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Free Heat From An Old Window And Some Soda Cans.

By David Quilty • Published July 1st, 2009 • Further Reading  

This article was originally posted at my site The Good Human, but because it is “EcoTech” oriented, I figured it should probably be here as well. Enjoy!

Some of you may remember a post I wrote back on my birthday that offered a sneak peek of a top-secret project I have been working on in my garage, and asked you to guess what the picture might be. Here is the picture that I posted on that day:


Well, the time has come to unveil more pictures of project timeline and all its finished glory, followed by some information as to how I made it, what its for, and what I will be doing with it now that it’s done. Let’s first take a look at a few pictures I took as I was building this solar space heater…












So, now can you guess how this thing works? As air enters the 2 holes on the sides near the bottom, the sun is heating up the soda cans all painted black to absorb the heat. The cans have holes drilled in the bottom, so the air being drawn in at the bottom works its way through all the heated cans and gets hotter and hotter as it approaches the top. With convection, more and more air is drawn in through the bottom and the heat rises. A single hole drilled in the top of the frame is where all this heat comes out, and I have to tell you – it’s friggin’ hot and it comes flying out of there at full speed. That’s the basics of how it works. But how was it made? Well, if you cannot see from the pictures, the ingredients include:

One old window frame w/glass intact
Empty soda or beer cans, spray painted black, with holes drilled in the bottom
Duct tape
A piece of insulation
Plywood for the back (I only have cardboard on it right now, so it’s not even sealed properly)
A dryer vent to hook to the top to direct the heat where you want it to go
Small screen to cover the 2 intake holes at the bottom

That’s it – it’s basically a free heater. However, now you may be asking how/where it could be used? Well, what I was initially going to use it for was to heat my garage during the winter, so I could work out there all day without freezing to death. My plan was to lean it up against the outside of the garage, right below a south-facing window, and let it collect the sun’s rays there. And then, I was going to build a custom window-shim out of a piece of wood that would let me prop open the window a bit but keep it sealed, and then cut a hole in the wood to attach the dryer vent to, which would bring the hot air into the garage. Kind of like this:


And finally, if I wanted to, I could mount a tiny fan to blow the heat further into the garage. But judging by the temperature reading coming off the air at the top, I might not even need to do that. It was up to over 105 degrees the other day around 11am. Amazing! And as I mentioned, it’s not even properly sealed yet.

But while that was my idea for it at my house, I think I might give this one away to someone who has trouble affording to heat their home during the winter, so at least they could have heat during the day. I have to do a few more tweaks, and finish the back, but other than that, it’s a solidly-built, indestructible free heat source that should go far to keep someone warm…during the day. Unfortunately, the moon just doesn’t shine bright enough to power it. ;)

Thinking of building one of your own for your workshop, garage, or even house? Let me know if I can help. It was quite a lot of work, but totally worth it in the end to know that I built a source of free heat that actually works!

  • jrfosterjr
    If you can modify your design to accommodate some heat sinks (bricks, sand, etc), then you could likely reap another hour or two of heat out of it, maybe more.
  • moescorner
    Fascinating concept. Living near Lake Michigan lake effect clouds always present challenges for harnessing solar energy in the winter.
  • Shane
    Cool piece of engineering there. I don't understand how the convection process works though. How does it draw in the air without a motor/electricity? Also, do you have a backup for overcast days?
  • Mary
    Great idea but I don't know when it gets cold outside do you leave the gadget in the sun outside? Will that work? I am not the smartest cookie in the box. So please don't think my question is stupid.
  • Great idea. I'd like to try something like this when I get a place of my own.
  • kev2009
    Awesome idea.
  • unclejack120
    Great project David, do you have any more detailed plans? I would like to try this one, but not sure of the air intake hole size and other ?'s If you can or would I would appreciate the info, thanks

    jack7morg@aol.com
  • unclejack120
    Great project, I have looked at several and this seems to be easiest and most efficient, do you have any more detailed plans of this? Thanks if you can forward any.

    jack7morg@aol.com
  • unclejack120
    This seems like a very worthwhile project, I have seen others but this seems to be the best so far. Do you have any dimensions or other info for this project?

    Thanks
    jack7morg@aol.com
  • hunterthompson
    please send me step by step how to build on if u dont mind please send it to thompson579180@yahoo.com thanks hunter
  • Awesome. I have been trying to think of a good way to heat our small house here in Miyako. It is sub tropical so it doesn't get to cold, but winter time can get a bit chilly. Something like this might work pretty good considering we do get a lot of sun.
  • xlch
    i have got waisted for over 3 weeks so far.. but i almost have the cans
  • unclejack120
    I like the means for the supplies, but you must be making one to heat the mall! I usually can supply the cans in a few days, nothing like a few cans away from a beautiful day! FLH jack
  • homebrewpower
    Hi there, I actually covered similar stories on my website

    http://www.homebrewpower.co.uk
  • Mike
    My Father-in-law died in 1985. He was a retired high school shop teacher and sort of a tinkerer, although I never knew him. When cleaning out his garage 25 years after his death I ran across a device, the function of which I was not clever enough to deduce; until I saw this! It was so similar to this that I am sure I now know what it was.
    His was about 30"h x 60"w x 3"d thick. The sides, one masonite and one aluminum were painted a lime green. Pop cans were cut in half and attached to the aluminum side, with pop rivets as I recall, several inches between them. Also attached to the aluminum side were 4 baffles also made of aluminum, that ran not quite the width of the box, dividing it up into 5 areas approx. 12" x 30". The cans were all attached within the center 3 sections. Two regular floor heat registers, one at each end and both on the masonite side allowed for air flow; one vent had a computer cooling fan attached.

    I have several photos I took while dismantling it which I would be willing to share with you if you like. Let me know.

    Thanks for solving the mystery!
  • Name
    I'm just wondering if your idea would work for a small greenhouse? Although being up north were we really don't get much sun light during the winter, I'm thinking there isn't enough sun light to produce much heat.... But the concept is very good.

    Anyone use this set with a greenhouse?

    thanks
  • parker120
    Please do not say "free heat" it is in no way free. you can not make nor can you destroy it you can
    change its form from solar to thermal energy. I know what you mean but it peeves me and i find
    if a 12 year old cant say it with out being lectured in school nor should others be aloud without being lectured.
  • robbsimms
    hey parker,
    how much does the heat cost?
    that's right, it costs nothing.
    it is free.
    you're confusing the conversion of energy, which is clearly happening here, with the cost in dollars of said energy. The energy is not being created from nothing, however it is not being paid for. hence it is free
  • Justice
    you really need a life, this guy has made this awsome thing and all you can do is preach on what he should be calling it. 'nor should others be aloud' ALLOWED i think is the proper grammer here, im sure a 12 year old would have picked up on that.
  • Deanna
    If you're going to be an intellectual snob, at least use the correct word: I think you mean "allowed," not "aloud."
  • Too funny Deanna. I tend to ignore those who correct me when their corrections are full of grammar and spelling mistakes. :)
  • Jason
    Just chill out! How can such a thing bother you?
  • That's great - finally found some use of the internet
  • gravitygardener
    Hello,

    I have been experimenting with a freestanding version of a passive heater. It heated up pretty quickly, but now trying to figure out the best way to pipe the heat into my garage or living space. I used black pipe (the same as my heat chamber) but it was a bit clunky.

    Anyone have this type of design and if so did you use something like a vacuum hose to transfer the heat into the living space several feet away? Just curious.

    You can see some of my pics @ http://gravitygarden.com/powergarden/?page_id=11 if interested.
  • JJLII
    Do you think that if you make the cans larger at the bottom and progressive smaller as you get to the top it would be a little more efficient?
  • If your looking to install suntouch or nuheat radiant heated floor mats look me up at
    Radiant Heat Experts
  • Name
    If this collector is inside the house, I question whether it really accomplishes anything. Radiant energy from the sun is entering the house through the window. If it strikes your collector, it will certainly be 'concentrated' creating a warm airflow as you just described. But consider if your collector is not in front of the window - the exact same amount of energy will hit and be absorbed by (and cause to warm) the couch, floor, wall, whatever. The net effect on the room's temperature will be nil, since the collector did not really collect more energy, it just concentrated it, at the expense of the less concentrated heating that would have 'been applied' to the room's normal surfaces.

    Now of course if this collector was outside, in front of the wall or on the roof, and you piped the warmed air into the house, thats a whole different thing, and you would have a net heat gain.
  • Name
    Disregard the above. I'm a dolt. Immediately after I posted this, I reread the article and realized that indeed the collector was to be mounted outside and the heated air pipe in.
    Note to self - pay attention!
  • Name
    No, good comment. Even though it does say that, I didn't notice until I read your comment and reread the article. I actually came down here to post the same thing you did.
  • Kimecakes
    Could you find something like bricks or stones that you could put above the hot air outflow to hold the heat during the day and slowly release it at night? That might be helpful for those who can't afford to heat... This is a great idea, and if I had direct sunlight on my place in the winter I would build one in a heartbeat!!
  • villecruz
    cool
  • copernicus66
    OH!! I've been trying to design a way for my south porch to provide heat passively. I almost had it but didn't trust my design. Now that I've seen what I wanted to do in miniature, it makes total sense. I was planning on making the windows as air-tight as possible, tiling the floor with a dark tile, and strapping water-filled, black-painted PVC pipe against the inside wall so they'll be in direct sunlight part of the day. There's a cat door in there, so that can draw cool air, and if I cut some vents on the top of the walls through to the house side, in comes the heat, right? (There's a closed door from the inside of the house out to the porch.)
  • Guest
    A very clever solution
  • I liked the concept, but the idea of drilling that many cans was a bit more work than I wanted to do.

    i used non-perforated sewer pipe for my heat chamber and it worked pretty well.

    I put a youtube together if interested. Not fancy but it worked

    http://gravitygarden.com/powergarden/?page_id=11
  • Finally a use for all those old beer cans!

    All jokes aside though, that's a really cool idea. And while I'm not lacking heat in my own home (it usually gets TOO hot) I can think of a few people who would appreciate such a thing.
  • Herbie
    Wouldn't painting old aluminum blinds black and hanging them inside your south facing windows do the same thing without having to construct something? Though I appreciate the innovation in this, seems to me black aluminum blinds are much simpler and every homeowner could manage a can of black paint. I see those old aluminum blinds in many thrift shops.
  • Not really - the cans allow time for the air flowing through them to heat up, before being forced out the top. Aluminum blinds painted black would get warm - but wouldnt warm up or move the air into the room.
  • Bob
    you don't mention what the ambient air temp. was before entering your heater so i wonder what the actual temperature rise was. It might be a good idea to insulate the back side of the heater. Would like to see the temperture rise on a cool but sunny day. Good job.
  • OK: An excuse to drink a few more sodas. :-)
  • thomas_r
    Great idea, thank you for sharing!

    A few small thoughts from me:
    One could use corrugated tin cans with different diameter - one fitting inside the other.
    (In some countries there's a deposit or refund on soda cans.) In addition, making it from tin cans would open up for using other techniques holding things together, as they are more sturdy than soda cans. The corrugated surface would also provide more area to absorb heat.

    Tin foil covered shutter(s) working as mirrors focusing more sunlight into the device.
    The hot air can heat bricks or stones which would work as heat reservoir.
  • Kay
    I see this working perfectly in my garden during severe frosts.
    Excellent idea
  • I've been considering building one of these myself. Looks like it's a definite viable addition for winter heating.
  • elearning
    hey great idea mate, I was wondering how you have arranged the soda teen to pass air from one to another. as it will be difficult to arrange the circulation without heat leakage.
  • Great idea. Wonder how many to heat the house!
  • vert
    awesome! way to think it through..
  • Scitt
    Very Nice
  • tyler
    i doubt that would work well in the winter time when the suns rays are very indirect and the colder temperatures outside would drastically cool the air before it exited the device
  • Jake Mcguin
    I saw the exact same thing on the side of a small apartment complex probably 30 years ago. Same design except the cans were arranged a little differently and on a much larger scale. Literally the entire side of the complex.
  • Brilliant! We might need one of these some day..
  • Gayla
    Keep up the good work.. We will need these great ideas.
  • African
    Cool! I mean Warm!

    In Africa the sun shines all day in winter but its usually cold in houses during the day because of poor insulation. Average temperature in my house is no more than 12 C on average as our winters are becoming colder.

    And of course cost is an issue here.

    Any way to make the hot air boil water and a steam driven device charge batteries for power use at night?

    Our power supplies are erratic as our power grid becomes older and fall apart. Now they are hiking electricity by 35% a shot to get money to so call upgrade the system, most of it is "lost" however.

    Will give this a try for sure!
  • polyparadigm
    >to make the hot air boil water and a steam driven device charge batteries

    You'd have better luck using a corona discharge to charge the moving air, harvesting the high-tension DC from the top of your solar chimney (which could be made of compressed earth) in the fashion of a van de Graaf generator. This voltage could then be stepped down to suit the needs of your battery charger. Sort of like one of those ionic filters, running as a turbine instead of a fan.

    You'd need someone who knows what they're doing to design the circuit, but the components won't be all that expensive, and a lack of moving parts would be a very good thing. Step-down transformers can be a lot more efficient than step-up transformers, and energy could be stored as heat (since convection is stronger in cold air) rather than in batteries.
  • I had a similar idea, but it was using a heat conductor(like Aluminium/iron rods) to heat a medium that would store the heat energy(like mineral oil) during the day. That energy is then released during the evening.
  • AJ
    great!
  • totally cool.
  • mgl
    Very good design. And Cheap.
  • Dan
    Hello Folks

    Here's my solar heater project. http://drobicho.com/blog/solar_furnace_instruct...

    About two years ago I came up with this. This solar energy project received second place in the 2007 Bordeaux Energy Colloquium's Annual Sustainable Energy Futures Casestudy Competition, an international competition for the most innovative renewable energy initiative.

    Thanks for reading!
  • A
    cool
  • Kenzie
    This is amazing and freaking crafty!!! Nice job!
  • at
    if you know what you are doing with electricity transfer, you could attatch a fan to the end and let the hot air spin it as it comes out, and store that energy to power small appliances, or charge your ipod, etc
  • Anon
    As Matt said half cans with the open side towards the sun might be more efficient.

    Also if the cans are touching the window the box can be made significantly thinner, stick some wood/paper/whatever behind the cans to hold them in place and you don't need any duct tape to hold the cans in place, plus it works as insulation. But it'll be annoying cutting the cans in half.
  • maria
    what about making a mini one and sticking it in your car? would that be a fire hazard or anything...? if not im totally making one! i live in chicago and would love not having to wait for my car to heat up every morning ;)
  • Scott Osburn
    solar power out of old objects nice work man
  • matt
    Couldn't help but think I'd seen this project done somewhere before...
    http://www.theworkshop.ca/energy/collector/coll...
  • The weak link here is the duct tape here. If it comes to high temperatures the adhesive on it will not work over a long periode of time. I would suggest 3M nuclear tape if you have/chosen to use duct tape. Would suggest using 3M DP810 adhesive (or DP810NS - non sag version)
    note: this is not an ad - I just like 3M products and find them reliable (but pricy)
  • Gaz Reynolds
  • Jay
    You could store the heat from the day in a insulated barrel. Use a liquid instead of air to move the heat. I have seen similar concepts for cooling applications in large buildings with chillers. At night you freeze the ice. During the day you use the cold ice to chill the building.
  • Too awesome.
  • wheelnut53
    great idea good survival tool if needed other than the epoxy to secure the cans I can't think of any improvements
  • haha......WOW cool........but i live in INDIA so guess i won't be needing one after all........but a great idea.......cool mate:-)
  • sarah29673
    Ah Jester, but just think - all that hot sun in India could equal lots of "free power" if its hooked up right...
  • Chuck
    Is it possible to hook up a solar cell(s) to power a fan that would pump the air out into the garage at a faster rate, which should aid in dispersing the heat throughout the area?
  • Eric
    For the issue with heating the place at night, couldn't you make something else to heat water during the day (which goes into a decently well insulated tank), and then draw heat from that at night? I think you could even use another one of these for heating it, just have the water pumped through some copper tubing and coil said tubing up. Then run the dryer vent over them (IE, have the coiled tubing inside the vent pipe).
  • Jamin
    Simply amazing! Have you thought about a cooking application with this? Perhaps some sort of convection oven by diverting the heat into an old toaster or suitable container? That way: cook up your hotpocket/boca burger/ toast while you work!

    And thank you! You and people like you are an inspiration of effort for me and my projects! :D

    Happy 4th!
  • sue
    Sounds like something I'd like to experiment with. I was facinated by the comment about using such a device to heat heat water. I'd like to try building an indoor collection system of water jugs (or some such),and running the hot air collected by the cans around and among the water jugs. Can't think of how to do it without it being quite clutzy, but want to hear thoughts about its feasibility. I'm thinking it would be good to keep a greenhouse productive during winter.???
  • Kyle
    I have seen this before months ago on a different site. neat.
  • Ingenious idea to re-purpose items that are going to the landfill and reduce your energy consumption. A tip of my hat to you :)
  • Scott, I spoke with Bob Ramlow on this subject (well known author about solar energy), and he told me to cut the cans in half with the open ends toward the sun all painted black, and the efficiency will be through the roof! Interesting idea...have not played with it yet.
  • This is really cool.getting free heating could save you an arm and a leg over the course of a decade.Or even just to supplement your heating to reduce usage.
    I'm no engineer but would foil inside improve the performance?
  • It shouldn't matter at all, Scott. If it does, I didn't see any issues!
  • Looks like a fun project! However, As we can see from the photos, the drilled hole in the can is 1/4 the size of the premade opening. Does it matter what orientation the cans are for this to work?
  • Mike, I imagine that would work fine - as long as you don't mind having a box full of cans in your window. :)

    Sonja - the problem with the whole house is that there is no heat at night from these, so they do work better for garages/workshops/etc, where you work during the daylight hours.
  • raj
    wow cool man!!
  • Nice one, good work…

    What about making a bank of them big enough to cover a wall or section of a roof? Seems the cost would be fairly low? How efficient would that be? Could you heat a whole house?

    As in the U.S. most homes are forced air I wonder how hard it would be to connect it to the existing ducting system that distributes air around the house? If you made a stack of them, say 10ft high how hot or how fast would the air be?

    Have you considered getting these manufactured and selling them on the internet? Sounds like a small business idea?

    Would love to help…
  • Love the idea. In fact, I made a box like this last year. 4'X8' box containing 320 "beer" cans painted black. back and sides have a minumum R value of 21. the glazing I purchased (nothing but plexi-glass). In the dead of winter (south central wisconsin), we had temps of over 170 degrees C coming out of the box (circulation through the box through the use of an old computer fan). our outside temps at this time were anywhere from -10 to 40 degrees outside temp. I didn't put any holes in the cans, or attach them together in any way. they are just stacked cans painted black. our latitude is approx 43 degrees N, so the ideal winter heating tilt of the box is 58 degrees (I built mine at a generic 60 degree angle). so far this summer, I've only seen it top out at a little over 100 degrees (the sun is higher in the sky, so less direct sun on the panel). We have budget billing in our home for gas/electric. the budget billing WENT DOWN $28/month because of the box I built and installed on the outside of our home. Now that I've learned more, and am on a continual "experiment" mentality on my home, this box is going to be removed and improved this fall when I have more time to work on it. Great idea...thanks for sharing! /Users/matthewbolton/Pictures/iPhoto Library/Originals/2008/Nov 26, 2008/IMG_0226.JPG
  • Mike
    I was wondering if it might be possible to create a frame without using an old window frame and then place flush against the windows already installed in my apartment. Assuming I was able to get it sealed where the two meet. Does this sound like it would work the same?
  • It's boiling outside at the moment...but I'll save this one for the winter
  • Bret Engineer
    It is true the light is converted pretty efficient already through the preexisting windows, but this heater easily provides more surface area than the small portion of the window that is blocked, so it will provide more heat that way. One big benefit would be that you could use it on a window that is in the shade, just as long as you have enough dryer vent to reach sunlight with the heater. You don't need an old window frame either, you could make your own frame out of 1 x 4's and a piece of glass that could be whatever size you want. The additional tools you would need are a table saw with a dado blade and a brad nailer.
  • MH
    Great idea! IMHO, I would reconsider duct tape as a fastener. I would recommend epoxy: put a little smear around the bottom rim of each can and press it onto the top of the next one and it should seal well and set permanently. Not only do you want to avoid ever having to go back and replace degraded tape but you also want to really seal the cans end-to-end to maximize convection efficiency.
  • David
    The window doesn't get blocked when you use it; not at all.
  • Real Scientist
    There is a significant flaw in your deductions joe, the black cans almost certainly have a lower albedo than the random surfaces that the light would fall on if it was simply shining through the window.

    The other flaw in your reasoning is that you failed to take into account the fact that the overall collector is much larger than the wooden insert for the window. That alone means that the collector will deliver more heat than the window un-aided.
  • Anthony
    Wow this is a great idea should be patented or something. This could really go somewhere in a place like alaska where it is sunny 24/7 half of the year but still snowy. THINK ABOUT IT
  • joe scientist
    You might as well just leave the window open. This device helps make sure that most of the light gets converted to heat, but that happens with pretty high efficiency, anyway, when light just shines in the window and bounces around in your garage. Since you need to block the window to install this thing, your garage will not get much warmer. One slight caveat: it will help "concentrate" the heat, so that if you are standing right in front of it, you will feel warmer before the heat dissipates into the garage at large.
  • David
    Anon - yes, I know.

    Maht- I havent tested it in winter yet - have to wait a few more months. But at this altitude, the sun is VERY warm even in the dead of winter. 10 degrees outside feels more like 45.

    Larry - It would require a pretty big awl to punch a decent-sized hole in the bottom, but that could work. Also, your indoor air idea could work, for sure.

    John - Nope, he rented both his houses the day after they went on the market. Gotta be quick for these great properties! :)
  • anon
    Aluminum could corrode but, will not rust.
  • What is the daytime temp in winter? Is there really enough light based heat to make a difference when it's 0 deg c ?
  • Brilliant project. Three thoughts: 1) Guinness cans might be easiest since they are already mostly black and extra long. 2) Could skip the drilling and just punch a bunch of small holes in can bottoms with an awl, 3) Might be more efficient if the air intakes brought air from inside the room you're trying to heat.
  • Since I'm from Taos, too, my primary bewonderment is that you actually have a garage. :-)

    This kind of solar collector has been around for some time -- decades ago in Mother Earth News, I remember -- but you seem to have been able to improve it significantly. Congrats! It just astonishes me that every house here doesn't have such things, but then very few houses in Taos have windows that open like that. (I'm sure this must sound loony to people who actually live in America, which northern NM is not.) ANYWAY, good for you, and does your landlord still have another house like yours for rent?

    :-)
  • Draow
  • KomieCid - With water, whatever you use would have to be rust proof, etc, so it would have to be made with some sort of plastic or copper tubing. Not sure thin aluminum cans would be the best conductor for water heat.
  • stellarseeker
    We have used wood or pellets for heating for decades with no ductwork. The bathrooms are the farthest from the stove so, I am thinking of making one of these to assist warming at least the one with the south facing window! I have seen some others creations with the same principal but this looks like something I can do and afford. Do you think Plexiglas would work as well as glass? I have a choice of windows here to use.Thanks.
  • KommieCid
    I have to say this is absolute INGENIOUS. I have been considering something like a twisted tube of aluminum foil stuffed with one side out inside insulation, but this would be so much simpler! what gave you the idea to use cans? do you think it would work from a skylight setup?

    as another thought, do you think daylight water heating would work in a similar fashion, or would I need to have a completely different setup?
  • rob
    Nice job. Now the question is could a huge one spin a small turbine to generate power.
  • Bill
    Amazing! I really want to try to build some of these for the winter this year. Very very interesting.
  • Nan
    Hey, nice window! ;) Great job. You are so creative this way. I love it, and keep it up!
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