I have a kitchen and bath on the other end of the house from the existing water heater and I am thinking about one of these or just a small tank to get some fast hot water. Right now you have to let the water run close to a minute, just to wash your hands if you want hot water.
Plan B would be my "attic" water heater idea. Just a large diameter pipe running at ambient attic temperature and a heat trap at the water heater. The problem is finding large diameter CPVC pipe.
Right now the water pipes run close to the ceiling drywall under the insulation, a northern idea.
