# Solar water heater idea



## anim8r21 (Sep 4, 2009)

I have an idea to preheat water before it goes into my hot water heater. If I understand the system correctly, the hot water heater only uses electricity when the water cools down or empties out.
So I'm thinking take the cold water flow going into the heater and pipe it up onto the roof to run through a series of pipes or hoses to let the sun heat it up before it goes into the hot water tank.
That way it will already be hot and the electric heater shouldn't have to work as much. Any reason it shouldn't work?
I also thought I could use shut off valves to cut the roof system out of the line during cold weather and let it drain so it doesn't freeze.
Thoughts?


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## Caribou (Aug 18, 2012)

This is a viable system. One problem you may have is that if the water just sits there in the sun it may get way too hot. This can be dealt with by a circulator on an aquastat and a tempering tank.


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## anim8r21 (Sep 4, 2009)

What happens if it's too hot? Damage to the system or a scalding hazard?
I have a large family and we go through an enormous amount of hot water, so I don't know if we would have as much trouble as a smaller family. Our water rarely sits still!


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## zombieresponder (Aug 20, 2012)

It will work, but you will have to add a pump to circulate the water through the water heater and back out to be heated again by the sun. If there is no pump, the solar heated water will just sit in the pipes outside until a hot water tap is turned on in the house and water is drawn from the tank. I would guess that the electricity drawn by the pump would be far less than what the water heater uses though.....or there are probably 12v versions with a built in panel that would only run when the sun was out.

There may be some way to design the system to work as a thermal siphon and eliminate the pump.


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## anim8r21 (Sep 4, 2009)

I only planned to have the water move when a faucet is turned on.


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## Caribou (Aug 18, 2012)

The problem with not having a circulator, or thermosiphon, is that the water can get above the boiling point. A day outside playing or working, school, shopping or a thousand other things that leaves the water uncirculated for an hour or less on a sunny day can be a problem.

You'll need a thermostatic mixing valve on you water heater and possibly at each faucet in order to prevent scalding. With a solar water heater you will have two problems. First is too little heat but far more dangerous is too much heat. This is quite doable but it needs to be designed properly to avoid the problems.


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## hiwall (Jun 15, 2012)

I have to say that I really really doubt that the sun would boil the water. If that was a credible concern then a relief valve could be installed at the top of the system to remove that worry. I think the OP's idea is sound but I do not know if he would get a return on his investment very quickly.
The water in the solar system could easily reach 150 degrees but would be automatically tempered when it was drawn through the water heater.


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## squerly (Aug 17, 2012)

A water heater works by using a thermostat that turns the heating elements off when the water gets to the desired temp. Lets say that is 115* But when you use the sun, or other uncontrolled heating source, you can't just turn it off when it reaches 115*, so the water in your holding pipes and water heater can become much hotter than the 115* you want.

To regulate this and keep people from getting scalded, you will need to put a mixing valve on the side of the water heater that feeds the house. A mixing valve will add cool water to hot water that is over the desired temp, bringing it back down to the level you want and avoid scalding someone.


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## hiwall (Jun 15, 2012)

squerly said:


> A water heater works by using a thermostat that turns the heating elements off when the water gets to the desired temp. Lets say that is 115* But when you use the sun, or other uncontrolled heating source, you can't just turn it off when it reaches 115*, so the water in your holding pipes and water heater can become much hotter than the 115* you want.
> 
> To regulate this and keep people from getting scalded, you will need to put a mixing valve on the side of the water heater that feeds the house. A mixing valve will add cool water to hot water that is over the desired temp, bringing it back down to the level you want and avoid scalding someone.


This is possibly true except in the case of the OP as he will not be having any circulation. So his water heater would be at whatever temp he has it set for and when he turns on a tap water will come from his solar system down however many feet of unheated pipe then enter the bottom of the water heater through the dip tube that is located inside. The hot water he uses will be naturally drawn off the top of the water heater so the 'pre-heated' water will have little effect on what comes out of his tap.


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## squerly (Aug 17, 2012)

hiwall said:


> This is possibly true except in the case of the OP as he will not be having any circulation. So his water heater would be at whatever temp he has it set for and when he turns on a tap water will come from his solar system down however many feet of unheated pipe then enter the bottom of the water heater through the dip tube that is located inside. The hot water he uses will be naturally drawn off the top of the water heater so the 'pre-heated' water will have little effect on what comes out of his tap.


I guess you're assuming he doesn't have more water in the heating pipes than he has in the water heater. I didn't get long on the earlier post but we need to know how big (in diameter) and how many feet long his heating pipe is going to be.

Roughly speaking, I think a 4" pipe 50' long holds about 35(?) gallons of water. I have no idea how big (gallon wise) his storage pipe is gong to be. If it's only 5 he's just wasting his time, if it's going to be 50 then the volume can significantly affect the temp of the water in the water heater. I'd play it safe and install a mixing valve.


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## labotomi (Feb 14, 2010)

I doubt this system will be able to recover the cost of installation within a lifetime. Yes, it would reduce the initial heating required of cold water entering the water heater but wouldn't do anything about the constant heat loss of the water sitting inside the heater itself. Adding a circulating pump would address this but then you would have a constant electrical load that would cost money to operate, plus the roof piping would cause a loss of energy during the night and cooler months. Adding a single loop temperature controller to only circulate water when the heater is cool adds additional equipment costs and installation and requires an understanding of several factors that need to be addressed when programming the controller. 

Then, what happens in the winter when the roof temperature is below freezing? Is the system to be drained in the winter?


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## squerly (Aug 17, 2012)

anim8r21 said:


> I also thought I could use shut off valves to cut the roof system out of the line during cold weather and let it drain so it doesn't freeze.


According to his original post, a bypass and drain was in the design for Winter.

As for recouping his costs, I guess it depends on whether he has access to free pipe or he has to buy it. These kind of ideas always intrigue me. When I was growing up my Grandma/pa used to heat their water in a big green tank on top of the "shower room". Water flowed down a hand held hose and into the shower. Every evening, after shower time, we filled the tank back up. Obviously nobody took showers early in the AM.

And then later in life I found myself living in a log cabin in the mountains of Oregon, without electricity. I welded two 50 gallon tanks together, one on top of the other, and used the top tank to store water and the bottom tank to hold a fire. Then I gravity flowed the hot water down to the cabin. Worked just fine. A side benefit was the area around the cabin was always free of twigs, limbs and brush.


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## Tirediron (Jul 12, 2010)

If one lived where the solar collector could be installed below the existing plumbing, considering a conventional pressure water system, a decommissioned water heater tank could be painted flat black and installed in an insulated box with the south & or side being covered with a pane of glass the solar collector could thermo syphon into the existing hot water heater (if there is interest, I will expand this) and keep the gas or electric from cycling as often, a simple insulated cover could be used at night to keep the nightsky from reversing the cycle.


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## hiwall (Jun 15, 2012)

Cheapest and easiest way would be to buy a roll of 3/4" black poly pipe and throw it on the roof.
Tirediron- one of my neighbors has his set up like that.


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## smaj100 (Oct 17, 2012)

someone already mentioned it, but add a small 12v water pump run off a solar panel and you would have not net losses trying to operate the system. I plan on trying something similar this spring, to help preheat the well water entering the tank.


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## LincTex (Apr 1, 2011)

Tirediron said:


> a decommissioned water heater tank could be painted flat black and installed in an insulated box with the south & or side being covered with a pane of glass .


That very similarly describes the "summer" system at my bug out cabin. No insulation on mine - just a "tank on a tower"... It'll get hot enough in the summer to scald you easily.


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