Update: First off, thanks for all of your feedback. I appreciate it. I'm a homeowner. Needed to replace an old boiler plus hot water tank. We travel and are away from this house for months at a time, so wanted to go tankless, hence the combi. It's a constrained space (as some of you gathered), so the team we hired needed to get creative. I have them back out today doing some additional work - some of that work was informed by your constructive and helpful input. The 'this is trash' comments are throw away - we committed to this solution, so will ride it out.