# Solar water heat for Radiator baseboards



## ToddB (Oct 10, 2008)

Anyone ever use a solar hot water heater hooked into radiant baseboard heat. I have oil fired baseboard heat and I'm thinking about changing to solar hot water pumped through it.


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## wy_white_wolf (Oct 14, 2004)

Solar has a hard time producing water hot enough for base board heaters.

Solar Gary has some info on his site about this http://www.builditsolar.com/ from when he was building is solar shed. He installed radiant floor instead.


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## wendle (Feb 22, 2006)

I just recently (this summer) installed 6 2X7ft. solar panels for heating water. 
When the days were longer I was getting some nice hot water, about 150 degrees in late summer. Now I'm only seeing 120 degrees, and for shorter periods of time. From about 10 AM until 4 PM . The rest of the time it needs to be shut down, as the panels cool very quickly once the sun is off of them. Mine are set up along the south side of the house, with no insulation behind them(not on the roof). I plan on closing in the back to help, and my outside plumbing needs to be insulated before it gets too cold. For winter I decided to go with an outdoor wood boiler as a back up heat source. The panels do work great for sunny long days as the only water heating source. I no longer use my propane water heater, and that's a huge savings. 
It might work to supplement the heat , and reduce your overall bill. So far this year as long as the temps are about 30 or more at night I am able to rely on solar heat (water and air). Another less expensive option you might consider is solar panels that heat air. These are pretty simple to make and work well. I used them last winter along with an attached greenhouse with great results. As long as the sun was out I didn't need any other heat source. At night of course I had to use my back up heat. Last December we only had about a week of sunshine here, so I did need a good back up heat. 
Being kind of a ******* cheap person I just went with what I could get set up for reasonable used, or that I could make.


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## genebo (Sep 12, 2004)

I'm accumulating the valves and supplies to add solar hot water to a propane fired hot water forced air system.

During the cold months, the water won't get very hot, and you get no hot water during the time you need it the most, after dark. I'll be using mine to raise the input temperature of my propane fired system, reducing the amount of propane required, but not eliminating it.

I'm aiming for two water tanks. The existing 80 gallon, plus another 80 gallon pressurized tank for the solar heat exchanger. Fresh water will always flow into the solar tank, then into the propane fired tank. Any time the temperature of the solar tank exceeds the temperature of the propane fired tank, a pump will draw water from the propane water tank into the solar tank, causing mixing.

During heating cycles, no fresh water is drawn into the propane fired tank, so the mixing pump will come into play. It will operate separately from the circulating pump for the air exchanger, enabling the heater to operate just as originally designed, any time there is not enough heat in the solar tank.

I don't expect big gains in heating, just some relief from propane prices. During the warm months, I want it to supply all our hot water.

I hope it will be a worthwhile project.

genebo


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## SolarGary (Sep 8, 2005)

Hi,
There are a couple challenges to doing this:

The first is that the way baseboards are sized, they will probably require 140F to 160F (hot) water to meet your homes heat needs in really cold weather. Solar collectors will heat water to these temperatures, but they are much more efficient producing water around 100 to 120F. Your baseboard heat output will be cut in half (or more) using the lower temperatures. This may still be enough to heat the house for many weather conditions, but not for really cold weather.
This doc gives baseboard heat output vs water temperature:
http://www.slantfin.com/documents/327.pdf


The other thing you need to work out is how to interconnect the two systems so that you can use solar heat when you have it, but revert to the oil burner when you don't. I think that the best scheme to do this is to basically have an electrically controlled valve that switches between the two heat sources -- when there is enough heat in the solar storage tank it uses that heat source, otherwise it uses the oil burner heat source. Schemes that attempt to "boost" the temperature of the solar water up to what is needed probably won't work.

Another alternative to think about:
- Use solar air heating collectors instead of solar water heating collectors. These would just operate in addition to your existing heater. They would just dump solar heated air into the house to reduce the load on your existing system. The nice thing about solar air collectors is that they are cheap and easy to build. They don't include storage except in the thermal mass of the house itself, but you don't really need storage until the collector area exceeds 8 or 10% of the home floor space -- this is quite a bit.
Depending on what kind you build, and what you have on hand, simple solar air collectors can have a payback period inside of a year.

Have a look at:
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm
for more ideas.
and:
http://www.builditsolar.com/Experimental/experimental.htm


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## gwest (Oct 9, 2008)

Hello everyone,
SolarGary is correct in heating with solar air collectors. They can be built cheap or for what ever amount of money you want to put into them depending on absorber material,glazing,enclosing the system etc.
www.builditsolar.com has some great DIY collectors there.


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## okiemom (May 12, 2002)

Would the solar panels help in raising the temp so the oil burner will not have to work as hard? It might not heat up to 160 but if the water is up to 100 deg. then the burner will only have to raise the temp 60 deg. instead from outside temp? Like the theory of geo-thermal?


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## Kevingr (Mar 10, 2006)

The incoming water temp on a boiler is typically in the 140 deg. range. You'd lower the temperature of the water.


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