Design Manual

9 R-TRWH-E-02 Rev D
Tank Water Heaters in a Circulation Loop
The following applies when using a tank water heater (gas or electric) to provide heat for a circulation loop. Drawing
WH1-RGE is an example.
The heat output of the tank must be equal to or greater than the calculated circulation loop heat loss.
(Reference page 7, Step 1 on calculating heat loss).
Electric Tank Water Heater
Since the input and output are the same for an electric tank water heater, this can be expressed as:
Electric Tank Input (Kw) > Circulation loop heat loss (Btuh)
3413
(1 Kilowatt = 3,413 BTU)
Gas Tank Water Heater
When using a gas style water heater, the efficiency of the tank must be taken into account.
Available Btuh output = (Btu input of tank) x (efficiency) > Circulation loop heat loss (Btuh)
Example:
30,000 Btuh input gas tank
0.62 EF
30,000 x .62 = 18,600 available Btuh output
Additional Guidelines
Rinnai water heaters not recovering a storage tank: In applications involving a commercial dishwasher, a hot water
circulation loop feeding the dishwasher is required.
Rinnai water heater recovering a storage tank: In applications involving a commercial dishwasher, a hot water
circulation loop feeding the dishwasher may be required depending on the distance between the dishwasher and the
storage tank. Refer to local codes when determining the need for circulation loops to dishwashers.
When using a Rinnai product as the heat source for a circulation loop, the piping systems should be designed with a hot
water circulation loop having a minimum circulating flow rate of 3 gpm. You must also review pressure drop curves for
the Rinnai when sizing circulators.
Rinnai water heaters cannot be used in applications requiring 180º-195º F water at a DISHWASHER, unless a booster
heater capable of producing 180º-195º F water is provided at the dishwasher. The Rinnai water heater is not to be used
as a booster water heater in these applications.
For beauty salon applications, a hot water circulation loop feeding the head wash stations is highly recommended. This
provides instant hot water to the head wash stations and reduces the possibility of cold bursts at the stations. (Refer to
the piping schematics in this manual.) Insulation of circulation piping is also recommended for heat retention.
Exhaust gases from beauty salon applications and fume hoods of commercial dish washers with chemical sanitizers can
be highly corrosive and may cause premature failure of water heater components. Care must be taken to ensure that
the water heater and vent termination are installed away from that area. An uncontaminated supply of combustible air
must be maintained for optimum performance of the water heater.
If the intended installation is located in hard water area, a softener or similar water treatment system must be used.
Always remember to perform routine maintenance.
For any applications requiring temperatures above 140º F, an MCC-91 temperature controller must be purchased
separately.