# Passive hot water pre-heater?



## tinknal (May 21, 2004)

Obviously this would only work in the summer.......I was thinking I could install an old well insulated waterheater, or a an insulated storage tank in front of the water heater. Before the water enters the pre tank it would circulate through several hundred feet of hose on the roof of my house, absorbing solar heat. Would this work?


----------



## SouthWesteader (Jul 21, 2005)

That is similar to a setup in my garage. The water first goes from the supply onto the roof, down through 1/8-in. steel pipe under slight magnification, and down into the storage tank. As hot water from the regular heater is used, the storage tank supplies heated water to it, so it doesn't have to heat the supplied water. Right now, though, it does not work, because of a burst pipe, which taught me a lesson; at the first frost, shut off your roof system, and completely drain it. Otherwise, the water will expand as it freezes, and crack your pipes, which can cause some real headaches. So for summer use, I think your idea would work.


----------



## ET1 SS (Oct 22, 2005)

Sure it would work.

Or make shallow boxes [say roughly door sized], with a sheet of glass so they are three to six inches deep and 6 foot by 3 foot, and fill that with garden hose. It will work year around to solar heat your water.


----------



## wy_white_wolf (Oct 14, 2004)

tinknal said:


> Obviously this would only work in the summer.......I was thinking I could install an old well insulated waterheater, or a an insulated storage tank in front of the water heater. Before the water enters the pre tank it would circulate through several hundred feet of hose on the roof of my house, absorbing solar heat. Would this work?


If you are depending on household water pressure to push water through the hose on the roof a preheater tank is uneccessary and my even lose all the heat gained. Just dump the water directly into you water heater since it is only going to flow when your using water.

Also you would need something a pesssure relief valve for if the water got too hot and flashed to steam. And a backflow preventer to keep the pressure from backwashing it into the cold water pipe.

How are you going to keep the hose from getting to hot when your not using any water?


----------



## tinknal (May 21, 2004)

wy_white_wolf said:


> If you are depending on household water pressure to push water through the hose on the roof a preheater tank is uneccessary and my even lose all the heat gained. Just dump the water directly into you water heater since it is only going to flow when your using water.
> 
> Also you would need something a pesssure relief valve for if the water got too hot and flashed to steam. And a backflow preventer to keep the pressure from backwashing it into the cold water pipe.
> 
> How are you going to keep the hose from getting to hot when your not using any water?


I'm not sure I follow. All I'm basicly doing is adding pipe and storage before the heater. How can this cause a steam flash?


----------



## ET1 SS (Oct 22, 2005)

Assuming that your solar panel was so good that it heated the water, to steam and pressurized the system.

I am thinking that if your solar panel was that good, you should hook up a steam turbine and make power for the utility company.


----------



## tinknal (May 21, 2004)

ET1 SS said:


> Assuming that your solar panel was so good that it heated the water, to steam and pressurized the system.
> 
> I am thinking that if your solar panel was that good, you should hook up a steam turbine and make power for the utility company.


LOL, better yet, I patent it and retire on the royalties.


----------



## ET1 SS (Oct 22, 2005)

We are in the process of making a water heating 'loop' to feed our radiant heat system.

1- from the well the water goes to a filter,
2- filter to a check-valve and then a Tee onto the loop,
3- solar water heating panels then,
4- propane water heater then,
5- wood-burning stove with water tank then,
6- a Tee one-way thru a check-valve to domestic hot-water uses [dishwasher, clothes washer, etc], the other flow from the Tee goes through another check-valve and then,
7- PEX tubing radiant loop under the floor then,
8- circulation pump [12v from car battery with charger so power can go out but I will not lose heat] then,
9- back to the beginning of the loop.

If the sun is out, then the solar panels would heat the system.
If not, then the propane water-heater can heat the system.
If I feel like it, I can fire-up the wood-stove and burn waste-wood and peatmoss.


----------



## wy_white_wolf (Oct 14, 2004)

tinknal said:


> I'm not sure I follow. All I'm basicly doing is adding pipe and storage before the heater. How can this cause a steam flash?


Since he is talking about a passive system (no pump) when he isn't using water it doesn't flow. Thermosiphoning will not work with the tank mounted below the collector. Without flow the water in the hose would keep getting hotter and hotter leading to the possiblity of steam flash. Part of the reason to circulate water is to keep the collector from overheating.


----------



## wy_white_wolf (Oct 14, 2004)

ET1 SS said:


> Assuming that your solar panel was so good that it heated the water, to steam and pressurized the system.
> 
> I am thinking that if your solar panel was that good, you should hook up a steam turbine and make power for the utility company.


Many panels will flash to steam if you halt water flow long enough. They keep collecting heat with no way of shedding it.


----------



## ET1 SS (Oct 22, 2005)

wy_white_wolf said:


> Many panels will flash to steam if you halt water flow long enough. They keep collecting heat with no way of shedding it.


Okay, but I dont see it.

So any sealed tank full of water left in the hot sun will continue to collect heat and eventually super-heat the water into steam and explode!

Cool, I just thought that there is some point where the water and tank are really hot, but it just stops getting much hotter.


----------



## tinknal (May 21, 2004)

wy_white_wolf said:


> Many panels will flash to steam if you halt water flow long enough. They keep collecting heat with no way of shedding it.



Basicly what I'm talking about is leaving a hose out in the sun. I do not believe that the water will ever heat beyond the boiling point, which is needed to produce a steam flash.


----------



## wy_white_wolf (Oct 14, 2004)

ET1 SS said:


> Okay, but I dont see it.
> 
> So any sealed tank full of water left in the hot sun will continue to collect heat and eventually super-heat the water into steam and explode!
> 
> Cool, I just thought that there is some point where the water and tank are really hot, but it just stops getting much hotter.


While Tinknal's idea may not get that hot because it's not insulated, It is something I wouldn't want to find out later. Ounce of prevention is better than a pound of cure. At the very least if it did steam flash it would pop the relief valve on his water heater. Towards the worst side it would burst the hose while he's gone for the day and end up flooding the house. I'd consider the possiblity and put in a relief valve and a backflow preventer as cheap insurance and would rather plan for it and have it not happen then not plan and have it happen.


----------

