Re: Min clearance between Heating fule line and hot water pipe?
not knowing types of fuel line piping nor plumbing piping makes this an unknown
but IMO there should be a true gap of some measure between both pipes to prevent other potentials also such as electrolysis as well as from heat.
In a residential setting, I would imagine that 1" thick code approved insulation for hot water piping would satisfy this if - properly secured to prevent slippage out of place
__________________ My comments towards your questions & concerns are based on my work history, knowledge, & past experiences; they are my opinions given freely in hopes they truly help/bless U. That said, if U don't consult with & or hire a licensed professional locally, then please don't blame me when You DIY... Bottom line - Safety 1st & Always; got that???