four inputs drive the selection. Entering air temperature and airflow set the load the coil has to carry. Available steam pressure determines the condensing temperature, and therefore how much capacity each row buys you. Required leaving air temperature fixes the total heat transfer. Face area and allowable air-side pressure drop cap how far you can go on rows and fin spacing before the fan runs out of static.
One question matters more on steam than on anything else: will the coil ever see air below freezing? A coil handling outside air needs a steam distributing — non-freeze — construction, where an inner tube carries steam the full length of the coil so no section sits flooded with condensate in front of cold air. Getting this wrong is the most expensive mistake in steam coil selection, because the coil does not just underperform, it splits. If the coil sits downstream of a cooling coil for humidity control, that is a reheat duty and our reheat coils are built for it.
Steam coils are replaced on condition, not on a calendar. The signs worth acting on:
On lead time: after a quote request comes in we contact you to go through the details and return a quote within one business day — in as little as half an hour in an emergency. Replacement coils can ship in as fast as 24 hours from order placement, which is usually the number that matters when a unit is down in heating season.
Steam coils are replaced on condition rather than on a fixed schedule. Inspect annually and replace when you find corrosion at the tube-to-header joints, water hammer on start-up, leaks at the casing, or a coil that no longer reaches its design leaving air temperature. Service life depends heavily on operating conditions, condensate drainage and maintenance.
A steam coil transfers latent heat as steam condenses inside the tubes, which moves far more heat per unit of flow than a hot water coil relying on the sensible heat of circulating water. Both put supply and return on the same side, but a steam coil also needs trapping, venting and condensate drainage that a hot water coil does not.
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