# Solar Air Heater Design?



## Justa Lane (Sep 7, 2018)

I was going to build a solar air heater for my off grid cabin but I stumbled upon someone giving some away from a house they purchased. They look pretty legit but nothing like the designs I have seen floating around the web. Has anyone seen a solar air heater like this?


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## Danaus29 (Sep 12, 2005)

I've seen plans for a homemade one similar to what you have. It works best on a direct south facing wall. I'm not sure which way is up but I think the holes are on top. There should be a glass front that goes over the fins.

I am jealous! That was one terrific find.

I may be wrong, the very few I saw on a quick search showed the big holes on the bottom, with fans in the holes. Did they tell you how it was installed? Did they have any pictures of what it looked like before they removed it?


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## doc- (Jun 26, 2015)

I built a passive solar collector a few yrs ago to try it out.... No need for fans-- hot air rises automatically. Holes at the top allow rising warm air to enter the room, while holes at the bottom allow cooler room air to enter the warming chamber at the bottom.

Located ~41*N (Chicago), with a sunny, cloudless sky in January, air coming out of the collector was 105*F (!!)

Two major problems-- (a) You only get sunny cloudless skies in winter in Chicago about once in 5 days, and even them it's only sunny enough to significantly warm the air from about 10AM to 2PM. The rest of the day, or on days where there are any clouds at all, You get no warming inside the unit...In fact, on cloudy days *and at nite*, all you have is a way for very cold outside temps to get into your room....

...and [2] very low "air turnover" from a small unit-- for easy arithmetic, let's say the unit is 10ft x 10ft x 6inches-- ie- 50cu ft. ..and let's say the room is 10'x10'x8' (800 sq ft)...and let's say the room would be 50degF without heat and you want it up to 70deg. (We'll ignore heat loss/insulation effects)....- I'm sure everyone here remembers those "mixing problems" from ha skoow algeber class and are way ahead of me here-- you need to "fill" that unit and "empty" it into the room 1125 times to get the temp up to 70....Ain't gunna happen-- and the example was a big unit and a small room and a not very cold outside temp.

If a wall mounted passive solar collector will work for you, then you don't really need one anyways. Just put in a south facing, double paned window. That may help reduce heating fuel costs a little.

BTW- welcome to the forum. I like your mindset and bet you'll contribute a lot here.
...


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## Justa Lane (Sep 7, 2018)

Danaus29 said:


> I've seen plans for a homemade one similar to what you have. It works best on a direct south facing wall. I'm not sure which way is up but I think the holes are on top. There should be a glass front that goes over the fins.
> 
> I am jealous! That was one terrific find.
> 
> I may be wrong, the very few I saw on a quick search showed the big holes on the bottom, with fans in the holes. Did they tell you how it was installed? Did they have any pictures of what it looked like before they removed it?


Thanks Danaus29 for the response. I was surprised to see them for free on the marketplace myself! He had 8 but I only had my small trailer and could only take 4, unfortunately. The entire frame is made of aluminum so I figured if it doesn't work I'll have use of it for something. There is a double pain glass (that is heavy) on each them.

You actually answered one of the questions I had for someone who had seen something like this, which way is up? They were originally installed on a roof so I think it didn't matter much for the original owner. The new house owner didn't have much information but he did say that the person that built this had a 12'x12' concrete heat "battery" in the basement that these ran into. I've been looking online for similar designs with possible installation instructions. I plan on installing on my south facing wall. The next question I had was, do I run duct from the floor up through the wall to the input or just input it at the same level of the output? Any ideas or recommendations are appreciated.

Thanks a ton!


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## Justa Lane (Sep 7, 2018)

doc- said:


> I built a passive solar collector a few yrs ago to try it out.... No need for fans-- hot air rises automatically. Holes at the top allow rising warm air to enter the room, while holes at the bottom allow cooler room air to enter the warming chamber at the bottom.
> 
> Located ~41*N (Chicago), with a sunny, cloudless sky in January, air coming out of the collector was 105*F (!!)
> 
> ...


Thanks, glad to be able to join! I studied for a couple years in Chicago back in 2000. Awesome place and hope to get back again someday! 

I really appreciate and see your point about the heat displacement. I have just started researching these and have seen a few comments relating to what you have said. I'm not completely sold on the idea of installing them yet but since I've gotten them for free, I'm leaning more on at least installing and see how they perform. My main heat is going to be a wood stove. When completed, I will have a solar array and probably a small split type to use when I'm feeling lazy.

Thanks for the insights!


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## manfred (Dec 21, 2005)

I built my own 20 odd years ago and I used a 100 cfm fan and ducted it into my house.
I'm sure it helped as I got hot air from the vents, had an automatic thermostat inside the unit to turn the fan on when temp got up
I later sold the house so don't


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## Danaus29 (Sep 12, 2005)

Are there any kinds of openings at the end opposite the holes. The cool air comes in the bottom, at floor level where the coldest air lays, and the warm comes out an opening at the top. The top should have a flap or cover that can be closed when you don't want the heat. It should also be set up so you can shade the glass front when the weather gets warm. That should not be too difficult because the higher summer sun does not shine in ground floor windows like the lower winter sun does.

The passive design is so that the rising warm air enters the room from the top. You might need a ceiling fan to mix the air or you could end up with chilly floors and warm faces. I prefer to have warm air low near my feet and cooler air near my face. Since manfred has actually used one, his info would be better than mine. I believe there should be some ductwork to bring the air into the room instead of just dumping it near the wall.

Somewhere around here might still be the plans I got to build one. I love the concept and did a lot of research on passive solar a lifetime ago. Unlike a huge picture window, the passive solar heaters keep your house warmer on grey sunless days because the original insulated walls are still in place and the ducts can be blocked. Picture windows are always poorly insulated against heat loss, it's just the nature of the product. Glass has better heat transferrence, despite all the hype about double paned argon filled windows.

To install passive solar on this house I have to give up my windows. I made a choice that pleases me, even if I have to keep feeding the woodstove.


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## doc- (Jun 26, 2015)

^^^ Yea, the pictures show the openings near each other on the short side side of the rectangle, therefore, they obviously needed a circulation fan to make it work-- kinda defeats the purpose. If you're gunna burn juice anyways, you may as well just get an electric heater that can be regulated with a thermostat, can be used at night and still works when there's poor sunlight-- all for just a few more W/d compared to a fan-- a small price to pay for reliability & versatility.

If you're gunna have wood heat anyway, Justa, this set up would only add a pittance of extra heat for you at the expense of putting holes in your walls which will let more cold in when the sun ain;t shining. than heat in when it is shining. Poor trade off.

My experience says this is more for Snowflakes looking to virtue signal and can't stand indoor temps of 65 in the spring & fall.

Passive solar water heating is a viable alternative for those in cold but sunny climates because you can save hot water in insulated tanks for many hours after the sun goes down or behind a cloud. You can't really do that with hot air.


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