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DHW/Space Heating collector/tank size  RSS feed

Posts: 17
Location: Central Oklahoma Zone 7A
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Hello all,
I have been doing research into domestic hot water and maybe radiant heating for my home in central Oklahoma. I think the best idea would be a PEX/CPVC collector with a storage tank to heat exchange incoming cold water.
For a 1500 sq ft house, what would be the approximate tank size, and collector square footage for
a. 100 gallons hot water/wk?
b. 100 gallons hot water/wk and 1 living area (300sq ft) of radiant floor heat?
Thanks in advance for the ideas.
Posts: 112
Location: Groton, CT
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Firstly, I wouldn't use PEX or CPVC as collector materials, even in a serpentine system. The plastic WILL degrade over time and if the system is pressurized it WILL burst. Soft copper is the best choice and is easy to form into perfect serpentines.

Now the question on size; that is a tough one to answer. I could just divide the usage by the insolation value in your area to get a rough idea, but in practice there is a lot more that goes into it, most importantly the heat losses from your tank and plumbing, the efficiency of heat transfer to the water lines, the real-world insolation values, etc.

For example, you could build something based on the average insolation, but then on particularly cloudy days you will have no hot water. So then you can design for the worst-case insolation, or better yet have a backup heat source. There really is a lot that goes into the design.
Posts: 34
Location: Amherst, Wisconsin
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I never would use or suggest plastic collectors. Copper has stood the test of time.

1 gallon of solar storage for every gallon of hot water needed per day. The size of the collector array depends on where you live. There is a chart in my book that shows that. It will vary from .75 sq. ft. to 1.25 sq. ft. of collector for every gallon of water you want per day (again, depending on where you live).

Space heating is too deep a subject to cover in this venue. I would be writing all night. There are several chapters in my book that deal with this subject.

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