I need to replace an oil boiler w/ tankless coil. The customer is very set on going with an electric wall hung boiler for the setup, likely a Slant/Fin. Is an indirect more efficient than an electric hot water tank? His new boiler will be off electricity anyway so in short the questions is does he add another breaker to the panel and put in electric HWT or use an electric indirect?
I'd install a tankless electric water hearer or three. Depending on the house layout and size, two or three smaller units can frequently work better than one big one. You can also squeeze them into a smaller (electrically speaking ) service. They will occupy 2-4 breaker spaces each (six for the big ones.) I've had good luck with Stiebel Eltron (and the company seems to be here for the long run, unlike a few others we've seen.)