Replies

1. 
   shelternerd | Mar 16, 2008 05:16am | #1

   The problem with trying to gain solar advantage on a staple up radiant project where you staple the tubing to the bottom of the plywood subfloor (which is no ig deal to do as a retrofit and generally we put it in last when we do them in new construction) is that in order to push the BTU's you need across the subfloor and finished floor you need a high temperature differential (AKA delta T) between the water in the tubes and the room temperature generally we're running satple up with the water going into the loops at 135 degrees or more and coming out at 120 or more back to the heat source. Solar preheat works better with the water coming back to the heater at room temperature.

   A slab type radiant system will return the water to the heat source at room temp as will a WarmBoard type installation where the foil on the plywood sucks a lot of heat out of the loop. Maybe if you used a whole bunch of heat plates under the floor you could get a staple up system to work with solar but it's going to tend to be not as effective.

   There is some more info on this at http://www.chandlerdesignbuild.com/files/demandWaterHeaters.pdf

   Be well

   M

   ------------------

   "You cannot work hard enough to make up for a sloppy estimate."

2. 
   GaryGary | Mar 16, 2008 05:52am | #2

   Hi,
   We retrofitted solar radiant to our floor. We took up the current finished floor, added half inch PEX floor loops on top of the current subfloor with 5/8 plywood spacers between. This required trimming the bottoms on some doors, but generally it was all straight forward to do.

   This all works fine. We have 240 sqft of collector, and I figure the system saves us about 340 gallons of propane through a typical heating season.

   The high today was 36F with snow showers in the morning, but a sunny afternoon. The system has been heating the house since late in the morning, and the 500 gallon storage tank is at 113F now, which will last through the night. Kind of nice with propane at $2.20 a gallon :)

   The system is explained in gory detail here:
   http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

   The floor part is under the "Heat Distribution in the House" link.

   In our system, the only thing heating the floor is the solar heated water. We kept our existing forced air furnace in place to provide the heat the solar could not. But, we like the floor heating so much better than the forced air that I plan to add a boiler to the system so we can do all the heating with the floor system.

   --
   On the PV. I believe that the going rate for grid tied systems is about $8 per peak watt. So, a $7400 system with no rebates might buy you a 1KW system. This might generate an average 3 to 5 KWH a day depending on how much sun you get. While most people use more like 30 KWH a day, you can get by with 3 to 5 KWH if you pay a lot of attention to efficiency and conservation. Some people manage on much less.

   Off grid system (with batteries) are more like $10 per peak watt.

   Gary

1. 
   talkingdog | Mar 16, 2008 06:28pm | #5

   OMG, you da' man! I read your article a while back
   and was blown away. Very inspiring.

2. 
   cqward | Mar 17, 2008 02:34am | #6

   Gary,Thanks so much for this answer. Husband has checked your website and may contact you himself with technical questions. But I am curious - what kind of flooring did you put down over your radiant heat panels?Christine Ward
   Williamsburg, VA

1. 
   GaryGary | Mar 17, 2008 04:11am | #7

   Hi,
   Feel free to email me at the address on my website.On the floor material:
   We thought for a long time we would use a "real" wood floor -- probably what they call an engineered floor that has a hardwood layer over a plywood like material with tongue and groove edges. This is supposed to hold up better than solid hardwoods over a radiant floor. But, in the end we went with one of the new laminate floors. The reasons being: 1) we have a pretty energetic and large dog, who would have been hard on real wood floor, 2) the new laminates are getting closer to wood in appearance with textures and grooves and all, and 3) we live in an open area with gravel roads -- its hard to avoid tracking in some grit and dirt once in a while.If you are thinking about a hardwood floor, I think this can work fine as long as you choose it carefully.Gary

3. 
   WIBuilder | Mar 16, 2008 08:20am | #3

   There is a lot of information here.  We are building new and are planning to use solar as well.

   http://www.radiantdesigninstitute.com/

4. 
   ronbudgell | Mar 16, 2008 03:30pm | #4

   cqward,

   I don't know where you live, but where I live, I heat the house for about half the year,

   When I install a solar heat collector here, it will heat the domestic hot water so that it will be paying back for the whole year.

   Ron