Solar Furnace – Results

Solar furnace installed

We finally had a sunny day yesterday and I was able to get some real results from my solar furnace .  I had to make a few changes for success though…

First of all, I discovered that the mercury switch was not sensitive enough to really work.    The cold air outside was messing up the way it functioned.  I could not insulate the part of the air box where the switch was since the switch has to be able to move (if you’ve never seen the setup, a mercury switch is placed on a temperature sensitive metal coil which moves and allows the mercury to open or close the switch).  I decided to experiment with wiring the solar panel straight to the fan which actually worked very well.  The fan only came on when the sun was out and shining pretty brightly which was precisely when the best heat was being made.

The pipes that run from the furnace to the house were white originally but it seems that enough cooling took place in the pipes to make the system not work as well as I had hoped.  I painted them flat black like the rest of the system and it worked like a charm.  The pipes absorbed heat from the sun while transferring the heat through the system, thus helping with the whole “hot air rises” thing.

Solar furnace installed

I also discovered that I had a few air leaks around the pipes and in the holes for the air pipes in the furnace.  I used silicone caulking (which will actually cure in about any temp regardless of what the instructions say) to patch all of the holes/gaps/leaks.

Once I made those three changes, I took temperature measurements of the cool air pipe from my family room floor and the warm air pipe from the furnace.  My floor air was 63 deg F and my warmed air was 84 deg F!  Hee-haw!  Eureka! Ding Dang, y’all!

Ok, so I was pretty happy with the results.  The fan kicks on and off with the sun which manages the heat pretty well.  I still need to boost the power to the fan to get a little more air flow.  I did some experimenting and was able to get a better temperature rise with a bit more air flow.  I will probably add another cheap-o solar panel to run the fan better.  I also need to find a better way to prevent backflow.  I really don’t like hanging a piece of plastic in front of the vent.  For now, it is working but I don’t like it as a long term solution.   I have glass to build one more furnace so I will probably build it out then figure out some way to deal with both systems.  Anyhow, for now, I am pleased with the solar furnace!

13 thoughts on “Solar Furnace – Results

  1. I am pretty happy with how this has turned out. I feel like I have been posting about it a lot but it is pretty exciting to me. I don’t know the end result of how it will effect our bottom line or our comfort bottom line, but it is bound to make some difference…though we are und conatsnt cloud cover lately it seems. Anyhow, if I can get this thing to perform even better, I’ll post again!

  2. I’ve gotta tell you, you’ve lost me on the technical side on these posts, but Eric has been following and enjoying them in my place. Glad you’ve had sucess!! 🙂

  3. Nuts, farm mom…I was hoping I wouldn’t make this too confusing. I had hoped to make things clearer but my wife assures me I can complicate any topic beyond comprehension! If Eric wants other pics or to have a discussion, gimme a holler!

  4. You have the right to be exited. It makes me want to try building one too. If only we had more sun in the winter here in MI. But I imagine that it would still be worth building for fall and spring use. Please keep us posted with your findings. These postings are not boring and there are probably a lot of people following your progress without commenting. Low building cost, free heat has to be a good thing!

  5. Grey Wolf, I didn’t think the sun shone in MI during the winter. I grew up in NW PA and it rarely showed itself there! I checked it again yesterday and has a 32 degree increase in temp…63 inside, 95 coming out. It was 45 outside…

  6. Warren, I have been in WV for the last few days and I have not got to see all the cool and warm things you have going on. I think you are well on your way to a pretty nice solar furnace. The next one will work even better I’m sure. Nothing like a second chance to make some adjustments. Oh, BTW, my brother in law lives just off the Mink Shoals exit. He’s one of those lawyer guys…lol

  7. nice blog, first time visitor. funny perspective and nice topics–right up my alley.

    to prevent back flow you need a check valve. if your pipe size were larger i’d say use an external drier vent with a flap. but any swinging piece of plastic that opens under flow and gravity seals it back up when no-flow.

    insulating your hot-out pipe will kick it up a notch–even further than painting it black.

    solar thermal works even through clouds–not all clouds though. congrats on the solar heater.


  8. Hey Chris – sorry we didn’t have any sun while you were here. It has felt a might scarce lately. Next time you are in town, gimme a message and I’ll let you buy me lunch!

    Karl – thanks for visiting…I had considered the drier flap but my fan just isn’t powerful enough to open it. I may add another cheap solar panel to boost the current a little and that may take care of it. I like the idea of insulating the hot pipe. I was looking at the pipe insulation they sell and it only goes up to 1″ standard so I would probably have to get a couple of pieces and piece it together. I think it wouldn’t be as nice as a single piece of insulatiopn but it would certainly work. Anyhow, thanks for visiting. I have been snooping on your site for a month or so too. I found you on Ron’s site,

  9. That sounds like the ideal thing here in FL. Believe it or not..we just put in a woodstove. We have 5 acres of wooded land and several big trees that came down during the hurricanes..we’re working on those. Most of it looks good. I have been thinking of doing something similar (have Jim do it, lol) to preheat the water before it goes into the hotwater heater.

    Anxious to see more of your projects

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