You have to do what you have to do on the nastys. I think you would be a little better off with the powermax on residential. It may leave some residue but at least it has a safe PH. You are cleaning with low flow chop stokes so you will leave residue from your prespray.
I would try to use a pre-spray like procyon that does not attract soil as much as possible. Those “Soap free” type pre-sprays are basically pure surfactants and work well on most soils if you get the water really hot. That should not be an issue when you get that kerosene heater installed.