Oil Miser 128 Hydronic Heater



The Oil Miser 128HH is the new and improved model from the Oil Miser 180. The Compact low-mass water heater with 87% AFUE efficiency saves customers as much or more than the leading cast iron boilers, at half the size! The 128HH provides continuous hot water and compact size for easy installation. 

New Features:

  • Improved Performance
  • Easier Maintenance
  • New Safety Features

The Toyotomi/Oil Miser water heaters are on-demand, which means there is no costly storage of hot water until it is needed. Like all Toyotomi products they are safe, reliable, and easy to install. You'll love the convenience, and you'll love your new lifestyle.


Required Accessories:


Requires the addition of one of (A) required accessories to complete the unit



  • 20476430  Chimney Vent Installation Kit
  • 20476440  Direct Vent Installation Kit



Continuous hot water

Compact size and weight allows for one person installation

OM-128HH has 1/2 inch drain and 3/4 inch pressure valve connections on the left side and 1 1/4 inch connections for supply and return on the right side

Choice of direct vent or chimney vent

Cold start capability

Very quiet and reliable operation

Heat exchanger has easy access for servicing from the top without having to disconnect any water pipes

New temperature fuse that attaches to the heat exchanger, to cause shut down in case the top of the heat exchanger gets too hot

New timing sequence for the photo eye.

Stainless steel heat exchanger and cabinet

Adjustable temperature differential for cycling control






Type combustion type – oil pressure vapor
flue pipe – forced flue/chimney vent
heating system – on-demand
purpose – hydronic heating(1)
Ignition high voltage discharge spark
Fuel Type: ASTM D3699 K1 keroseneEROSENE
ASTM D396 no.1 low sulfur fuel oil
ASTM D975 ultra low sulfur heating oil/ diesel
ASTM D396 no.2 fuel oil (home heating oil)
Efficiency 87.1%
Hot Water Input 148,000 btu/h
Hot Water Output 128,900 btu/h
Fuel Consumption 1.05 gal./h
Max. Hot Water Temperature 176°F (approximately)
Water Flow Rate/
Temperature Rise:
6.2 gal./min. (40°F rise)
4.1 gal./min. (60°F rise)
3.1 gal./min. (80°F rise)
Capacity of Heat Exchanger 5.10 gal.
Fuel System external tank(2) gravity fed
Dimensions (W x H x D) 12-5/8" x 27-3/4" x 22-1/2"
Weight 77 lbs. empty
Vent Pipe Hole 4-3/4" diameter
Max. Length of Vent Pipe 10 ft., 3 bends or less
Electric Rating 120 volts AC, 60 Hz
ignition - 120W
burning - 98W
Required Accessories fuel filter, flue pipe installation kit (Part #20476440) or chimney installation adapter kit (part#20476430 - 5 inch kit or #20476415 - 4 inch kit)
Safety Device over-heat protector,ignition safety device, heat exchanger bi-metal switch, dual-temperature fuse, fusible link valve
Exhaust Air Temperature less than 500°F
Nozzle quantity of vapor - 0.85 GPH
spraying angle - 60°
spray pattern: delavan type XA
Temperature Fuse 282° F
Electric Current Fuse 5A,
7A (for external circulation pump or accessory)


(1) Check state andlocal codes/ordinances for permitted use. Can also supply domestic hot water provided it is used with indirect storage tank.
(2) External tank to be purchased from local suppliers.



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