Boomerj said:
I'm still looking for the best DHW setup to implement myself so I'm no expert. It would appear that with it installed on the cold side of your water heater it is more of a pre-heater and the propane is still going to do much of the work heating the water and maintaining the temperature. If I'm going to spend the money on a plate exchanger, a mixing valve, and an aquastat I would want it to heat the water exclusively at least when my boiler or storage is hot. I'm wondering if a plate exchanger was plumbed similar to a sidearm on a tank water heater and a potatable type circ was used to circulate the DHW side. An surface or well type aquastat could be inserted in the piping coming out of the bottom on the the tank before the potable circ. My setup is Primary/Secondary, so that aquastat would turn on both the circ to the plate HX and the potable circ. The tank would probably stratify (ie. hottter at the top, colder at the bottom) so a mixing valve would be necessary and should probably always be used anyway. I think 120 degree water in my storage would still give me almost 120 degree water in my 80 gal tank and probably still be able to handle showers, laundry, etc. If I set the electric to the lowest setting and set the aquastat to keep the tank 20 to 30 degrees higher, I would think the electric would only come on when either the storage is below 120 degrees or if there is a huge DHW water demand when the storage is at it's lower usable temps. My initial thought was a sidearm plumbed this way would do the job but I haven't heard anyone doing that. An OWB with a plate HX will work without a tank because the OWB is always hot (ie. 160 degrees probably).
