I have an electric water heater in an unheated basement.
The water runs through about 20 feet of 1/2" copper pipe before it gets to my kitchen sink faucet.
Here's my mystery;
The HOT water is a lot hotter in the summertime.
Now, I know that the waterheater/thermostat doesn't care whether its summer or winter....... and the temp in the tank is probably constant.
Is there be that much ( winter ) heat loss in 20 feet of copper pipe ?
Just curious.