Fire place heat exchanger

Discussion in 'Back to Basics' started by oil pan 4, Nov 3, 2017.

  1. oil pan 4

    oil pan 4 Monkey+++

    This is version 1.
    It was used winter of 2010 and 2011 and it worked great. At the time we were living in a rented double wide with no heat.
    But it had a small fire place. Forced air was provided by a bathroom vent fan.

    I'm bringing it out of retirement. But it needs to go Lowes as the new place has a much bigger fire place.
    It's going to get longer taller tubes and 3 more rows added.
    I should be able to rearrange all the tubes so I can at least reuse everything and just add to my original design.
    For the fan I would like to use something quieter and DC powered.
  2. Out in the woods

    Out in the woods off-grid in-the-forest beekeeper

    In the 1970s my parents bought a house that had a device, much like that, inside its fireplace. It was not threaded black pipe with 90-degree angles, but rather bent tubing.

    My woodstove today has 50' of copper tubing coils in the secondary combustion chamber, we circulate water to a thermal bank, which is then circulated through our radiant heated flooring.

    Good luck :)
    arleigh, DuxDawg, chelloveck and 4 others like this.
  3. UncleMorgan

    UncleMorgan I like peeling bananas and (occasionally) people.

    Not knowing how much airflow you need, but you might consider either computer fans or the 12v motor & fan out of an ordinary hair dryer.

    One hair dryer puts out enough air to blow a queen-size air mattress up in less than 60 seconds. (One of my inventions from 'way back when.)

    They are really quite impressive.
    chelloveck, Ura-Ki and sec_monkey like this.
  4. Bandit99

    Bandit99 Monkey+++ Site Supporter+

    @oil pan 4 You want to give a brief explanation how it works for those of us who don't know. You always have interesting projects...
    chelloveck, Ura-Ki and sec_monkey like this.
  5. oil pan 4

    oil pan 4 Monkey+++

    The hot air output with a bathroom fan was like having 4 heat guns (not hair dryers) going at the same time.
    My inferred pyrometer was showing 900°F air coming out of the tubes.

    The new version will go from 4 pipes to 6. Be 2 inches taller(the vertical primary tubes will go from 8 to 10 inches tall, the bottom row of primary tubes will go from 10 to 12 inches.
    Then I bought 3 lengths of 60'' pipe to make the top row of tubes as long as nessary so they can be flush with the fire place.

    New pipes have cutting oil on them and it will need to be burned out before using it inside.
    Also don't use galvanized on the heat absorbing pipes. I used a few pieces of galvanized and they are getting replaced.
  6. Ura-Ki

    Ura-Ki Grampa Monkey

    I have something like this. Mine is made of cold rolled pipe .091 and I had it bent at thr local exhaust shop. I have 8 rider pipes with rolled venturi at the top, and forced air at the bottom using a variable speed fan from an R.V. heat pump! It can switch from A.C. to DC really easy for power loss. I early use my fire place any more with the wood stove and steam heat, but it makes a nice back up if I ever needed!
    @ Bandit99 this system works on the convection principle using the heat to draw in cold air at the bottom and force hot air out the top. Having forced air at the bottom encreases heat output greatly, but requires power. Mine uses both together or endependently, and with the venturi, i get almost the same air flow as a low speed small fan, with out needing the fan!
  7. Bandit99

    Bandit99 Monkey+++ Site Supporter+

    Wait. So, these pipes simple sit in the fireplace? Are they filled with water or anything? They're not connected to anything?
    Ura-Ki likes this.
  8. ghrit

    ghrit Bad company Administrator Founding Member

    Yup. Lay the fire in the center, stand back and enjoy the heat. While air will go thru the tubes by convection, the whole scheme will work better with a blower feeding air in the lower header. (Also the pipes will last a LOT longer with the air doing some cooling. Heating the pipes will cause them to rust, believe it or not. The metallurgy is a bit more complicated than that, but the net effect is the same.)
    DuxDawg, Bandit99 and Ura-Ki like this.
  9. oil pan 4

    oil pan 4 Monkey+++

    The fire place heat exchanger sits on the log holder, the coals are on the lower and rear pipes and the flames lick the top pipes.
    Mine uses forced air to push air through the inside of the pipes.
    Bandit99, Ura-Ki, ghrit and 1 other person like this.
  10. chelloveck

    chelloveck Diabolus Causidicus

    arleigh, Motomom34, DuxDawg and 3 others like this.
  11. ghrit

    ghrit Bad company Administrator Founding Member

    I did not see where it said stainless, and it looks to be galvanized. Zinc vapors are to be avoided, heavy metal poisoning ain't too good. Good design for the purposes.
    DuxDawg and Ura-Ki like this.
  12. chelloveck

    chelloveck Diabolus Causidicus

    Agreed, with regards to the hazards of galvanised iron hardware.
    Ura-Ki likes this.
  13. Bandit99

    Bandit99 Monkey+++ Site Supporter+

    That's a really good idea! I could have used this in the old house as the fireplace chimney damper wasn't built correctly so all the heat went up the chimney. Never heard of them before. Simple but elegant.
  14. DKR

    DKR Raconteur of the first stripe

    a commercial version in use

    different take on the same idea for harvesting the heat from a fire

    w/o the forced air

    for free-standing stoves - the idea of stack robbers has been around for -- well, for a very long time.
    arleigh, SB21, GrayGhost and 4 others like this.
  15. oil pan 4

    oil pan 4 Monkey+++

    Mine is pure diy, anyone with minimal to no tools can do.
    I do have the tools to do something more advanced but no point since this works and it's modular.
    Thunder5Ranch and chelloveck like this.
  16. Cruisin Sloth

    Cruisin Sloth Special & Slow

    My Water jacket I made is from 316 extruded Stainless sch 40 1 Inch tig welded to bulkhead fittings of 316 also that are internally pipe threaded for the transfer .
    Has worked for 8 years on my Airtight I bought new . The sales man came by & flipped that I had taken the NEW stove all part & installed my Jacket .
    I have hot showers in the winter & warm in the summer from Solar !

    arleigh likes this.
  17. duane

    duane Monkey+++

    Bandit99 points out the real problem with all fireplaces. Back in the 1700's Count Rumford figured out how to design a fairly efficient fireplace that limited the heat going up the chimney and to maximize the heat radiated from the fireplace. Without some device to transfer the heat from the fire to air and circulate the air, all the hot gases will go up the chimney and no hot air will come into the room. The devices shown, home made or commercial, will greatly increase the heat available from the classic open fireplace by transferring the heat to air that is then discharged into the room. The most efficient classic fireplace type stoves usually used a large masonry structure to transfer the heat in the hot gases to the mass, Russian type heaters, large central chimneys in early American homes, and the masonry actually heated the home. It still is a tight walk optimizing the air required for efficient burning and minimizing the heat lost up the chimney and not filling the house with smoke at some point in the combustion process in any open fireplace.
    chelloveck likes this.
  18. oil pan 4

    oil pan 4 Monkey+++

    The first year I moved to NM it was -10°F at night. I found that throwing the fresh wood in the back fire place and raking the hot coals to the front greatly increased heat output.
    Putting the fresh wood in the back of the fire also allowed all of its smoke to go out the chimney.

    I am probably going to get a wood stove furnace this year. Put it in the garage and run the ductwork into the house.
    chelloveck likes this.
  19. oil pan 4

    oil pan 4 Monkey+++

    The fireplace heat exchanger has been going good for about 6 weeks now.
    It has 6 rows, but I'm going to add a 7th.
    I found a quieter fan so that's kind of nice.
    Ganado and chelloveck like this.
  20. hot diggity

    hot diggity Monkey+++ Site Supporter+++

    The problem with all the pictures above is that the fireplace is open with no way to control the inlet air.

    I had a Great Aunt who lived alone in Northern Michigan with only a fireplace for heat. Her fireplace had a "heatalator" that allowed heated air to be delivered to the room, but more important, it had doors that restricted the combustion air and allowed control of the combustion to just enough to maintain a low fire that would last all night. As a child I marveled at this old woman loading the fireplace with "Gopher wood." (the outer wood and bark from logs after processing at the sawmill.) She'd select a "front log" which was larger and thicker than the others and then proceed to carefully stack wood behind it until there was no more room for wood and it was stacked almost up into the chimney. She burned two tractor trailer loads of this wood every winter for as long as I can remember.

    I've experimented with building rocket mass heaters that utilized my fireplace chimney, and in my mild climate they're the way to go if I must have wood heat only.

    An alternative, or addition to restricting inlet air is restricting combustion air with the damper. I remember a friends house with a fireplace, and a slightly squashed 12oz beer can stuck between the damper lever and chimney would warm the place up to 90 degrees in no time. If the can was not squashed the damper was closed so far that smoke would come out in the house, which was most unpleasant... and potentially deadly.
    SB21 likes this.
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