I recently installed a new walk in shower, with 3 body sprays and a 10" rain shower. All this will use 10 gpm. I am trying to find out, what will be the best way to replace my 40 gal gas water heater? I also have a 3 section boiler. Should I add a tankless heater to my boiler with a 50gal storage tank or should I get a direct fired heater?: