Heat Your House for Free!

You can heat your house for free and recover the cost to do it in one winter! It's amazingly cheap and simple to do with a solar collector.

Principle

Cold air is blown from the house into the bottom of the collector and is forced to travel through a U-shaped corridor which gives the sun time to heat it up. The walls of the collector are lined with tin foil to help bounce the sun around and heat up a heat absorber. Hot air exits the top of the collector and is returned to the house.

Parts list

  • 30" X 60" glazing made of Plexi-glass or Lexan
  • 1" X 6" X 20' stud
  • 30" X 60" furnace filter media
  • 4" 105+ CFM muffin fan
  • 4" X 25' insulated ducts
  • 2" X 4" X 12' stud (if mounting on the side of a house)
  • 10 watt photovoltaic panel (optional and expensive)
  • silicone
  • screws
  • tin foil
  • black high temp paint
  • Tools required

  • tin snips
  • scissors
  • screw driver or hammer
  • saw
  • Construction

    Take the 1" X 6" studs, cut two 58 1/2" and two 30", form a rectangle and screw it together. Cut another 58 1/2" stud and place it down the middle of the box. Cut away 4" X 4" of material in the middle of one end of the center stud. Take a 30" X 60" OSB and screw it to one side of the box. Line the interior with aluminum foil. Cut the furnace filter media to size and test fit it. Remove it and paint it with high temp black paint. Cut two 4" round holes on one of the 30" sides of the 1" X 6" studs. Cut four 4" pieces from the vent hood. On the inside of the collector, mount a 4" muffin fan on the cold air inlet so that air will be forced into the collector. Put the filter media in the box and then put the glazing on. Use L-shaped cabinet brackets every eight inches to secure the glazing.

    Pictures

    Ducts
    A 99 cent 4" X 24" tin hood vent from the dryer section of Home Depot can be snipped into 4" sections to make the duct connectors.

    Window
    The manifold is made from plywood and some insulation board. Ideally you would cut two round holes in the side of your wall or mount two dryer vents on the roof.

    Back
    Doesn't the back look pretty? This was the cheapest paneling I could find. However you should use oriented strand board (OSB) because it is more durable. Those silver things are the duct connectors. Cold on bottom, hot on top.

    Outside
    The collector and ducts temporarily sitting on the ground for test purposes. Ideally it would be mounted on the roof or wall with a southern exposure and you would run the ducts through the roof or side of the house.

    I recorded the following measurements on a 68 degree Fahrenheit clear day with fan running:

    Inlet - 68
    Inside collector - 205
    Outlet - 144

    What happens when the sun doesn't shine? Here's a recording I took on a partly cloudy day:

    Inlet - 68
    Inside collector - NA - I had sealed it before this test.
    Outlet - 118

    When the sun is not shining at all you will not get any heat. However there are folks that have built containment units that store the heat generated from their collectors for night time and cloudy day use.

    The collector above is used to heat my living room. It is the first one I have built and I am pleased with its performance. In fact, I need to get a higher output fan because the target outlet temperature should be 120 F. Mine was nearly 150 F with the fan running on a clear day! One collector in each room will heat the entire house. Cost is close to $65 per collector when buying everything new from Home Depot. The most expensive part is the glazing. If you can scrounge up some materials you could build them cheap.

    Mounted
    This is my second design. It is different from the first in these ways:

  • The outlets are mounted on the side to allow for flush mounting which I found to be a necessity.
  • The fan is internally mounted to aide in installation and eliminate noise.
  • The fan is powered by a 10 watt photovoltaic panel (top left) making it 100% free heat.
  • Final
    Shown with duct cover in place.

    Inside
    Inside you wouldn't know the house was heated for free. The wire goes to the thermometer.

    Frame
    This frame disintegrated. Don't try it at home. Use the flush mount pictured above.

    Mounting

    It was a lot of work to mount the collector on the side of the house by myself. I would suggest that you mount it on the roof unless yours is very steep. Rooftop mounts can be done with L-shaped brackets. Two dryer vent pipes can be installed on the roof and used to connect the ducts to. I chose to mount mine on the side of the house because it is a clear southern exposure and it was convenient to knock a hole in the wall.

    Using a PV panel

    Initially I ran a long wire to a 12V DC power supply and was planning on using that until it blew up. Evidently there was a short somewhere in the wire. That's when I decided I'd rather not mess with that and I bought a PV panel instead. The 10 watt PV panel is the smallest panel you can get by with to run the fan at full speed on a clear day. The panel costs more than the collector while plugging into the wall might cost $3 per month. There are some advantages in using a solar panel:

  • Easy to install.
  • Ne need to run a timer or build a temperature-based fan control circuit.
  • Provides free electricity.
  • Automatically optimizes air flow by slowing fan on cloudy days and running full speed on clear days.
  • And some disadvantages:

  • High cost but will pay for itself eventually.
  • Could be damaged by hail. My Siemens panel is rated to withstand 1" hail.
  • No way to turn the fan off although that could be remedied by installing a switch.
  • Here is a good link that has several stories on solar heating:

    http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

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