# Microwave water heaters? **URL:** \ **Category:** Factual Questions\ **Created:** [March 20, 2011, 11:59am UTC](https://boards.straightdope.com/t/microwave-water-heaters/575348 "2011-03-20T11:59:55Z")\ **Posts on this page:** 6\ **Page:** 3
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [March 21, 2011, 10:19pm UTC](https://boards.straightdope.com/t/microwave-water-heaters/575348/41 "2011-03-21T22:19:35Z")
> [@Reply](#): > > I see. And solar? > [@thelabdude](#): > > What I have seen of it looks like at my age, I might die before it paid for itself. Even at today’s interest rates, I would be better off with the money in the bank. 5 to 8 years is a short payback (for solar thermal) or a short life. ---
**Author:** ![thelabdude](https://avatars.discourse-cdn.com/v4/letter/t/dc4da7/32.png) [@thelabdude](https://boards.straightdope.com/u/thelabdude)\ **Post date:** [March 21, 2011, 10:43pm UTC](https://boards.straightdope.com/t/microwave-water-heaters/575348/42 "2011-03-21T22:43:56Z")
> [@beowulff](#): > > Not for Solar DHW. In most areas of the US, it’s a clear win, financially. Based on estimates about 10 times the amount we spend now. Same fallacies as tankless. ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [March 22, 2011, 4:58am UTC](https://boards.straightdope.com/t/microwave-water-heaters/575348/43 "2011-03-22T04:58:55Z")
> [@TruCelt](#): > > My neighbor had a solar system in the early 90’s. She said there was never any hot water first thing int he morning, when she really needed it. There was lukewarm, but seldom hot. > > I’m guessing the technology has improved substantially since then though. . . What **johnpost** and others said. It’s supplemental, not primary, heat. > [@thelabdude](#): > > Based on estimates about 10 times the amount we spend now. Same fallacies as tankless. If you’re sure you’re doing the calculations right, it’s entirely possible this just doesn’t make sense for you. I’ll take your word for it. ---
**Author:** ![anyuta34i](https://avatars.discourse-cdn.com/v4/letter/a/cc9497/32.png) [@anyuta34i](https://boards.straightdope.com/u/anyuta34i)\ **Post date:** [March 22, 2011, 5:56am UTC](https://boards.straightdope.com/t/microwave-water-heaters/575348/44 "2011-03-22T05:56:16Z")
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**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [March 22, 2011, 7:00am UTC](https://boards.straightdope.com/t/microwave-water-heaters/575348/45 "2011-03-22T07:00:33Z")
> [@anyuta34i](#): > > …As they danced around the fires，the season of the sun passed and the season of darkness would begin. Damned druids and their vicious crop-killing New York Asian escorts! This is why solar has such a bad payoff for you, thelabdude. The gods are obviously displeased ☹ (Oh, and reported for spam.) ---
**Author:** ![cplif](https://avatars.discourse-cdn.com/v4/letter/c/48db29/32.png) [@cplif](https://boards.straightdope.com/u/cplif)\ **Post date:** [March 22, 2011, 10:31am UTC](https://boards.straightdope.com/t/microwave-water-heaters/575348/46 "2011-03-22T10:31:14Z")
What we call aerotherms here are airto liquid heatpumps set on a more or less standard tank, the cost per use is very low, initial price here is circum 2400 euros. For large users it may be interesting on short term (salons de coiffure, etc) Hot water circulators are pretty greedy, even with well insulated pipes, the pumps themselves use very little, it’s the dissipated heat through the circuit that hurts. They are used mainly in hotel like installations, with several points of use, and long distances between production and use. They also eliminate some risk of legionella infection (stagnating warm water in dead end pipes or occasional circuits) Good quality solar is a beaut, initial price is still high for most homes, concept and regulation must be done with great care. The best schemes (from my experience) inject a few degrees from the cheapest available source, and then use electrical or gas to regulate to confort levels, but most of the are difficult to implement into existing buildings Instantaneous heaters are good for space saving, nothing else (except possibly blowing your fuses) [Previous page](https://boards.straightdope.com/t/microwave-water-heaters/575348.md?page=2)