Dual-fuel boiler

A lot depends on how well that boiler was treated in its former life.

Overheated? Long cold run cycles?, water quality or fresh water added often, fire tubes cleaned regularly, green or wet wood burned in it?

Solid fueled boilers require more maintenance, every two weeks or so I did a deep clean on my wood fired boiler, and I burned seasoned hardwoods all the time, coal occasionally.

Knowing the former owners burn habits would tell a lot about the boiler.

A multi fueled boiler is a bit of a compromise, between boilers built to a specific fuel use.

You have to be diligent about cleaning the HS Tarm OT model boiler as it has a multiple smoke passage design.

I have attached the installation manual in a separate file as well as an image of the exposed side view of the OT model from Popular Mechanics showing the smoke passages for the oil burner and the boiler vessel water baffles in the fire box.

The Internal domestic coil is fully inmmersed in the boilers water chest and can be replaced by removing the dome covering part of the vessel.

When you get around to pressure testing the boiler you should remove the top cover to check for a gasket leak at the same time you pressurize the boiler to 60 PSIG

I used my switzer wood and coal boiler for 33 years before I switched to a keystoker coal stoker in 2015. The stoker boiler works well but keystokers service/help is/was worthless.

Your plumber is correct and honest about this in his thinking in discussing this with you. The HS Tarm wood and coal boilers were excellent boilers. I would have purchased one but I could not afford the purchase cost.

You need to put 60 pounds of water pressure in the boiler vessel and see if it holds 60 PSIG for 12 hours just to be sure.

You will need to plug or cap all the exposed tapping's and use a jet pump to pump water into the boiler drain as you use a ball valve in a top tapping to vent the trapped air as you fill it.

You should have a second ball valve installed in the tapping where the jet pump is pushing water into the boiler vessel also to seal the boiler for the pressure test.

Anytime you intend to switch to oil you will have to reinstall the oil burner in the oil burner mounting flange weldment.

The only boiler I would recommend as a dual fuel unit to burn hand fed wood and oil is from Alternate Heating Systems. This boiler model is the E140 employs an induced draft combustion system creating gasification using a 2 pass system.

The boiler E140 boiler has a refractory lining, swirl chamber, cyclone ash collector and an oil burner chamber that is separate from the wood burning chamber and the heat and oil flue gasses also pass through the swirl chamber before it exists out the flue pipe. The unit also has a domestic hot water coil as well.

You should select only carbon steel for the boiler vessel as the steel preference.

Hello and good morning Mike4484.

No, you should not pressure test the boiler with air!!!

When the boiler was purchased were the pipe tappings capped or plugged when you bought it??? This question has to be answered first, If, it has been left open and exposed to the elements it will have rust in the water vessel and other members of the forum can answer this question better than I can as a cleaning product used to clean steam chests may be able to take care of this for you.

Is there any reason you cannot use household water pressure temporarily by raising the cut out pressure to 65 PSIG temporarily and pressurizing the boiler and then closing the ball valve?

If the water vessel has been sealed during the last seven years it would not hurt to see about renting a dry ice sand blasting unit for a day or two or hiring a painter that has one to sandblast the fireboxes of the boiler as using dry ice blasting does not damage the surface it cleans and leaves only the built up material that was in the fire box as residue.

Those Tarm boilers are very rugged - if it doesn’t have obvious corrosion issues and passes a pressure test with water it should be good to use. With that said, there are better options for burning wood. A gasification boiler like a Wood Gun will burn much cleaner and use less wood.