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FNT trap

Snowmelt Member Posts: 1,414
What’s the difference between FNT vs a steam trap after the rads, im assuming it has to do with volume of water, I notice the FNT is used with multiple rads vs steam traps tha are at the end of one specific rad.?


  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    by FNT do you mean "F&T" -- "float and thermostatic" ? If so, in a very real sense there isn't all that much in terms of function. Both of them have a float ;or similar mechanism which will lift and open a valve to allow water to flow, and both of them have a thermostatic element which will close off an opening when steam is present.

    However, that said, they are in other ways quite different. The typical radiator steam trap -- which can also be used in a number of other places, such as crossover traps for venting steam mains -- discharges both the water and air through a single opening at the outlet (usually the bottom -- they don't work all that well on their sides, and often not at all upside down!) to a single pipe which in turn conveys the air to a vent somewhere and the water --condensate -- to a return somewhere. They usually have a very large air flow capacity (hence using a modified one -- the B&J BigMouth as a vent). On the other hand, the F&T float opens what is essentially a drain, which connects usually to a return somewhere, while the thermostatic element opens a vent to somewhere else -- sometimes just out to open air. One advantage of an F&T is that if there is steam present in the line feeding the F&T the thermostatic element will close, naturally, and then the steam pressure present in the line can be used to force the water out of the drain and up to a higher elevation if needed. On the other hand, they often don't have that much air flow capacity and may need to have an additional vent, if air removal is a consideration (such as a steam main).

    They really serve different functions, and are not interchangeable. Other than the outlet from a radiator, which is obvious enough, which one should be used depends on what is feeding it --and where you want the condensate and air to go afterwards. One thing, though -- on a given line from, for instance, the steam main through a device (radiator? Fan coil? Brew kettle? Sterilizer?) or some other connection to a return, you want to have one and only one trap -- either one or the other.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Snowmelt
    Snowmelt Member Posts: 1,414
    Wow that was a detailed explanation, thank you