If it's not too expensive, I want to install a recirculation system for the master bathroom of our remodel, which is about a 45' pipe run from the water heater. I estimate we would have to wait about 35 seconds without recirculation before hot water would appear. (Kitchen and downstairs bath are very close to the heater.) Pipe is 3/4" L copper. I'd like to not waste water or have to wait a long time for hot water to appear, but I also don't want to pay for something that would take 10 years to recoup the cost.
There are 2 choices which are intriguing to me.
1. Gravity fed convection system. This should work since the water heater will sit in a utility closet at ground level, first floor is 2 feet higher above a crawl space, and master bath is on second floor. My understanding is that we need a 3/4" return line from upstairs with the whole loop insulated EXCEPT for 15-20' at the end of the return line (just before the water heater), and that this cooler section is what sets up the convection flow–albeit a slow flow, which I assume is good. If this doesn't work, it may be necessary to install a check valve going into the drain side of the water heater, and if THAT doesn't work, can I assume that a recirculation pump can be installed retroactively? My contractor is not experienced with gravity-fed systems.
2. Contractor recommends a (new) product that he has used in his last 3 houses. It uses a pump but does not require the installation of a return line. Somehow, the hot water at the end of the line trickles into the cold water side. Does anyone know what this product is and what might be the pros and cons?