# Solar Water Heater Propane back up

**URL:** <https://boards.straightdope.com/t/solar-water-heater-propane-back-up/805026>\
**Category:** Factual Questions\
**Created:** [December 22, 2017, 4:03am UTC](https://boards.straightdope.com/t/solar-water-heater-propane-back-up/805026 "2017-12-22T04:03:27Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Mangosteen](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)\
**Post date:** [December 22, 2017, 4:03am UTC](https://boards.straightdope.com/t/solar-water-heater-propane-back-up/805026/1 "2017-12-22T04:03:27Z")

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Winter (low sun) days with cloudy weather don’t produce much solar energy to heat the water in my storage tank here on the east side of the Big Island. of Hawaii.

My current back up uses electricity to heat the water, but my main solar array doesn’t produce much electricity under these conditions, either.

I have propane tanks on the property. Is there a propane solution that anyone is familiar with?

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**Author:** ![SmartAleq](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smartaleq/32/163_2.png) [@SmartAleq](https://boards.straightdope.com/u/SmartAleq)\
**Post date:** [December 22, 2017, 4:06am UTC](https://boards.straightdope.com/t/solar-water-heater-propane-back-up/805026/2 "2017-12-22T04:06:26Z")

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I have a tankless water heater that runs on propane, that what you’re asking for? They range from small under sink point of use units to ones that service an entire house. For the record, I love mine–endless hot water whenever I turn on the tap. And no bigass tank either.

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**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\
**Post date:** [December 22, 2017, 4:32am UTC](https://boards.straightdope.com/t/solar-water-heater-propane-back-up/805026/3 "2017-12-22T04:32:34Z")

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Are you on the electric grid? If so you should compare the cost of electricity from the grid vs the cost of electricity from propane.  
Propane hot water heaters are very common in rural areas in the mainland, but I don’t know how to connect your system in the appropriate way.

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**Author:** ![SmartAleq](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smartaleq/32/163_2.png) [@SmartAleq](https://boards.straightdope.com/u/SmartAleq)\
**Post date:** [December 22, 2017, 5:02am UTC](https://boards.straightdope.com/t/solar-water-heater-propane-back-up/805026/4 "2017-12-22T05:02:53Z")

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Oh, one caveat on the tankless–mine’s a midsize unit, 140,000 BTU rated. You need at least a 120 gallon tank to make those work, a little #40 tank doesn’t have the pressure or capacity necessary to run a whole house tankless system. If you have a big enough tank, you’re golden.

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**Author:** ![Mangosteen](https://avatars.discourse-cdn.com/v4/letter/m/6a8cbe/32.png) [@Mangosteen](https://boards.straightdope.com/u/Mangosteen)\
**Post date:** [December 23, 2017, 1:29am UTC](https://boards.straightdope.com/t/solar-water-heater-propane-back-up/805026/5 "2017-12-23T01:29:50Z")

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> [@PastTense](#):
>
> Are you on the electric grid? If so you should compare the cost of electricity from the grid vs the cost of electricity from propane.  
> Propane hot water heaters are very common in rural areas in the mainland, but I don’t know how to connect your system in the appropriate way.

I’m off grid. No County electricity or water or any utilities at all. Solar panels, propane and water catchment.