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Post by gadget on Nov 18, 2018 18:47:12 GMT -8
I want to have a hydronic heat loop when I build my heater. I saw a youtube video where they buried some PEX tubing in the bench for moving some heat around. I can't find the video now. Anyone have any experience running a loop buried in some cob? Seems safer then a heat exchanger in the flame path. Maybe not as fast heating up but should still work good once it gets going
I'm wondering how many feet of tubing in the heater? I was thinking 1/2 PEX, maybe 100 feet in the mass? Probably and open system with a small reservoir for topping off and a condensing vent tube. A small 5-24v DC brushless pump to move the heat. I use one in my greenhouse grow beds soil to circulate water in tubing that only pulls 10watts. I heat water to 80F and it keeps the soil between 55-60F.
Please share any thoughts.
-Gadget
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Post by coastalrocketeer on Nov 19, 2018 10:23:02 GMT -8
You would need to know that the pex tubing is is not going to get over 212F/100C. I would be hesitant to use PEX in contact with masonry materials that may exceed it's melting point.
I am more inclined toward open H2O tank, w/ closed exchanger coil in a water bath in that tank. Then you couod use PEX, but would likely be more satisfied with a copper coil, for higher heat exchange in a smaller space.
Anything else, with a high temperature exposed closed system, is prone to creating potentially lethal situations, even with any type of temperature/pressure relief valve you can obtain installed.
I would like to do a bench with a 15 gallon tub in a "high point" chamber that is part of the overall bell, near the beginning of the bench, and have hot water circulate from a coil in that tub, in a separate closed system, with water to air heat exchangers, and underfloor radiant PEX piping where applicable.
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Post by gadget on Nov 19, 2018 21:23:42 GMT -8
I guess the next question would be what is typical mass temperatures? I always thought they never saw much more then 120F. I like a large margin of error so if the mass never gets over say 140F I would be fine with using PEX directly. I'm not sure though since I have never ran a mass heater.
-Gadget
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Post by coastalrocketeer on Nov 19, 2018 23:49:06 GMT -8
The mass is a gradient during the heating cycle, evening out as it cools after firing... heat travels through masonry at about 1 inch per hour, if I am remembering what the heating gurus said... but nonetheless, this means that pipes embedded within in your mass will get significantly warmer at times than your mass surface temperature, moreso closer to the interior flue areas you go, and with a HIGHLY VARIABLE heat input intensity through a burn cycle. If I were going to put piping in a cob bench I’d be inclined to use copper within the bench at least, and pex once outside the bench. I have strong reservations about the design of a directly heated closed system by anyone who does not have a licensed boilermaker’s understanding of the issues involved. At the very least watch Mythbuster’s exploding water heater segment to understand the forces that can be unleashed when water is heated in a closed system without the required safetys. youtu.be/9bU-I2ZiML0 Boom Squish, indeed...
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Post by Dan (Upstate NY, USA) on Nov 20, 2018 5:16:57 GMT -8
I use a stainless steel barrel and 30 feet of steel pipe wrapped in concrete. When its very cold and we do several firings in a row the first section of concrete gets up to 180F.
If I had to do it again I would put some PEX in the cooler parts to preheat my water going into my hot water heater.
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Post by gadget on Nov 20, 2018 23:36:19 GMT -8
I guess it would be hard to know what kind of temps to expect till after your heater was built and ran. Obviously the further down stream the better for poly tubing.
I really like the idea of a lower temp loop far away from the burn chamber. Yes you need more tubing since the temperature gradient is less but that is ok because it is cheap. Copper may be to pricey since allot more would be needed with lower gradients.
I also really like the idea of not needing to have water circulating constantly to protect the tubing - assuming temps don't ever get to high in the area of the heater.
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Post by gadget on Feb 28, 2019 23:00:16 GMT -8
I just want to add a follow up reply to anyone thinking about burying tubing into mass. I know believe that it is not a good idea. I tired some 1/2 copper buried above the J tube. My conclusion is that heat moves to slowly through mass to provide any significant amount of heat to the water.
I would not recommend doing it if your looking for any decent amount of water heating.
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Post by 2twinkle on Oct 23, 2019 7:13:23 GMT -8
What type of system would work for in-floor heating? I believe this would need lower temperatures and several zones. I am pondering where to draw the heat off the system gently so as not to disturb the effectiveness of the exhaust draw.
I also am deliberating where and how to create a boiler in the system. I live in northern Wisconsin and want to stay toasty. A simple rocket would need more teeth here, not like the tropics of Oregon.
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Post by gadget on Oct 23, 2019 20:11:21 GMT -8
What type of system would work for in-floor heating? I believe this would need lower temperatures and several zones. I am pondering where to draw the heat off the system gently so as not to disturb the effectiveness of the exhaust draw. I also am deliberating where and how to create a boiler in the system. I live in northern Wisconsin and want to stay toasty. A simple rocket would need more teeth here, not like the tropics of Oregon. As you pull heat from colder areas, the surface area (size) of your heat exchanger must go up for same level of heat exchange. Pulling from the upper inside of a bell may be your most gentle option but I don't know how affective it would be. From my experience, it can be tricky to get a "useful" amount of water heating out of a system if you also want to heat a mass or room air at the same time. It is possible but you narrow your margin on draft reliability. Water absorbs a tremendous amount of heat but you probably already know this. The 2 things that kill the draft is the reduction of temperature and flow restriction from interacting with the heat exchanger media. I'm using a car radiator in a bell that works very well but I am drawing the gas through the radiator and I have a blower on the exhaust. This restriction would kill a draft. When you mention the word boiler, that is a whole new level of conversation with safety, local codes, insurance, regulation, etc....
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Post by thoracius on Oct 24, 2019 6:37:59 GMT -8
> When you mention the word boiler, that is a whole new level of conversation with safety, local codes, insurance, regulation, etc....
"Boiler" is just a term for a water-heating system. It does not actually mean the water is literally boiled.
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Post by 2twinkle on Oct 24, 2019 12:49:11 GMT -8
Thanks guys. Well slap me! OK, "Boiler" is not correct. I mean "the place where you draw the heat off the system so you can transfer it to someplace else." It might be called a phallenum but I probably spelled that wrong.
What I think is: To avoid any closed system explosions, an open water tank above the heating system may be best. Sets of Copper coils can be sunk into the tank for each of the heating zones, then into PEX tubing before running into the floor. That might work if the water doesn't boil and get too hot for the PEX. It would look kind of steam punk and I like that idea.
I'm not super focused on the radiant heat from the mass, I want to get the BTUs into the dirt floor.
Car radiators are very effective, but they are also funky and I think the heat I am looking for is much gentler.
The other thought I had was instead of an overhead water tank with submerged coils, the exhaust vent through the mass bench could be shortened, and the coils run above it, embedded in cob. Then they could be PEX, since the temps are lower. And no explosion worries.
So I am just in the planning stage. Or is that dreaming stage?
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Post by gadget on Oct 24, 2019 17:38:57 GMT -8
2twinkle,
I will tell you my experience heating water all last winter and this fall. If you want to heat allot of water quickly, say enough to warm a house, you are going to want to have your exchanger in the fire right after the burn. This will give you a higher temperature difference (gradient) and better heat transfer with all things equal. A large open tank with open pressure can work as your exchanger but it will need to get the bulk of the heat at the highest level possible, basically right after the burn. Copper pipes in the tank would work good to get the heat out and to where you want it. Since you don't need heat from a mass, the water tank could be your "mass" Your heater would mainly be needed for heating water only. If your planning on a RMH, plan on constant feeding for hours and hours.
I would forget about using a classic mass with the embedded coils. The heat just moves to slow through the mass at to low a temp. About an inch an hour. You need heat moving an inch a second to your water exchanger. You would not get enough heat to keep a chicken coup warm if you try and pull it from the mass. That is assuming you are talking about dirt mass.
If you have dirt floors with PEX barried you need to space the tubing with the mind set of 1 inch per hour so I would be at 12 inches max spacing if you wanted some kind of even heating. Your floor would need to be insulated from the ground below or you will loose 50% of your heat. A heated dirt floor once up to temp would be very nice and cozy
Water is the most efficient way to move heat around. A good long life water pump does not need much power to run.
If you want to know more, I would study the outdoor wood "boilers". They basically take a large batch of wood and burn at very high temps heating just water. The most efficient setups use a large insulated tank of water for storage, then distribute the heated water to the house as needed. This large mass of water is able to absorb all the heat quickly and bank it for later use. The really efficient ones use an extraction blower on the exhaust
I heat 385 gallons of water for my greenhouse. It takes a ton of heat to get it just up to 120F. My house heater I am building will be half air heating / half water heating. I run blowers so it makes it easier when you don't have to worry about a draft.
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Post by gadget on Oct 24, 2019 17:48:54 GMT -8
> When you mention the word boiler, that is a whole new level of conversation with safety, local codes, insurance, regulation, etc.... "Boiler" is just a term for a water-heating system. It does not actually mean the water is literally boiled. I think you are right but any appliance thats has boiler in the name goes along with all the codes, certs, etc....
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Post by mannytheseacow on Oct 25, 2019 9:01:08 GMT -8
2twinkle- I had a home on the Wisconsin state line for about 20 years, and had about 750 square foot of radiant floor on three zones on the concrete slab. 1/2" PEX at 8" spacing, kept 6" off the exterior walls, 500 gallon thermal storage, primarily heated by passive solar. When I built my J-tube I put a copper coil around a bypass in the exit flue. The bypass was primarily for cold starts on the stove, but then when the bench was hot, if I wanted, I could open the bypass again and use the fire to heat the coil -> heat the water tank. There are some photos here. The solar part was based on Gary's design at the builditsolar site. The system worked fine, though I primarily relied on the solar for water heating and the rocket for space heating. My contributions to this discussion: 1. I had a huge bench and it still went 150 degrees at the surface sometimes when I was really pushing the stove. I can't imagine what the interior temps were. Don't use PEX in your mass. 2. If I was building a heater just for water heating I would wrap a coil around the outside of the insulated riser, cold in the bottom, hot out the top, and take advantage of the thermosiphon idea. 3. If you want to heat your floor, the floor HAS to be insulated. If it's not insulated don't even bother... you will be wasting your time. I'm not sure what you mean by heating the dirt- If you mean you want to do a natural plaster earth floor over an insulated slab then that could be pretty cool. If you mean you have natural ground under your home and you want to heat it... I'm sorry to say you won't do it with PEX and a wood boiler. You could potentially bury your flu pipes underground and use the earth as your mass. I'd still be hesitant in your climate unless you have a very small Sq.Ft. you are trying to heat. If you do have an insulated slab, radiant heating only requires around 100*F water circulation temps to maintain a suitable ambient room temp.
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Post by gadget on Oct 25, 2019 20:36:44 GMT -8
If you do have an insulated slab, radiant heating only requires around 100*F water circulation temps to maintain a suitable ambient room temp. Hey Manny, I have heard this before and its great to hear you confirm it. Of course I won't be heating a slab but the air space just below a second level floor. I hope this math applies to that kind of setup. I like the idea of keeping the heat below 120F. Lower temps allow for much more affordable hardware, parts and much safer. I heat my greenhouse which has about 385 gallons of water mass. Last night I had it at 110F and by morning it was 90F(6 55 gallon barrels), just from radiating from the plastic barrel sides. I'm building another heater in my house and want to move heat to the far end to a force air radiator via PEX. I was thinking of running a bunch of PEX under my living room and kitchen floors(its second story with easy access for running the PEX in the downstairs ceiling) from the radiator return. Knowing that the temps don't have to be too high is comforting incase a line leaks with people under it. How much water heating did you get from RMH compared to room heat? I just built a heater in my greenhouse and tonight, I was able to raise 55 gallons at about 1 degree a minute temp rise at full heat output. Its the fastest water heating I have ever been able to do with wood heat.
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