Recently a rep has been pushing the Navien 98% efficient tankless with two stainless stell heat exchangers the lower of the two being condensing. The larger residential model the 240a puts out an impressive 7.2? gpm at 70 degrees of rise(not sure if that is exact but from what I recall if thats not it, its pretty close). Also comes with built in recirc pump and buffer tank. Supposedly with the recirc pump you can install grundfos comfort blocks under lavs and use the cold as a return. If any of you have installed this unit and know if in fact the recirc works with grundfos blocks I would greatly appreciate your feed back and experience with the units.