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



## airplanes20 (Jan 5, 2012)

I have a Tarm Scandic Solo plus 40 and also have 2- 220 gallons of pressurized water in my basement now.  I live in Thornton NH and on cold nights below 0 i only get like 6/7 hours out of a full burn cycle.  My house is brand new with spray foam insulation (so i cant do anymore insulation).  My basement is full and i have no more room for pressurized tanks (that would be ideal the 220 tanks are awesome).  
          I have seen people put septic tanks in the ground and put loops in the tank.  I didn't know if anyone on here has seen or used this method.  If anyone has any information and you would like to share please let me know.  

How long of loops did you run?
How big of a tank?
Did you line the inside of the tank?
Did you insulate the outside of the tank?
How did you connect it into the boiler loop? 
Pics?


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## stee6043 (Jan 6, 2012)

Tanks in the ground are less than optimal.  Earth is one big heat sink.  Based on the experiences I've seen on this website the insulation and waterproofing will be rather expensive and highly critical.


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## flyingcow (Jan 6, 2012)

What am I missing? Just reload the boiler? BTW, how big is your house? 

On cold nights, like tonight I have to reload boiler.


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## flyingcow (Jan 6, 2012)

BTW...IMO a septic tank for storage is really not a great idea.


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## BHetrick10 (Jan 6, 2012)

I have been known to think out side of the "Box"  sometimes a little to far. 

 I was just thinking the other day about putting a HX in my actual septic tank when the boiler temp drops.  Have a loop on a aquastat that when the storage gets so cold if a fire hasn't been made to circulate water through the actual septic tank.  For obvious reasons I would want a loop going from a heat exchanger in the tank to another one that the boiler water would go through so if is does leak or erode it wont contaminate the boiler water or drain you system into the septic.  Septic tanks seem to be nice and toasty between the warn water and other things that go into them plus the bacterial reaction.

 :cheese:   How far out of the box is that?


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## maple1 (Jan 6, 2012)

That's way out there...


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## Gasifier (Jan 6, 2012)

Would a septic tank be inefficient? I would not want a tank in the ground myself, but am curious as to it's efficiency, or lack of.


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## OT_Ducati (Jan 6, 2012)

if the septic tank was insulated well, above ground wouldn't the concrete mass add to the heat storage??


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## joemeintzer (Jan 6, 2012)

If you wanted to have a remote tank why not have it pressure rated and forget loops? I say an LP tank would do it. Insulating would be more challenging.


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## flyingcow (Jan 6, 2012)

i don't see where the amount of storage is the problem. If he's *burning 6/7 hours *and can't charge storage and heat the house? how big is house(heatload)? What kind of wood? how long has wood been seasoning? When he's done burning, is storage charged to the max? Need more info.


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## Gasifier (Jan 6, 2012)

For the number of nights it will be that cold, sounds like the easiest thing to do would be the reloading of the boiler. If the whole system is pressurized and the wood is seasoned well, I am assuming the limitation is proabably the size of the burn chamber. If you did have more storage. Would you be able to heat it with the demand of the house and anything else that demands it, like DHW?


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## maple1 (Jan 6, 2012)

flyingcow said:
			
		

> i don't see where the amount of storage is the problem. If he's *burning 6/7 hours *and can't charge storage and heat the house? how big is house(heatload)? What kind of wood? how long has wood been seasoning? When he's done burning, is storage charged to the max? Need more info.



+1. I'm not understanding how more storage will extend burn times.


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## in hot water (Jan 6, 2012)

airplanes20 said:
			
		

> I have a Tarm Scandic Solo plus 40 and also have 2- 220 gallons of pressurized water in my basement now.  I live in Thornton NH and on cold nights below 0 i only get like 6/7 hours out of a full burn cycle.  My house is brand new with spray foam insulation (so i cant do anymore insulation).  My basement is full and i have no more room for pressurized tanks (that would be ideal the 220 tanks are awesome).
> I have seen people put septic tanks in the ground and put loops in the tank.  I didn't know if anyone on here has seen or used this method.  If anyone has any information and you would like to share please let me know.
> 
> How long of loops did you run?
> ...



It's tough to keep the heat in a tank buried in the ground.  Any ground water, even rain run-off will wick away the energy very quickly.  I have tried buried concrete septic tanks as solar storage, even with an expensive 4" of foam on all sides it was not a very efficient heat storage.  i'd move that type of installation to the bottom of the list.

I have also tried concrete tanks above ground, in my own shop actually.  They do require a liner as the thermal expansion causes hairline cracks.  It also developed a smelly
bacteria of some sort when it cooled down in the summer.

But it did end up making a nice water trough for the cattle.

I'd be more inclined to build a super insulated building, maybe an ICF building to house an above ground tank.  At least you could keep an eye on things and make adjustments and modifications.  Plenty of nice un-pressurized "kit" tanks on the market.

hr


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## 711mhw (Jan 6, 2012)

airplanes20 said:
			
		

> I have a Tarm Scandic Solo plus 40 and also have 2- 220 gallons of pressurized water in my basement now.  I live in Thornton NH and on cold nights below 0 i only get like 6/7 hours out of a full burn cycle.  My house is brand new with spray foam insulation (so i cant do anymore insulation).  My basement is full and i have no more room for pressurized tanks (that would be ideal the 220 tanks are awesome).
> I have seen people put septic tanks in the ground and put loops in the tank.  I didn't know if anyone on here has seen or used this method.  If anyone has any information and you would like to share please let me know.
> 
> How long of loops did you run?
> ...


What is your storage temp. at the end of your burn cycle? If your home is as insulated as well as it sounds, with a good temp. of your storage, your storage should carry you thru the rest of the night. It sounds like you just need to play around with your operation of your system, that is when cold nights are expected, start charging your storage earlier in the evening and head in to the night with a head start. This, from a guy with no storage, but it's how I understand storage to work.
How are you heating? (radiant, air...)


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## Gasifier (Jan 6, 2012)

What is your storage temp. at the end of your burn cycle? If your home is as insulated as well as it sounds, with a good temp. of your storage, your storage should carry you thru the rest of the night. It sounds like you just need to play around with your operation of your system, that is when cold nights are expected, start charging your storage earlier in the evening and head in to the night with a head start. This, from a guy with no storage, but itâ€™s how I understand storage to work. How are you heating? (radiant, airâ€¦) 

This is a good point 711. I try to get my 400 gallons of storage up to 180 Â°F  before I go to bed. If my wood runs out in the boiler before I get up the tank takes over and carries me a few hours more. It isn't until the aquastat on the tank gets down to 155  Â°F that the other fuel kicks on.

airplanes20, Just out of curiosity. How are your tanks insulated? What temperature do you usually have them at when they are at their hottest temperatures? I am also curious about your spray foam insulation for your house. You must be pretty air tight. I have spray foam in my garage and love it. What type of air system do you have in your house? Did you have to install something that would keep humidity at a certain point? Is the spray foam in the walls and the ceiling of the top floor? Just curious. I heard at one time that if your house is too air tight with the spray foam that you might develop a problem with humidity that could lead to mold. I have never seen that, but did hear that a guy had a problem with his house being to air tight. I don't have to worry about that with my house.  :lol: I have some places that are insulated fairly well and some that are not fairly well.  :lol:


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## Tennman (Jan 6, 2012)

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. Now if you blew foam on that septic tank before you lower it in the dirt.... just kidding. But really just dig a pond and heat it, about the same performance.


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## mikefrommaine (Jan 6, 2012)

maple1 said:
			
		

> That's way out there...



Two words.

"bore holes"

http://www.dlsc.ca/borehole.htm


Just takes a few years to get up to temp,but then you can just coast for the next decade!


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## stee6043 (Jan 6, 2012)

BHetrick10 said:
			
		

> I have been known to think out side of the "Box"  sometimes a little to far.
> 
> I was just thinking the other day about putting a HX in my actual septic tank when the boiler temp drops.  Have a loop on a aquastat that when the storage gets so cold if a fire hasn't been made to circulate water through the actual septic tank.  For obvious reasons I would want a loop going from a heat exchanger in the tank to another one that the boiler water would go through so if is does leak or erode it wont contaminate the boiler water or drain you system into the septic.  Septic tanks seem to be nice and toasty between the warn water and other things that go into them plus the bacterial reaction.
> 
> :cheese:   How far out of the box is that?



Hah....ohh man, sometimes these things are real mind benders!

I can't even imagine what kind of WILD growth you'd get in a septic tank if you kept the temps above 100 degrees on a consistent basis.  This aside from the comments above really suggesting the efficiency of this setup would be horrible at best.  

No need for ridex!


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## rkusek (Jan 6, 2012)

BHetrick10 said:
			
		

> I have been known to think out side of the "Box"  sometimes a little to far.
> 
> I was just thinking the other day about putting a HX in my actual septic tank when the boiler temp drops.  Have a loop on a aquastat that when the storage gets so cold if a fire hasn't been made to circulate water through the actual septic tank.  For obvious reasons I would want a loop going from a heat exchanger in the tank to another one that the boiler water would go through so if is does leak or erode it wont contaminate the boiler water or drain you system into the septic.  Septic tanks seem to be nice and toasty between the warn water and other things that go into them plus the bacterial reaction.
> 
> :cheese:   How far out of the box is that?



Septic tanks are for poop.  That would be like saving money on installing faucets in your home by just dipping your drinking water out of the toilet. 
My local NRD (rural water system) sent me a questionaire about what kind of interconnections I have:
1.  Do you have a sprinkler system?  
     If yes, is it protected by a testable backflow prevener?  

2.  Swimming pool or hot tub?  
     If yes, is it protected by a testable backflow preventer?

3. Boiler heat or water to air heat pump?
    If yes, it protected by a testable backflow preventer?

It won't surprise me now when they add the question below.

    If yes, does your boiler plumbing come in contact with your poop tank or lagoon?  If so, we may need to check it for leaks because that would make our drinking water taste like chit!


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## BHetrick10 (Jan 7, 2012)

This thought came to me after I read articles on some of the huge dairy farms that collect methane and are "Green in operation"  pulling BTU's out of there holding tanks is something they've done.  It was a really neat article.  Collected the Methane,  used it to run water cooled generators to powers everything.  The water that cycled through the rads went through HEX for heating the water.  I have never seen tanks as big as those before. They were buried underground ans some where in the range of 50' wide 30' high 100' long.  He referred to them as digesters.  Had to maintain a certain temperature for the bacteria to produce methane he even added food scraps from local restaurants. 

I also worked in a very old house that had a big water tank in the attic.  I guess they used the heat to preheat the water.  If I remember correctly the tank was filled with sand, and the water lines passed back and forth through it a few times.

I think as others have stated before. .  sounds like a shed out back with some more storage in would be ideal if you cant feed it wood more often.


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## airplanes20 (Jan 7, 2012)

The house is 3000 sq ft, i have radiant in the basement, and forced hot water upstairs.  I do put a full load on the tanks at night my last time out to the boiler is around 10-10:30, the tanks get up to around 180.  I then wake up around 4:30 am and the tanks temp are down to 110 or so, i try to keep the tanks from going under 110.  After i start the boiler in the morning it takes about 2-3 hours to be back up to 180.  I am using seasoned wood, so i know thats not the problem.  I just need more storage if i had another 200 gallons i think i would be all set, but like i said i don't have any room in the basement.  Reading everyones post guess ill go another direction.  Thanks for all the info


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## airplanes20 (Jan 7, 2012)

airplanes20, Just out of curiosity. How are your tanks insulated? What temperature do you usually have them at when they are at their hottest temperatures? I am also curious about your spray foam insulation for your house. You must be pretty air tight. I have spray foam in my garage and love it. What type of air system do you have in your house? Did you have to install something that would keep humidity at a certain point? Is the spray foam in the walls and the ceiling of the top floor? Just curious. I heard at one time that if your house is too air tight with the spray foam that you might develop a problem with humidity that could lead to mold. I have never seen that, but did hear that a guy had a problem with his house being to air tight. I don't have to worry about that with my house.  :lol: I have some places that are insulated fairly well and some that are not fairly well.  :lol:[/quote]

The tanks have 2-3 inches of spray foam, when they are at 180 you can put your hand on the foam and its not even hot, so i know the tanks are holding the heat very well.  the houses has 2inches of spray foam with an R-11 bats.  Gives my walls an R28  but i didn't need and air purifier like your talking about.  I have heard the same thing from people.  The guys that insulated the house told me if i had put 6 inches of spray foam in the wall i would need the purifier installed.


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## flyingcow (Jan 7, 2012)

have you done a heat loss calc? that will give you a better idea than just throwing another tank at it. No doubt it would help, but you might need more than 200gals. I have a baseboard complimented by my kitchen that is radiant. My radiant is staple up and I have to keep the water about 135/140 in the deep of winter to keep the floor warm.  But that being said, I have a set back thermostat on BB heat, because if it stays set in the 70's at night I loose alot out of my storage. same goes during the day when no ones home, T-stat sets back during the day. i drive my 820 gals of unpressurized storage up to about 175ish at night(by 9pm) let the fire go out, thats after starting it about 3pm. The other night it was -7 with a 10 to 15 mph breeze. We had to do a fire again by 7amish to get thru the day because my wife was home. I live in a 1800sq/ft, 2 story house, on a hill, in northern Maine, that has average insulation. By no means not as well insulated as yours. My unit is an Innova-30, a little smaller than yours.


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## maple1 (Jan 7, 2012)

airplanes20 said:
			
		

> The house is 3000 sq ft, i have radiant in the basement, and forced hot water upstairs.  I do put a full load on the tanks at night my last time out to the boiler is around 10-10:30, the tanks get up to around 180.  I then wake up around 4:30 am and the tanks temp are down to 110 or so, i try to keep the tanks from going under 110.  After i start the boiler in the morning it takes about 2-3 hours to be back up to 180.  I am using seasoned wood, so i know thats not the problem.  I just need more storage if i had another 200 gallons i think i would be all set, but like i said i don't have any room in the basement.  Reading everyones post guess ill go another direction.  Thanks for all the info



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.


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## flyingcow (Jan 8, 2012)

i think Maple1 might be on to something.


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## woodsmaster (Jan 8, 2012)

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


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## Gasifier (Jan 8, 2012)

It sounds like your boiler is outside, and your storage is in your basement? Is that right? Seems to me that youâ€™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 itâ€™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.


			
				flyingcow said:
			
		

> i think Maple1 might be on to something.



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?


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## airplanes20 (Jan 8, 2012)

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?


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## 2.beans (Jan 8, 2012)

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.


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## 2.beans (Jan 8, 2012)

BHetrick10 said:
			
		

> I have been known to think out side of the "Box"  sometimes a little to far.
> 
> I was just thinking the other day about putting a HX in my actual septic tank when the boiler temp drops.  Have a loop on a aquastat that when the storage gets so cold if a fire hasn't been made to circulate water through the actual septic tank.  For obvious reasons I would want a loop going from a heat exchanger in the tank to another one that the boiler water would go through so if is does leak or erode it wont contaminate the boiler water or drain you system into the septic.  Septic tanks seem to be nice and toasty between the warn water and other things that go into them plus the bacterial reaction.
> 
> :cheese:   How far out of the box is that?


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


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## Gasifier (Jan 8, 2012)

airplanes20 said:
			
		

> 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?



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.


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## Tennman (Jan 8, 2012)

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.


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## Clarkbug (Jan 8, 2012)

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?


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## maple1 (Jan 8, 2012)

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.


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## 2.beans (Jan 8, 2012)

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.


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## bpirger (Jan 9, 2012)

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....)


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## stefan66 (Jan 9, 2012)

airplanes20 said:
			
		

> 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?



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


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## airplanes20 (Jan 9, 2012)

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.


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## maple1 (Jan 10, 2012)

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.


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## Tennman (Jan 10, 2012)

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.


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## stefan66 (Jan 10, 2012)

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.


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## airplanes20 (Jan 10, 2012)

stefan66 said:
			
		

> 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.



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


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## mwk1000 (Jan 10, 2012)

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 70Â°F [21Â°C] and the
temperature outside is 20Â°F [-6Â°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). Letâ€™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
20Â°F [-6Â°C] outdoor temperature. 

The 4' [1.2m] that is below the frost line will be exposed to a
relatively balmy ground temperature of 50Â°F [10Â°C]. With the upper 4' [1.2m] of the basement
wall exposed to 20Â°F [-6Â°C], and the bottom 4' [1.2m] exposed to 50Â° F [10Â°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.


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## stefan66 (Jan 10, 2012)

airplanes20 said:
			
		

> stefan66 said:
> 
> 
> 
> ...



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


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## maple1 (Jan 11, 2012)

stefan66 said:
			
		

> airplanes20 said:
> 
> 
> 
> ...



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.


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## mwk1000 (Jan 11, 2012)

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.


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## Tennman (Jan 11, 2012)

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


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## maple1 (Jan 11, 2012)

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.


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## stefan66 (Jan 11, 2012)

maple1 said:
			
		

> 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.



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


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## airplanes20 (Jan 11, 2012)

Tennman said:
			
		

> 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




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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## Splitz (Jan 12, 2012)

I have an almost new 2000 Gallon concrete septic tank behind my shed that I used as a holding tank for two years.  I have been trying to think of what to do with it and the idea of thermal storage crossed my mind, but I wasn't sure it was worth it.  I thought of insulating it but leaving above ground to avoid water issues.  If anyone has any constructive ideas on how this might be accomplished I would love to hear them as I already have the tank and it's too heavy (expensive) to move or sell.  This has been an interesting thread, like most people here I hate to be "inside the box" or we would all have modulating propane boilers or be slaves to the oil companies.  
(p.s. using the ACTUAL sh*t tank is a little out there!)


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## maple1 (Jan 12, 2012)

I don't think I would try one above ground - they are designed to be fully contained (surrounded by dirt) when full. Not saying it would burst, but don't think I'd chance it full of 2000 gallns of hot water.


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## 2.beans (Jan 12, 2012)

sorry for the late post. i do know someone that spray foamed a 500 gallon propane tank and put it under his addition on his house. no fixing it or knowing if ground water is affecting it. its  been working fine.


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## Tennman (Jan 12, 2012)

Airplane, and all.... Most all of us understood you weren't planning on heating poop as energy storage.... just that some of us just couldn't resist the temptation of going there. Speaking for myself, they just beat me to the obvious jokes. But it was symptomatic of the fact that a discussion of using a septic tank as storage was a novel topic.

Maple1, Yeah my last caveat post stating it's all about the insulation was not to imply I thot the septic tank was a good idea!! I'm a closed system guy with autofill backflow preventers managing pressure and chemicals managing rust. Since I'm around large industrial and government facilities I just think that way. Quite a few posts here about folks happy with non-pressurized systems and lined plywood storage tanks. I'm a closed, pressurized kind of guy.

AND just about the time this thread is running out of steam... Splitz reenergizes it.  Splitz, if you lived near me you'd make a tornado shelter out of it.... If you want to use it for storage..... just insulate the CRAP out of it.... sorry just couldn't help myself. I'm going to stop before I talking about how energy always is trying to find a way to get to a LOWER energy state. All our btu's are relentless and untiring in that law of the universe.

Ya'll have a good day... now I gotta make some money.


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## Splitz (Jan 15, 2012)

Yeah, maybe a bomb shelter...or after seeing Steve's post on Happy Greenwood owners, an outdoor boiler shed...hard to burn down concrete!


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## HeatFarmer (Jan 26, 2012)

woodsmaster said:
			
		

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


The plus side is you could run your BBQ off-in the fumes.....if you didn't smoke too close to the tank........KaBOOM.


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## roknwoe (Jan 28, 2012)

BHetrick10 said:
			
		

> I have been known to think out side of the "Box"  sometimes a little to far.
> 
> I was just thinking the other day about putting a HX in my actual septic tank when the boiler temp drops.  Have a loop on a aquastat that when the storage gets so cold if a fire hasn't been made to circulate water through the actual septic tank.  For obvious reasons I would want a loop going from a heat exchanger in the tank to another one that the boiler water would go through so if is does leak or erode it wont contaminate the boiler water or drain you system into the septic.  Septic tanks seem to be nice and toasty between the warn water and other things that go into them plus the bacterial reaction.
> 
> :cheese:   How far out of the box is that?



You have a very stinky idea!    (pun intended).    I am jealous I didn't think of it.

Actually, I think this would not work in the long run, because similar to "stealing heat off a hot smoke pipe of a stove to heat your house", it cools the pipe too much and can/does create creosote on the inside of the pipe and perhaps clog it up.   

If you cool off the septic tank too much, it might clog up the septic system because heat works with the good bacteria to break down all the nasties inside your septic tank, on its way to the drain field.  You might acquire some BTU's for your home at the expense of creating trouble in your septic tank and drain field...which would be very costly to fix.  

The bottom line:

--dont mess with mother nature!


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## senoiaslim (Feb 15, 2017)

Ok, been a while for this thread, but here goes.  Lets say you insulate the crap out of the tank, put a copper coil in the tank, to make it a closed system going out of the tank to the mix valve and blend it with your hot water heater.  You run the water from the septic tank to the wood boiler in an open system. Does anyone think that would be a good idea?  Basically I am looking for a system that would be able to shut down without freezing during some times in the winter if we are not at home.

One other thing, how would I figure out the size of the copper coil to have in the tank that would run to the mix valve?


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## Tennman (Feb 16, 2017)

Sooo.... why do you care about keeping the poopy water in the septic tank warm?

Resurrecting this thread from when I was younger may just be the highlight of my day. Well, I've changed since then but the physics hasn't. Thanks for the memories.


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## tom in maine (Feb 17, 2017)

No doubt it will work for a while. I have some customers in the Southwest who have used septic tanks for solar systems.
There is an issue with concrete being affected strength-wise when heated over 140F.
We made liners for those tanks in the SW. Apparently the contractor had issues with cracking as well.


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## E Yoder (Feb 17, 2017)

What I'm wondering about how copper would hold up in a corrosive environment like an "in use" septic tank.  
 Maybe SS or Pex.


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## E Yoder (Feb 17, 2017)

This thread is priceless. 

I actually fed about 50+' of 3/4" Pex into a septic tank once by mistake. Homeowner had buried a 4" PVC conduit from basement to outdoor boiler. We were feeding a 3/4" Pex pipe down the conduit to couple to the insulated pipe to pull it back through... We fed about 50' into the tank til we smelled a whiff.... Tried to pull it back- not happening.... Then the homeowner comes over apologizing for showing us the wrong 4" pvc pipe.... !! Was stubbed up through the slab for a future upstairs bathroom that never happened. The right pipe was behind the drywall. 
Had to dig up the tank covers to get the pex out. 
Wow, precious memories.....  Wish I had a picture.


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## tom in maine (Feb 18, 2017)

E Yoder said:


> What I'm wondering about how copper would hold up in a corrosive environment like an "in use" septic tank.
> Maybe SS or Pex.


Wouldn't that be a fun experiment. I have a friend who is a septic expert. Was a mom to 7 kids, went back to college and got her PHD in microbiology, specializing in the biology of septic tanks. She was very casual about working in tanks, testing the fun stuff in them.

I would not consider using PEX in a tank with any fittings. Would use AL/Pex or stainless. And no fittings inside. There is a risk of contamination sneaking through a fitting joint. Not sure it is significant but it is not work the risk.
Would be interesting to see how things stood up.


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