Sine the self-install of a short 40 gallon gas water tank....
Everytime I use the cold water in the house, every faucet, I get about
15-20 seconds of hot water. It starts off cold, then warm/hot, then
cold. This happens during winter and summer, so I can rule out the
furnace warming the pipes.

The copper pipes go directly to the water tank... could I be missing a
backflow valve? or something in that effect? The water lines are not
touching, nor are they touching the exhaust.

Thanks for any advice.

r3rjr