So I have 3/4" piping running throughout my house and a 40 gallon water tank. I couldn't get the water for my shower/bath to stay hot for longer than 2 mins, then it would go from hot to freezing in like 30 seconds. So we went out and bought an 80 gallon tank, i figured that was the problem. No such luck, I just got it up to 5 mins of hot water and it would go from hot to lukewarm. Well, the tub had a single knob to turn the water on. So we went out and bought a two handle set up, I figured the single knob was mixing too much cold into the water. No such luck. Now the water heater is turned up to 125. When I had it higher, the water got hotter, just didn't last longer. And the heater is on the other end of the house from the bathroom. Is it the 3/4 piping? Only thing I can think of. It's not insulated, so I was thinking of boxing in the I-beam and insulating it after I ran my electric for the basement. Any other ideas as to why this may be?