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Hot water heating options


Joined: Dec 12, 2010
Posts: 11
I have a house that is solar powered, I have two 250 watt panels and 2 12V AGM batteries. This system powers everything very nicely, as long as I keep energy use to a bare minimum. The only bugaboo is the hot water. I have an electric hot water heater that is re- wired for DC (heating element is DC) BUT... it takes too much juice. Since I dont have the $$ to buy another battery right now, I am wanting to try to do this passively (or actively- as long as I can get it more efficient on its power use).
Still being winter, Im just not sure that there is enough sun to heat the water with passive solar. I DO have a dark green metal roof and think I will try putting a 100 foot hose up there and piping the water through after we get some sun and seeing if any heated water comes out.
Another option is wood fired heat. I have a good woodstove, puts out good heat. I do most of my cooking on it. Seems like it SHOULD be easy to heat something on the woodstove and pipe water through it.
I am also considering the compost pile heating method. I have access to heaps of manure and already have a little compost pile going.
Any ideas greatly appreciated!!
Steve Palmer

Joined: Jan 28, 2012
Posts: 18
You do already have your ideas, I would refer you to pauls video where there was a compost pile that heated for an outdoor shower. I am not sure it could be done any more simply than that. There are many versions of the solar water heater out there. They are not complicated and can be made easily and cheap. The drawback might be, not always having hot water exactly when you need it.
Elliot Everett

Joined: Dec 20, 2011
Posts: 29
Location: Coastal Uruguay. Wet winters, hot and dry summers. 1000 mm annual rain.
Are propane powered on demand water heaters available in your area? I know a few people who have them and they work well. They use 13kg propane tanks.

Passive solar heating works great too, if you have year-round sunlight and a correctly facing roof. I think it would be neat to combine passive solar and a wood stove to heat water in one system. If its cold and rainy, your stove will be on and you will have hot water. If its warm and sunny, you'll still have hot water. Potential drawbacks could include Legionaire's disease and dangerous steam build up.
Brian Knight

Joined: Nov 02, 2011
Posts: 554
Location: Asheville NC
Not sure about you climate but Heat pump water heaters are pretty awesome. They make a sidecar type that could be hooked up to your existing tank. Solar hot water is the way to go and your hose on roof idea could be great solution for the summer months. A black hose would be best and it probably doesnt even need to be on the roof.

"If you want to save the environment, build a city worth living in." - Wendell Berry
David Bates

Joined: Dec 05, 2011
Posts: 79
Location: Mountain Grove, Ontario, Canada
Elliot Everett wrote:Potential drawbacks could include Legionaire's disease and dangerous steam build up.

Legionaire's disease is easy to avoid, stay away from conventions. I'm building a solar/fire hot water system this year. To get around the dangerous steam problem I am going to put my hot water tank in the attic (cistern). It can be open at the top (vented outside). Also, this means that I do not need to pump the water to heat it. The bottom of the loop (where the cold water will fall) is going to be below the tank. The tank will be at the top of the loop. Easy.

Cistern hot water tanks don't have to be under any pressure at all, if they are high enough above your shower and sink then water falls out your taps at a good rate.

much of what my neighbours consider to be good I consider to be bad
Brian Knight

Joined: Nov 02, 2011
Posts: 554
Location: Asheville NC
Ive played with thermosiphon SHW sytems quite a bit. The most simple one was a black pipe that ran down a south facing hill and back up. I insulated both sides and glazed one side with plastic. It brought 50 degree water up to about 95 on a sunny 50-60 degree day. With thermosiphoning dont use any tubing smaller than 3/4" and avoid 90 degree bends at all costs.
dan murf

Joined: Feb 17, 2012
Posts: 50
Location: Michigan West Side
If you have 12v water heating elemits in your water tank alread?
I would make a windmill, if you know how to its the cheapest answer for you, I bet!
simply find a bad 12v car battery. (voltage regualtor) wire it in line between the windmill to the water heater.
Make sure you wire through the over temp relay switch that you should aready have, it turns off?opens contacts to keep you from over heating.
You simple reset after using your hot water.

"to Tinker or not to tinker, that is the question!"
If you build it better than the one profiting from it, don’t tell them, they'll get pissed! "I challenge anyone to challenge me" ... Murf! "I am responsible for the comment in this comment section"
Mike Bonser

Joined: Jul 04, 2012
Posts: 2
We're about to try out the compost hot water approach and was wondering if anyone has any advice on the balance of green and brown that's optimal for us.

We've got a good pile of woodchips which have been sitting a few months. There's heat in places in the wood chip pile but not very much - I reckon this is because we haven't added any nitrogen material (green or urine). This is good for us because we didn't want the woodchip to start decomposing before we set it all up. We're probably going to have a pile of 3 or 4 cubic metres with a pipe coiled in the middle. From research it looks like if we mix about half green (grass cuttings or similar) with brown (woodchips or maybe straw or old leaves) this is about the best mix if you want to get it really hot (about 55 degrees C). But since we're wanting it to stay hot/warm (about 45 degrees) for longer then what sort of mix should we use?
Any ideas on whether we're better off using grass cuttings or cow manure as the green (nitrogen) element?

We've also got easy access to lots of urine for starting the process off!

Also has anyone done this and knows more or less how long we'd be able to get heat from it?

We're in Wales where it's really wet at the moment, so we shouldn't have any problems making sure the material is damp, but maybe it could be too damp - we'll cover it if it looks like it's heading that way. (But we're also going to make sure it has air going in by putting the pile on a pallet with air flow at the bottom.)
Thanks very much.
Cory Arsenault

Joined: Mar 03, 2011
Posts: 55
Location: Ottawa, Canada
If you don't have any money right now to make any major changes I'd suggest that you begin by assessing what you actually need the hot water for and if you could heat it by other sources.

For example, if you use hot water for washing dishes by hand it would be more energy efficient to warm the water in an electric kettle and pour in into the cool water in your sink until you reach the desired temperature. Using the kettle to warm the water when you need it will cost less than keeping the water warm in the tank all day until you need it.

Something like taking showers would be more difficult to manage but you could replace that with bathing (and adding boiled water to a cold bath) or by washing from the sink.

Another possibility would be to add insulation to the tank and turn down the heat if you haven't already.
David Bates

Joined: Dec 05, 2011
Posts: 79
Location: Mountain Grove, Ontario, Canada
We have been getting our hot water "for free" for a couple of months now. In the morning when we get up and start the coffee we put two large pots of water on the stove. They stay there all day, getting warmer with each meal we cook until around sunset. Then there is enough to do the dishes and wash in the tub in our lane way. It's a staggering combination of laziness and "life-styles of the rich and famous", I think.
Burra Maluca
Mother Tree

Joined: Apr 03, 2010
Posts: 7358
Location: Portugal Zone 9 Mediterranean Climate
Cory Arsenault wrote:Something like taking showers would be more difficult to manage but you could replace that with bathing (and adding boiled water to a cold bath) or by washing from the sink.

Some of the houses here have a shower system with an open-topped, small tank (about the size of a bucket) fixed up on the wall that is filled with hot water, presumably heated in a kettle and poured in. There is a pipe at the bottom, with a tap, and this joins another pipe fed from the cold water system, also fitted with a tap. The flow from each can be adjusted until the water coming out the end, which is fitted with a shower head, is the right temperature.

It's a bit basic, but not as basic as the 'bucket with holes in the bottom for hanging on a tree branch' system, which is still available in older shops and from market stalls.

How works

What is a Mother Tree ?
Cory Arsenault

Joined: Mar 03, 2011
Posts: 55
Location: Ottawa, Canada
Ha, that's awesome.

I recall when I was in Costa Rica that some of their showers had flow-through electric heaters where the heating element was in the shower head. I never used it though because the one in the house that I stayed in had a throw switch to turn in on which was located inside the shower! I was paranoid of electrocuting myself so I took cold showers the whole time ha ha
leila hamaya

Joined: Jun 30, 2012
Posts: 998
Location: northern northern california
after too long procrastinating, drawing, visioning a solar hot water system, even getting some panels (though they are old and not in perfect shape, they seem to do ok passing the water through them)
.... i scored a propane on demand tankless water heater for free. hoping it works (it should) and quite a bit intimidated and confuzzled atm trying to install it all...but maybe soon, hot water =)

i'm dreaming of a hot shower! just like the ones i used to know..... is the running joke i've been singing to myself.....

i know, the solar hot water heater thing would be much better...but...well...this is what seeming like the thing for now...and especially would be cool if later i get more time and energy to actually do the solar hot water thing and combine them.
or make it so you can use the propane when it not sunny.
solar isnt the best here, rainforest grey....
but together they would work really well.

but well...the whole water...ah so many things, to figure out to do it, theres kind of a lot of weird things about where i am @......and its a bit tricky for me to figure out how to put it together. i have zero experience with plumbing i am just...well working it out as i go along...and thinking maybe to get some assistance to put it together.

as it is i only have a small storage container that i can cram myself mostly into, heat a bunch of water on the stoves.
works better in the winter when i already have the wood stove going. i really need something better, not being able to bathe regularly has gotten really really old.

love the ideas on this site about the rocket stoves, and read one thread where someone had set up a really cool one that heated water....yeah i've spent a lot of time reading about the rocket stoves and in a different circumstance i would go with that method.
I agree. Here's the link:
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