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Adding a septic tank with water for heat Storage????

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by airplanes20, Jan 5, 2012.

  1. woodsmaster

    woodsmaster Minister of Fire

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    Imagine the smell coming out of the vent pipe with 180 F poo.

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  2. Gasifier

    Gasifier Minister of Fire

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    It sounds like your boiler is outside, and your storage is in your basement? Is that right? Seems to me that you’re losing a lot of heat somewhere - wondering if it could be between your storage & boiler? In my mind that much storage should last quite a bit longer than 6 hours with a full firebox and the house up to temp. My house is 15 years old, 2700 sq.ft. on two levels plus an unfinished unzoned insulated basement. My furnace is dirty & inefficient, with no storage except for it’s own 30 gallon capacity, and I can make it from 10pm to 7am by loading full at 10 with the house up to temp. Things might be a bit chilly downstairs by 7am (downstairs gets set back over night), and the boiler is down to 140 or so, but I just have to rake the remaining coals and re-fill it with wood and away I go again.
    It does sound like something isn't right. With a well insulated home, a boiler and two tanks up to temp., it seems like you should be able to go longer than that in your situation. I am guessing your pipes run underground? What size pipe runs from your boiler to your tanks? How are they insulated? How far do they run?
  3. airplanes20

    airplanes20 New Member

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    Yes my boiler is outside. I ran inch and a quarter lines to the house, its about 75 feet from the shed to the house, i put 4 inches of blue board styrafoam insulation around the pipe. In the morning when i go out to the boiler the boiler temp is around 140-150, when the tanks are down to 110-120. Last night it was up to temp (180) around 10 pm, it stayed 30 degrees overnight and its now 8 am and the tanks are at 150. So they hold the heat well as long as the temp is about around 20. But once the temps dip down then thats when the tanks dont last long (overnight). Durning the daytime I leave for work at 6:30 am and again the tanks are up to temp (180), i get home around 4 pm and start the tanks aroud 5pm, at that time the tanks are running around 130-140. I have noticed the snow on the ground around the house is melted about 2 feet from the foundation. Im thinking mabye thats where im loosing some heat, don't have any insulation on the outside of foundation. Again i think the system works great, just on really cold nights it doesn't last as long as i would like thats why I wanted to add storage. Is it possible to build a building outside with the boiler and put tanks outside, with the 2 tanks in the basement?? How would that work because i thought the tanks had to be tied into each other?
  4. 2.beans

    2.beans Minister of Fire

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    can you bypass the tanks and directly heat the house on the real cold nights? when it gets cold 10* or lower 440 gallons would last me maybe two hours with my heat load. i have 1000 gallons and that gets me about four hours. when it gets real cold i can bypass the tanks and heat the just house. i heat my 1000 gallons to 165* to the top of the tank.
  5. 2.beans

    2.beans Minister of Fire

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    i know someone who heats his tank to keep the bacteria happy thru the winter.
  6. Gasifier

    Gasifier Minister of Fire

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    I will start by saying I am glad your system is working well for you airplanes20. No more oil/gas!!! I have no experience with underground pipes and insulation of them. But it would seem to me that you could be losing more heat to the ground with that type of insulation. How did you enclose the pipes with the insulation? Is the insulation like a box around them? The size of the pipe sounds good, the distance of 75 feet is not to far. But it would seem like you could lose a good amount of heat with hard, rigid insulation around the pipe. Could you give us an idea of how the underground insulation was done? How far under the ground are they? The reason I ask is I am curious as to the best way to improve your length of time you can get between firings and for efficiency of course. I am certainly not trying to pick your system apart brother. If you determined you were losing a lot of heat underground. How hard would it be to dig it up? Take the top of the insulation off and spray foam around the pipes, inside the rigid insulation, and put the top back on? Pain in the ass, I know. But if that was the problem, maybe the best solution for many years of good efficiency ahead.
  7. Tennman

    Tennman Minister of Fire

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    Sorry for short reply here but from my phone. Did I understand you to say the only underground insulation is the blue board? If your answer is yes then it's almost certain your pipes are enclosed in water. Just posted some basic underground transit performance in the underground sticky. Read it and when I get to a real computer we can get better details. But if you answer only blue board you'r probably screwed.
  8. Clarkbug

    Clarkbug Minister of Fire

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    Tennman is on to something here.

    Are your pipes further insulated, or is it just the blueboard placed around pex pipes in the ground?

    Can you measure the temp difference across the lines to and from your boiler without the house pulling heat?
  9. maple1

    maple1 Minister of Fire

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    I think you need to measure some pipe temps.

    Leaving & entering your boiler room, and entering & leaving your house. Sure sounds like you're losing heat to the ground - it can suck out all of your heat especially with some water next to your pipes.
  10. 2.beans

    2.beans Minister of Fire

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    had my pipes like that once. now i use them for an air line from my shop to my house to blow out my irrigation system.
  11. bpirger

    bpirger Minister of Fire

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    And becareful with the extruded polystyrene in the ground....it does suck up water in time. I dug some of my old line up, which had the polystyrene "box" around the conduit it was in....and it was very heavy...very wet. No where near the R value when it went in, I'm sure! (If it helped at all at that point....)
  12. stefan66

    stefan66 Member

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    No insulation around the foudation-------melting snow equals major heat loss!
  13. airplanes20

    airplanes20 New Member

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    I put the lines in the ground around 3feet deep, I am not worried about water at all, my house lot was all sand i dug down with a 325 Cat escavator and didn't find a drop of water ( I was hoping i didn't need to drill a well ). With the pipe being down 3 feet i figured it would be below the frost line so the temp of the ground should be around 55 all the time, i am sure there is heat loss but not that much. When i first hooked the boiler up the heat coming out of the boiler was like one degree warmer (if that) then the temp coming into the tanks.

    I cut the blue board on a table saw so they were all straight then i put two pieces on the ground laid the pipe on them and then duck taped the sides and the top onto the bottom piece. Maybe i am losing some temp. due to the pipes in ground but i don't think thats the problem. If i was losing that much heat out of the pipes the snow on the ground would be melted, just like the snow around my foundation. I have seen other peoples houses that have pipes under the ground and there is a clear line from the boiler to the house where the snow has melted about 3 feet wide.

    I just wanted to know what people thought about using a septic tank of if anyone has tried, thanks for trying to help me out and suggest other problems but i honestly think the way its set up is great. Im just looking to add more storage, im currently looking for a 500 gallon propane tank. Ill have to build another building beside where the boiler is and insulate it and the tank then figure out how to circulate the water having another set of tanks.
  14. maple1

    maple1 Minister of Fire

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    I'd still measure my temps now, just to be sure. Moisture can seep in over time and conduct heat away like crazy.

    Good luck.
  15. Tennman

    Tennman Minister of Fire

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    Airplanes, As an airplane guy, your handle catches my interest. Given the depth you placed your lines, a lack of snow melt may not be a reliable indication of pumping a lot of btu's into the ground, particuarly if you live in a very cold northern latitude. As I worked thru all my first year problems it was as important to find out what was not wrong as well as what was working right. If you do measure the underground transit temp loss, it should be in the .004-.006 degF/ft underground (and that number is conservatively ~30% high). That will be on par with off-the-shelf insluated products. From memory I'm thinking you said 30' of underground??? If I'm right on the underground run length the deltaT underground should be way less than .5*F total for both ways. Do a search on water absorption for expanded polystyrene (EPS). You'll see it's R value drops dramatically in underground applications with time as it absorbs water. The underground DeltaT number will let you know if a significant fraction of your boiler's output is going into the ground. Which was just one of my big problems my first year. Best Wishes.
  16. stefan66

    stefan66 Member

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    I am currently using a concrete septic tank for storage.
    Installed aprox. 120 feet of 3/4 inch copper as heat exchanger.
    Works allright for me.
    Mind you there is nothing but water in the tank.
  17. airplanes20

    airplanes20 New Member

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    Thats what i was thinking about doing, but most everyone on here has told me its a bad idea.
  18. mwk1000

    mwk1000 Member

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    You mentioned no snow around the home and I though of this article:

    http://www.quadlock.com/technical_library/bulletins/R-ETRO_Value_of_Basement_Insulation.pdf

    If you are only trying to move the timeline on cold days, for the money and effort this approach might be worth it
    and it will pay back all day every day. If a tank 220 Gal tank is worth 220gal * 8.3 lb/gal * 70 degrees usable 127,820
    BTU's give or take. This is a way to add more tanks to your system without adding any tanks :)


    Here is a excerp:

    Imagine a 20' x 30' x 8' [6m x 9m x 2.4m] high basement with 8" [20cm] thick concrete walls
    and 2' [.6m] exposed (above grade). If the temperature inside is 70°F [21°C] and the
    temperature outside is 20°F [-6°C], the heat loss through just the 2' [.6m] exposed portion of
    the wall is 15,625 BTUs per hour (370,000 BTUs per day). Let’s further imagine that the house
    is located in a cold winter climate where frost extends 2' [.6m] below grade. This means that
    the 2' [.6m] above grade and the 2' [.6m] in the frost zone will all essentially be exposed to the
    The entire area above the frost line is subject to huge heat losses. Below the frost line, heat loss is significant
    but not as extreme.

    2' [.6m] Above Grade
    2' [.6m] Above Frost Line, Below Grade
    4' [1.2m] Below Frost Line
    20°F [-6°C] outdoor temperature.

    The 4' [1.2m] that is below the frost line will be exposed to a
    relatively balmy ground temperature of 50°F [10°C]. With the upper 4' [1.2m] of the basement
    wall exposed to 20°F [-6°C], and the bottom 4' [1.2m] exposed to 50° F [10°C], the total heat
    loss through the cement walls would be 43,750 BTUs per hour (1,050,000 BTUs per day!).
    This equates to over four cords of oak or sugar maple firewood (at 20% moisture content) to
    warm only the basement over three winter months.
  19. stefan66

    stefan66 Member

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    My storage is under the slab--- 4inches green rigid styrofoam on sides
    ---2 inches underneath--- 6 inches on top
    ---weeping tile 2 feet under tank
    Storage losses are around 2 degrees per day in fall with no heating demand
  20. maple1

    maple1 Minister of Fire

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    Sure sounds like the tank is working for you pretty good - two degrees per day seems like pretty low heat loss. How long have you had that setup? I wish at times I had this house of mine to do over again - there are a lot of things I would do differently. Not sure I would go the tank in the ground route, but would definitely find some way to incorporate heat storage in the overall design.

    I don't think I mentioned it was a bad idea - just thought the mention by someone of using a real septic tank with real, well, stuff inside was a bit out there. I did also think though that it sounded like you might have some large heat losses in your current setup.

    Good luck.
  21. mwk1000

    mwk1000 Member

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    The whole discussion got me thinking about putting one in uninsulated for the SUMMER and using it instead of the AC. Since the cost of electricity has doubled litteraly over the last 5 years I am looking for ways to use the pumps / exhangers/ thermostats and put them to work in the summertime to same me money like they do in the winter.
  22. Tennman

    Tennman Minister of Fire

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    Airplane, this thread has been so entertaining because it's been like bungee jumping, about the time it was going in one direction, we got jerked in another. Great fun... from poop to foam. But for me personally, in your original post, you said you've seen others use septic tanks for storage and sure enough stefan66 chimed in saying it was working for him. In my 3 years of hanging out here this is the first discussion I've seen about septic tank storage. My response back on the 6th, "Horrible idea. Coefficient of thermal conductivity of generic concrete = .7, rigid polyurethane foam = .018-.02. Concrete transfers heat about 40 times faster than a foam insulated vessel." I was not imagining foaming a septic tank or insulating it, just concrete against the dirt, i.e. a standard tank install (where the laws of physics still stand). Which in my mind would be far more complex and painful than just buying another propane tank and foaming it. My point is the energy integrity of a thermal battery is all about the quality of the insulation, not how the liquid's being contained. Been fun! Cheers
  23. maple1

    maple1 Minister of Fire

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    I would maintain, though, that the possibility of in ground storage working out or not is mostly dependant on local site specific conditions like soil type, grade, and water table height. No matter how much you insulate, if you're in a place with a high water table and poorly draining soil types, in ground storage is likely not a good idea.
  24. stefan66

    stefan66 Member

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    Good point. I was told if there was any moisture within 5 feet it would'nt work.
  25. airplanes20

    airplanes20 New Member

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    LOL i know its been fun reading post every night, I asked one question and i get so many different anwsers and only a few anwsered my question. Like i have said before the soil on my lot is all sand, so water shouldn't be an issue other than moisture from the ground. If i was going to put in a septic tank I was going to have a spray foam company spray 3-4 inches all around. I wasn't going to put poop in it, just regular water. I do dirt work all summer long, so the easiest way for me to add storage would be to dig a hole and fill it back in, rather than building. If i can get a propane tank for 400 bucks its cheaper then a septic tank, then i still have to buy the copper coils. Ill have to get on putting insulation around the foundation, didn't have the money when i built the house to put insulation around foundation, just have to keep loading the boiler.

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