Hello out there!
I have searched the threads and found somewhat similar problems but none with a concrete slab. My house has pipes running through a concrete slab and it's a 65 foot run from the water heater in the garage to the kitchen sink. It's about 4 minutes from turn on to hot water in the kitchen. I understand the heat loss due to the thermal mass of concrete. However, is there a solution? Any suggestions would be kindly appreciated.