I was researching the possibility of recovering some heat from the exhaust of my oil fired boiler to heat domestic hot water. Came across this thread: https://terrylove.com/forums/index.php?threads/harvesting-waste-heat-from-my-water-heater.43640/ which talked of recovering heat from a gas fired water heater. (along with many off topic discussions on nuclear, wind, shower drain heat recovery and PV power)
Currently I have an oil fired boiler for space heating (6 zones) with an indirect water heater tank that has it's own circulator pump, the water tank is treated as an independant zone as far as the furnace is concerned. My boiler has a power vent in the exhaust which I believe would eliminate the issues of condensation and back draft brought up in the previous forum as the power vent pulls air through the stack.
My intention would be to put a coil inside the first foot of vent pipe, before the automatic draft vent, as this is the hottest point, after the auto draft vent the gases are cooled somewhat with the fresh air from the room. The coil would be attached to a water tank much like the range boiler that stood behind my grandparent's wood fired kitched range. (water circulated by convection) See attached pic. Cold water sitting in that tank is heated by the coil in the stack, outflow goes into the existing tank. One of the issues I would have to overcome is finding a flexible tube to link the coil to the tank, as the vent pipe has to be removed to clean the furnace once a year. I don't want to have to drain the tank and disconnect the coil to do this. Need a material flexible enough and able to tolerate that kind of heat.
Another thought that was also mentioned in the other thread is to put an uninsulated tank in the same room as the boiler, no connections to the boiler stack, just the water sitting in the tank would have the chill taken off it by the ambient temperature in the room. My boiler, oil tank and the indirect water heater are in a room separate from the rest of the house, fresh air comes in through a vent in the outer wall, exhaust is vented out by the power vent in the stack. When we bought the house this room was like a dry sauna. Since then I've insulated every pipe that I can access as well as the expansion tank. The room still stays in the +30C range (86 F), the water heater is set to 60C (140F) so that should make a considerable difference with mimimal cost would it not?
Something else that has come up as a possibility is to capture some of this room heat by inserting a long length of pipe in the cold water line before it gets to the existing tank. Maybe a full 100' length of 3/4 pex in a coil suspended from the ceiling, or some baseboard rad units (minus the housings) strung together. How much pipe would it take to see a difference in the temperature of the water?
Maybe someone has already tried one or the other of these. I encourage sharing of thoughts, and as much as I'm interested in other alternate sources of energy, please try to stay on topic.
Currently I have an oil fired boiler for space heating (6 zones) with an indirect water heater tank that has it's own circulator pump, the water tank is treated as an independant zone as far as the furnace is concerned. My boiler has a power vent in the exhaust which I believe would eliminate the issues of condensation and back draft brought up in the previous forum as the power vent pulls air through the stack.
My intention would be to put a coil inside the first foot of vent pipe, before the automatic draft vent, as this is the hottest point, after the auto draft vent the gases are cooled somewhat with the fresh air from the room. The coil would be attached to a water tank much like the range boiler that stood behind my grandparent's wood fired kitched range. (water circulated by convection) See attached pic. Cold water sitting in that tank is heated by the coil in the stack, outflow goes into the existing tank. One of the issues I would have to overcome is finding a flexible tube to link the coil to the tank, as the vent pipe has to be removed to clean the furnace once a year. I don't want to have to drain the tank and disconnect the coil to do this. Need a material flexible enough and able to tolerate that kind of heat.
Another thought that was also mentioned in the other thread is to put an uninsulated tank in the same room as the boiler, no connections to the boiler stack, just the water sitting in the tank would have the chill taken off it by the ambient temperature in the room. My boiler, oil tank and the indirect water heater are in a room separate from the rest of the house, fresh air comes in through a vent in the outer wall, exhaust is vented out by the power vent in the stack. When we bought the house this room was like a dry sauna. Since then I've insulated every pipe that I can access as well as the expansion tank. The room still stays in the +30C range (86 F), the water heater is set to 60C (140F) so that should make a considerable difference with mimimal cost would it not?
Something else that has come up as a possibility is to capture some of this room heat by inserting a long length of pipe in the cold water line before it gets to the existing tank. Maybe a full 100' length of 3/4 pex in a coil suspended from the ceiling, or some baseboard rad units (minus the housings) strung together. How much pipe would it take to see a difference in the temperature of the water?
Maybe someone has already tried one or the other of these. I encourage sharing of thoughts, and as much as I'm interested in other alternate sources of energy, please try to stay on topic.