I normally only use my wood boiler for heat during the winter months. I have 2 electric hot water heaters in my house.
I'm thinking of adding sidearm heat exchangers to both water heaters and burning my wood heater in the summer months also.
My question is, since my home thermostat will not be cutting the pump on and off, how much should I run the pump to circulate hot water for the sidearm heat exchangers to be efficient? Should I run them continuously?
Sidearm heat exchangers slowly heat your hot water so constantly circulating the water I believe would work the best. It takes longer for the hot water in the tank to "recover" since the sidearm heats the water slower than the electric coils inside the tank. I think running the pump intermittently would lead to problems and not effectively heat your hot water.
When I run my outdoor wood furnace the circulation pump runs constantly whether or not my inside hot water/baseboard zoned thermostats are calling for heat. When my inside furnace needs heat it uses a separate circulation pump to pump water through the plate heat exchanger which warms the water to heat my house.
My setup runs from the wood furnace to a plate heat exchanger (which heats the water that circulates through my house) then on to my sidearm heat exchanger which is attached to my hot water heater, then back to the wood furnace where the water is reheated.
The setup works pretty good but the only downfall is my hot water heater is located on the opposite side of my house so the 1 inch copper tubing that plums my sidearm heat exchanger runs the distance of my house as well. In the summer time I can really notice the radiant heat coming off the 1 inch copper lines. Although this is nice in the winter, I don't need any extra heat in my house in the summer......usually.
With the commitment of adding wood throughout the summer and the extra radiant heat from the copper lines, I have chosen not to burn my outdoor wood furnace throughout the summer just to heat my hot water, but that doesn't mean you won't have a better experience.
I hope this helps!