First shower of the day has hot water then only lukewarm water, pipes at the heater feel luke warm even for quite a while after the first shower. By morning there is one shower of hot water available. The hot water source is a 50 gallon conventional natural gas water heater, with an insulated circ. Loop to the whole house.

Does this happen only in shower? After your shower, do you good hot water at other area's like the kitchen sick, bathroom sink etc?