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Thread: Homemade propane forced air heater (picture intensive)

  1. #1
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    Homemade propane forced air heater (picture intensive)

    A few days ago I went to light up the woodstove, but had trouble getting good draft in it. Come to find out the stovepipe elbow (which wasn't really stovepipe) had rusted through. So I ended up replacing the elbow and a few straight pieces with 24 ga. stovepipe. There was one 24" straight piece of the old pipe that was still in pretty good condition, so I decided to experiment using my propane furnace burner as the heat source into this pipe to see what kind of heat output I could get. I ran a hose from the bypass wastegate on the blower into the tube for extra airflow.




    Here's a video of lighting it:
    http://www.youtube.com/watch?v=NCD6ibbVvDw

    So this was nice and had good heat output, but the pipe ran quite hot due to the fact that there was not air circulation over it, which meant that I was losing some energy to radiant heat that could be transferred to the air. Also I needed to remove my furnace burner for this, which wasn't a big deal, but it would be nice to have a standalone model with it's own air source and burner.

    ... and so the project began ...
    http://i735.photobucket.com/albums/w...b48726/015.jpghttp://i735.photobucket.com/albums/w...8726/104-1.jpg The most valuable piece of equipment to the low-budget metalcaster is a second-hand vacuum cleaner.

  2. #2
    That sounds like a pretty expensive way to heat your garage ...

    Radiant heat is actually a good thing:
    - lower room temperature required, the room feels warmer then it actually is.
    - more uniform spreading of the heat because it radiates 360 around.
    - less losses, more complete combustion.
    It's better to know something about everything then to know everything about something.
    Discovering the first everything is an adventure, discovering the second is a bore.

  3. #3
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    I had a fan from a stove draft hood that was about perfect for this. It has a diameter of just over 6" so it wouldn't fit in a 6" piece of ductwork. At the hardware store I found a 6" duct clean out cap which would serve as the air burner-side end of the inside tube. I picked up a piece of 8" galvanized duct as well for the outer shell.



    I drilled holes in sets of three around the top and bottom of both tubes for the alignment bolts that would hold the inner tube in place, then put the cap on the inner tube, drilled some holes in it for the air to enter (not very pretty but it works) and a hole in the side for the gas line and nozzle to run in. I figured that I could just run the gas into the center of the tube and the incoming air through the holes would mix with it and ignite properly (boy was I wrong :?).



    After mounting the fan to the end of the outer tube, I found that it was actually sucking the gas and air (and flame) in through the middle of the fan and blowing it out the sides :x. My solution to this was to get a 6" x 8" increaser and mount the fan inside this, hoping to create positive airflow through the intake to the inside of the burner. This was a good idea, as the fan and end cover were now a single, removable unit. This worked better, but unfortunately there was just not enough air moving into the inner tube for proper combustion, I kept getting just yellow flames and carbon.

    A reducer ring around the outer tube would channel more air into the inner tube, but I didn't have one of those. My solution to that was to take a piece of leftover stovepipe that I had cut off and make a diverting collar to go over the inner tube to channel more air inside.



    ... but that didn't have much effect, so I cut and bent more slits in it.



    That worked a little better, and I guess you could say that it worked at this point, but it still had cool yellow flames and if I turned it up too high it would produce soot. It ran cool on the outside (except for one hot spot that I couldn't figure out) and put out okay heat, but I want 200,000 BTU's out of this thing, and inefficient combustion is one of my pet peeves.
    http://i735.photobucket.com/albums/w...b48726/015.jpghttp://i735.photobucket.com/albums/w...8726/104-1.jpg The most valuable piece of equipment to the low-budget metalcaster is a second-hand vacuum cleaner.

  4. #4
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    So this is what I had at this point:




    Not very good. I think it was around here that I realized that I was better off with the hollow tube and my furnace burner.

    So I thought that drilling more/bigger holes in the end cap might let more air in.



    that was a little better, but not by much. I realized that most gas burners mix the gas with the air in a venturi style nozzle, so I decided to put another reducing collar inside the inner tube just after the gas nozzle.



    Of course it didn't dawn on me that a modified piece of 6" pipe would not fit inside another (duh! :roll So I cut it in one spot and overlapped it inside the tube. Of course without anything to hold it in place it just rattled around in there and went all over, so I screwed it to the cap.



    ... which yielded this result:



    That was even worse than before, so I removed the inner collar and scrapped that idea. This thing is SO CLOSE, if I could just get it to burn right. It looks nice at least, almost like something that might actually work!



    As a last resort I cut and bent to end of the outer tube to reduce against the inner tube, creating back pressure inside the outer casing that would hopefully force more air to the inner section. Right now with the outer tube almost completely restricted, it makes yellow flames with a nice swirl around the inner tube, but I still can't turn the gas up very high.

    Maybe the open nozzle in the center is a bad idea. I know the ones you buy have kind of a spread out blue flame with yellow at the tips, but I'm not sure what kind of gas nozzle they use.

    So this is where I'm stuck at as of right now, anybody got any ideas on how I could crank this think up?
    http://i735.photobucket.com/albums/w...b48726/015.jpghttp://i735.photobucket.com/albums/w...8726/104-1.jpg The most valuable piece of equipment to the low-budget metalcaster is a second-hand vacuum cleaner.

  5. #5
    Ive seen these things for sale for heating workshops etc, and what I remember is that they are completely open at the back. There is no plate with a few holes drilled into it. Perhaps you could try removing the back.

  6. #6
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    Quote Originally Posted by Sylar
    Radiant heat is actually a good thing:
    - lower room temperature required, the room feels warmer then it actually is.
    - more uniform spreading of the heat because it radiates 360 around.
    - less losses, more complete combustion.
    Radiant heat is okay if the garage is 50F and you want to take the chill off. Not so good if it's 10F and you have work to do in more than one area.

    The thing I don't like about radiant heaters is that they concentrate heat in one spot, the farther you are away from the heater, the colder you are. And if you put the thing right next to your work area then it's too hot right next to it but colder if you walk away. Granted that eventually the surfaces will heat up and heat the air. But I have a wood stove for that. What I need is a heater that I can light up and will heat the air in the garage in a short time for situations in which I may have just a small project where I don't want to light the wood stove, or just when it's really cold waiting for the wood stove to heat up.
    http://i735.photobucket.com/albums/w...b48726/015.jpghttp://i735.photobucket.com/albums/w...8726/104-1.jpg The most valuable piece of equipment to the low-budget metalcaster is a second-hand vacuum cleaner.

  7. #7
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    Quote Originally Posted by mantrid
    Ive seen these things for sale for heating workshops etc, and what I remember is that they are completely open at the back. There is no plate with a few holes drilled into it. Perhaps you could try removing the back.
    I tried that several times throughout the process. The problem is the fan that I'm using likes to suck air in the middle and blow out the sides. With the back removed it just intensifies this effect. If I could find a way around this problem it may very well work.
    http://i735.photobucket.com/albums/w...b48726/015.jpghttp://i735.photobucket.com/albums/w...8726/104-1.jpg The most valuable piece of equipment to the low-budget metalcaster is a second-hand vacuum cleaner.

  8. #8
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    I found this video on YT the shows nicely the gas flame spreader used in one of the commercially sold models. Perhaps if I could mount a flat plate over the nozzle it would have the same effect, but I'm not sure what I could use to do that. I also notice that they only have holes in the tube end around the outer part, this may explain why mine doesn't work even though it's built the same.

    EDIT: oops, here's the link: http://www.youtube.com/watch?v=AlnbWYv9ons
    http://i735.photobucket.com/albums/w...b48726/015.jpghttp://i735.photobucket.com/albums/w...8726/104-1.jpg The most valuable piece of equipment to the low-budget metalcaster is a second-hand vacuum cleaner.

  9. #9
    I like your idea but why not build a waste oil burner for heating your garage or workshop?

    I think I may have talked about it before, but take a look at thisburner,
    http://www.youtube.com/watch?v=uxQQp20wAc0

    it gives off a lot of radiant heat, it's based on the "Turk Burner" I just put in Turk oil burner on google and youtube and found that one, there are several

    I started one a long time ago, but it is buried in the corner to be finished one day, I'm gonna mount it into my cast iron coal stove


    Ron SS
    If ya cant cast it, Forge it RSS

    http://metalmaster1766.webs.com/

  10. #10
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    Quote Originally Posted by Ron Smith
    I like your idea but why not build a waste oil burner for heating your garage or workshop?
    I would love to heat with waste oil, except for the fact that the combustion gases must be exhausted outside. This requires a bit more construction and materials and is more difficult to bring/keep the heat inside. I have tried running waste oil in the wood stove but without a high pressure pump this proves to be difficult.

    Besides, if the steam generator ever becomes a reality, that will produce more than enough waste heat for the garage and maybe the house. But these things require careful planning (which I am NOT good at) and a good chunk of change for the materials.
    http://i735.photobucket.com/albums/w...b48726/015.jpghttp://i735.photobucket.com/albums/w...8726/104-1.jpg The most valuable piece of equipment to the low-budget metalcaster is a second-hand vacuum cleaner.

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