Propylene glycol solution is commonly used in a closed loop where freeze protection is required. Its
density is lower than that of water, resulting in lower thermal performance at a given flow and pressure.
Generally, a 50%:50% solution of propylene glycol and water requires an increased system circulation
rate (gpm up 10%), and system head (up 20%) to provide performance equivalent to straight water.
These boilers are designed for use within a closed loop, forced circulation, low pressure system. A 50
psi pressure relief valve (¾" NPT inlet, 1" NPT outlet) is supplied for field installation in the relief valve
fitting on top of the boiler. An optional relief valve, with a rating of up to 150 psi, can be used where
required on closed loop systems. Relief valve discharge piping must terminate between 6" (15 cm) and
12" (30 cm) above the floor or per local code.
Warning
During operation, the relief valve may discharge large amounts of steam and/or hot water.
To reduce the potential for bodily injury and property damage, install a discharge line that:
Is connected from the valve outlet with no intervening valve and directed downward
to a safe point of discharge.
Allows complete drainage of both the valve and the discharge line.
Is independently supported and securely anchored, so as to avoid applied stress on
the valve.
Is as short and straight as possible.
Terminates freely to atmosphere where any discharge will be clearly visible and is at
no risk of freezing. terminates with a plain end which is not threaded.
Is constructed of a material suitable for exposure to temperatures of 375° F or
greater.
Is, over its entire length, of a pipe size equal to or greater than that of the valve outlet
(1" NPT).
Do not cap, plug or obstruct the discharge pipe outlet.
3.8.1 General piping best practices
Primary/secondary piping, or the use of a hydraulic separator (such as the Caleffi 549 SEP4™ 4-in-
1 Magnetic Hydraulic Separators) is recommended for maximum flexibility in multi-load
applications. Piping loads in parallel is also encouraged in systems that only have two loads, or
when loads are operating simultaneously. The extremely low pressure drop through the heat
exchanger of the EX series affords more flexible options unavailable in other designs.
3.8.1 General piping best practices
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