# Converting Propane Tanks to thermal Storage.



## HappyHome (Feb 17, 2017)

Hello, all.

  I have someone designing a new hydronic heating system for my home, and we are stuck on the thermal storage issue.  The designer would like to use pressurized storage; I have a finished basement with cinder-block walls, and getting anything wider than 30" through the door will be very tricky.

  I need 300 gal capacity (as a minimum) up to 550 gal capacity (ideal).  I'm open to outdoor storage, but that would probably require excavating. Plus, winters here bottom out at -40, so we'd have to make extra sure of the insulation.

  What ideas have people come up with for DIY storage tanks; and where can I find articles about how to make 'em?

  Also: Is there a commerical option for this that is so good or so popular that people don't bother?


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## maple1 (Feb 17, 2017)

What can you get for LP tanks? I would have to check, but I was thinking the 100 gallon one I got for expansion is 2' diameter. I could be wrong though.

You could build an open storage tank in place, and use coils for heat exchangers. Storage would be open, but rest of system would be closed/pressurized. Insulated wood box with plastic liner, basically. Search 'American Solartechnics' - he is a member on here. Quite a few guys on here are running those - would also drastically reduce expansion tank requirements.

(Don't know what you have for a boiler, but I have 660 gallons & would love more. IMO even 550 is just adequate).


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## Fred61 (Feb 17, 2017)

Conventional preference on this site seems to favor pressurized storage over unpressurized which leads folks with difficult installations or space constraints to "jump through hoops" and shell out big bucks for complicated plumbing and install in less than optimal locations but I don't see the reason for it.

I have a 500 gallon unpressurized retired stainless chemical tank and if I had to do it over I would install the same set-up. All my boiler does is heat the water in the tank and all the distribution originates from that battery. I know and understand that the argument is that if the storage temperature is cold and the zones are calling the priority is the heat to the zones. I have run into that situation probably twice in the 9.5 years I've been running this with little consequence. The zones continued to produce heat albeit at a lower temperature and the only other visible result was the slower temperature rise in the tank during my daily charge session.

I don't have large expansion tanks or side arms for DHW.  The two main copper coils within the tank supply all my heat and domestic hot water. Heck, just for giggles I installed a separate coil in the bottom of the tank that is hooked up to a boiler overheat zone. Because I wanted to keep the hot water make-up separate from the distribution I did install a FP exchanger so that cost me the price and operating cost of an additional circulator but that only runs during my 3 to 4 hour daily burn.


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## peakbagger (Feb 17, 2017)

I have an American Solar Technics unpressurized tank. I installed it myself and the way its designed its easy to fit in a tight spot. Unlike a modified propane tank there are no potential boiler code issues. ( I don't know how Ontario treats pressure vessels)

It requires a heat transfer coil but doesn't need anywhere near the expansion tanks of a pressurized solution

http://www.americansolartechnics.com/products/heat-bank-storage-tanks/


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## HappyHome (Feb 17, 2017)

Hello, Maple1 and thank you for responding!  I'm getting an Econoburn EB-100 boiler, and the salesman said I could 'get by' with 300 gal, but that 500+ would be preferable.  American Solartechnics is a product that I'm familiar with and I am considering using it.

  I'm also in touch with a local septic tank mfgr. There's an excavator working next door throughout the summer, if I need a large enough thermal storage I may just pay them to bury a septic tank with 6"-18" of polystyrene insulation wrapped around it - in the yard under the front patio.


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## Bad LP (Feb 17, 2017)

Tarm has 300 gallon tanks that are 30" diameter. ASME rated so there's no potential problems with your insurance company. I just bought 2 300 gallon tanks from them.

There is no way I'd give a single second of thought into installing tanks in the ground under any circumstances.

There is a used Solortechnics non pressurized tank for sale on the forum. It will be a few pages deep. I bought his boiler but was only interested in pressurized storage. Nice guy to deal with as well.


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## HappyHome (Feb 17, 2017)

Bad LP said:


> Tarm has 300 gallon tanks that are 30" diameter. ASME rated so there's no potential problems with your insurance company. I just bought 2 300 gallon tanks from them.
> 
> There is no way I'd give a single second of thought into installing tanks in the ground under any circumstances.
> 
> There is a used Solortechnics non pressurized tank for sale on the forum. It will be a few pages deep. I bought his boiler but was only interested in pressurized storage. Nice guy to deal with as well.


 The Solortechnics tank might work for me.  I'll have to find out where in my basement I can squeeze a tank with a 6 ft square footprint, but it's still promising.


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## peakbagger (Feb 17, 2017)

AST has changed there design of the liner slightly over the years and experimented with liner materials. If you are considering a used one it would be worth given Tom the owner a call.


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## Sparky (Feb 17, 2017)

Check out builditsolar.com for tank ideas
If needed I can help with making coils it is pretty easy
I had 550 gallons storage wasn't enough for my heat load
I have 1200 gallons works perfect one burn a day


Sent from my iPhone using Tapatalk


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## Beagle Dad (Feb 18, 2017)

I used 120 gallon propane tanks which are 30" wide. The tanks were modified by cutting them in half and added to the middle using steel plate which was rolled into a cylinder and welded. Since the tanks were modified they are no longer certified. Here in Ontario a non ASME tank must operate at under 15 psi. Then link to the post below shows some pictures of the completed tanks

https://www.hearth.com/talk/posts/2112829/


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## velvetfoot (Feb 18, 2017)

Would you have better stratification in an unpressurized tank since there is no flow stirring things up?  Or, isn't that a factor with a big pressurized tank?


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## woodsmaster (Feb 18, 2017)

velvetfoot said:


> Would you have better stratification in an unpressurized tank since there is no flow stirring things up?  Or, isn't that a factor with a big pressurized tank?



 Better stratification but you lose a few degrees with the heat exchager.


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## velvetfoot (Feb 18, 2017)

woodsmaster said:


> Better stratification but you lose a few degrees with the heat exchager.


Plus I imagine the coil would be resting on the bottom of the tank.  The tanks are usually not tall though.


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## Beagle Dad (Feb 18, 2017)

I went through a similar process to select a storage tank system. Maximizing the storage was important and given that I have radiant floor heating which is the majority of my load with a return water temperature of 90 Deg F a tall tank would be the best fit. The solution was 4 tanks in series for a total of 920 gallons. With this configuration the BTUs stored is maximized by having the greatest temperature difference for the available mass of water. When burning once a day the bottom of the tank stays around 90F and the top varies from 175 to 165 F.

See Idronics 17 which talks about usable heat. The best way to achieve this is to keep the top of the storage as hot as possible. My system has 4) 90" tall tanks which can have up 40 Deg F difference from top to bottom. Therefore a pressurized system was selected.

http://www.caleffi.com/sites/default/files/file/idronics_17_na.pdf


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## salecker (Feb 19, 2017)

Don't bury a heat storage tank in the ground.
If you can get the excavator cheep,dig out beside your basement and cut a large enough hole in the wall to get your tank inside.Then fill the hole in the wall and back fill or leave it as access to the basement with a poured retaining wall with steps,or frame walls and steps from PWF wood.


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## Fred61 (Feb 19, 2017)

salecker said:


> Don't bury a heat storage tank in the ground.
> If you can get the excavator cheep,dig out beside your basement and cut a large enough hole in the wall to get your tank inside.Then fill the hole in the wall and back fill or leave it as access to the basement with a poured retaining wall with steps,or frame walls and steps from PWF wood.


There are several reasons not to bury a heat storage tank including access but there is one stand alone reason not to that trumps them all. If there's any chance that moisture will come in contact with the tank it will lose it's heat to the ground. 
Any moisture will draw the heat away. 
This was one of the most important warnings in all the books in the early days of solar heating and storage. 
Any heat lost to the earth is lost forever.

Sent from my SM-G900R4 using Tapatalk


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## nhtreehouse (Feb 19, 2017)

While I myself would never bury an energy storage tank, the folks at Cold Climate Housing Research Center (CCHRC) in Alaska buried a 25000 gallon tank a few years back.

Here is a link to the video: , Inside CCHRC: Thermal storage

The idea here was to take what gassers do on a daily cycle and move it to a season cycle. That is, store solar energy in the summer and use it in the winter. I have no idea how it worked out for them.

More of a curiosity than anything else. I totally agree with the other comments - as soon as the buried tank gets wet, you're in trouble.

Chris


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## Fred61 (Feb 19, 2017)

They're probably still trying to get it up to temperature. 

Sent from my SM-G900R4 using Tapatalk


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## tom in maine (Feb 20, 2017)

A couple unpressurized tank comments.
Most tanks we make are 4' tall. We have made them up to 8' tall in smaller volumes. As tanks get taller, the cost rises due to increased strength requirements. That being said, 4' tanks stratify very well upon discharge. When charging they heat to one temp.
I have not see real concern with a 4' tank and the level of stratification. 

Of course, if you are heating hot water baseboard, you need higher temps. But if you are heating HWBB from storage, you are compromised in using your storage to its maximum potential. Radiant panels or radiant slabs or fan convectors make a lot more sense to draw storage down for the most btu's per firing.

Our heat exchangers hang in the tank. They do not sit on the bottom. They span the bottom to the top and are used for charging and discharging heat.
We have completely transitioned to stainless steel. It is lighter, less expensive and in most cases more durable than copper.

Using our tank is analogous to using a pressure tank, there is a connection for the top of the tank and the bottom.

The big difference is you can add heat exchangers or plumbing by simply popping the top. And we can and have made a lot of size variations
to match a customer's floor space.


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## mark cline (Feb 20, 2017)

Beagle Dad said:


> I went through a similar process to select a storage tank system. Maximizing the storage was important and given that I have radiant floor heating which is the majority of my load with a return water temperature of 90 Deg F a tall tank would be the best fit. The solution was 4 tanks in series for a total of 920 gallons. With this configuration the BTUs stored is maximized by having the greatest temperature difference for the available mass of water. When burning once a day the bottom of the tank stays around 90F and the top varies from 175 to 165 F.
> 
> See Idronics 17 which talks about usable heat. The best way to achieve this is to keep the top of the storage as hot as possible. My system has 4) 90" tall tanks which can have up 40 Deg F difference from top to bottom. Therefore a pressurized system was selected.
> 
> http://www.caleffi.com/sites/default/files/file/idronics_17_na.pdf


How did you pipe to the individual tanks to balance the flow and return ? Did you use balancing valves or stepped piping . I want to configure 3 -  435 gal tanks in parallel.


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## Beagle Dad (Feb 20, 2017)

mark cline said:


> How did you pipe to the individual tanks to balance the flow and return ? Did you use balancing valves or stepped piping . I want to configure 3 -  435 gal tanks in parallel.



My tanks are in series to create one every tall tank. The coldest water enters the bottom of tank 4. The boiler sends water to the top of tank 1.


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## sardo_67 (Sep 5, 2018)

tom in maine said:


> A couple unpressurized tank comments.
> Most tanks we make are 4' tall. We have made them up to 8' tall in smaller volumes. As tanks get taller, the cost rises due to increased strength requirements. That being said, 4' tanks stratify very well upon discharge. When charging they heat to one temp.
> I have not see real concern with a 4' tank and the level of stratification.
> 
> ...




i was going to go for the propane tank system but the more i look the better your system seems for me, this is my first house and first wood boiler system so something i can change around later on it needed seems better to me.  

i sent you guys an email


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## Chris Hoskin (Sep 7, 2018)

Beagle Dad said:


> My tanks are in series to create one every tall tank. The coldest water enters the bottom of tank 4. The boiler sends water to the top of tank 1.
> 
> 
> 
> ...


Beagle, how long have you been using your set up?  Is the parallel tank set up working as expected / are you pleased with the performance?


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## warno (Sep 10, 2018)

I have 3) 250 gallon LP tanks plumbed together for my storage. Each tank was 29" in diameter I believe it was.


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## sardo_67 (Sep 10, 2018)

warno said:


> I have 3) 250 gallon LP tanks plumbed together for my storage. Each tank was 29" in diameter I believe it was.
> 
> View attachment 229464




that's exactly what i have been looking for, just impossible to find the tanks unless i just go and buy new ones for around 1,100 each.

so the way you have yours plumbed there is an in on the bottom and out on the top?

is that where you have them or did you move them somewhere with insulation?


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## warno (Sep 11, 2018)

Here is how the flow runs through my tanks.







And here you can see my supply and return headers. My headers are 3" pipe. Each with 3) 1" connections.






And the water flows from tank to tank via a 2" 90° elbow that couldn't have fit better in its location. 






I built the stack laying on its side on my garage floor then stood up the bottom and middle tank as 1 unit and set the top tank on top while in location. I had my father help with a skid loader for all that. It was fun considering my stack is 93" tall and my garage ceiling is 96". And yes I did later box in the stack and insulated everything.


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## sardo_67 (Sep 11, 2018)

wow, very nice, i just wish i could fine tanks like that used around here in CT or even within a 2hr drive.  all i find are new ones for like 1100+.

i have 2 500 gal tanks now but they had diesel fuel in them for years, i cut one in half, cleaned it and tonight i am going to burn it clean, then stand them up on end and weld a flat piece on the open end making two 250 gallon tanks that will fit into my basement.  giant pain in the ass but it's all i have for options right now unless i drop thousands on other tanks.

i think 500 gal in 2 tanks plus the 55gal my HS tarm holds would be enough for my house, only 1600 sq feet and a 24x24 insulated garage with a 60k BTU modine heater, my goal is to run the boiler only once every 48-72 hours


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## warno (Sep 11, 2018)

I think you are going to need to burn alot more than every 2-3 days. I've got 750 gallons of storage and only heating a 21ft x 24ft garage and I was burning twice a day in the dead of winter. I mean the garage isn't fully insulated in the ceiling but still. I could go from 180 to 140 in 12 hours time in my storage. 

Also if you are putting a flat bottom on your storage tanks I hope they won't be pressurized. A flat bottom that big without stay rods will bulge out with less than 5 psi. Flat plate doesn't like pressure.


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## maple1 (Sep 11, 2018)

I need to burn for 6 hours each day. With 660 gallons.

Edit: and yes be very careful what you do to your tanks if there will be any pressure at all in them.


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## sardo_67 (Sep 12, 2018)

warno said:


> I think you are going to need to burn alot more than every 2-3 days. I've got 750 gallons of storage and only heating a 21ft x 24ft garage and I was burning twice a day in the dead of winter. I mean the garage isn't fully insulated in the ceiling but still. *I could go from 180 to 140 in 12 hours time in my storage*.
> 
> Also if you are putting a flat bottom on your storage tanks I hope they won't be pressurized. A flat bottom that big without stay rods will bulge out with less than 5 psi. Flat plate doesn't like pressure.



i didn't thing about that, would a cross with angle iron be enough to hold it?  they will be  a pressurized system.  I am going for this here in the attached pic, 2 tanks with my boiler and current oil boiler to run as needed either when not running the wood or fall/spring time when it's not cold enough to run the wood.

you were only heating the garage with that storage?  what temp were you going for and what was your heating source, radiant or a Modine type?
my garage will be set at 40* unless i am working in it and i also have a wood stove that i'll be running if i'll be in there all day or for an extended amount of time.
if heating is just too much then i'll have to stop heating it till i fully insulate the roof.

as for burning i'll see what happens, this is my first winter with a wood boiler so i'm sure there will be a steep learning curve, i am not expecting it to be that efficient right away but my end goal is to dial in the system so that i can feel it once a day or less.


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## maple1 (Sep 12, 2018)

Not sure anybody here can or will say that this or that is OK to do when it comes to cutting & welding an LP tank & changing its configuration. I know I won't - pressure vessels are engineered to stand the pressure. And the ends are rounded for a reason.

You can get a rough idea how long your storage will last between burns with a bit of math. 1 BTU is one pound of water one degree F. Work that math out using your tank capacity and high/low useable temps and compare to the heat load of your space. Which might need a heat loss calc - which there are online calculators for. I figure my 660 gallons stores about 225,000 useable BTUs, depending how hot I charge them. That's not much heat loss spread over 24 hours. Even 20,000 btu/hr is a pretty low figure - so mine would only get about 12 hours +/- with no fire at that load.


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## sardo_67 (Sep 12, 2018)

i have seen that before, does tank insulation come into play at all?

or does most of the cooling come from sending the hot water tru the heating devices in the house?


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## maple1 (Sep 12, 2018)

Your house needs heat. It would come from the boiler or tanks. And tanks only hold so much heat.


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## airlina (Sep 12, 2018)

I burned my Econoburn boiler for 5 years  before I realized the advantage and convenience  of adding storage to my system. To help me in this pursuit, I enlisted the help of these guys at www.hydronicspecialtysupply.com to do the transformation on a 500 gallon used up propane tank I found at a local suppliers yard. I transporter the tank to them and they took it from there. Pictures tell a better story than I can, so I will let them do the talking. The completed tank has performed very well since installing it in my system and I now can utilize my wood boiler the way it was intended.


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## sardo_67 (Sep 12, 2018)

airlina said:


> I burned my Econoburn boiler for 5 years  before I realized the advantage and convenience  of adding storage to my system. To help me in this pursuit, I enlisted the help of these guys at www.hydronicspecialtysupply.com to do the transformation on a 500 gallon used up propane tank I found at a local suppliers yard. I transporter the tank to them and they took it from there. Pictures tell a better story than I can, so I will let them do the talking. The completed tank has performed very well since installing it in my system and I now can utilize my wood boiler the way it was intended.




oh wow!   are you selling that on CL right now?  i saw a dual 500gal tank system on there last week out in mid/western NY.

my issue is the idiots who built my house made the ceilings 7ft 3 or so, basement as well which greatly limits my storage capacity, plus my house isn't that big to begin with and horizontal 500s won't even fit into my basement thru the bilco doors.  hence why i was going to cut these down.

then i made the mistake/ran out of patients and bought 2 tanks that had been used for fuel storage for decades.  

i am in CT and can't find anything unless i buy brand new at over $1,000 per tank, all of the gas places near me won't sell out of date tanks, the scrap yards near me won't sell the scrapped tanks as i need a scrap license.  this is all becoming very aggravating.

I started burning the tank i opened up to clean it and it has worked well i will see about shortening it then rewedding it so i have the correct rounded ends then use vertically.


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## maple1 (Sep 13, 2018)

Have you checked out American Solartechnics tanks? They are modular. A break down box that you assemble then line with a liner. It's an open tank but you can use heat exchanging coils for your pressurized system. I think they can build a tank/box to fit your space.

I am quite sure my 330s would fit into that space also. Or mutliple 100's.


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## salecker (Sep 13, 2018)

sardo_67 said:


> then i made the mistake/ran out of patients and bought 2 tanks that had been used for fuel storage for decades.


I don't think you made a mistake getting those tanks.The residual fuel in them is easy to clean,you have to alter them or any tank to fit in your space.You got them cheaper than your alternative.
A little elbow grease and you will be good to go at a fraction of the cost.
I got old propane tanks and they needed to be cleaned on the inside as well.10 min with a pressure washer did the trick.
 As for cutting and welding the tanks,others have done it.If you are standing the tanks on the flat end that you are welding on that should help with the pressure against the flat plate.If you are worried about the chance of it bulging,go to a scrap yard and find some 1/2" plate to use as the new bottom,or thicker,add some cross bracing like you said,and i would be satisfied if it was going in my basement.


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## maple1 (Sep 13, 2018)

Seems I remember reading somewhere on here sometime before about someone cutting the end off their LP tank, then flipping it over & welding it back in again. So the curve was inside the tank. Then they stood it up on that end. That was a while ago & don't know how it worked out, and it likely added way more stress to the tank where it was welded back together than the original tank design resulted in, with the curve like that. But may have still been OK? Need to be very competent & thorough with the welding for sure, however, no matter what the reconfiguring is that's being done. I was also thinking from the other pics you posted that they looked thinner walled than typical LP tanks, but can't really tell by pics sometimes.


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## warno (Sep 13, 2018)

maple1 said:


> Seems I remember reading somewhere on here sometime before about someone cutting the end off their LP tank, then flipping it over & welding it back in again. So the curve was inside the tank. Then they stood it up on that end. That was a while ago & don't know how it worked out, and it likely added way more stress to the tank where it was welded back together than the original tank design resulted in, with the curve like that. But may have still been OK? Need to be very competent & thorough with the welding for sure, however, no matter what the reconfiguring is that's being done. I was also thinking from the other pics you posted that they looked thinner walled than typical LP tanks, but can't really tell by pics sometimes.




I remember that as well, but also can't remember who did it or the end result. It's on here somewhere though.


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## sardo_67 (Sep 19, 2018)

after looking at stuff i am going to use both thanks and shorten them by re-welding the rounded end on the shorter body bringing the OAL of the tank with legs to 6ft even leaving me about 12" of clearance in my basement for insulation.


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## jeffesonm (Sep 20, 2018)

Sardo - A bit of a drive but there's a guy just north of Philadelphia who sells 220 gallon tanks for $150 each.  I bought a few to use for storage but never got around to installing my boiler.  More info here Looking for some input on storage


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## sardo_67 (Sep 20, 2018)

jeffesonm said:


> Sardo - A bit of a drive but there's a guy just north of Philadelphia who sells 220 gallon tanks for $150 each.  I bought a few to use for storage but never got around to installing my boiler.  More info here Looking for some input on storage



yes i found those as well, however it was AFTER i got my tanks, plus those are 1/2" thick and almost 1,000 pounds.  

I'm not thrilled with the tanks i have but i'll have to make them work


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## sardo_67 (Oct 17, 2018)

did someone here say they have a PDF file on how to calculate the exact volume of the a tank that has been cut down or modified?


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## warno (Oct 17, 2018)

Just do the math on what you cut out.

3.14 x R^2 x length cut out in inches.  Then divide by 1728 and multiple by 7.48. This will give you gallons removed from your tank.

So if your tank was 30" round and 6 feet long and you cut out 24".

3.14 x 225 x 24 = 16,956

16,956 ÷ 1728 = 9.812

9.812 × 7.48 = 73.39

So that would be 73.39 gallons removed from your original tank if those were your measurements.


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## sardo_67 (Oct 17, 2018)

oh hahah ya i didn't think about that, i was on google doing conversions and cubic inch conversions on the dome ends when i could have just done the area of the section i REMOVED......

ya my tanks are 280-300gal tanks.

i was over thinking that, my bad


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