Hi- I'm hoping that I can get some suggestions to bring to my engineer. I'm working on a tough project where we have an existing 4 story building that we would like to convert to one and two bedroom apartments (none over 800sqft). Most of the units will be stacked. We would like to use natural gas as a heating source and would like to individually meter the units it possible. We would also like as inexpensive system if possible. . . We had planned on using gas PTAC's with a little electric resistance as backuyp in the two bedroom units. It turns out the building is likely historic and we won't be able to make too many penetrations to the exterior so PTAC are definately out.

So we are back to the drawing board.

I recently toured a townhouse that used a tankless water heater to provide both domestic hot water as well as hot water to wall-mounted hydronic heaters that had little blowers in them. I am wondering if anyone has any experience regarding the efficiency or durability of this sort of system. I was also wondering if it would be possible to vent these vertically, in series, potentially as far as 35'. We have exsiting penetrations through the floors for some of the old stacks and may be able to reuse them.

Any other system sugestions are also greatly appreciated. We are in the Northwest where there can be a bias against using natural gas due to the low cost of electric so outside experience is greatly appreciated.