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Plumbing condensate return through an F&T trap

tseethof Member Posts: 2
We replaced the 80 year old steam boiler in our condominium with a one. In the boiler room, the contractor connected the old condensate line, two steam lines (the terminal ends), an F&T trap, a vented feed water system and the boiler like this:

Condensate Line -> Steam Return -> Steam Return -> F&T trap -> Vented Feed Water-> Boiler

It seems to me that the condensate line will be at atmospheric pressure so long as there is no steam or condensate in the F&T trap. But, when steam arrives at the F&T trap, the door to the atmosphere closes, radiators stop taking steam, and steam from the terminal runs will want to flow up the condensate line.

The contractor says some radiator steam traps may have failed. Seems like bad plumbing to me.

Am I missing something?


  • Steamhead
    Steamhead Member Posts: 16,948
    Nope. That's called "master trapping" and it's WRONG. Your assessment is correct.

    First off, if any steam does come back to the tank, either fix the bad traps or turn the steam pressure down.

    If this is a system with traps on the radiators, the pressure should probably not be higher than a pound or so. If more pressure is needed to get steam to some radiators, find out why the air isn't getting out of them. If the pressure is too high, the hotter condensate can flash to steam when it hits atmospheric pressure.

    If the guy is concerned about steam reaching the tank and maybe damaging something, he can put an aquastat on the return line near the tank inlet, wired to stop the burner if it gets over 180° or so.

    Where are you located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • tseethof
    tseethof Member Posts: 2
    Thanks. The boiler runs 5-7 psi.
    We are in Portland Oregon.
  • Lyle524
    Lyle524 Member Posts: 1
    So I have a 2" steam main which i have to install an f&t trap at the end of a run. When do i reduce the steam main down to connect to a 3/4" f and t trap? Can i reduce down to a 3/4" valve,strainer,and union. Or does the strainer need to be 2"
  • Steamhead
    Steamhead Member Posts: 16,948
    tseethof said:

    Thanks. The boiler runs 5-7 psi.

    Why? I bet you could run it on half that. Click on the link in my signature to see some pics of a job where we got the pressure down to ounces.

    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    JUGHNE Member Posts: 11,093
    Lyle524, you should start your own post.
    Include pictures of the end of the steam main if you can.
    How did this work before w/o trap??….something must have changed??
  • dopey27177
    dopey27177 Member Posts: 887
    The steam trap at the end of run needs to be sizes to the maximum pounds o steam per hour the boiler puts out at the coldest day of the year.

    If you are using a 3/4" steam trap I or one would install a 1" trap as the maximum condensate load is about the same or a 3/4" steam trap. This will give you a larger strainer,

    Remember the capacity of the steam trap is based on the pressure differential of the steam main and the return.

    Your open to the atmosphere condensate pump set/ boiler feed unit will always have steam vapor exiting the vent pipe. In your two pipe system if you have radiator traps blowing steam out of them you will see steam not vapor exiting the vent.
    You can install a thermometer in the condensate receiver to monitor return temperature. If the temperature exceeds 200 degrees you have a series of failed radiator traps.

    One other thing to remember is steam pressure is based on the resistance caused by the piping in the building which was determined when the building was built.

    One consideration is the altitude that the building is at.
    Unless the radiators in the building were sized to heat at a lower steam temperature (not pressure) you may need to fiddle with the pressure.

    at sea level water boils at 212 degrees
    at 500 feet water boils at 211 degrees
    at 1000 feet water boils at 210 degrees
    at 1500 feet water boils at 209 degree
    at 2000 feet water boils at 208 degrees

    Remember an EDR is based on 215 degree steam.

    Steam at 0 psi is 212 degrees
    Steam at 1 PSI is 216 degrees
    Steam at 2 psi is 219 degrees
    Steam at 3 psi is 222 degrees
    Steam at 4 psi is 225 degrees
    Steam at 5 psi is 227 degrees

    Since you are Portland Oregon and you may be in a mountainous location I posted the above values to helpyou determine the proper operating steam pressure.

    One other thing if it worked well before leave the pressure alone.

    These acts and others are in my book
    Steam the Perfect Fluid for Heating and Some of the Problems

    Available at Dan Holohan's library, Amazon, Barns and Noble or the publisher Dorrance in Pittsburgh Pa.

    Jacob Myron
  • Kicks52
    Kicks52 Member Posts: 1
    I want to divert condensate thru a kicks pace heater in a steam system,using a diverter tee.it will go directly back to boiler.done it thru baseboard brfore.ever hear of problems with that?
  • pedmec
    pedmec Member Posts: 994
    it would probably fail due to sediment build up. condensate return is mostly acidic too.

    i doubt the diverter tee would work as its just gravity return. why would you take the long route when you can go straight.

    I had buildings that we had commercial fin tube installed on the horizontal returns to heat the basement apartments.