Small DIY water heater ?

Hi,

I'm experiencing a rapid increase in the cost of electricity (I live in France). Assuming that energy prices will continue to rise (that's a pretty safe bet :) ), I'm trying to cut my consumption further down.

Considering that :
- I live alone most of the time,
- I wash 90 % of my dishes with cold water (I only need say 4 L / day of hot water for the greasy pans),
- I either take very short showers or wash with a wash cloth,
- I have no other use for hot water,

I thought that for part of the year (I'd say at least 3 months) I could do with a few liters of solar-heated water, and turn my electric water heater off completely.

I'm pretty sure that 20 L would be enough. But 10 L would be too little (that's the capacity of "solar showers" they sell in my country, which are just black plastic bags with a pipe). I don't need the system to be connected to the mains. I can do with a bucket to collect hot water and refill the heater with tap water as well.

So I need a real low-tech, lightweight, super simple design. BUT, I don't want to use just any black plastic container, because I now most plastics don't do well in direct sunlight (the plan is to reduce my elecricity consumption, not to add more microplastic to the world).

Any idea ?

Try one of these, they are awesome, extremely efficient and versatile. Just hook up a water hose and 20lb propane bottle, hangs on a nail, unlimited instant hot water, only heating when in use, adjustable temp, take it anywhere -

Tankless Water Heater Propane, GASLAND Outdoors 1.58GPM 6L Portable Gas Water Heater, On Demand Water Heater Propane, RV Camping Water Heater, Overheating Protection, Easy to Install https://a.co/d/6uMZON0

They use a battery powered electronic ignition so no pilot and I would recommend this water strainer to protect the heater -

SHURFLO (255-313) 1/2" Twist-On Pipe Strainer https://a.co/d/4MTqvrK

And a lead free water hose is always best -

Camco 50ft TastePURE Drinking Water Hose - Lead and BPA Free, Reinforced for Maximum Kink Resistance 1/2"Inner Diameter (22753) https://a.co/d/21HtIDO

If you wanted permanent indoor electric, this one can be mounted under the sink where you want the hot water. It requires a 30 amp/120v circuit and only heats when you turn on the faucet...

Thermolfow 110V~120V 3.5kW Mini Tankless Electric Water Heater, Point of Use On Demand Instant Hot Water Heater for Sink Washing, Wall Mounted, CSA Certified Hard Wired https://a.co/d/bdFz26f

Before I installed my on-demand water heater, I stretched out about 65m of garden hose in a spot that got direct sun.  This would get me scalding hot water by about 4pm.  Too hot to shower with directly, so I plumbed it into my hot water plumbing, and tempered that water temp with cold water.  Found I had about enough hot water in the hose to take about a 4-5 minute shower.  I just got used to showering in the late afternoons

Later, I removed the hose, and plumbed in a battery powered on-demand heater powered by propane.  I have it connected to a 20L barbeque tank.  That now supplies all my cabin's hot water needs.

I have this one...
https://www.sportsmansguide.com/product/index/eccotemp-l5-15-gpm-portable-37500-btu-liquid-propane-outdoor-tankless-water-heater?a=1588405

Don't know if you can get this one, but I'll assume you have something equivalent in France?

There seems to be lots of options that people have already made. I suspect you would be surprised at how warm a simple black tank could get in a few hours of your sun.

I quite like this one which uses a triple wall polycarbonate roofing sheet




But if you want to avoid plastics then this one, which uses the radiator of an old fridge may be more appropriate.




With both of these you'll need a container and pipes to cycle the water into.

Alternative static designs involve putting a black water tank into a glazed box like a cold frame. This one used a water trough and a mirror to increase the incident light.




(All pictures taken from this source)

(edited spelling)

Pierre Ma wrote:

So I need a real low-tech, lightweight, super simple design. BUT, I don't want to use just any black plastic container, because I now most plastics don't do well in direct sunlight (the plan is to reduce my elecricity consumption, not to add more microplastic to the world).

One thing to be aware of is that if the water doesn't get hot enough for long enough, it can act as an incubator for any bacteria that might have survived treatment (that's more or less what happened with Legionnaire's disease. That said, one can control for that with thoughtful design and use. For example, making sure the container you use gets *fully* emptied and solar heated to kill nasty stuff fairly frequently. Also, for washing greasy dishes, you could add "solar heated water" to an electric kettle to finish bringing it up to boiling to sterilize both the water and the dishes. This would still be more efficient than running an electric water heater continuously.

Also be aware that some hoses are considered "potable" and some not. Some hoses can have pretty nasty stuff in them and heat may encourage that stuff to enter the water more easily.

Since you've identified 20 liters, the suggestion of using an old propane tank and painting it black sounds promising. Putting it in some sort of box with glazing to multiply the sun's effect could extend the season and help get the temperature higher.

However, anytime water is being heated, beware of the risks of it going boom! Make sure you design in some sort of expansion room/overflow pipe with a place for the flow to go!

Just using a long garden hose left sitting in the sun for several hours can produce a lot of hot water.

I am guilting of this when trying to water plants in the late afternoon.

Rig an overhead container to be filled with this hot water would work.

Since I have never been to France I know nothing about the weather there.

Here are solutions we have in Australia
The tank heater sits on a fire and is filled with water, and left to get hot.
As water is required cold water is poured into the funnel which exists inside but near the bottom of the tank and hot water runs out the side overflow.
The Chip heater takes small bits of wood and again hot water is obtained by putting cold water into the water tank.
The funnel heater comes in a few sizes, the one shown is large, others go down to 1L capacity.
The base of the heater forms the base and has air holes to permit combustion.
A fire can be lit with dried grass dropped down the internal flue around which the tank forms a water jacket,
with twigs and sticks latter. When the water is hot on the smaller units the device is used as a kettle.

Building on Nancy's suggestion for a black tank while keeping with Pierra Ma's desire to avoid plastic, consider a black painted copper tank for this application. I use a 20 liter copper tank for holding drinking water that was made in India. Its intended purpose is to heat water. Copper is a natural anti-microbial.

Jay Angler wrote:
However, anytime water is being heated, beware of the risks of it going boom! Make sure you design in some sort of expansion room/overflow pipe with a place for the flow to go!

Oh yes - I've seen solar panels boiling a kettle in Wales, so do bear this in mind please!

Kelly kettles aren't 100% perfect because they do burn wood but they are fast & efficient.

one source

manufacturer's website

Don’t forget about compost heat reclamation. Coil a good length of hose (30-to 60 miters works best, the more hose, the more hot water) through a fresh compost pile and reclaim the heat. My compost usually hits about 50c. It’s not much, maybe 15-20 liters at a time but the smaller the hose diameter, the faster it will pick up the heat. This obviously only works if you do a lot of compost. Temporary solution for peak season.

Anne Miller wrote:Just using a long garden hose left sitting in the sun for several hours can produce a lot of hot water.

I am guilting of this when trying to water plants in the late afternoon.

Rig an overhead container to be filled with this hot water would work.

Since I have never been to France I know nothing about the weather there.

I would suspect the weather is similar to Ontario Canada seeing as it is located a similar distance from the equator. That said I have been to France; what a gorgeous country! Albeit my trip to France was several years ago, we travelled in February and the weather was similar to Ontario GTA.

I agree the hose method would work well but unfortunately only in the summer or on hot days in fall or summer.

I think the best thing would be to have two systems: One for the colder times in the year. Something that could capture the heat from a wood stove if you have one. And one to capture solar energy during the hotter months. Yes solar works just fine in the winter but at least in my opinion (my home is fully solar) the winter months are harder to capture solar energy if it is snowing heavily or if the days are not sunny.

Jay Angler wrote:Pierre Ma wrote:

So I need a real low-tech, lightweight, super simple design. BUT, I don't want to use just any black plastic container, because I now most plastics don't do well in direct sunlight (the plan is to reduce my elecricity consumption, not to add more microplastic to the world).

Also be aware that some hoses are considered "potable" and some not. Some hoses can have pretty nasty stuff in them and heat may encourage that stuff to enter the water more easily.

This should be emphasized among the other mentions of using hoses with warm water. Many older hoses contained lead, which is being replaced with plastics as the industry plays the green washing game. Have there been any studies on micro plastics accumulating in garden soil?

I had long thought i would use the elegant hippie hack of a tractor tire inner tube on a South facing roof eave, with the air valve replaced with some sort of spigot, for shower water. Now i suspect, much like Paul finding out about tires in earth ships, i don't want to know what they make big inner tubes out of...

This may be over simplifying it, but when we lived in the Philippines we would just heat up some water in a kettle as-needed (via propane stove.) For showering we used the Tabo method: mix the hot kettle water with some cold water in a bucket and use a pitcher to pour it over yourself. Same thing to wash dishes except a different bucket.

It was supposed to be a temporary thing, I was certain I would need to get an on-demand hot water heater at first but found that I actually preferred it. It uses so much less water than an overhead shower and works just as well.
Plus, you probably already have a stove and kettle, (we got the largest one we could find from a restaurant supply store) but you could also just use a pot.

For our off grid camp here in the states we're going to do the exact same thing.

Travis Tambay Kano wrote:This may be over simplifying it, but when we lived in the Philippines we would just heat up some water in a kettle as-needed (via propane stove.) For showering we used the Tabo method: mix the hot kettle water with some cold water in a bucket and use a pitcher to pour it over yourself. Same thing to wash dishes except a different bucket.

It was supposed to be a temporary thing, I was certain I would need to get an on-demand hot water heater at first but found that I actually preferred it. It uses so much less water than an overhead shower and works just as well.
Plus, you probably already have a stove and kettle, (we got the largest one we could find from a restaurant supply store) but you could also just use a pot.

For our off grid camp here in the states we're going to do the exact same thing.

I AM SO GLAD YOU MENTIONED THIS! I was going to suggest it too but didn't want to offend with such a simple suggestion. This is by far the most economical way to heat water and like you said: most people already have a kettle or the very least a pot, and therefore this method costs nearly nothing.

Here is something to consider perhaps.

I saw some videos from one guy with a lot of ideas around solar water heaters. Here is one of them:



There are lots of options for using different tubing, something clay based instead of concrete, and plenty of insulation options. I really like the idea of using some sort of front face to take the brunt of the intensity from the sun and radiate the energy as infrared heat to a water container or tubing underneath. Perhaps set up like a solar dehydrater but for heating water. Additional thermal mass that is well insulated will help carry that heat well after the sun goes down. With the right design it is certainly possible to have sufficient hot water from solar even in freezing temperatures.

I recently made a solar water preheater that takes advantage of the solar oven design that most houses in my area seem to have for a roof. Injury has prevented me from adding thermal mass or closing things in with insulation, yet it still works well enough that I can wash my hands, dishes, or take a quick shower from late morning to late afternoon and the preheated water goes in to the water heater, meaning the water heater doesn't turn on. When I'm able to get around better I will share some pictures and ideas for different designs, but most of what I have in mind came from Van Powell's videos. He goes into great detail and explains his reasons for doing things, as well as options for people to make changes to suit their needs.

I've used the on-demand propane showers, and they work very well, though they do use fossil fuels and require water pressure -- ether from a hose at household pressure, or a gravity feed with adequate head.

The solar heating options are all more in line with the OP questions.  I've installed around 3 dozen solar hot water systems, plus a few designed for space heating.  The only time hot water can go BOOM! is if its a closed system that can develop pressure.  If you circulate water in a tank or other vessel, make sure its either open to atmospheric pressure, or there's a pressure relief valve in your design.

For a thermosyphon system, the solar collector must be lower than the tank.  I've seen -- but not designed or installed -- a small system that used a small home-made solar collector (black plastic tubing in an insulated box with a plexiglass cover) plumbed in series with a 55-gallon barrel supported by a wood frame structure about 3' higher than the top of the collector.  There are small 12-volt circulator pumps that can be purchased online and powered by a 10-20 Watt solar (PV) panel, so the system only runs when there is enough sunlight to heat the water, and runs faster in bright light than dim -- a nice feature.

Probably the best tubing choice is standard black plastic water pipe, commonly available in hardware stores and building supply businesses here in the US;  hopefully, in France, too!  It is stable in direct sunlight, not very expensive, and will last for many years.

Really simple, low tech, very hot water. Coil a black rubber hose, say 100ft of 5/8 inch in a single layer(holds 0.57 gal), on the roof or other sun exposed surface. Cold water in, hot water out. for winter use cover with a plate of glass and protect the sides (do not let anthing shade the hose). the rubber hose is usually not damaged by freezing, and can be drained if this becomes a problem. frozen black rubber will thaw in just a few minutes or hours after exposure to sunlight. Do not try to put this water directly on your skin mix it with cold water. It gets very hot! If you need a larger quantity just attach more hoses together or increase the diameter of the hose ( 100ft of 1 inch hose holds 4 gallons). All black rubber hose does not crack or break like the plastic and combination material  hoses. You do not want or need reinforced rubber hose, just pure rubber.

Hi Pierre,

I note many replies are suggesting propane et for heating but since you want to insulate from energy prices, and the whole permie ethic of "earth care", I'm presuming you don't want to use fossil fuels to save electricity.

A real simple answer is to use TWO of the solar kits you can find in France if one is not big enough...just double it up!

If you want another step of complication (but not really complex), there is coiled copper tubing like this link...https://siamagazin.com/diy-solar-thermal-copper-coil-water-heater-easy-diy/

let us know what you ultimately  do - - it will be good for everyone to know options and how they pan out for you.

good luck!

Ron Barnes wrote:Really simple, low tech, very hot water. Coil a black rubber hose, say 100ft of 5/8 inch in a single layer(holds 0.57 gal), on the roof or other sun exposed surface. Cold water in, hot water out. for winter use cover with a plate of glass and protect the sides (do not let anthing shade the hose). the rubber hose is usually not damaged by freezing, and can be drained if this becomes a problem. frozen black rubber will thaw in just a few minutes or hours after exposure to sunlight. Do not try to put this water directly on your skin mix it with cold water. It gets very hot! If you need a larger quantity just attach more hoses together or increase the diameter of the hose ( 100ft of 1 inch hose holds 4 gallons). All black rubber hose does not crack or break like the plastic and combination material  hoses. You do not want or need reinforced rubber hose, just pure rubber.

Ron, do you know of anyone making pure rubber hoses any more? My first dip into cyberspace in search of one turned up only something made by Briggs & Stratton called a "rubber hose" that in the details just mentions 'rubber coating'. An Amazon reviewer posted secret spy pics of the packaging not shown in the ad that carries the "California Death Sentence" warning about unnamed toxins in it. It is still, of course, labeled a "garden hose".

Anyway, seems like something that would be available, but would need to find some sort of specialty source for it...?

Drinking water hoses I've had have always been blue or white with a blue stripe. I guess dark blue might work almost as well as black, but I think those are some sort of food-safe plastic. Besides not wanting to buy plastic stuff if avoidable, I particularly avoid plastics around heat...

https://www.mcmaster.com

Enter potable water hose in their search window. Many options to choose from.

Kelly Finigan wrote:Hi Pierre,

I note many replies are suggesting propane et for heating but since you want to insulate from energy prices, and the whole permie ethic of "earth care", I'm presuming you don't want to use fossil fuels to save electricity.

A real simple answer is to use TWO of the solar kits you can find in France if one is not big enough...just double it up!

If you want another step of complication (but not really complex), there is coiled copper tubing like this link...https://siamagazin.com/diy-solar-thermal-copper-coil-water-heater-easy-diy/

let us know what you ultimately  do - - it will be good for everyone to know options and how they pan out for you.

good luck!

This is a pretty sensible solution ! I might end up trying that.

Thank you all for your ideas. I don't want to use propane because I cook with natural gaz anyway (I could just heat my water in a big pot). Someone's remark about using a kettle got me thinking. It might actually be more energy efficient to use a kettle a couple of times a day, rather than leave my electric heater on all the time. I'll have to check.

I'll keep you posted. It's been raining on and off for a week now, so no hurry !

Kelly Finigan wrote:
A real simple answer is to use TWO of the solar kits you can find in France if one is not big enough...just double it up!

Reading back I don't see what 'solar kit' you are talking about. The shower systems that were mentioned?

Any idea what kind of plastic those bags use Pierre?

Amazon has a slew of interesting and affordable camp shower options online that use polyester-based TPU, which has relatively good heat resistance but poor microbial resistance (compared with polyether TPU according to a no-longer referenced Wikipedia article). I guess the temps from heating up the water are supposed to take out any potential build up of bad microbes? Plastics sure are one hell of a windy rabbit hole...

I’m not sure if this would save you electricity or not… but in Mexico I had friends who used portable electric emersion heaters in buckets of water to heat water for dishwashing & for bucket showers.

I don’t know what brand they used or where they bought them. I wouldn’t even come close to knowing how to DIY one but it seemed like a useful tool to have.

This is what a quick search on Amazon found: Limited-time deal: GESAIL 1000W Electric Immersion Heater, Bucket Water Heater with 304 Stainless-Steel Guard, Submersible Bucket Heater with Thermostat and Auto Shutoff, Heats 5 Gallons Water in Minutes https://a.co/d/jlUkyHD

Growing up in Africa in the old days we all had a Rhodesian boiler. A 44 gallon drum on walls with a fire under the drum.
came standard with the houses, the 3 walls were built to support the drum and high enough to gravity feed to the house. The fire box was at eye level.

We lit the fire in the evening so we would have hot water to shower and wash up.

Here is a blog on it, https://rhodesianboiler.blogspot.com/2013/11/my-first-donkey-boiler.html

The compost water heater has the advantage of working at night/early morning, you don't have to wait on the sun.  But not very effective in winter unless you move the compost into an insulated barn/shed.

I've been thinking about recovering waste heat with water - for instance using your refrigerator coils to warm water.  Another idea, specifically useful for campers and vanlifers, would be to add a heat exchanger loop to your vehicle's coolant system - it could heat up a 20-gallon (or so) insulated tank of water every time the vehicle is driven - there would have to be safeties built-in to prevent overheating and to turn it off in low water situations, but otherwise, it would just be extracting free heat.  Basically, any system that needs to be cooled down is a possible source of hot water.

Bonjour Pierre.

We're in Sologne and use absolutely no electricity at all for heating water. I've detailed our particular build on my website. Our setup is obviously larger than your 20 litre requirement, but I can confirm it works very well. Maybe you'll get some ideas from it!
Summer heating: https://www.la-darnoire.com/solar-thermal-panel.shtml
Winter heating: https://www.la-darnoire.com/boiler-stove.shtml

This thread is just one more example of why finding this site is the best thing I've discovered on the internet.  So many useful ideas and things to be thinking about as we get close to start homesteading a piece of property.  Nice to have all this early on in the planning stages.

Appreciation to all for taking the time to input.