My savings would be a lot more (don't know if that is good or bad news). As far as the effort goes, I want to start treating WMO for my Deuce anyway, but just now I am not in a position to use it as often as I'd like. So, the HHO option gives me a chance to familiarize myself with the process and develop my own procedure for doing same.If I were to supplement 20% of my heating oil with UMO, it would save me about $400/year in fuel expense.
To do this would cost additional money and time and effort(and mess). Factor in the desire to have a very reliable heating system, and I just don't see it being worth it.
If time and labor were not such an issue, making bio-diesel and supplementing with that, would be my first choice(better choice IMHO). But given the time, mess and expenses involved, the savings would be even less that using UMO, so you would need to supplement at least 50% of your annual fuel consumption to make a reasonable savings.
Manufactured waste oil furnaces/boilers/heaters are out there. Most are well designed and function well, but the fuel(UMO) still needs to be water free and filtered. I've never seen one that was as care free as a normal fuel oil system.
So far, it sounds like the worst I have to worry about with a 20% mix is clogging a filter or a nozzle. That does not sound too risky, so it might be worth a shot.
I never mentioned it, but I have a second HHO tank full up. This tank would not see any WMO. So I have backup if I run into a bad clog.