Measurement Guide

Application Manual Greentherm T9800/9900 SE/SEO/SEi | 9

Bosch Thermotechnology Corp. | 12.2019

Data subject to change

4.2 Domestic Hot Water Recirculation

Hot water recirculation is a technology that provides hot water virtually instantly

at the point of use by circulating hot water through the home’s domestic hot water

pipes.

The beneﬁ ts of hot water recirculation are the reduction in the amount of water

wasted and wait time for hot water to arrive at the point of use.

The Greentherm 9000 models have been designed for hot water recirculation.

All Greenthem 9000 models have the capability of controlling an externally

powered pump by switching power ON and OFF.

The T9900 models have an integrated pump, which is controlled and powered by

the tankless.

The Greentherm 9000 models offer multiple recirculation settings, such as

recirculation scheduling, comfort levels, and on-demand recirculation via app.

For information on how to change these settings, refer to the installation and

operations manual.

The ﬂ ow rate through the recirculation system must be larger than the

activation ﬂ ow rate of the water heater, 0.45 GPM.

For direct domestic hot water recirculation and tank loading

applications:

Run the system for 30 minutes to remove debris

from the plumbing. Then remove the unit‘s inlet water ﬁ lter to decrease

pressure drop through the system. If the inlet water ﬁ lter, when removed,

contains debris, it is recommended to install a 40 mesh Y-strainer

(installer supplied) on the cold water inlet.

Domestic hot water recirculation will increase appliance operation time,

and consequently increase maintenance requirements.

4.2.1 Recirculation system types

There are two basic types of recirculation systems.

 Dedicated return line making a complete hot water loop from the water

heater to each water point of use and back to the water heater (Figure 3).

 Cross-over valve that connects the hot water line to the cold water line

at the farthest fixture (Figure 4).

4.2.1.1 Recirculation system with dedicated return line

The preferred recirculation system uses a dedicated return line. See ﬁ gure 3.

Figure 3 Recirculation application with dedicated return line

[1] Cold water supply

[2] Check valve, ﬁ eld supplied

[3] Circulator pump, ﬁ eld supplied

[4] Expansion tank, ﬁ eld supplied

[5] Circulator cable accessory

[6] Greentherm T9800 SE / SEC

[7] PRV

[8] Shutoff valves, ﬁ eld supplied