Mine is mounted horizontal, but that is how my furnace is. I red my manual and it says nothing about vertical or horizontal mounting.
Since the pump is pushing the water, does it even matter?
I know in my case, horizontal was the only option, and my dealer installed it, and we had no issues. I have a side arm for DHW, so that is vertical by definition.
good luck.
I recently installed an OWB to heat my house and DHW. I fired it for the first time this weekend and with the exception of one minor leak in on of the copper adapters to my heat exchanger everything is working great.
However, as I was cleaning up I picked up the manual for my heat exchangers and noticed that it said that they must be mounted vertically. I somehow didn't see this when I was installing them and mounted both a 5"x12" 30 plate for DHW and a 5"x12" 50 plate that heats my house horizontally. The horizontal mounting made the piping a lot easier and 'cleaner'.
Did I make a mistake? Will the heat exchangers still function correctly mounted horizontally?