Crown Boiler TWZ175 - Manual (Page 18)

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2) Flow Restrictor (Recommended) - If water is drawn from the tankless coil at a rate in excess of the rating in Table 1b,
the temperature of the hot water may be too low to be of use. The use of a flow restrictor will prevent this problem by
limiting the rate at which water can pass through the tankless heater. If a restrictor is used, select one having a rating
in GPM approximately equal to the rating shown in Table 1b. If possible, locate this restrictor at least 3 feet from the
tankless heater inlet so that it is not subjected to excessive temperatures when no water is flowing through the coil.
3) Pressure Relief Valve (Required) - Limits the pressure in the tankless heater and piping. Use an ASME constructed valve
designed for domestic water service, such as the Watts #3L. Note that this is a pressure relief valve, not a T&P valve.
Select a valve with a pressure setting less than or equal to the working pressure marked on the tankless coil. Pipe the
discharge to a safe location using piping the same size as the discharge connection on the valve.
4) Hose Bib Valves (Recommended) - These valves permit the coil to be periodically “backflushed” to remove sediment.
5) Globe or Ball Valve (Recommended) - Used to adjust the flow through the entire tankless heater system if needed.
6) Unions (Required) - Tankless heaters may require periodic gasket replacement or other maintenance which requires
removal of the heater from the boiler. Install unions anywhere in the tankless heater piping that will facilitate removal of
the heater.
VIII tanKlEss HEatEr PIPInG
If the TWZ is installed with an optional tankless heater, pipe the heater as shown in Figure 14. The components in this
system and their functions are as follows:
1) Mixing Valve (Required) - During the heating season, the water exiting the tankless heater may be 180 degrees or more.
The mixing valve blends hot water leaving the tankless heater with cold water so as to maintain the hot water supplied
to the fixtures at a fixed temperature. This saves energy, increases the amount of usable hot water available to the
homeowner, and reduces the risk of scalding.
Install a mixing valve with a setting range of approximately 110 to 130F. Follow the manufacturer’s instructions for
installing this valve. Usually a “heat trap” will be required between the coil and the “hot” connection on the mixing valve.
WARNING
A MIXING VALVE DOES NOT ELIMINATE THE RISK OF SCALDING.
• SET THE MIXING VALVE AND BOILER LOW LIMIT ADJUSTMENTS AS LOW
AS POSSIBLE.
• FEEL WATER BEFORE SHOWERING OR BATHING.
• IF ANTI-SCALD OR ANTI-CHILL PROTECTION IS REQUIRED, USE DEVICES
SPECIFICALLY DESIGNED FOR SUCH SERVICE. INSTALL AND MAINTAIN
THESE DEVICES IN ACCORDANCE WITH THE MANUFACTURER’S
INSTRUCTIONS. DO NOT USE THE MIXING VALVE AS A SUBSTITUTE
FOR PRESSURE BALANCING VALVES OR OTHER DEVICES REQUIRED BY
PLUMBING CODES TO PROTECT AGAINST SCALDING.