soda can passive hot air panel, worth the hassle?

[rollandelliott]

So I've seen these soda can passive heaters? Do they actually work well in an area like Charlotte, NC in the winter?

Also they look like a pain in the butt to make. My rough guesses:
1.5 hr to gather cans
1.5 hrs to paint them
2 hrs to cut them and glue them together
Total of 5 hours in just material prep!

I calculated you can get a roll of Black prepainted 24" x 50 feet Aluminum flashing for $75 and that would make one 4x8 panel. Using a 3" diameter tube and some aluminum tape I'm guessing. you could cut the material and tape it to make 64 tubes in about 2 hrs

Not sure it is worth 3 hours of my time to save $50.

Cost estimates:
$75 aluminum flashing
$ 5 for aluminum tape
$40 for clear coroplast window
$20 for foam insulation
$10 for dryer vent
Labor maybe $20?
$170 for this! seems too expensive

anyone actually make one and think it was worth the effort?

[russ]

Hi Rolland,

I have not built one but have seen the reported results on the net from people that I trust and they can be a big help with home heating - if you live in an area that gets a good amount of sun during the cold season.

I checked PV Watts for Columbia - annual average insolation of 5,1 kW/m2/day - lowest months are December and January at 3.8 kW/m2/day. Quite good and I suppose it must be correct - coming from the government and all.

With a good southern orientation and no shade you can capture maybe 50% of that. Lots of heat!

One of the members, Mountain, has built an air heater that he is happy with. Living in the Canadian Rockies is the perfect place to try out such a project!

I would probably not go the can route - I will look up the URL for a site with a slightly different style that I think is probably easier and better. When I dig it out I will post it here.

Russ

[bucketboy]

I built one of these can heaters and i have about 35 hrs into it and and about 500 dollars in materials. It does work but i wonder how i can inprove it and its performance.

[flyingdog]

I actually was thinking about trying to sell these on ebay last year...before I had ever tried building one...

I saved up cans and when I had enough started cutting them with what I had available - a box cutter utility knife and a can opener...after a couple hours and almost losing a finger I threw them in the recycling bin!

I'll stick to flat panels - they've always worked well enough for me

[bucketboy]

how do you built a flat panel?

[flyingdog]

how do you built a flat panel?

Just mean a flat collector plate, be it cardboard, wood or metal that's painted black... they're generally efficient enough, especially when you're talking about smaller sized collectors built on the cheap

[bucketboy]

the pop can heater i m currently building , i m doing a little different.....i cut the tops off and used a pinch bar to star the botoms. i read another article that indicated it caused a swirling of the air inside the cans. i wondered if i tied the two together with the same fan if they would give me good output or if i have to use a seperate fan for the second one. i think they are worth the time and effort......free heat is free heat. in ontario we heat for 8 months a year

[rollandelliott]

you don't really need to cut the tops and bottoms just stagger them. The air flow will be less, but it will work fine.

[russ]

I read the same article about causing the air to swirl. The air is just slowly drifting through the tube. Not adequate velocity to impart any real turbulence.

Sounds nice but not real.

If you tie the two panels together (possible) the problem becomes air distribution between the panels. Again, no problem but you need a damper.

If you don't force the air flow through the cans but just stagger them in the frame you would loose substantially - not a good choice.

Contact between the aluminum and air causes the heat transfer.

[bucketboy]

someone took the time to submit a heat transfer graph on the net and the staring of the bottom seem to be the greatest heat gain . it is a pile of work to make all the cans ready but if the heat output is more than i would try it again.

[russ]

I saw where someone used a small drill press and a hole saw. They would use one of the polyurethane (or similar) beer can holders to grip the can by hand.

They claimed it went real fast.

I tore the tops out with a pair of side cutters and plan to knock the other end off with a disc grinder - no drill press available.

Russ

[matt2602]

Just Made one - Not Sure

I'm just about finished making one of these soda can heaters and I don't think I'd do it the same way again. It takes a long time to deal with the cans and I don't see why you wouldn't get just as good results if you used a flat sheet of aluminum flashing.

[Naptown]

Search downspouts here some have had some experience using downspouts instead of cans. certainly easier.

[russ]

Agreed- the down spouts would be easier and one can rig a string of baffles to insert in the down pipe to provide turbulent flow for better heat transfer.

[Pappio]

First post, forgive me if I maek a mess of it.

Keep the task in mind. Sunlight hits an object and warms it, we need to get the heat out of the object into the air. Two things that help this are air turbulence and surface area.

The cans have a big advantange over downspouts because if made with holes in the ends smaller than the can, the air passing through will become turbulent and strip the heat off the metal surface more effectively.

Second advantage is the remaining end material of the can increases the area of metal exposed to the air flow. This is like having fins attached to the inside of the can to help heat the air. A bunch of baffles inside will increase turbulence, but unless they are firmly attached to the outside of the can they won't increase the heat transfer area.

Smaller holes slow the air flow, but they should be worth it. Haven't made tests, my gut says holes about half the diameter of the can would be about right.