Instruction Manual
7
1.
Circulator Sizing.
Refer to Table 2 for the minimum ow through the water heater coil and the pressure drop at minimum ow. Calculate the
pressure drop across all piping and ttings connected to the water heater zone. Be sure to include all zone valves, check
valves, and shut-off valves. It is recommended that the water heater zone be piped with 1” pipe around the entire loop on
typical residential sites.
A. System Zone Control
The water heater must be installed as a separate zone from the space heating system. The water heating zone’s piping
and circulator must be sized for the minimum ow rate with all the zones in use and a maximum ow with only the water
heater in use. Zone control with circulators normally gives the best performance.
The three most common systems are:
1.
Zone Circulators - Space heating zones use a circulator for each zone. The water heater is controlled with an
additional circulator.
2.
Hybrid System - Space heating zones use zone valves for each zone. The water heater is controlled with an
additional circulator.
3.
Zone Valves - Space heating zones use zone valves for each zone. The water heater is controlled with an
additional zone valve. Select a valve with a low pressure drop, and assure minimum ow with adequate pipe
sizing.
B. Priority or Non-Priority for Hot Water
1.
Option 1 – Priority. The demand for space heating is interrupted until the hot water demand is satised. This
option provides the maximum delivery of hot water.
Priority is recommended when:
A. The boiler output is less than 100,000 Btu per hour, or
B. The boiler output required to satisfy the hot water demand is more than 50% of the boiler output needed to
satisfy the space heating demand, or
C. When an interruption in space heating can be tolerated during long domestic hot water draws.
In most cases the delay in space heating will not be noticed because of the rapid recovery of the water
heater. It must be recognized however that certain water heater malfunctions, such as a failed thermostat or
circulator, could delay space heating indenitely.
2.
Option 2 – Non-Priority. Boiler output is divided between space heating and water heating. Heating of
domestic hot water can be reduced during simultaneous space and water heating demands. The amount of
reduction depends on boiler output, number of space heating zones calling, and amount of boiler water ow split
between space heating zones and water heater zones.