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Need help getting this heat-moving experiment to work

Post in 'Classic Wood Stove Forums (prior to approx. 1993)' started by xpauliber, Jan 29, 2013.

  1. xpauliber

    xpauliber New Member

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    The house I just bought has a basement that is uninsulated. There is a fireplace down there that I would like to try to use to provide some heat the the upstairs of the house. There is a stairwell near the wood burner and I can get the basement up to 80 degrees, but I can't get the heat to circulate upstairs. Eventually, I'm going to put some cold-air return registers in the far corner of the upstairs to help to circulate the air, but I don't want to do that until I get the exterior basement walls insulated so I'm not losing alot of my heat through the cinder blocks.

    So in the near-term, I built this sheet-metal shroud to retain the heat that is coming off of the firebox. I then boxed the end off with a round 6" aluminum duct and then ran the duct in the rafters to a register that I cut in the floor upstairs. You can see the shroud and ducting here:

    [​IMG]

    Some heat trickled up through the ducting, but not enough to make a difference in the temperature upstairs. Additionally, the shroud was getting very hot which means there was a lot more heat that could be harvested. So I bought a 300cfm inline fan and put it on the "downstream" side of the shroud blowing towards the register. The inlet side was drawing the hot air from under the shroud and pushing it through the ducting to the upstairs. I drew a picture so you can see what I'm talking about. (the fan is depicted in green):

    [​IMG]

    This worked GREAT as I was able to feel heat blowing like crazy out of the register and I was able to get the upstairs up to 77 degrees if I really burned hot in the fireplace. I ran into a problem however in that the air on the downstream side of the shroud must have gotten too hot for the fan, and it tripped the thermal protector switch and killed the motor.

    So I purchased another inline fan (this one 400cfm) and figured I would put it on the upstream side of the shroud and have the fan pull cold air from the basement, and push it through the shroud and up the ducting. You can see a picture of this here:

    [​IMG]

    I bought the bigger fan because I thought that the extra "oomph" it provided would be enough to push enough volume of air through the open space of the shroud and still have decent velocity coming out of the register. That didn't seem to work though because the shroud isn't completely sealed and it was barely moving any air out of the register so that isn't going to work for me.

    So, I need to somehow have the fan not be exposed to the heat on the downstream side of the shroud, but still be effective at moving the hot air from under the shroud into the ducting. I am thinking about putting a "T" on the downstream side of the shroud and connecting the fan to push straight up the ducting and having the 90-degree opening attached to the shroud to hopefully have the airflow create a vacuum that would suck the hot air into the ducting with the air that will be moving from the fan running. What do you guys think of that approach? Here is an example of what I'm talking about:

    [​IMG]

    If the air being blown by the fan wanted to back-feed into the shroud instead of going up the ducting, I was thinking about fabricating a small piece of metal that would block the opening back into the shroud but would still allow air from the shroud to enter the duct, kind of like this (yellow would be the diverter):

    [​IMG]

    So that's where I'm at, and I'm open to any/all suggestions for how I can get this to work like it did when I had the fan directly on the downstream side of the fan, but I can't have the fan exposed to that much heat. Thanks a lot everyone!

    -Paul

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  2. Adios Pantalones

    Adios Pantalones Minister of Fire

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    Why not put the fan where the green inlet/blue arrows are?

    I would look at fire codes. I'm no expert, but mods scare me a bit (though it looks like a cool idea). I imagine dust in that duct building up... worse than a dryer.
  3. xpauliber

    xpauliber New Member

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    I had the fan in the inlet side of the shroud, but the shroud isn't air-tight so alot of the forced air escapes and doesn't get forced into the ducting.

    I understand about mods with fireplaces being a bit scary and that's another reason that I like the idea of putting the "T" fitting in: it will combine colder air with air coming from the shroud to hopefully create a nice steady flow of 90-100 degree air. I just don't know if the flow of air in that configuration will produce a significant vacuum from the shroud side.
  4. Adios Pantalones

    Adios Pantalones Minister of Fire

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    The worry is not overheating the duct- it's a single ember/spark. If any spark gets in there, and hist any dust buildup- then what you have is a bellows blowing efficiently on the driest, best firestarter that you ever saw (people here collect dryer lint for this purpose, and yours is- by definition- being dried well by heated air!)

    Where does the spark come from? Paper burns just over 450F, so if the stove runs up to 600- then you've got an ignition source.

    You spent a lot of time on this, and may not abandon it. I'm not here to disparage- I just would hate to see someone get hurt.
  5. sailor61

    sailor61 Burning Hunk

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    Cool idea, you've done some good work but need to look into a spark/flame arrestor to go into that line.
  6. xpauliber

    xpauliber New Member

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    Underneath the shroud is nothing but cast-iron. The shroud is simply sitting on top of the enclosed woodstove with no exposure to any open flames or sparks. The flames/fire are inside the closed doors.

    I don't have a picture of the stove without the shroud on it to show you right now.
  7. TradEddie

    TradEddie Minister of Fire

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    First, be sure you have a carbon monoxide detector in that space, and wherever that air is being blown to. There are several reasons why what you're trying to do could be very dangerous.

    A regular T won't create much vacuum by itself, but if you make a constriction on the fan side of the T, you will increase the venturi effect, that diverter you propose might do that too. A simpler way would be to put the fan upstream of the T, then slowly restrict one side or other until you find the right mix.

    TE
  8. Adios Pantalones

    Adios Pantalones Minister of Fire

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    My last comment- the surface of the stove gets to a temperature over the ignition point. No exposure to the inside required. Dust buildup, sucking in something interesting, drop a log during reload- there could be major trouble.

    That's all- something to consider.
  9. bryan

    bryan New Member

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    I'll second the scary perhaps not code, but cool comment.

    What if you put the fan in the same place you had the first fan, but some how bled cool air into the air coming off the shroud so it isn't so hot that it trips the thermal switch? I don't think you'll get enough vacuum using the t setup as you currently have it. I guess my thought is to use a t setup but have the t before where the first fan was and simply use the t as a source of cool air. You could put a damper on the cool side of the t to control how much cool air is bled into the air from the shroud. If you wanted to get fancy you could have the damper thermostatically controlled based on the temp of the air coming into the fan.


    Be sure you have CO/CO2 monitors where this air is exiting.
  10. sailor61

    sailor61 Burning Hunk

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    I lost a house in a fire that, in the words of the final report, was "....accidental and unexplained. While the installation was in full accordance with applicable codes, the fire clearly arose from the area surrounding the woodstove" A single misplaced inadvertent spark is all you would need to potentially have flames shooting out of the upstairs end of the duct work.
  11. xpauliber

    xpauliber New Member

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    Ahh, you guys are definitely making me think about just scrapping the whole setup and try to get some whole-house circulation going with or without the basement being insulated.
  12. Adios Pantalones

    Adios Pantalones Minister of Fire

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    Whatever you do- I honestly applaud your ingenuity and industriousness.
  13. sailor61

    sailor61 Burning Hunk

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    Don;t scrap it ..it's a great approach to the problem. Just go the extra to safeguard the work you're doing.
  14. xpauliber

    xpauliber New Member

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    Can someone recommend a good inline spark arrestor?
    The CO/CO2 detector at the register end is easy-enough as well.
  15. sailor61

    sailor61 Burning Hunk

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    Unfortunately I can't -- I'ld say try a coupe of local HVAC shops and/or google online. You look to be pretty good in the shop so there may be some plans out there for ones you could build or assemble yourself.
  16. Dune

    Dune Minister of Fire

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    Put the fan back to the inlet side, the only place it will work.
    Seal up the box.
    You will never get the inside of the box hot enough to cause ignition as long as the fan is blowing. Forget about the tee idea.
    Your whole problem is that the box isn't air tight.
  17. jay_blu

    jay_blu New Member

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    I helped a friend do this with water and car radiators, we put one in each room. Basically he wrapped his wood stove in flexible copper and ran a line to a manifold witch fed the radiators. Then the water would drain back to a 55 gallon drum for a reservoir. The pump was right off the reservoir so the water going through the rather large pump was not too hot for it. He also had ball valves on each radiator so he could dial in the temp, and fans on the back to move the air. This was on a two story house with the stove in the basement.

    No fire wories, if something failed horribly you would just melt copper... but even with the pump off the thermosyphon should move water enough so it dont melt. you probably could automate the whole thing with some thromstats, auto sprinler valves, float sensors and auto top off.
  18. TradEddie

    TradEddie Minister of Fire

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    You or your friend have obviously never seen a steam explosion. Not saying what you built was dangerous, but if you never considered the power of steam flashing, it probably wasn't as safe as you think.

    In reality, I'm just jealous, it's miserable to be sitting beside a scorching hot stove, knowing that rooms at the other side of the house are still cold.

    TE
  19. jay_blu

    jay_blu New Member

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    yea that would be bad... hmm pressure reliefs? and this was not a closed loop system. Im not saying that couldnt happen but the risk would be reduced alot. what about a non flamible oil that wont turn to gas? does that exsist? also that car radiators had there caps so they would have relieved if the temp/pressure got too high....
  20. Adios Pantalones

    Adios Pantalones Minister of Fire

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    Every boiler system has a simple pressure relief valve. Pops up, blows off steam, shuts automatically. Super cheap insurance.
  21. TradEddie

    TradEddie Minister of Fire

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    Hypothetical scenario, fire running, pump shuts off but its an open system so the hot water and steam vents into the reservoir tank. Thermosiphon doesn't work and 5 minutes later power comes back on, sending water into a scorching hot pipe, high pressure steam and boiling water flashes out the open line, scalding anyone within 10 feet of the other end, depending on where its pointing. Youtube has lots of aftermath videos from this sort of setup.

    TE
  22. Dune

    Dune Minister of Fire

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    This thread is going way off topic.
    The OP is discussing a hot air setup.
  23. eyefish2

    eyefish2 New Member

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    A couple thoughts to maybe help get more warm air upstairs 1). Put a large box fan at the base of your stairs and blow the warm air upstairs with the door open. Keep fan on low or medium 2) remove your duct and put a small fan over your vent upstairs with the suction side of the fan pulling the warm air from the basement.
  24. begreen

    begreen Mooderator Staff Member

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    Consider putting a stove upstairs instead of fighting heat loss in the basement. If possible, install a stove on the main floor where you can enjoy the warmth and fire view.
  25. HaTaX

    HaTaX New Member

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    I like the idea, and will echo pretty much the same comment as everyone else, just be careful.

    Simple fix for the fan, affix it to the wall, and cut the flex line where it is vertical 2 - 3 feet from the shroud outlet. Air travels the path of least resistance, if you put a T in with a fan at the bottom, the shroud won't be moving much air along with it, you were on the right path in that you want this fan sucking the hot air, not blowing it. (At least with the current setup, if the shroud was airtight it would be a different story)

    An idea for possible flamage in the shroud.... Maybe a damper of sorts with a spring that pulls it shut, tie a length of something thin and flammable to hold it open inside the duct. If there's a fire in the shroud or temps get dangerous, it will break and the spring will shudder the passage of air up the duct. It's not perfect, but at least it would cut off the supply of oxygen and prevent it from becoming a mini blast furnace inside the duct. For the thin "something" maybe some very light gauge aluminum wire would work? There's quite a few things you could use here, and I bet you can take that idea and come up with something better. At least from the looks of what you've got going on, you know how to improvise and tinker!

    And I'll finish again with be careful, fire can completely change it's attitude in a moments notice and it's best to be over prepared for it.

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