My 2nd solar furnace just finished with video.

Bigtruckin85

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Nov 16, 2021
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If you need any help with parts to use & or technical advice, just holler.
Will do. I'm going to do my best to figure it out from what you've already documented, but I'm sure you'll hear from me one way or another! Thank you.
 

markansas

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Nov 23, 2021
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My cabin furnace draws air from inside. The other way around wouldn't be a good idea to me 'cuz you'd be drawing the hot air thru the blower which if it got too hot could curtail it's lifespan. I just use a simple thermal switch I got off ebay that monitors the box temp & fires up the blower when it reaches a good toasty temp, same for my new 1. The baffles you mention would only add marginal heat retention & since I'm into my 2nd furnace, it isn't a significant enough gain in effeciency to justify the extra build work. My cabin furnace puts out some serious heat so I'm not even thinking about modifying that but the shed furnace is drawing in much cooler air as it's not insulated as good as the cabin so I may tinker with some thin brick backing to see if it'll help but likely next winter. The blowers are bullet inline 4" ipower's I thought were 150 watts but just checked & it's only 90 watts @ 190 cfm. They move the air at a pretty brisk pace. I'm using 4" 3034 sewer line pipe for the ducts on both furnaces.
Along the lines of sunshine_eggo, I was wondering about some kind of baffles in the box, not necessarily to direct flow, but more like heatsinks to create more surface area and potentially hold heat longer. Maybe chunks of black painted 2x4 or something to give some extra area, and maybe a little bit of restriction. (I'm typing slow, I see you thought about this in your replies).

ok how bout black inscect screen wire the air will flow threw it nice and there will be lots of metal to heat up and cheap
 

Bigtruckin85

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Nov 16, 2021
Messages
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Location
PNW
Along the lines of sunshine_eggo, I was wondering about some kind of baffles in the box, not necessarily to direct flow, but more like heatsinks to create more surface area and potentially hold heat longer. Maybe chunks of black painted 2x4 or something to give some extra area, and maybe a little bit of restriction. (I'm typing slow, I see you thought about this in your replies).

ok how bout black inscect screen wire the air will flow threw it nice and there will be lots of metal to heat up and cheap
Without actually experimenting with different things, It's really hard to say what actually would improve it over the original. The screen wire could probably be good if you had enough of it in there strategically placed. I think it would sort of act as a filter, slowing down the cool air so the air would build heat from the heat mass. But I don't know how well the air would flow being pushed through something. I am kind of feeling like pulling the air would be my first thing to try as long as the temp didn't stay above 120f or so with the blower I have. If you are pulling the air, it has to be pulled from the cold air intake and will try to get to the outlet in the most direct way, so diverting some would spread the flow. Pushing it, I feel like it does work with no obstructions, but adding something to slow the air would probably end up causing the frame of the unit to gather heat and some dissipate out before making it into the house. I really don't know, but it's fun to think about.
 

markansas

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Nov 23, 2021
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Without actually experimenting with different things, It's really hard to say what actually would improve it over the original. The screen wire could probably be good if you had enough of it in there strategically placed. I think it would sort of act as a filter, slowing down the cool air so the air would build heat from the heat mass. But I don't know how well the air would flow being pushed through something. I am kind of feeling like pulling the air would be my first thing to try as long as the temp didn't stay above 120f or so with the blower I have. If you are pulling the air, it has to be pulled from the cold air intake and will try to get to the outlet in the most direct way, so diverting some would spread the flow. Pushing it, I feel like it does work with no obstructions, but adding something to slow the air would probably end up causing the frame of the unit to gather heat and some dissipate out before making it into the house. I really don't know, but it's fun to think about.
close to free heat .. you got me thinking on makeing a box.. and its seem so easy in my head . now to build on .. i got lots of scrap tin and wood. and oh ya glass.. what do you use for the input and out put pipe .. i think 4 inch pvc seems real easy .. still thinking if a computer fan will push enough air. or not.. they are 12v . small panel.. lots of ideas to sleep on seems to come together in my head after a good nite sleep... thanks for the ideas and nite
 

Bossrox

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May 21, 2021
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157
Location
Columbia, SC
close to free heat .. you got me thinking on makeing a box.. and its seem so easy in my head . now to build on .. i got lots of scrap tin and wood. and oh ya glass.. what do you use for the input and out put pipe .. i think 4 inch pvc seems real easy .. still thinking if a computer fan will push enough air. or not.. they are 12v . small panel.. lots of ideas to sleep on seems to come together in my head after a good nite sleep... thanks for the ideas and nite
Computer fan? No way, too weak. use 3034 sewer pipe, cheaper than pvc, check craiglist for old sliding glass doors or place a wanted ad. You'll get better heat mounted on a wall rather than my new 1 where some heat escapes out the back even tho it's insulated.
 

Bigtruckin85

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Nov 16, 2021
Messages
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Location
PNW
close to free heat .. you got me thinking on makeing a box.. and its seem so easy in my head . now to build on .. i got lots of scrap tin and wood. and oh ya glass.. what do you use for the input and out put pipe .. i think 4 inch pvc seems real easy .. still thinking if a computer fan will push enough air. or not.. they are 12v . small panel.. lots of ideas to sleep on seems to come together in my head after a good nite sleep... thanks for the ideas and nite
Bossrox used the sewer pipe. I think that would work good. You would probably want whatever you use, to be somewhat close or at least adaptable to the fan you use. I don't know what kind of CFM a computer fan has, but I don't know if it would do it. My blower is pretty good size because I am moving the air a good distance. It's more of a sealed unit though, vs what I think of with a computer fan. I pull about 112 watts with this one.
Edit: If I did mine again, I would not use the flexible pipe for the majority at least. I'm sure it reduces air flow, but I had to go from my garage into the attic, and then back into the house. I didn't want to spend a bunch on galvanized ductwork for it to end up not working. I was a lazy kid at the time. Lol.
 

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circus

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My different take on solar hot air. No fans, thermal mass, high temperatures, ducting, electricity, nightly heat loss, monitoring. Only problem was the temperature swings, tired of only wearing underwear when -10° outside, solved with 1500 two liter water bottles (thermal mass) stacked against the wall.
You don't want heat stored in the collector, you don't even want it to be hot. Wasteful.
The efficiency is determined by how much makes it through the glazing minus radiant loss. 60% to 90% instead of the 10% to 20% of PVs

Air.jpg

ducts reduced.jpg
The slightest amount of heat is captured and the slightest amount of loss is prevented by the check valves of feather light plastic film. Watching hot air flap them like a flag in a hurricane never gets old.
 
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markansas

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Nov 23, 2021
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i like simple .. i have a 50 foot south facing wall on this old building .. this would be a easy add on., one odd question what about summer do you cover the panels or just close the output vent.. or is it a problem?
 

circus

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Jul 8, 2021
Messages
271
i like simple .. i have a 50 foot south facing wall on this old building .. this would be a easy add on., one odd question what about summer do you cover the panels or just close the output vent.. or is it a problem?
Roof overhang, an awning and deciduous trees keep them shaded. The glancing sun angle also produces little heat. The first year I did seal the plastic to the vents with magnetic strips but found it was not needed.
 
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Bossrox

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May 21, 2021
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Columbia, SC
I kinda get the concept on the water bottles absorbing heat & using convection to disperse it but wouldn't those same water bottles freeze overnite then take forever to reheat?
My 1st solar furnace has an overhang that blocks the sun in mid summer but I do have to cover it in between seasons, the 2nd furnace will have a butterfly valve on top to allow the blistering heat to escape since there's no shading available.
 

circus

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I kinda get the concept on the water bottles absorbing heat & using convection to disperse it but wouldn't those same water bottles freeze overnite then take forever to reheat?
I suppose if all the doors and windows were left open for two day the bottles would freeze and I'd have a hell of a time reheating but that would be the least of my problems. Burst water pipes. The water bottles are in the living space buffering the temp swings. Days are 80 instead of 95, nights are 70 instead of 55. Solar air doesn't replace the furnace, it replaces fuel.
I did go without running the furnace in my garage. Half the collector/sq ft than my house. In the Wisconsin Jan & Feb. Pails of water never froze. As long as the doors are closed, most of the time, the concrete helped buffer the temp.

Heating a 1380 sq ft garage

collector B minus drawing reduced.jpg
 
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Ironman

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Nov 29, 2020
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I can't remember where I saw this but a simple window screen mounted in that box about mid way front to back will boost output.
It's black and has a huge surface area to collect heat.
 

circus

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I can't remember where I saw this but a simple window screen mounted in that box about mid way front to back will boost output.
It's black and has a huge surface area to collect heat.
Larger area/air ratio doesn't collect more heat, it's transfers more heat to the air. Runs cooler so less conductive and radiant loss, boosts output.
 
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Bossrox

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May 21, 2021
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Columbia, SC
Well the 1st chilly day test on the solar furnace looks pretty good. Got the shed up to 75 degrees with the propane & electric heaters. After the box temp reached a steady 95+ around 10am where the blower quit cycling, I shut down the heaters & waited to see what the shed temp would bottom out to. With the outside temp of 41, the furnace was holding the shed temp at 69. Pretty good results I'd say.
 

markansas

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Nov 23, 2021
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Well the 1st chilly day test on the solar furnace looks pretty good. Got the shed up to 75 degrees with the propane & electric heaters. After the box temp reached a steady 95+ around 10am where the blower quit cycling, I shut down the heaters & waited to see what the shed temp would bottom out to. With the outside temp of 41, the furnace was holding the shed temp at 69. Pretty good results I'd say.
yes i like that
 

Dacflyer

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Jun 5, 2020
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years ago i built a solar heater, made from tons of soda cans. drilled out the cans with 1-1/2" holes in the top n bottom, then glued them into sections, about 15 cans each.. and about 8 rows, these sat into a board about 4 inches wide.. i made headers so all the rows of cans sat on the boards, top n bottom.. so the bottom header had a cool air duct and hot air duct went into the house... the case and cans were all painted worth flat black paint, i used foil covered foam board as insulation, and i had a thermostat controlled fan to pump the cool air in, and hot forced out... the glass was an old sliding glass door with the frame removed.. the whole setup was mounted on a rack right out side the window. on a cold sunny day I'd get nearly 180F out the vent.. it got the room hot, and a fan in the room pushed the heat out into the living room.. the only downfall i had was the flexduct didn't last out in the weather. I didn't know of a solution to use..
so after a while i retired the project... but it was great otherwise...
 
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