The vertical stainless steel inox-crossal heat exchanger offers ideal conditions for intensive utilization of hot gases, resulting in efficiencies of up to 98% the smooth stainless steel surfaces allow the condensate created by the condensing process to simply run off downwards this creates a permanent self-cleaning effect, ensuring high efficiency, long service life and reduced maintenance. I've left a message with the installers to call me in the morning again!!! so hoping they come first.