I've got a 9 year old boiler (Crown) and indirect water heater (40 gal Bradford White) system. The domestic water heater is leaking into my boiler loop causing my boiler pressure relief valve to leak. I've read in these forums the efficiency advantages of the indirect water heaters. However my concern, is are they really over-all more efficient? My boiler / water heater is in a small room ( 4.5' x 10") with an outside air intake directed to the boiler. The room is warm to hot all year. Especially in the summer. So it seems to me that while the indirect water heater is quite efficient and has very low heat loss, I'm still heating up this large boiler all year and have a lot of heat loss from the boiler and the pipes in the summer. It's a 4 zone system, including the water heater, so it's quite a mass of pipes in the room giving off heat even though I've got them insulated. Would I be better off staying with this system or should I consider switching to a separate natural gas fired water heater. I understand that the separate heater would be less efficient then my boiler but it sure seems like I'm heating up lot of water and loosing efficiency the extra pipes in running the indirect water heater.
If I stay with the indirect water heater, is there any recommended boiler and water heater temp settings to maximize the efficiency? I'm assuming that the boiler temp setting should be some minimum temp above the indirect heater setting.