Why do schematics always show backup water heater in line?

kjkrum · May 9, 2012

In reference to schematics like the first one on this page: http://homepower.com/basics/hotwater/

Why do schematics like this always show the backup heater in line with the output of the solar heater? Wouldn't you then always be using your electrically-heated water first? It makes more sense to me to install an electric heater in parallel with the solar heater, with isolation valves so you could run the backup heater only when needed.

If it makes a difference, I live in Tucson, AZ. I know people around here with solar HW systems with no backup heater at all.

BobL43 · May 10, 2012

kjkrum said:
In reference to schematics like the first one on this page: http://homepower.com/basics/hotwater/

Why do schematics like this always show the backup heater in line with the output of the solar heater? Wouldn't you then always be using your electrically-heated water first? It makes more sense to me to install an electric heater in parallel with the solar heater, with isolation valves so you could run the backup heater only when needed.

If it makes a difference, I live in Tucson, AZ. I know people around here with solar HW systems with no backup heater at all.

To keep the water pipes from freezing in areas that need such protection? Or/also to provide enough heat when its dark out and you need hot water when your storage tank is not hot enough?

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Terry · May 10, 2012

The diagrams look right to me.
The last thing in the line should be a conventional water heater. What happens at night if you don't have a heater?
The Solar goes before the heater, and the heater is only needed if the solar hasn't done it's job.
I like the tempering valve to prevent scalding too.

Why do schematics always show backup water heater in line?

kjkrum

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BobL43

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Terry

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