Toyotomi Oil Miser OM-128HH On Demand Hydronic Heater

A water heater with a boiler attitude for Hydronic Heating*

This versatile on-demand continuous flow water heater with 87% efficiency saves as much or more than the leading cast iron boilers, at half the size!

  • Continuous hot water
  • Compact size and 81 lb. weight allows for one person installation
  • Inlets/outlets on two sides for easy installation
  • Choice of direct vent or chimney vent
  • Cold start capability
  • Flow rate of over 4 gallons per minute with 60°F rise in temperature
  • Approximately 180°F maximum hot water temperature
  • Very quiet and reliable operation
  • Stainless steel heat exchanger
  • Adjustable temperature differential for cycling control
  • Safe:  ETL and home and mobile home approved
  • Proven trouble-free performance.
  • Limited 10 Year Warranty


Flow Rate/Temperature Rise

6.2 gal/min (40°F rise), 5.0 gal/min (50°F rise)

4.1 gal/min (60°F rise), 3.5 gal/min (70°F rise)

3.1 gal/min (80°F rise)


High Voltage Discharge Spark


87.1% AFUE rating

Fuel Consumption

1.05 gal/hr

Capacity of Heat Exchanger

5.10 gal

Temperature Differential Settings

3.6°F, 18°F, 36°F (3 settings by selector switch)

Fuel System

External tank***

Dimensions (WxHxD)

12-5/8 x 27-3/4 x 22-1/2


81 lbs. Empty

Vent Pipe Hole

4-3/4 diameter (for flue pipe installation kit)

Maximum Length of Vent Pipe System

10 ft., 3 bends or less (exhaust pipes for flue pipe installation kit)

Electrical Rating

120 Volts AC, 60 Hz

Fuel Type

ASTM D3699 K1 Kerosene

ASTM D396 No.1 Fuel Oil

ASTM D975 Ultra Low Sulphur Diesel (ULSD)

ASTM D396 No.2 Fuel Oil (Home Heating Oil)

Required Accessories

Flue Pipe Installation Kit or 4 or 5-inch Chimney Adapter Kit

Safety Device

High Limit Thermistor,

Heat Exchanger Bi-metal Switch,

Temperature Fuse, Fusible Link Valve

Exhaust Air Temperature

Less than 500°F

Nozzle Size

0.85 GPH

Spraying Angle


Spray Pattern

Delavan Type XA

Temperature Fuse


Electric Current Fuse

5 A (Main Control)

7 A (Auxiliary Port for Circulation Pump., etc.)

*Check State and Local codes/ordinances for permitted use.
**Heat and vaporized water are produced by the combustion process of this water heater. This rating does not take into account heat loss due to condensation of water vapor.
***External tank to be purchased from local suppliers.

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