Quote:
Originally Posted by AC_Hacker
It is very interesting what you have said.
It looks like you have a solid understanding of payback time, which some other people understand as break-even.
Could you please show us your calculations (graphical would be even better) so that we can understand your point?
Sincerely,
-AC
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Give me the COP specs for the unit you are considering. COP falls as ambient tempature drops and more work is needed as incoming water tempatures drop. If you have to use a lot of resistance supplimental heat at low tempatures then a lot of the savings get wiped out.
Also consider that payback time gets extended if a repair on the unit is required. Keep in mind there's no running down to lowes and picking up a thermostat/heatign element if one goes out. Parts are special order from the manufacturer and I doubt they are cheap. Lowe's used to sell the heat pump water heaters but discontinued them because they weren't selling. A homebrew solution that you DIY could have a significantly shorter payback time than a commercailly made unit depending on what the parts cost and what your time is worth.
I've even looked at Natural Gas tankless water heaters and the payback time just isn't there when compared to an old school tank water heater. Natural gas prices need to double before payback time becomes reasonable.