The A in 240 A designates a circulating system with buffer tank. I didn't see the circulation loop return line installed or tied in at the bottom of the unit, the condensate drain line installed, or the temp and pres. relief valve drain installed. In the attic I would question the rigid plastic water filter and cannister unless in a warm climate. Code requirements here do not allow the condensate drain to tie into the T & P drain line. They also require a pan and pan drain under the tankless water heater.