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  • New Greenhouse heater

    This project has been in the works for awhile as I had just been relying on about 1000' of 1/2' black poly tubing strung in the GH rafters and water pumped through it for an additional heat source. The solar heat worked ok (barely) last winter to heat the 9000 gallons or so of water in the GH. On a cold night I could lose 5 degrees in the water and the solar was only capable of a 4 degree rise per day. It worked out but if I would have had a long stretch of cold nights and cloudy days I would have been in trouble as the fish can only take to about 45 degrees and even that is very bad. I really wanted to make it so the water did not get below 60 degrees

    The design is pretty simple, all it is is a 300 gallon tote with a wood fired hot tub heater inside it. These heaters are designed to be submerged in the water with just a few inches of them above the water line. The heaters are very efficient due to being submerged much more of the heat is transferred to the water. The tote is located outside of the GH about 40 feet away. There is a 1" run of PVC pipe coming from the additional pump that feeds the water filled tote. The second line which is 2" is encased in 4" tubing and that tubing was then filled with perlite cement to insulate it. So the 1" line pumps water to the tote and the 2" line takes it to the main pumps sump barrel simply by gravity as the new tote is exactly the same level as the totes in the GH.

    Click image for larger version

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    I built an enclosure around the tote and filled it with 16 cubic feet of perlite for insulation. After the fact I do not believe that insulation was needed at all. The 2" line that takes the hot water out of the tote is located about 3" below the surface of the water and when you light the heater while the water deep in the tote is still very cold the surface water gets hot fast. In 20 minutes after lighting the fire the surface water temperature will be over 100 degrees and even once the pump is turned on the water never dips below 79 degrees. After an hour or so of burning the temperature rises to 86 and tends to stay there. Running the heater for 12 hours my goal was to be able to raise the 9000 gallons of water by 8 degrees and has far exceeded my goal. In 8 hours of run time I gain 10 degrees+ and that is without the help of the solar tubing. Being so small it does not burn much wood at all, it is basically a small rocket stove.

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    This picture was before I put the top on the tank which is also twinwall or filled the side walls with the perlite.
    Cutting sales on willsfigs.com started Nov 1 and will continue till about March 1.

  • #2
    Awesome! Very similar to what I’ve been considering for my (future) greenhouses.
    Bryant...Franklin County, VA...Zone 7a. Wish List: a 32 hour day....more sleep

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    • #3
      Great job WillsC, very nice idea. This would work great for people off grid or not.
      Zone 5B: Rotterdam, NY

      YouTube

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      • #4
        Very impressive.... I've never seen a wood fired hot tub heater before.

        How do you feed and/or empty the chamber?

        Could there be an issue with overheat if it burns too hot? Or is that automated somehow?

        Guildwood Village - Toronto, Canada - Zone 6

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        • #5
          Very innovative Wills...

          Rey

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          • #6
            Originally posted by TorontoJoe View Post
            Very impressive.... I've never seen a wood fired hot tub heater before.

            How do you feed and/or empty the chamber?

            Could there be an issue with overheat if it burns too hot? Or is that automated somehow?
            Joe,

            That is the beauty of it, it CAN'T get too hot. Because the unit is down under water it never gets hot. Only about 5" of the unit sticks above the water line, just the feed shoot and the outlet for the smokestack is above water line. You can put your hand down in the water and hold it on the side of the heater and it is not more than lukewarm, the water pulls the heat away. When I put the twinwall on the top I cut out around where the smoke pipe is and I figured once it melted the plastic back from the metal I would then seal it. Much to my surprise it did not melt the plastic back at ALL and the plastic is withing 1/8" of the stove pipe, that is just how good the water conducts the heat away from the metal.

            Because the 2" outflow is just 3" under the waters surface the water can't get any lower than that which is about 4" above the top of the heater.



            Second pic, see the lid with the wooden handle? That is how it is fed. The unit comes with a clean out shovel made to fit inside the unit to clean it out. It actually came with 3 of them lol, an oops by the maker I am assuming as the were plastic wrapped together and I guess the person crating it thought it was all one. The lid is also the airflow control. See in the pic below, that is looking straight down inside the unit. The air is pulled down the shoot to the left in pic and directed under the fire. The unit is a product of your home country Came from Manitoba. It is called a Timberline Volcano.

            Second pic below.......See how close the plastic twinwall is to the metal where the smokestack is? No melt back at all. I have had it up and running about two weeks now, burnt it 6 times and no melt back.

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            This isn't where I bought it but the pic shows the full unit with ash scoop. Because I don't have it in a hot tub I did not use the insulated perforated section shown, it slides over the stovepipe and it is just designed to keep the hot tubbers from touching the stove pipe.

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            Cutting sales on willsfigs.com started Nov 1 and will continue till about March 1.

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            • #7
              Brilliant design!

              If using it for a tub you'd definitely want to keep the wood close by. Getting out of a hot tub here in February would not be pleasant!
              Guildwood Village - Toronto, Canada - Zone 6

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              • #8
                Really cool I was just getting ready to build a wood boiler this is cool!!

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                • #9
                  The problem I have with most wood boilers is how smokey they are, this being a rocket stove once it is lit and hot there is almost no smoke at all.
                  Cutting sales on willsfigs.com started Nov 1 and will continue till about March 1.

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                  • figwood1
                    figwood1 commented
                    Editing a comment
                    Thats really cool have to check those out!!

                • #10
                  I called rocket heater when you mentioned it a few weeks ago. That is a gorgeous piece of craftsmanship right there.
                  May the Figs be with you!
                  ​​​​​

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                  • #11
                    How is the water heating system working for the greenhouse during this cold spell?
                    North Georgia 7b
                    Wishlist: Smith

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                    • #12
                      AWESOME. Without it the fish would have been dead......with it not a care in the world.
                      Cutting sales on willsfigs.com started Nov 1 and will continue till about March 1.

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                      • #13
                        Wills... How much wood does this thing eat up? Are are you using pellets?
                        Guildwood Village - Toronto, Canada - Zone 6

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                        • #14
                          666,400 BTU! 9,000 gal x 8.33 lbs/gal x 10 degree change. Divide 666,400 by 8/hr to get the BTU/hr.

                          Calculated by water temp change; if the greenhouse was also being heated the BTU output would be higher.

                          Probably some heat loss due to the piping and heat loss from the water containers would raise the BTU output of the stove. Small error because of water density too.
                          Johnson1
                          Zone 9b
                          S of Tampa Bay, FL

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                          • #15
                            Willsc great looking set up there is a guy that invented a rig that compresses leaves into logs it might be of some use to u it seems much easier than chopping fire wood
                            JLB zone 8b south Mississippi. Wish list really good figs thay don't split with all this dang humidity

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                            • #16
                              wow I had one of those stoves over 30 years back in a hot tub I also had a military heater that ran on gas scarey but it heated water

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                              • WillsC
                                WillsC commented
                                Editing a comment
                                Hobo,

                                Those diesel or gas heaters you are talking about is what led me to the wood fired ones I saw them, military surplus and thought that MIGHT work and if there are gas ones there may be a wood fired one, sure enough there was.

                            • #17
                              Originally posted by JLB View Post
                              Willsc great looking set up there is a guy that invented a rig that compresses leaves into logs it might be of some use to u it seems much easier than chopping fire wood
                              I have a 22 ton gasoline log splitter and an unlimited supply of wood thanks to the storms and hurricanes, mostly oak and hickory. I even built a homemade log lift that is powered by the return stroke of the splitters piston that will effortlessly lift 400 pound logs so don't even have to pick them up.
                              Cutting sales on willsfigs.com started Nov 1 and will continue till about March 1.

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                              • #18
                                Originally posted by Johnson1 View Post
                                666,400 BTU! 9,000 gal x 8.33 lbs/gal x 10 degree change. Divide 666,400 by 8/hr to get the BTU/hr.

                                Calculated by water temp change; if the greenhouse was also being heated the BTU output would be higher.

                                Probably some heat loss due to the piping and heat loss from the water containers would raise the BTU output of the stove. Small error because of water density too.


                                That is pretty darn close.......the manufacturer states its output is 100,000 BTU's an hour, a claim I was VERY dubious about. It is so small but so so efficient due to being underwater as you don't lose all that radiation heat to the air.

                                AND....I thought this was cool.......

                                This was simply an accident..... a few weeks after I had set it up I noticed something. In the late afternoon I would fill the unit with wood and close the lid/damper completely. I did it so I would have a nice bed of coals in the morning and would not have to relight it, even though lighting the thing is so easy and fast. One morning before I had added any wood and the pump that sends water to the heater tote was off and had been off since the previous afternoon I was in the GH and happened to walk by the sump. I have a digital temp gauge screwed in to the hot water line and noticed it was at 80 degrees. I was confused as it should be same temp with the pump off as the tanks in the GH. I looked at the temp gauge in one of the tanks and it was 70 degrees. Thinking the other digital gauge was broken I pulled it out and put the sensor in the fish tank where it dropped to also 70 degrees so it was working. Popped it back into the outflow pipe and put my hand down in to the sump water and sure enough 80 degree water was flowing at a decent rate out of the pipe even with the pump not running. I was a bit perplexed. I went out and looked through the access window on the heater tote some 40' outside the GH and sure enough cold water was flowing in to the tote and hot water was flowing out of the tote, maybe 5 gallons a minute?? I just did not understand how that was possible with everything off. Even the main system pump that sends the water to the tanks and through the filters was off, it is on a timer and runs only during the day, 3 2 hour cycles. Came back in the house and googled and found the answer, I had made an inadvertent thermal siphon.....had no clue such a thing even existed. So even without the pump running cold water still goes to the tote and warm water still flows back to the sump using no electricity at all. Now that thermal siphon is not enough volume to heat the tanks given how many gallons I have but still even with the system off the GH is still heated.

                                For those that don't want to look up a thermal siphon..in a nut shell.......Cold water being heated makes it expand so the volume of water in the tote is increasing and that hot water flows out and back to the GH. That hot water leaving draws more cold water in and and on the process goes. It is a constant slow exchange, like I said, maybe 5 gallons a minute with no electricity involved.

                                Btw I have now added more tanks, finished a couple weeks ago adding 3 more 600 gallon tanks to the front GH so up to about 12,000 gallons now +/- 1000 gallons.

                                Once burning well it is 100% smokeless. The only time you see any smoke is when you first light it and for a few minutes after you add more wood.


                                Cutting sales on willsfigs.com started Nov 1 and will continue till about March 1.

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                                • #19
                                  Originally posted by TorontoJoe View Post
                                  Wills... How much wood does this thing eat up? Are are you using pellets?
                                  DAMN little. I fill it when heating about once an hour, I would not have to fill it that often but want it to stay super hot so water temp comes up as fast as possible, why run the second pump more than I have to, right? Each fill is 3-4 split pieces of wood 5" wide x 5" high X 15" long pieces of wood.......thats it. A person could easily design a self feeder for one using pellets and automate it, not a hard job at all. Just the auger that feeds a meat smoker would be more than enough.
                                  Cutting sales on willsfigs.com started Nov 1 and will continue till about March 1.

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