leowis1 wrote: If its a 50gallon tank and the hot water passes thru it, doesn't it drop the water temp too low? I can't see how you get hot water if you're mixing 50gallons of cool water with a 1/2" supply of hot water?
You have a unused supply of hot water in your furnace when you aren't drawing on it, you circulate that through the tank constantly. Basically you'll be banking the hot water created when no one is using it in the hot water tank.This can be done naturally or with a small pump designed to run continuously. You only need to create a loop, that's what the drain on the bottom of the tank is for of course.
The benefits is you have a cool down period for the water and you have larger supply of hot water. We use a system like this and the hot water supply is inexhaustible, you'd have to be running the dishwater, the clothes washer and taking two showers to run out.
The other option is to simply route the hot water from the furnace to the cold supply on the water tank, it may run more often if you don't use a lot of hot water but at the very least it's screaming hot when it goes into the tank as opposed to cold tap water.
Now if you really wanted to get crazy, get a copper or stainless tank to temper the water to room temperature prior to going into the heating loop. That would really be unnecessary unless you used large amounts of hot water.
Funny story, my brothers has the same setup and his son had a friend over for a sleepover. The kid goes to take a shower and is in there forever. My brother goes to investigate and the kid says "I like taking showers so I wait until the hot water runs out". He'd of been in there all night...