Utica Boilers H2OI Dual 安装指导

Refer to Table 2 for the minimum flow through the water heater coil and the pressure drop at minimum flow. Calculate the 

pressure drop across all piping and fittings 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 flow rate with all the zones in use and a maximum flow with only the water 

heater in use. Zone control with circulators normally gives the best performance.

The three most common systems are:

Zone Circulators - Space heating zones use a circulator for each zone. The water heater is controlled with an 

additional circulator.

Hybrid System - Space heating zones use zone valves for each zone. The water heater is controlled with an 

additional circulator.

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 flow with adequate pipe 

sizing.

B.   Priority or Non-Priority for Hot Water

Option 1 – Priority.  The demand for space heating is interrupted until the hot water demand is satisfied. 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 indefinitely.

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 flow split 

between space heating zones and water heater zones.