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# Steam Pressure

Member Posts: 66
I was reading "The Lost Art of Steam Heating" and there seems to be a discrepancy. One suggestion is to have the steam pressure at a few ounces to overcome the internal friction of the pipes. But it is also written that the steam at the radiator is measured at 1 psi. So the total steam of the system should be 1 psi + the few ounces of internal friction?

Any ideas?
Burnham Independence IN8

## Comments

• Member Posts: 17,025
More of a simplicifcation

One pipe and conventional two pipe systems were generally sized to have a pressure drop on the order of 1 psi between the boiler and the radiators.  Combined with the loss through the radiators and returns, 1.5 psi at the boiler (more or less) is normal and 1 psi at the radiators, with the system warmed up, would not be out of line at all.  Traps and vents can handle that quite happily.  I think Dan's idea was more that the pressure should never be over 1 psi at the radiators, than that it should be exactly 1 psi.

However... first, there is no real reason to have the pressure that high, provided that you have enough venting on the mains (patience, vapour systems coming up here) to allow the air to get out fast.

Second, a surprising number of two pipe steam systems are vapour systems, and those are designed from the beginning to run on no more than a few ounces of total pressure differential between the boiler and the ends of the returns -- 8 to 12 ounces max.  Some of them -- the types with traps -- will work on slightly higher pressures, but aren't really happy with them.  Some of them -- the types which depend on water seals or orifices -- may not work at all, or if they do, remarkably poorly, at higher pressures.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 2,752
edited August 2013
Pressure

Most systems are (hopefully) designed for a pressure loss of 1-2 ounces per every hundred equivalent feet of piping on the longest run. You only need that much pressure, plus a little extra for safety, to operate correctly. This puts 90% of residential homes at an operating pressure of 8 ounces or less.

I think what the book refers to, if I remember correctly, is just an example using round numbers to make the math easier.
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