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 (¾" NPT).
Do not cap, plug or obstruct the discharge pipe outlet.
6.6 Relief Valve
Ensure that the pressure relief valve is installed indoors; third parties sell combination relief valve /
vacuum breakers for easy mounting on top of a buffer tank
Make sure the relief valve outlet is piped with unobstructed piping (minimum 3/4" diameter) to a safe
discharge location.
6.7 General piping best practices
Primary/secondary piping, or the use of a hydraulic separator, and the use of a properly sized
buffer tank is recommended for maximum flexibility in multi-load applications. See Buffer tank
sizing on page 34 and Quick calculation for buffer tank sizing on page 34.
Very large-zoned radiant floor systems (warehouses for example) may be able to do without a
buffer tank by virtue of the thermal mass of the slab. It is essential in this case that the smallest of
the slab zones is large enough to absorb the heat pump output in warm weather. For this design
IBC recommends, presuming 12-inch tubing centers, a six-inch slab with a minimum equivalent
area of 34 feet by 40 feet for the HPX 3 and minimum 34 feet by 50 feet for the HPX 5.
6.7.1 System piping
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General