Hooking OWB without a HX?

I have a friend who is an oil burner man who does this regularly.
He says there are no issues.
I am skeptical. The system surely has to be treated with corrosion inhibitor.
And it needs to be regularly monitored.

If there is a corrosion problem, it could take out the OWB and the oil boiler.
If something outdoors pops off or springs a leak, there is the risk of the oil system running dry.

The physics of the basic concept is kinda cool.

I hooked up my first CB owb direct to the oil boilers in two different houses (6300 sq ft total). I did repipe the oil boilers to get pumps on the supply side. All water is treated. Sold the CB and hooked up a Portage and Main 250 this yr to see what it could do. Have not been cold yet. It sure can heat hot water. Got a Vigas here ready to go on line for next year. Perhaps i can cut the wood consumption some more. The boiler room floor is same elevation as the basement floor. Houses are two story.

AFA the corrosion goes, your oil boiler will do better if it is separated from the OWB, as most OWB's are open systems & are subject to far more O2 getting into the system on a continual basis. This extra O2 will speed up the corrossion in your oil boiler if it gets the chance. Thats where an Hx comes in, protects other components in the system from that extra O2.

That's why OWB co's recommend a Hx, so you can protect other components from that extra O2 that keeps on entering the OWB. Cheaper to replace a rusted out OWB, than one plus everything that is hooked up to it as well. In your case that would mean an oil boiler as well.

While your at it you may want to plumb the boilers so the OWB is not warming the oil boiler as the oil boiler will be sending btu's up the chimney causing you to burn more wood for nothing. In parallel rather than in series.

Lets see.. 2.31' = 1 psi. so 15psi x 2.31=34.65' elevation difference. (sea level of course).

The problem I see is if you aren't adding and O2 scavenger oxygen will be getting introduced into the water when it rises back up to the wood boiler and taken back down to the oil boiler.

In a high head open exp tank, system water is not "circulated" through it like you are doing. It is basically a weight that is raised and lowered on temperature swings.

Just my 2.

I have often wondered how much less wood I will burn when I get my boilers piped in parallel rather than in series as they are now. I have also wondered how much better still, it may be if the actual Garn water was circulating through my radiation.

Pick and choose your poison, as the saying goes. Note from my recent post on the WG E500 and Garn WHS3200 that the heat exchanger used on the Garn had a 5* approach temp, and that's at 75 gpm both sides. Pressurized and glycol on the system side, water on the Garn side. It basically "boils" down to matching the HX and circulator with system needs, and then paying the piper to get the combo that achieves the desired result. Cutting corners doesn't work very well.

I also had an OWB plumbed directly into an LP boiler system, no HX. My OWB was slightly pressurized, about 2 psi, and had a bladder expansion, so it also was mostly a sealed system. Single story house with the boiler at a slightly higher elevation than the baseboards in the house, LP boiler in the basement of the house. A few times each heating season I added sodium sulfite to the OWB. The system was in use more than 10 years without evidence of a problem.