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Branch off heating main question.

Wynston Member Posts: 3
Quick question to see if I can settle a small argument at work.  We are installing a heating system in a two story building, black iron mains are running in the ceiling space between the 1st and 2nd stories.  The engineer is having us take all branches off the top of the main to serve the upper and lower stories.  Basically the rads on the lower floor are stepping of the top of the main on a 45 degree angle, into a swing joint made with two 90's, going over to the outside walls, than down to the rads.  Is piping the system this way going to lead to air problems

The boiler looks to be drawn correctly in regards to pumping away from the expansion tank and all that good stuff.  It is a 2-pipe system (not reverse return), zone valve at every rad.

There is talk amongst us installing the system that air may be a problem and that the lower rads should step of the bottom of the main.  Just see what others think. Need any more info let me know and I will provide it. 




  • Tom Blackwell_2
    Tom Blackwell_2 Member Posts: 126
    It Depends--

    It depends on where you plan to get the air out. Any air trap will require a way to vent the trapped air out, unless the system design will allow a velocity of at least 5 feet per second to move the air. Ideally, the lower floor radiators should take off of the side or bottom, so air will migrate back into the main. The top floor would be ok off of the top to allow trapped air to end up in the radiators where it can be bled. Remember that any trap for air will become air bound over time, even if you manage to get it working initially. Dissolved air in the water will come out of the water over time, driven by temperature changes.
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