Our current hot water is acting up (a blue Amtrol unit with a dedicated boiler) and I am considering trying an on-demand system. Our current system also heats the garage via a `box’ thru which hot water is circulated from the dedicated boiler. A powerful (noisy) fan then pushes heat into the garage. I have this boiler running very hot—up to 240 degrees F ! The hot water from the Amtrol water is also hot— about 150 degrees F My question— is it feasible to use an on-demand unit to ALSO provide heat to the garage.

There are several possible problems with what you are proposing. First most demand water heaters do not get hot enough to provide the heat you are needing. Second, it is doubtful they would stand the constant running that would be required. Now they do make a similar unit that is used for in the floor heat that might do the trick for you. There is a big difference between 240 degree water and the 120 to 140 degree water that demand heater produce. Your present boiler is probably operating at about 15 pounds pressure and you have a separate coil that gives you endless hot water for household use. If the water that is used to heat your garage is lower in temperature you will probably need a larger coil to get the same heat into the garage space.

My last house had on demand hot water in place of a water heater. It was also integrated with the baseboard heating system for the whole house. It was a fantastic setup but I no longer live there and forget who the manufacturer was. I wish I still had it.

This sorts of sounds like a boiler with a coil within – the coil produces the domestic hot water – while the supper hot boiler circulates thru the base boards– sound right?? PS-my problem was a bum zone valve-I got off cheap!