Takagi makes two models of recess boxes, the TK-RB01 and the TK-RB02. The TK-RB02 is made for outdoor applications while the TK-RB01 is made for indoor applications. Use a TK-RB01 with any indoor Takagi Tankless Water Heater such as the TK-4 for natural gas.
Takagi heaters and Takagi tankless heaters can be found at www.supplyhouse.com
Takagi heaters and Takagi tankless heaters can be found at www.supplyhouse.com
