Highest efficiency/lowest cost solution, recirc loop

[milesdf]

I currently have a mod/con boiler, buderus gb142-30. I'm thinking about upgrading my hot water heater, which is nearing end of life, to take advantage of the high efficiency boiler, and I've been looking into indirect hot water tanks, which seem to cost about 1000$ or more. I've also been planning on adding a recirc loop to my house, with a bronze or cast iron circulator, and a dedicated return line. One thing that worries me is the reliability of the boiler, especially in a couple years, so I was shopping for indirect tanks with backup heating elements, and they seem to be extremely expensive.

So, I've been looking into other options. Has anyone ever used a plate heat exchanger with a circulator and aquastat to create instantaneous domestic hot water from boiler water? I wouldn't recirc the tank water through the heat exchanger, only cold supply water when hot water is being used. I would trigger the priority DHW zone and circulator on my boiler from a temperature controller on the potable output of the heat exchanger. My thinking is I could feed a relatively inexpensive electric tank with hot water from a set up like this, use the house recirc loop with the electric tank, and the electric elements would only rarely be used (when enough heat was lost in the recirc lines, or when the boiler is broken).

Would I still get the efficiency gains of the mod/con boiler with a heat exchanger, vs a indirect hot water tank? Interestingly enough, the cost of a heat exchanger, temperature controller/aquastat, and electric hot water heater is lower than the cost of a single indirect hot water tank.

 

[Jadnashua]

The recirc system will need either a bronze or SS pump...you cannot use an iron one for this application - being potable water, it will have dissolved oxygen in it, and the iron pump will fail quickly.

Not sure why you'd want an indirect with backup electric...

Unless the boiler min temp is maintained year round, a plate type 'instant' WH will be slow to respond and has the potential of being quite variable depending on the volume of hot water being drawn. Put the indirect on a priority zone, and go on with life...

 

[Sponsor]

 

[milesdf]

My boiler will allow a dhw priority zone which will override the outdoor reset temp, so I can dial in a setpoint for water to the heat exchanger. I can understand the comment about having shaky results using a plate type heat exchanger, which is where I think having a tank would be an advantage, wouldn't this buffer the slow response of the heat exchanger?

I guess my major goal here is to have a backup hot water source. I suppose this is neither common nor viewed as necessary?

 

[Charlie.f308]

Are you looking for like a timer? I have a digital timer connected to my water heater to cut back on energy.