This is a solar air convection heater for my garage that is powered by the low angle winter sun. It's easy to build and it works very well. With enough building insulation, this can be a primary heat source with a secondary needed for cloudy days. The idea and design is from Mother Earth News December/January 2007

2x8 lumber
2x6 lumber
2x4 lumber
2x2 lumber
glass, plexiglass, or some kind of clear material.
black aluminum window screen
caulking, paint, screws, lag screws, staple gun + other tools

I have some results on temperature differences from the first weeks of operation. Just like when you put up your first wind generator, the wind won't blow for days/weeks, I had overcast and mostly cloudy weather the first few days operating this thing. The heater puts out 87 to 104 degrees F at the vents on partly cloudy days to sunny days. The uninsulated garage hits about 17 to 30 degrees F above outside temps, very comfortable for me. It seems the colder it is outside, the bigger the temperature difference between the garage and outside. If you want more heat in an uninsulated area I would recommend possibly 1/3 more collector area than the ratio I give in the instructions. Seal up any drafts, it will do a lot to hold the heat. This thing works great.

Step 1: Frame and Fit

Make a box to mount on the wall of building (A south wall, SE and SW also can work.) This should be mounted vertically on a wall; the higher in the sky summer sun won't hit it as directly as the low winter sun. The walls of the box are 2x6 lumber; the angled "roof" of the box is a 2x8. I found it good to prebuild the box on the ground and then mount it to the wall. Make the box based on stud spacing in the walls; I have 24" studs, so my box is 8' wide with vents cut into four sections.

I sized the solar collector based on the numbers from the Mother Earth article where the guy built 160sq ft. of collector for his 700 sq ft building; using that ratio I built a 48 sq ft collector for my 200 sq ft garage.

<p>Nice ! Genius ! Great Job ! I like it ! Super !</p>
<p>Great detailed design. I was wondering, having some vents at the top on the outside solar, do you think you could have the system work in reverse, an almost solar cooler in the summer. So as that as the solar heats up as standard, the natural convection is to flow out of the top outside while while creating a vacuum and sucking air from that house via the base inlets? </p>
<p>WOWWWW! Thank YOU!!!! a million times!!!</p>
Hello All,<br><br>I have had success with a design similar to this. I used black spray-painted aluminum sheets, polystyrene (i think) insulation, scrap 2x4's, and a ton of caulk. It was by no means perfect and some of the glass is even cracked, yet just after peak sunlight today (about 60 degrees in January, weird) it was pushing around 130 degrees consistently. I was surprised. It is a small unit, between 6 and 7 ft tall and 1 and 1/2 ft wide. I was expecting less, honestly.<br><br>My question is, then, how would it perform if the box was taller or wider and if it was perfectly sealed. Would either of these modifications make a large difference? I would like to build a non-prototype model of this for actual use, but was wondering if anyone would be able to assist me by answering these couple of questions. <br><br>Thanks<br><br>ND Dell.
Yup, I felt exactly the same way. How can something solar and so simple put out so much heat? I'm amazed these aren't installed on most cold weather region buildings. <br><br>Yes, more box area gathers more energy, so bigger box = more heat energy collected. Perfectly sealed helps with heat loss of the building itself, like leaving the window cracked open a bit; this hurts most on windy days.<br><br>Good luck Nddell
I did have one more question.<br><br>What is the difference between using plexiglass (perhaps glazed, or double glazed) and using two panes of actual glass? Does one conduct heat better than the other? <br><br>Thanks<br><br>ND Dell<br>
I would think a layer of plastic type glazing is better than a single layer of glass for insulation value. But if money weren't too big an issue, double pane glass might be even better because of the insulating value and the clarity to let in light. Double glazed plexiglass might not let as much light inside as regular glass.<br><br>Here's a great link for more home build solar ideas: http://www.builditsolar.com/<br>
The only problem I have with finding newer glass is that a lot of it includes some kind of UV protection or reflective surface. I don't know if I am completely wrong on this issue, but how would using two separate panes of single pane glass with a small gap of space (insulated of course) affect the heat collection? For money reasons, that is how I arranged the last project that I did and it worked well.<br><br>What about plexiglass used for greenhouses? I feel like that would be a good choice as it is made for the purpose of creating an environment hot enough to start plants in late winter and spring. <br><br>If it is the best option (or most reasonable costwise) then I will probably go with plexiglass of some sort. I have also considered the idea of making a really giant collector and using insulated piping to transfer the heat from the collector to the house. This, I'm sure will create a whole new set of issues, though.
<p>just wondering if you had the reflective glass surface and faced it to reflect within, wouldn't that keep the heat within, I know nothing about any of this but just found the site and very interested in attemping this design to use perhaps on a camper or rv?</p>
Wow, I haven't even thought of any of this for a couple years. I can't say for sure, but to me the reflective glass would be reflective either way you put it and prevent light from coming in the from the only way it can. <br><br>As for designing for an rv or camper, you'd probably want to specifically pick very light materials. It'd probably have to be readily removed and installed or protected for movement. On certain models of camper you have to worry about modular structural component.<br><br>That said it'd be the right amount of space to maybe pull it off, since campers are so small.
Good point, no Low E glass or anything like that. Personally I think you'll get plenty of heat out of a single pain of glass or plexiglass without too much loss.<br>Fogged glass might be an issue with the homemade double pain. Anything clear for greenhouses would probably work here.<br><br>Let me know if you run duct work or pipes off of the collector or make an instructable; I'm thinking the same for my house. I'd like to see your version; maybe it'll need small booster fans.<br><br>
Yes, we were seriously considering the fan idea. we have been running with a crazy amount of ideas lately (like removable units that blow air into the floor, then let it rise slowly, hoping that it would help with heat storage). I'm sure what we end up doing will in no way resemble what we have been talking about now, but I will do my best to document it well enough to make an instructable page. <br><br>On that note, this might be quite a long time in coming, since I am trying to balance this with College and job (note what is capitalized and what is not). <br><br>And yes, fogged glass has been a problem with the small prototype unit I built with homemade double pane. On one hand, it works just fine (130 degrees on any day in direct sun) given that it is cracked and very very small. On the other hand I do wonder how much less efficient it is (that drives me insane!). <br><br>Also, does anybody know how to theoretically calculate the amount of heat produced by any given system using specific heat and physical properties?<br><br>Thanks,<br><br>N.D. Dell<br>
<p>Your work is appreciable but you can get more sun light on roof.</p>
More sun on the roof is good for electricity but that's not the point of this design; this is a passive heating system that works with the tilt of the earth as not to overheat during the summer.
<p>Hey I've been wanting to do something like this. Since I was originally inspired by the soda-can designs (but I don't drink any sodas), I've saved a ton of clean cat food cans to use as a heat medium. It seems the most efficient way to use them is sideways however, vs the usual vertical arrangement used in the soda-can designs. Maybe arrange them along the face of the screen used hear, and paint that whole interior surface black. Feedback?</p>
What about night time ? Doesn't it get drafty ?
Its a sealed window. <br>
why don't people use reflectors with these kind of systems? made from plywood and aluminium foil it would remain cheep and would improve the performance quite a bit.
After reading about these heaters, here and on the web, I built a mini version ( 2' x 1' ) out of some scrap wood and window screen laying around the shop. Of course it was cloudy and snowy the last couple days, but I got to check it out today. Sitting in the window sill for an hour, with the house at 68 F the air coming out of the contraption is approaching 90 F. Time to go full size on one of these. Thanks for posting this idea here.
so cool, great job and thanks for sharing.
wow, such a great idea.
What a great idea. Non technical. <br> Have seen one made with gutter drains but a lot more work. <br>There is a site that is just solar, they make all kinds, the hot air collectors, solar cells and water heaters. <br> <br>They have experimented with plastic and metal screen...make a 1x2 frame and wrap one long piece front and back. <br>They said the results seem as good from the plastic screen as the metal. Some of them used 4 inch pvc to run an air vent from the top and one from the bottom. on the inside of the house they ran 4 inch pvc down to the floor to collect cold air. <br>.. <br>seems if you want a fan there is a small one that you can connect to the hot side of the pipe (fits inside) with a thermo switch that cuts on when air gets to 90 degrees and off at 80. <br> Also had a vent flap on the hot side so that at night hot air didn't go back into the collector. The vent only opened when the fan runs...like a dryer vent... <br>As for the summer, they suggested covering collector with one of those reflective &quot;survival&quot; blankets and it would stop the collector from collecting heat. No wiring required, just plug the fan into a regular wall socket. <br> <br>I have a video of them building the screen part of the collector at <br>http://solarplanet1.blogspot.com/ <br>May need to scroll down. If you go look there shoud be a link to the simply solar site also. <br> <br>Cararta
I have one important warning and one reason why you wouldn't want to do this on your house.<br/><br/>First the warning: <br/><strong>In the summer block off the sunlight to the collector (cover it) don't just close off the vents.</strong><br/><br/>I bought a house with a homemade passive solar heater attached. It was mounted wrong (bad airflow) and didn't work well. I decides to remove it. <br/>While the house was vacant it had been &quot;turned off&quot; by shutting off the air vents into the house.<br/>The outside frame work was wood. It had gotten so hot that the interior had caught fire. The only thing that saved the house was the lack of oxygen. The fire smothered itself.<br/><br/>P.S. This was during the winter - ouside temperature doesn't mean the collector isn't going to get very warm.<br/><br/>Okay now why you wouldn't want this on your house.<br/><br/>A passive (no fan) solar panel should be mounted lower than the area you are heating. Otherwise it turns into what is called a &quot;heat siphon&quot; on cloudy days or when the sun goes down and will cool instead of heating.<br/><br/>The reason for this is simple: heat rises. If the panel is on the same level or higher with the area you are cooling once the temperature inside it gets lower than your inside temperature the airflow reverses and it draws the warm air from your house instead of heating it.<br/><br/>This can be defeated by mounting it lower than the area being heated or by having the vents shut off at night or in cloudy weather. (see earlier warning).<br/>
As to it causing inadvertent cooling because of the heat siphon effect, isnt that the reason for the plastic flaps--to act as valves preventing the siphon effect?<br><br>As to the risk of fire, I'm surprised. Wood doesnt combust, I think, until about 540 F. Maybe the paint caught fire, though?
Yes the plastic flaps are for the siphon effect. Fire doesn't happen with passive solar. Combustion of paper is like 412 F; I belive what the above guy is talking about is creosote in the siding of an old house. My interior siding looks black and burned, but it has never been burned. Concentrating solar with mirrors and magnifiers is what becomes hot and causes fire in a good way.
Fahrenheit 451. A book and the temperature at which they will ignite.
Hi I'm puzzled by your experience with the passive solar collector. I have measured the hot day temperatures in mine with the air vents shut off, and never seen more than 185F. This is a long long way from what is needed for combustion, and not that much different that occurs in window cavities with insulated shades or even in hot attics under dark roofs. On my collector, I included a set of outside vents that could be opened to allow air to circulate through the collector to take the stagnation temperature down when the vents to the insider were closed -- I have since closed them up permanently because they do not appear to be necessary. The reverse flow cooling at night or on cloudy days is not an issue on this design because the collector has poly film back draft dampers that prevent reverse flow. They are quite effective. These simple little 2 cent dampers were invented many years ago, and should get the Nobel prize for simple things that work :) Gary
GaryGary, Sorry I took so long to get back to you (haven't visited here for a while and didn't get notification about peoples posts till today -?-). As far as the heat build up goes there are many factors that could be keeping your passive heater from reaching combustion temperatures. Where it's positioned, air leaks, shadows, the insulation in the sides of the heater, sun angle, etc. Also you may not have let it sit closed up on a sunny day long enough to build up the temperature. I hope it never reaches combustion temperature. Robberfest has made a very good suggestion with the deciduous trees. As far as it working as a heat siphon, unless you close off the vents at night there isn't any way that it wouldn't function as one - this is basic thermodynamic law. It may not be enough that you physically notice it but it is still happening.
Hi Dropkick,<br/><br/>The flapper valves that stop reverse flow are very very effective. The pressure differential that the reverse flow causes sucks the light plastic film against the hardware cloth that backs them up tightly enogh that you can see the pattern of the wire mesh through the film. They are actually more effective than the commercial motorized dampers that are used in some systems because they don't have any leakage around the edges. Have a look at the pictures in the Home Power article at this link, and I think you will be convinced:<br/><a rel="nofollow" href="http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm">http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm</a><br/><br/>On the issue of collectors causing a fire: I run a solar website that gets 4000 visitors a day -- including many that own collectors. Yours is the first case of a non-concentrating collector causing a fire that I have ever heard of or read about. <br/>Gary<br/>

About This Instructable




Bio: Dad and hubby, good food enthusiast, solar energy, boating, making stuff, melting stuff, and raising chickens.
More by robbtoberfest:Crow Beak N Claw Mask Dragonfly Fairy Wings Ford Escape Tailgate Fix 
Add instructable to: