said by Draiman:Did you look at the specs on that unit? It shows the gpm flow based on the unheated water temp. If your water is 40 degrees for example and you want 110 degree shower that's an increase/rise of 70 degrees so that unit can only sustain 1.59 gpm's at that rate. It means you need a low flow water saver shower head and nothing else can be running to get the proper water temp. That will vary based on the water temp so in the Summer you'll be much better off but in the Winter you'll peak it out easy.
I did but...based on the replies (which are actually helpful) it's quite obvious I have no clue about what is a good replacement.
It's seems like a lot to figure in. this is all new to me.