heating...no pressure at top floor

Terry St.james

Thanks for the reply...unfortunately we have not had the chance to get to that job. We were just hit with 35-40 cm (14-16 inches in your language) of snow. Building owners wait until the last moment sort of like car owners...they wait until the snow falls to get the winter tires on and then can't figure out why it can't be done right away.
I do have a little more info...boiler is 2 levels below 1st floor and air cushion tank is on the top floor and water feed is there also. Maybe I'll get there tomorrow just finished a triple shift so I am off to la la land.

Terry St.james

I was just cruising around this site when I got a call from a fellow worker. We just took over another building to service and has some serious heating problems. The problem there is no pressure at the 16th floor...literally .5 psi...should be at least 5 to 8 psi
besides checking the pump size tomorrow...any other suggestions?
By the way its a 2 pipe system.

Brad White_2

The pump

really has nothing to do with the system pressure. It is the cold-fill pressure that establishes system pressure. The circulator (pump) just moves the water around, not unlike a ferris wheel. It creates a difference in pressure across it but does not add to system pressure.

The desired pressure at the top of the system you note at 5-8 PSI is acceptable by the way. (I consider 4 to 5 PSI at the top a minimum.)

This pressure would be set by the fill valve at whatever elevation that happens to be. If it is in the basement and your 16-story building has 12 feet per floor (192 feet more or less), the required pressure would be in the range of 88-90 PSI at the bottom. This is above most commercial ASME relief valves which typically run at a 60-75 PSI setting. You can get them higher and the location (elevation) is what makes this more critical.

I would find out where the system was filled (from what elevation), find the relief valve and see if it has dumped or weeped recently.

As a hunch, I find that 0.5 PSI at the top of the system a balance point after a relief valve incident; pressure settling to what was left...

tim smith

Brad, one thing he has not told us.

Maybe it is a roof boiler, then relief valve setting not an issue to handle the pressure there.

Brad White

A good and fair question, Tim!

But then the boilers would be dry and there would not be heat anywhere, let alone just on the top floor. (Thus far the term "serious heating problems" would wrap around this issue pretty well!)

But a fair point that I am glad you brought up. Thanks!