# Need Advice - Solar Heater



## MoonRiver (Sep 2, 2007)

I need some advice. Built a solar heater (pop cans inside of aluminum downspouts). I made it with 1" x 4"s, insulated inside with foil backed insulation sheet, and used a piece of plexiglass for cover. The size is 4'h x 3'w.

I tested it outside with the intake and exhaust both disconnected - in other words, I didn't have anything connected to them. On a warm day, I was getting temperatures around 220 degrees out of it. 

I have a brick house. I took 1 brick out and want to bring the heat in through that hole. After I figure out how to do this, I will repeat process at a lower level for input.

Today it was about 65 degrees outside. I have a 2"+ stub coming out of the heater and I clamped a 3" diameter dryer duct to it and ran it up to a 2.5" diameter piece of PVC pipe that I have going through the hole into the bedroom. 

The heater sat in direct sun all day but the temperature of the air coming out of the pipe only got up near 100. I took a small vacuum and put the hose into the input on the fan and blew air into the heater. This raised the temperature to about 110. When I turned off the vacuum, the temperature dropped right back down to 100. From past experience, I feel pretty confident that the air inside the heater was at least 200 degrees.

Advice needed.


I need a more efficient method for moving the hot air. I'm losing too much with this approach. 

Being as I am limiting my input to the size of a brick, what can I buy at Lowes or Home Depot that I can use to get the air from the heater into the house? I tried forcing the 3" dryer duct through the hole and that didn't go well. I can go with a slighter larger diameter piece of PVC and I could get another 1 or 2 pipes into the hole. 

I want to be able to switch the heater on and off. I'm thinking that I might use one of those switches that let you vent your electric dryer inside or outside. I would have to go outside to switch it, but that's not a problem. Any other ideas on how I might accomplish this?

I bought a computer fan to use to increase air flow. I know very little about electricity and electronics and need to have someone explain to me in real simple terms, what I need to do to user a solar panel for power and have the fan come on when the inside temperature is below 70 and the air in the heater is above 100. I just picked those numbers to give you an idea of what I would like to do. I just bought an electronics lab from Radio Shack so I'm hoping I can build it on my lab and get to understand it before I do it for real.

I would love to mount the heater flush on the outside wall. The problem I have now is my exhaust stub extends about 2" and the PVC pipe extends about 2" out the hole. If I add the dryer switch that adds another 6" or so. So I end up with almost 12" that the heater needs to be offset from the wall. So I need some ideas on how to mount the heater. It will be semi-permanent, meaning I may leave it up year round or I may not.


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## Nature_Lover (Feb 6, 2005)

I'm not sure I can help with solutions, but I have some thoughts.

If the temp in the heater was 200Âº and the output was between 100Âº and 110Âº with forced flow, it sounds to me that you are losing too much heat from the dryer duct tube. 
Try insulating that tube. 
Depending on how long it is, it's losing heat through the wall of the duct tube. If the exterior of that tube was also 65Âº it would cool the heated air, and if it's not pulled so the walls of the dryer duct are as smooth as possible, in addition to the extra surface area cooling effect, the friction from the ribbed surface in the duct slows the airflow too.

If it was drawing 65Âº in at the bottom today, and you got 100Âº at the output, you got a gain of 35Âº. Try standing it on something tomorrow, so you can line up the outlet with the hole in the wall and eliminate the dryer duct, just to see if you get a better heat gain without the dryer duct slowing it down and cooling it off. However, I suspect that if you insulate the dryer duct enough, it will also approach 200Âº at the heater, and the hot vent is going to draw the air faster. This might mean that the air only gets to 160Âº or 180Âº in the heater, but you're likely to see 140Âº or 160Âº coming into the house at a faster flow without a fan.

When you mount it on the wall, put the cutoff diverter at the bottom, on the intake. Most of these heaters I've seen are slanted with the bottom out from the wall for greater solar gain anyway.

It will be interesting to see how you build that fan.


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## Roadking (Oct 8, 2009)

I've made a few of these, so I can give some input. 
1) insulate the dryer duct. IIt will help with the heat loss.
2) I used one of those $9.99 solar panels from harborfreight (12v, 1.5 watt...actually, 20v in full sun) hardwired to a computer fan, 12v. Not a ton of force, but it did increase the flow when the sun is out. when the sun goes away, it doesn't run, possibly deleting your need for a switch.
3) My glazing is greenhouse roofing sheets (I don't remember the brand, but its like a corregated box; 2 sheets of thin plastic with groved channels), which gave me less heat loss than single layer plexiglass.
4) My next step will be using a fluid, rather than air medium. Simply, a 3/8 or 1/2 inch garden hose with a mix of water and antifreeze and a 12v bilge tpye pump circulator to get a radiator effect instead of forced hot air.
Looking forward to your results, and best luck. So far, mine have prevented the need to us the furnace in the rooms in which they are placed (except, of course, on cloudy days...LOL)
Matt


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## MoonRiver (Sep 2, 2007)

I'm making a little progress. I have the heater about 4' in the air and aligned with the hole in the wall. I am now getting a tad over 140 degrees in the house. I think that is about maxed out without a fan to force the air through. 

I am thinking about putting the input and output on the top and bottom of the heater instead of on the back. I think the PVC might be the best way to go. 










Need more advice.

Say I use a T-connector at the top of the heater and have the 180 degree hole facing up and the 90 degree hole facing the house. I put a coupling on it and run PVC into the house and cap the hole facing up.

Question - If I take the cap off the hole facing up, will all the hot air escape through the hole or will some of it still come into the house? I'm hoping that this might be a simple way to leave the heater installed, but disconnect it so hot air doesn't come into the house during warm weather. Ideally I would like some way to toggle between the 2 positions.


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## Fat Charlie (Sep 9, 2010)

Mounting "flush" to the wall is easy. Just mount it the way it needs to be mounted and then build a cosmetic box back to the wall. You can go anywhere from matching your siding to thin plywood painted a reasonable color, and even without insulating it, it'll have an insulating effect. 

If you have to go outside anyway to disable the heater and prevent overheating, the easiest way is probably to cover it.

Lots of good ideas and info here:
http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm


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## MoonRiver (Sep 2, 2007)

Fat Charlie said:


> If you have to go outside anyway to disable the heater and prevent overheating, the easiest way is probably to cover it.


I want to try using it as a chimney in the summer to draw cool air into the house. That's why I want to leave the heater in place, but vent the hot air outside instead of bringing into the house.


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## Fat Charlie (Sep 9, 2010)

I like it. I don't know if convection alone will generate enough airflow, so for best results you might just be better off with an exhaust fan. Of course, passive systems are hard to argue with.


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