HTP 399M - Manual (Page 20)

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C. SEPARATE LOW WATER CUTOFF
A low water cutoff may be required by state and local codes, or by some insurance companies. A low water cutoff is also required if the
boiler is installed above the piping level. Check code requirements before installing the boiler.
If required:

Use an electrode probe type low water cutoff designed for hydronic installations.

Install in a tee on the supply piping above the boiler.
 Follow low water cutoff manufacturer’s instructions.
D. BACKFLOW PREVENTER
Use a backflow preventer specifically designed for hydronic boiler installations. This valve should be installed on the cold water fill
supply line per local codes. (See piping details at the end of this section.)
All piping methods shown in this manual use primary/secondary connection to the boiler loop. This is to avoid the possibility of noise or
actuator problems in zone valves because of the high-head boiler circulator. For other piping methods, consult your local HTP
representative or refer to separate piping details in this manual.
E. SYSTEM WATER PIPING METHODS
EXPANSION TANK AND MAKE-UP WATER
1. Ensure expansion tank size will handle boiler and system water volume and temperature. Allow 3 gallons for the boiler and its piping;
4 gallons for 399 models and piping.
Expansion tanks must be sized according to total system volume. This includes all length of pipe, all fixtures, appliances, etc. Failure to
properly size system expansion could result in wasted time, money, and possible property damage, personal injury, or death.
Undersized expansion tanks cause system water to be lost from relief valve and make-up water to be added through fill valve. Eventual
failure can result due to excessive make-up water addition. SUCH FAILURE IS NOT COVERED BY WARRANTY.
2. Expansion tank must be located as shown in Piping diagrams, or following recognized design methods. See tank manufactu
rer’s
instructions for details.
3. Connect the expansion tank to the air separator only if the separator is on the suction side of the circulator. Always install the system
fill connection at the same point as the expansion tank connection to the system.
4. Most chilled water systems are piped using a closed type expansion tank.
DO NOT install automatic air vents on closed-type expansion tank systems. Air must remain in the system and return to the tank to
provide its air cushion. An automatic air vent would cause air to leave the system, resulting in water-logging the expansion tank.
DIAPHRAGM (OR BLADDER) EXPANSION TANK
Always install an automatic air vent on top of the air separator to remove residual air from the system.
F. CIRCULATORS
DO NOT use the boiler circulator in any location other than the ones shown in this manual. The boiler circulator is selected to ensure
adequate flow through the boiler. Failure to comply could result in unreliable performance and nuisance shut downs from insufficient
flow.
SIZING SPACE HEAT SYSTEM PIPING
1. See Piping Details in this section. In all diagrams, the space heating system is isolated from the heating loop by the
primary/secondary connection.
2. Size the piping and components in the space heating system using recognized design methods.