in dan's

Hvacman

The highest point of the system should have 3 psi... this insures that water will flow at that highest point... The only easy way we can tell the the top of the system has pressure is to take the indicated pressure at the boiler and compare it to the height of the system because pressure equals altitude. Short answer is that your system will operate with 5 psi indicated at the boiler because your highest point in the system is only less than 6 feet above the boiler.

[Deleted User]

primary - secondary pumping made easy,

he states on page 113; 'the fill pressure........top of the system.......keep it under 3-psi once it's there.'
and then goes on to use a 12, 18, 30 example. how does the 3 fit in? my creative math doesn't create a place for it

DanHolohan

There should always be

about 3 psi at the highest point. So you figure how much pressure you need to lift water to that point, and then you add 3 psi to that. It doesn't have to be exact, but that's the rule of thumb for this. The goal is to have positive static pressure at the top so that you can bleed air from the system, and so that water won't flash to steam when the circulator shuts off (assuming the water is very hot at that point).

[Deleted User]

thanks for the prompt response

then, is it another way of saying what i read elsewhere, i'm not sure where, 'figure out the pressure that you want the system to run at, and add 4psi for the boiler'?

hvacfreak

The boiler is already " under water " ...I wouldn't add any more for it. - M

Static height plus 3-5 psi to ensure a positive pressure at the top...and I learned that here...thanks Brad White

Total system height * .433 + 5 psi
( Total system height is boiler gauge to highest pipe or device in the structure )

[Deleted User]

Total system height * .433

which is the inverse math of dan's, sys hgt/2.31

which brings up another question. if it was a 3-story blgd at approx 24' sys hgt, the math would raise the total sys press above 30psi; 15.39+15.39(tank)+heat. so, the 30psi p/tv that usually comes with the boiler would need to be changed to a 35ish psi. no?

and another question; dan said adding the 3ish psi aids in bleeding air. at the 'top'? but, if it's a radiant floor system, there's only one vent, at the air scrubber. so is the extra 3psi necessry in a rad flr sys?

and.......since my little burnham is mounted off the floor on legs, the gauge is only 56" from my single story staple-up tubing, then the math would be; 4.67'x.433+3ish psi(if needed) = 5psi. 5+5(tank) = 10psi tot sys press. which is an embarassment for me due to the pumps that i over
'purchased'

opps edit - even though it's there, i didn't mean to add the above 5s to make a total sys press as 10psi

DanHolohan

The top of the system

is the highest boiler pipe in a radiant system when all the tubing is below the boiler, and that's where you need the extra 3 psi.

This is static fill pressure. It's not the circulator pressure differential. It's easy to confuse the two, but they're two separate things. The static pressure fills the system and keeps it under a positive pressure (that's the job of the fill valve); the circulator "turns" the wheel of water, much like the motor on a Ferris wheel. The circulator's pressure differential is there to overcome the resistance as water flows through the longest run of tubing that's in the floor.

[Deleted User]

i'm lost dan

"is the highest boiler pipe in a radiant system when all the tubing is below the boiler"; when using my personal sys as the example, i don't have any tubing below the boiler, and the highest point, radiant floor, is 56" above the boiler gauge.