First a little background. This is a big hot water boiler I'm referring too and the coil is very large, probably about 20 feet taking a guess. He has a extra somewhwere and that would be my guess. when he originally hooked it up about 25 years ago he had it going directly to the hot water supply, no hot water heater. He had to switch it becasue it was too hot.
homeguy wrote:. When you say he has it going from the furnace to the hot water heater-Do you mean that he has a coal furnace and rund that directly into the hot water tank?
Correct that is how he has it set up now.
You also wrote he use to loop it, naturally circulate and then he got lazy
He had it looped by adding a return line from the hot water tank from the drain on the botton of the tank.
I'm not a plumber and I'm not exactly sure if that if he had it reversed with the drain being the hot water feed for the hot water tank but basically you have the cold water supplly coming in from the street with a check valve. This goes to a T. On the one side of the T is another check valve to force the water to go into to the coil which in turn was fed to the cold water supply on the tank. The loop was completed by feeding it back to the other side of the T. Since the water in the furnace is hotter than what is in the tank it's going to want to force its way into the tank which will give you a natural circulation.
Also, what is the temp of the water at the tap?
Pretty constant even with it being fed directly, as a bonus it will last practically forever. With that set up you could run the disawasher, clothes washer and still take a shower.
If you have teenagers this may not be a very good idea as your water bill will go through the roof.