COLD STATIC FILL PRESSURE
The cold static fill pressure (CSFP) in a closed hydronic system has to be high enough to
accomplish three things.
1) Overcome the static head (height) between the fill point and the highest point in the system.
2) Provide adequate pressure (minimum 4 psig) at the top of the system for proper air venting.
3) Maintain adequate pressure at the inlet of the system pumps to prevent cavitation.
The formula for calculating the required CSFP to satisfy points 1 & 2 is:
(Static height in feet/2.31) + 4 = CSFP in psig.
As an example, the CSFP for a system with a static height above the fill point of 32 feet would
be:
(32/2.31) + 4 = 18 psig.
For most closed hydronic systems operating below about 210 F, maintaining the minimum top-
of-system pressure at 4 psig will be adequate to prevent pump cavitation even if the pumps are at
or near the top of the system as well.
IMPORTANT NOTE – For air-charged diaphragm or bladder tanks, the air charge in the tank must be
adjusted to equal the cold static fill pressure before it is connected to the system.
Summary of Contents for DMF Series
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