Raytherm® Hydronic Boiler, 0042B-0180B

Quit struggling with bulky, heavy, out-of-date cast iron boilers. Raytherm copper fin tube boilers are low-mass and have high recovery rates. They’re small enough to fit almost any space and fuel-efficient for utility savings. With five sizes to choose from, there is a copper fin tube Raytherm for every application.

Raytherm® Hydronic Boiler, 0042B-0180B



 Model Number
Full Input in BTUH
Firing Mode
Flue Dia.
 AFUE Ratings
 H4-0042B  42,000  On-off  4"  84.0
 H4-0066B  66,000  On-off  5"  83.0
 H3-0090B  90,000  2-Stage  5"  82.7
 H3-0135B  135,000  2-Stage  6"  82.8
 H3-0180B  180,000  2-Stage  7"  83.2


Operates down to 105 °F return water temperature without condensing – perfect for the low temperature needs of radiant floor and snow melting systems.

Built-In Pump and Bypass
Offers maximum application flexibility.

Honeywell IID Ignition

Standard S8600 IID eliminates off-cycle fuel consumption; Standing pilot available on Models 90-180.

“Spark-To-Hood” Pilot

Eliminates erratic pilot ignition and lockout.

Motorized Vent Damper
Prevents heat loss during off-cycles.

Electronic Controller
with outdoor reset varies the setpoint as the air temperature changes.

Available for natural gas or propane.