I just discovered this forum a few days ago and have been reading up on many of the threads that sounded at least somewhat related to my situation. I even gleaned a lot of useful information from the seeming endless, two year old tank/tankless argument.
I've been in this house for approaching three years now. It's my first experience with tankless, an ELM Aquastar 170VP. It took a little while, but I figured out that this unit is just too big to supply a comfortable shower. When I mix in enough cold for comfort, the burner can't quite throttle down far enough and cuts off.
My thought is to add a small, say 10-15 gal, tank downstream with a stat controlled pump and perhaps a flow switch. In low flow situations, like showers or shaving, the tank would contain sufficient hot volume for the need and as it cooled down the stat would run the pump at sufficient flow rate to keep the burner firing.
I already plan to insulate the pipes and would further insulate the tank. I'm thinking standby temp drop in the tank would be pretty small and so, in deference to green theory, could use the flow switch in series with the stat so that the system would only heat the tank during actual use.
Opinions or suggestions? My wife will be much happier when I get something to work...