# Is EPDM for tank liner a catch-22?



## Rory (Jan 13, 2009)

I sure hope not, because I just started using my home-built tank-n-Tarm system.  But, the real question involves storage strategy.  The liner supposedly shouldn't be regularly heated beyond 170F, yet that is precisely the temperature at which my plumber claims my baseboards really do their thing well.  Wouldn't we want to heat a bit beyond ideal and cool down not much below it?

For example, last night I elected to not stoke anymore wood because my tank had reached precisely 170.  When I woke up this morning, it was down to 140.  I wasn't confident that 140 would be enough to keep my house warm all day, so I had another fire this morning, and the evidence indicates that that was probably a good decision.

I guess I'm wondering what temperature regimes are typical for effective heating of a typical house in a cold climate.


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## NHFarmer (Jan 13, 2009)

I have 1000 gallons of storage with an EPDM liner.I run my tank up to 170*-175*.I have gotten up to 180*,but that has been my max so far.I also load with smaller loads as I start to reach my desired temps.You can also turn down your thermostat on the Tarm and just let it idle.You will loose some efficiency but you will be able to extend your burn time


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## pybyr (Jan 13, 2009)

this is the reason I decided to launch into a one-off 409 stainless tank; 

the delta -T between the max temp of your tank and the minimum effective output temp of your heating system defines the useful capacity of your storage

the closer to boil you can push your storage (which you cannot do with EPDM), the greater net effective heat storage you can acheive


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## Vtgent49 (Jan 13, 2009)

I run 140 thru my baseboards all the time. Depending on ambient temp and the load it may be plenty. You'll have to develop a feel for it.


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## Dave T (Jan 13, 2009)

The more BB you have the lower temps that you can run, if your house is like mine 160 and above is ideal but again I can install more BB and heat with cooler water..Dave


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## Nofossil (Jan 13, 2009)

I run my baseboards all the way down to 120. I'm adding a radiant zone for the main floor to allow me to use water down to 100 or so to extend my storage. I have a stainless unpressurized tank, and I rarely get it above 170 at the top.

At lower water temps the baseboards can't keep up if it's very cold outside. For that reason, I plan my fires for late in the evening so that I'll have the hottest water at the coldest time of the day. I also heat the house 2 degrees warmer when I'm heating direct from the boiler vs. when I'm heating from storage.


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## stee6043 (Jan 13, 2009)

I'm able to heat with a water-to-air HX all the way down to 120ish on warmer days (upper 20's, lower 30's, a little sunshine).  But once I hit low 20's and below my furnace has to run non-stop with the cooler water.  180 degree water running through the furnace is prime.  If I could keep my tanks above 160-170 24/7 I would be in heaven...


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## Eric Johnson (Jan 13, 2009)

Consider that EPDM is used for roofing, where I'm sure surface temps exceed 170, especially in the South, on a regular basis. And those roofs last for 20 years or longer, and see a lot more abuse than a tank liner. Just a guess, but I think the 170 spec (I thought it was 180) is probably a tad conservative.


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## Grover59 (Jan 13, 2009)

I get my tank up to 165 most of the time, however the reason I installed radiant heat is because I can get a lower tank temp and still heat the house, I do use my baseboard and it will keep the house warm even at 140* but may not take  the house up to 70* The radiant floor heat gives me alot more useable BTUs out of my tank, and is more comfortable at lower temps. The way I have my system set up now is the circulator on my baseboard will only kick in if my boiler loop between the oil boiler and wood boiler is up to 180* and this is only when my wood boiler is fired and running. Most of the time I start a fire when I get home at about 5:30 or 6 and the base board will just start working once the loop gets to 180* all the rest of the day the house is heated with only the tank by the floor heat or my forced hot air set up. Because no one is home during the day we do set the temps back to 65 just to save a little, this so far has worked very well. I have been using nofossils burn calculator to set up my burn time and it works well, say if I have my tank at only 150 I can look at the calc for the next 8 hours or so just to see if I would have enough btus to get by until I get a chance to start a fire, I have skipped fires based on that calculator, and came home to see that my tank temp was just about where I thought it would be. Thanks Nofossil

Steve


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## Nofossil (Jan 13, 2009)

Maine said:
			
		

> I have been using nofossils burn calculator to set up my burn time and it works well, say if I have my tank at only 150 I can look at the calc for the next 8 hours or so just to see if I would have enough btus to get by until I get a chance to start a fire, I have skipped fires based on that calculator, and came home to see that my tank temp was just about where I thought it would be. Thanks Nofossil
> Steve



Geez - somebody's using it! I guess I won't take it down.....

I'm glad it's helpful to others. I use it every day, and it's pretty darn good once you get the heat loss factors dialed in.


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## Grover59 (Jan 13, 2009)

nofossil said:
			
		

> Maine said:
> 
> 
> 
> ...



Yes when I got the right numbers in it was very close, I did modify my heat loss a little, is this written in perl on your server?

Steve


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## DaveBP (Jan 13, 2009)

This thread is a good illustration of why it is so difficult to answer the frequent question "How much storage do I need?".

Different heat emitters work best and are sized to work at different temps. 

Baseboard is the most problematic for wood boiler/heat storage systems, both because it is so common and typically is expecting the highest temps. Those buildings that heated adequately on the coldest nights when supplied by fossil fueled boilers @ 180F are going to struggle when the woodboiler storage tank temps drop below that. 
For this very reason, some on this forum are being wedged into a cold corner now that January is doing its stuff.

While this is an argument in favor of pressurized storage ( it can be used to higher temps ) it's no help for those who already have unpressurized rubber-lined tanks or simply can't get a steel pressure vessel into their basement (not everyone is so eager to put another taxable structure in their yard).

If you can't get enough heat out of your storage tank to use with the baseboard you have you can simply put in more baseboard. A very well known radiant heat designer here in Maine uses regular Lowes Depot finned-tube baseboard where radiant heat can't be installed. He uses them down to 110F. It requires using more than double the linear footage but that can get a lot of usable BTUs out of you storage tank. Back in the glory days of local town dumps (sigh) you could find usable baseboard piled up for the taking. No longer free but it's still relatively cheap. For lower temp usage it's best not to install them one over the other up the wall.


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## tom in maine (Jan 15, 2009)

I think EPDM has proven itself over the years. However, there are so many variants out there, that I think some EPDM pedigree would be nice to have for heat storage.
There are a lot of additives that can be put into roofing material that might not be very good for a storage tank for long term water storage.
Occasional roof wetness is a little different than a fully wetted tank that goes to 170 or 180 every night.
That being said, EPDM is everywhere and is reasonably priced.
I am somewhat concerned about longevity, both of the EPDM and its breakdown and how it affects copper heat exchangers.
Once again, you need to buy a liner from someone who knows about the use and has some track record.
I guess there are not too many people out there who have used EPDM for long enough to answer that question. And there is also an issue as to what the EPDM
was produced for.
The issue with the wood boiler storage marketplace is that it is a tiny, tiny market when it comes to EPDM. I suspect not many people are producing for us.

That being said, it does work. For how long and how hot, we get to figure that out!


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## BioHeat Dealer Guy (Jan 15, 2009)

we recently had a customer who had been using an EPDM lined tank for seven years that was now weeping.  He had regularly run his tank to 180+* and the liner had become soft - kind of breaking down a bit - in some places.  As I understand it we would normally expect at least a ten year lifespan out of the EPDM liner with lower temps.  This is only one example, but gives some insight, I hope.

Others have mentioned the argument for pressurized storage - pros and cons - and I agree.  I would also like to point out that our square tanks offer a welded and fitted PVC liner that is more tolerant of higher temps in an unpressurized storage tank.  Not so accessible to DIY'ers though, I guess.

One last thing is that the tank/heat storage system is not typically playing a major role in the heat delivery during the coldest days of the year when highest water temps are required.  Most if not all of the heat being generated would normally be going straight into the house with a much more frequent wood loading too.  Is this what people are typically seeing?


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## free75degrees (Jan 15, 2009)

This whole epdm issue is my only concern/regret with how I set up my system.  In the end I am not sure if I had any other options though.  Are there any other options for the do it yourself tank builder with the constraint that the parts have to be small enough to fit through a standard doorway?  The only other thing I can think of, and I wish I has pursued, was a solid concrete storage mass.  Concrete has half the heat capacity as water per volume, but I'd be willing to make it twice as large if it meant that I'd never have to worry about it again.  My thought is a large mass of concrete with 1/2" embedded pex and with no more than 2 or so inches between each run of pex.  I'd also add lots of strips of aluminum flashing embedded in the concrete to help spread the heat.

Anybody ever do anything like this?  Any thoughts on whether it would work?  I definitely push my tank to 180* so if it starts to weep in 7 years I may do this.


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## BioHeat Dealer Guy (Jan 15, 2009)

free73, I don't think you should have serious regrets about having used EPDM.  We have sold lots of tanks for years with EPDM liners.  From a price / practicality perspective for the DIY'er, I think it's hard to beat.  Also not too bad to replace when the time comes.

As far as your concrete storage mass, my only comment would be that I don't think concrete and aluminum go well together(?).  With the kind of spacing you are talking about for the PEX, I doubt you would have any heat transfer problems.  Very cool idea.

Chris


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## WoodNotOil (Jan 15, 2009)

free73degrees said:
			
		

> This whole epdm issue is my only concern/regret with how I set up my system.  In the end I am not sure if I had any other options though.  Are there any other options for the do it yourself tank builder with the constraint that the parts have to be small enough to fit through a standard doorway?  The only other thing I can think of, and I wish I has pursued, was a solid concrete storage mass.  Concrete has half the heat capacity as water per volume, but I'd be willing to make it twice as large if it meant that I'd never have to worry about it again.  My thought is a large mass of concrete with 1/2" embedded pex and with no more than 2 or so inches between each run of pex.  I'd also add lots of strips of aluminum flashing embedded in the concrete to help spread the heat.
> 
> Anybody ever do anything like this?  Any thoughts on whether it would work?  I definitely push my tank to 180* so if it starts to weep in 7 years I may do this.



Concrete doesn't last forever either and I would be skeptical of what would happen to it over time expanding and contracting.  It would definitely last longer than an EPDM liner (no question about that), but in the end would be much harder to get rid of and replace.  Imagine what someone 50-100 years from now would have to deal with.  Also, I think it is much slower in transferring the heat when you try to draw it back.  

As a side note I am the 8th generation of my family to live on my land and we have to deal with several concrete structures from the 30s and 40s that are large crumbling messes taking up space.  Most of them have to do with cisterns for holding water.  Think about your legacy when building things of concrete.  Especially big things.  We are often short sighted in our building techniques these days.


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## steam man (Jan 15, 2009)

free73degrees said:
			
		

> This whole epdm issue is my only concern/regret with how I set up my system.  In the end I am not sure if I had any other options though.  Are there any other options for the do it yourself tank builder with the constraint that the parts have to be small enough to fit through a standard doorway?  The only other thing I can think of, and I wish I has pursued, was a solid concrete storage mass.  Concrete has half the heat capacity as water per volume, but I'd be willing to make it twice as large if it meant that I'd never have to worry about it again.  My thought is a large mass of concrete with 1/2" embedded pex and with no more than 2 or so inches between each run of pex.  I'd also add lots of strips of aluminum flashing embedded in the concrete to help spread the heat.
> 
> Anybody ever do anything like this?  Any thoughts on whether it would work?  I definitely push my tank to 180* so if it starts to weep in 7 years I may do this.



I think the biggest problem you'd face is that concrete would probably not like the temperature cycling and especially higher temps of up to 180 F. There are electric boilers that use off peak rates to store heat in high temp ceramic mass. Forget the aluminum plates. They would probably just corrode.

Mike


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## tom in maine (Jan 15, 2009)

A thicker slab or storing heat under a slab is a very valid concept. You cannot heat it much over 120, without comfort/concrete degradation issues.
However, a small temp swing in a massive slab yields a very large storage effect, much larger than most tanks. Obviously, you must set it up to not thermally shock
the boiler, but it has some legs. Do the math. You can assume the specific heat of sand or concrete at about .2


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## free75degrees (Jan 15, 2009)

Ok, so i think i am being convinced that concrete is not so good.  I would have tried to do it mostly under my basement slab to avoid the issue of a huge chunk of nuisance concrete 50 years from now, but the high temp degradation concerns me.  However, maybe degradation doesn't matter in this case.  If it is all below grade so that the concrete does not need structural integrity, maybe some cracks and crumbling would matter.  It might reduce the heat transfer a bit.  I dunno.

How about sticking to water and an alternative to epdm?  Can anybody think of an easy wat to attach sheets of metal to form a good, permanent seal?


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## DaveBP (Jan 15, 2009)

Using any affordable solid for storage will always run up against 2 disadvantages.

The first one is thermal conductivity. How fast the heat can be drawn away from the supply water from your boiler. Fast enough to keep your boiler from idling its life away? Fast enough to supply the heat demands on these January nights?

 But even if you had a 20 ton block of copper cast around your copper heat exchanger tubing you would still encounter the very great advantages of water. With careful design it can stratify as it stores heat and remain stratified as it gives up heat to the loads. With any solid ( assuming it can conduct the heat fast enough) you will have the temperature of storage rising evenly throughout with the amount of heat stored. The hotter the storage the lower the temperature difference between the boiler and the return water from storage. So it becomes harder to extract the heat from the boiler as the burn continues. With a stratified liquid the hottest fills in at the top and squeezes the coolest at the bottom out to return to the boiler because they don't mix. You have the coolest water returning to the boiler for the most efficient heat transfer out of the boiler up until the end when the hot water makes it down to the bottom and the tank is full of hot water. How perfectly this works depends on lots of variables but that's the ideal.

When you throw in the fact that water is still pretty cheap and stores more heat per pound (or per kilo if you use metric water ) than almost any other material around... water looks pretty good. If it just didn't have the nasty habit of looking for a place to leak it would be almost perfect. 

There are materials called eutectic that can throw in some extra heat storage per volume into the design. If you had one that liquified at 160F or so you could store more heat at the higher temps that baseboards prefer but they are expensive and maybe corrosive. I haven't followed that stuff for decades now.

Water is pretty much where it is at. But the image of a 20 ton block of copper is awesome, isn't it?


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## leaddog (Jan 15, 2009)

years ago I built a HASHA which was a fire box surrounded with sand enclosed with concrete. The fire box had a steel top on which there was a copper hx going up into the sand. The spacing for the tubes were about 6in and there was also a pvc hx with 6in spacing about 6in above the fire box top. The whole thing was about 8ftx8ftx8ft. I insulated it with fiberglass and blown insulation 10in thick. The instructions said to build SMALL fires as the heat transfer was slow. I need more heat than I was getting so I started to build larger fires. Pvc WILL exspand to the size of a softball at 20lbs pressure and leak. My temp. just above the 4in layer of sand got to be 220* and the sand wasn't able to absorb the heat fast enough. Ended up taking the pvc out, putting in all copper. I did work but you need a fire going most of the time and getting the heat out wasn't fast either. I had to shut it down when I got a leak in Jan and the middle of the tank was still over 50* in May. Water still is the easiest to work with. 
But on the same thought if you wanted to build a huge heat sink under the floor and could insulate it with out having any water infiltrating the insulation it could be done but you would need lots of pex and would take a long time to get up to heat. You would have to keep the temp down but with alot of thought it might work BUT if you had problems I wouldn't want to be the one digging it up and reengenering and repairing. It would be a one time thing and hope it works.
leaddog


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## Fred61 (Jan 15, 2009)

I built a passive solar house in 1980 with 360 sq. ft. of site built collector in the roof. Heated air was ducted down into the basement and pushed through 1000 concrete blocks laid on end and back to the collector. Bear in mind now this was the whole floor. On top of those blocks was about a foot of concrete with six inch duct work laid in it about every two feet. Total weight estimated to be about 50 tons. The whole idea was to capture the heat from the collector with the blocks and run the house air through the ducts, thus tempering the living space air when the living space was overheating during the day and bring it back when the house started cooling.
It worked to a certain extent! The problem was that I couldn't transfer the heat fast enough either in the heating cycle or the retrieving cycle. The air from the collector came down at about 140* and returned at about 139.9* and the house air stayed too warm on the storage cycle and wouldn't grab enough heat on the warming cycle. Concrete is a poor conductor. 
Water is the standard and has a specific heat of 1 and everything else (with the exception of some eutectic salts) is less than 1 and it is a good conductor.
Eutectics have been used in some experiments and in some wealthy person's projects but with the high price and still having the problem of conducting the heat toward the salts remains a problem. Eutectics are usually sealed in a pvc or other plastic tube and some medium, whether air or water must carry the heat to them. Water will probably still be used because these phase changing salts usually freeze at 100*f to 130*f and it takes a temp of a little higher than that to turn the salts into liquid in the storage phase.
The only advantage is a lot of storage in a little space. Not worth the money!


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## DaveBP (Jan 15, 2009)

> How about sticking to water and an alternative to epdm?



The Holy Grail of unpressurized heat storage. 

There are polypropylene tank liners that take higher temps than EPDM. Way more money and not as flexible. Shipping is more complicated if something that large can't fold down neatly. It's industrial stuff.

You could look into welded stainless steel sheet metal. I spoke with a guy at a maple syrup equipment manufacturer about it. They make thin stainless sheet metal tanks all day long. You would need to build the frame around it to take all the weight of the water same as rubber and shipping would be expensive if you didn't pick it up yourself. But if would take any temp and last a long, long time. You could have welded fittings that won't leaks put anywhere you want. I never got any price quotes. I came up with some propane tanks.


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## Fred61 (Jan 15, 2009)

Wanna stanless tank? How much do you want to spend? One call to these guys ad you'll have a quote the same day and have a photo of the tank. You decide if the price is worth it.

http://www.jlmercer.com/

I've talked to polypropylene tank manufacturers and they say they will tolerate the heat but they run about twice the price of polyethylene.


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## tom in maine (Jan 16, 2009)

The issue with rigid polypropylene tanks is the potential stress loading. A number of people over the years have used them for solar storage.
Unfortunately, they can stress crack over time. A generalization is that plastic can tolerate temperature or pressure, not both together.
That is a broad generalization, that you might overcome with expensive plastics, which we cannot afford.

I have sold tank liners for rigid tanks that have stress cracked from heat stress. The bottom of any tank over two feet deep is taking a tremendous load.
An 820 gallon tank has about 7,000 pounds of water in it. All that weight loads the lowest area of the tank walls.


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## jebatty (Jan 16, 2009)

On the concrete tank idea, if also (you probably thought of this) you put 3/8" or 1/2" rebar between most of the pex lines, you may get a stronger tank and more heat transfer. Just an idea.

The best IMO is the new or used propane tank. My 1000 gal used propane tank is problem free. But it is a beast.


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## free75degrees (Jan 16, 2009)

I like the idea of the solid copper block heat storage.  While I am at it i think i may swap out my refractory bricks for diamond bricks, cause I heard they last forever ;^)


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## WoodNotOil (Jan 16, 2009)

jebatty said:
			
		

> On the concrete tank idea, if also (you probably thought of this) you put 3/8" or 1/2" rebar between most of the pex lines, you may get a stronger tank and more heat transfer. Just an idea.
> 
> The best IMO is the new or used propane tank. My 1000 gal used propane tank is problem free. But it is a beast.



Having read a lot in the boiler room, I agree that if you have the room and access to put in pressurized storage it is probably the way to go.  If you don't have access, I still think EPDM lined tanks are a good alternative.  The slightly lower temp can be overcome by sizing the tank slightly larger and by altering the zones to perform better with lower temp water.  I have no complaints so far with my homemade tank and fully expect to have to replace the liner at some point in the future.  I have a few tweaks to do to the way it connects to the heating system, but that comes with the DIY territory.


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## free75degrees (Jan 16, 2009)

jebatty said:
			
		

> On the concrete tank idea, if also (you probably thought of this) you put 3/8" or 1/2" rebar between most of the pex lines, you may get a stronger tank and more heat transfer. Just an idea.
> 
> The best IMO is the new or used propane tank. My 1000 gal used propane tank is problem free. But it is a beast.


Yeah i'd live a propane tank but i can't get one into the basement.  Plus I'd have to abandon my expensive copper coils.

Well I have at least several years to think about it.  I just hit 181 at the top of the tank last night, which is typical, so i think I'll have to do something different eventually.


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## free75degrees (Jan 16, 2009)

DaveBP said:
			
		

> With careful design it can stratify as it stores heat and remain stratified as it gives up heat to the loads. With any solid ( assuming it can conduct the heat fast enough) you will have the temperature of storage rising evenly throughout with the amount of heat stored.



I think the aspect of a tank that allows stratification is the fact that heat always enter at one place and leave at another while charging and reverses while discharging.  I see no reason why this would not work with a solid heat mass.  I bet you could even make the heat separation happen horizontally.  If one really wanted to take the concept far, one could make a series of separated heat masses - the 1st one would always be the hottest and the last one would be the coolest.  There was some discussion about water stratification in a previous thread where it was argued that water does not stratisfy on it own like a column of air might.  Instead water would lose its stratification over time.  The density difference between hot and cold water isn't enough to cause stratification.  Water may lose its stratification slower than a mass of concrete, but i am not so sure.  Water has the density difference working in to its advantage - i.e. even though density is not enough to cuase stratification, it probably helps a bit to maintian it.  However, any solid with lower heat conductivity than water would have the lower conductivity in its favor.  Which of these two advantages is greater is unclear to me.  It's a very interesting discussion anyway.


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## DaveBP (Jan 16, 2009)

As long as we're kicking this around and because the coffee isn't done yet...

 I have a problem mixing up my mental models of storage tank operation. Water storage can be done in at least 4 different configurations that I can think of so there must be more than that. Pressurized and closed, unpressurized and open are the two main categories kicked around in this forum. How each of those are plumbed effects the details of how it works but the principles are the same.

Water or air will stratify on their own (if you mean not being pushed by a pump) as long as heat is being added or extracted. You could have an open tank with the boiler supply coils wrapped around the outside, not in the liquid, and the warmer liquid will end up at the top. It's better to say the colder liquid will settle to the bottom. HEAT DOES NOT RISE!. Colder, denser liquids or gases settle down because gravity pulls it down. It's the denser material being pulled down that pushes the warmer less dense material up. Sorry, just one of my pet peeves... Which is why you're right; you could 'stratify' a solid mass horizontally; or  upside down/hot on the bottom for that matter. But I will bet this cup of coffee that I just poured that if a tank of carefully stratified water (or air ) were insulated very well and just allowed to sit, it would lose its stratification and be the same temperature throughout. Might take a while. I don't know how long.

Yes, fascinating topic. Glad I found some propane tanks so I know which direction I'm headed. And I'm glad I put that 44" wide door into the basement.


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## Der Fuirmeister (Jan 16, 2009)

free73degrees said:
			
		

> This whole epdm issue is my only concern/regret with how I set up my system.  In the end I am not sure if I had any other options though.  Are there any other options for the do it yourself tank builder with the constraint that the parts have to be small enough to fit through a standard doorway?  The only other thing I can think of, and I wish I has pursued, was a solid concrete storage mass.  Concrete has half the heat capacity as water per volume, but I'd be willing to make it twice as large if it meant that I'd never have to worry about it again.  My thought is a large mass of concrete with 1/2" embedded pex and with no more than 2 or so inches between each run of pex.  I'd also add lots of strips of aluminum flashing embedded in the concrete to help spread the heat.
> 
> Anybody ever do anything like this?  Any thoughts on whether it would work?  I definitely push my tank to 180* so if it starts to weep in 7 years I may do this.




Thermal storage is a big advantage of in-slab radiant heat with PEX.  Wish I had installed it in my home when we built.  We installed it in our shop.  You still need to insulate under the slab.  Water has so many advantages over concrete that I would not consider concrete over it.  How much does a EPDM liner cost vs. all the required PEX tube?  How hard to replace (once every 10-20 years)?

If available a silicone material liner might be considered, but I'll bet the cost / benefit ratio would lead you back to EPDM.

What about fiberglass over EPDM?  Has anyone tried this?


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## Der Fuirmeister (Jan 16, 2009)

DaveBP said:
			
		

> As long as we're kicking this around and because the coffee isn't done yet...
> 
> ... HEAT DOES NOT RISE!. ....




Don't tell that to a hot air balloon pilot.


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## jebatty (Jan 16, 2009)

> What about fiberglass over EPDM?



Several threads on this - a search would reveal lots of discussion.

Reference:
http://www.proco-fwi.com/pdf_files/selecting.pdf


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## DaveBP (Jan 16, 2009)

> Don’t tell that to a hot air balloon pilot.



The hot air balloon pilot knows that hot air that is much less dense than the surrounding air will rise through that surrounding air until it gets to the altitude where the air density is the same as the hotter air inside the balloon. The air up there is way colder than the air down at lower altitude. That doesn't mean that heat sinks.
Heat and hot air, two different things.


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## pybyr (Jan 17, 2009)

free73degrees said:
			
		

> DaveBP said:
> 
> 
> 
> ...



hmm- not sure I know the definitive answer, but if what you assert is true, then how is it that many stationary and Ag engines up until roughly the 1940s or 1950s made do with no water pump, relying solely on thermosyphon for coolant circulation, 

and how is it that ponds and lakes go through certain seasonal turn-overs at certain times of year based on the difference between the prevailing temperatures at the surface, where they contact the air, and the underlying earth/ rock?


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## Der Fuirmeister (Jan 19, 2009)

DaveBP said:
			
		

> > Don’t tell that to a hot air balloon pilot.
> 
> 
> 
> ...




Guess I should have put one of those smiley faces on my attempt at a joke so that everyone would get it.......

I've been a pilot for 22 years, and well aware of the principles of flight.


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## DaveBP (Jan 19, 2009)

> Guess I should have put one of those smiley faces on my attempt at a joke so that everyone would get it.......



I had an inkling that there was an invisible smiley there. I'm a little touchy about certain basic physics concepts. The result of too much righteous indignation about the education system in this country. Sometimes I drop into lecturer mode and make a nuisance of myself.

This forum has taught me no end of new applications for old physics. Downright fascinating. I hope to understand more than 1/3 of it someday.

 Makes me want to defend it from misinformation, sometimes. I've noticed it has the same effect on others, too.


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## mwk1000 (Jan 19, 2009)

When I was planning a pond outside I looked into spray on polyUrea a material similar to truck bed liner. I was pretty neat in that you just needed a smooth surface and it made a very durable and elastic covering. It is being used in many comercial tank resurfacing projects. You can have someone from the pond industry do the spray. For a 1000-2000 gal tank the cost might be reasonable, It was a bit high for my 40x60 pond so I did EDPM. 

I was not as concerned since I am doing well at 170-100 range with my tank. I will reline it at the first sign of moisture, it is not that hard to do.

You might check on the temperature tolerance for PolyUrea as a possible DIY liner sprayed right on wood, insulation, concrete, whatever. I know it is health enough for KOI fish ( and they are pretty picky critters )

Google polyurea and you will get a bunch of data. Might be worth looking at as the application systems are becoming much more DIY frendly.

Update, I looked and while some are only rated for 175 * F there are others rated to 250* F "Polyshield HT" was one I found with a high temp rating.


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## Fred61 (Jan 19, 2009)

I talked to the people at Herculiner, the do-it-yourself bedliner and they gave me a maximum high temp rating of 230*. They did specify "water only" no chemicals. Im considering coating a 500 gallon steel tank with it.


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## mwk1000 (Jan 19, 2009)

Interesting since one of the things particularly good about polyurea is its resistance to chemicals, However many of the bed liner products are not polyurea. Not sure about Herculiner. You can probably get the material saftey sheet for it and get more detail.


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## Fred61 (Jan 19, 2009)

Perhaps it's the rubber chips suspended in the material or perhaps chemicals-OK --- heat-OK but chemicals and heat-NO.


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## free75degrees (Jan 19, 2009)

I used herculiner in my truck and it sucks.  It dries out and gets all powdery and if you brush against it you get black crap on you.  And it is wearing down to nothing in some spots now.  Maybe this is due to the sun, but i would never buy it for a truck again.


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## Rory (Jan 19, 2009)

The top of my tank's 170 right now, so I decided not to stoke.


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## peakbagger (Jan 19, 2009)

I used to have flat industrial roofs done on occasion and over the years, I switched over to white PVC as the EPDM didnt seem to last in a pulp mill environment. Plus the white PVC kept the temp in the buildings a little lower as it reflected heat in the summer. The roofer that did the work brought it over in rolls and heat bonded the seams, with a pretty simple resistance heating device (basically an electrically heated roller). He used an IR thermometer to check the temp on occasion and would do test strips every few rolls. When a load was applied to the strips, the material would fail rather the joint. A similiar product was used on an "inside out" roofing system for specialized applications over heated damp processes (like papermachines) where the roof temps could exceed 140F. The PVC was laid down directly on the roof decking and then heat welded to roof drains, then insulation blocks topped with concrete were set on top of the roof. The roof systems had a 20 year guarantee.

This leads me to believe that a PVC liner would work and if you find the right roofer, he might be able to make you up a liner fairly quickly. Its been several years but Gracie Roofing out of St Johnsbury VT was the one that did the roof work.


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## tom in maine (Jan 20, 2009)

We use high temperature PVC for our liners that is custom made for us. Many vendors tell me that their material, PVC, PVC alloys and the like with stand up to 180+F. 
I would be very careful trying to use roofing material in a tank environment. A roof that is occasionally wet and occasionally hot is a lot different than a tank that is up to temp every day during the heating season. Welds also have to withstand a lot more pressure than some simple ponding that occurs on a flat roof or a parapet.
Liner welding is more of an art for liners than it is for roofing!

That being said, we have researched materials for over 30 years trying to find the most appropriate material for this application and for solar tank applications.

One bit of advice, being the first one to use something new for a tank liner carries the potential for leaks. That is from experience. Expensive experience.
The reward might be great, but the failure sucks. 

If you want to use a readily available liner, EPDM is a reasonable DIY material. Use 60 mil. And treat the water regularly since EPDM does do funny things to water over time.


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## mwk1000 (Jan 20, 2009)

Treat the water with what ? That is something that has been on my mind since I will have to do something soon.


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## tom in maine (Jan 20, 2009)

To be honest with you, I am not sure.(I want to say baking soda, but that is from the foggy recesses of my memory!) I believe the pH needs to be a little basic. I am sure others here know better than I.
We do not use EPDM for our products.


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## flyingcow (Jan 20, 2009)

mwk1000 said:
			
		

> Treat the water with what ? That is something that has been on my mind since I will have to do something soon.



while researching what i wanted for a heat system, I talked to STSS that supplies the epdm lined tanks for tarm, and it was mentioned to check water for ph. At least I think that was it. Contact STSS.


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## flyingcow (Jan 20, 2009)

I'm using the square tank you see in tarms website. PVC liner, works great,hx heat coils transfers heat very well(haven't hooked up the dom coil yet). Easy set up. I liked the idea of having to not watch my water ph(and yes its baking soda that will effect ph, or you can get a little better grade from pool supply house) and not having to be so careful about trying to stay below 170/175. If I had the option of using anything else, I would have located my storage in the garage and used an old S/S milk tank from a dairy farm. These will be discarded because of problems in the freon system developing a leak. But it will hold water and its S/S, no rust problems. They have a big cover so a man can enter from the top, easy access for coils.These tanks are designed to hold lquid and water is very close to the weight of milk. Call any installers of these and get put on a list for the old ones. 1000 gal tank will be about $1000.  my .02


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## mwk1000 (Jan 20, 2009)

Thanks, STSS Manual says PH at 8.2-8.3 it is on the basic side as said here. Baking soda , if I remember my chemistry is a buffer to help keep the ph in a stable range. In any case , that is a big help since I still have my college text book and can look up the situation. I think the idea is to set the water with a base chemical ( all the base chemicals I know are nasty like lye,"drano", etc ), and then buffer it with sodium bi-carbonate. I'm not sure if the baking soda by itself will raise it up that much. 

Know that I know what to aim for I can find a suitable additive, I'm pretty well versed in pH from my aquariums. I have all the test gear from that hobby.


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## Fred61 (Jan 20, 2009)

When I was electroless nickel- cobalt plating in another life, I used ammonium hydroxide to raise the pH of the baths where lime or sodium bicarbonate could not be used. I would goto a hot tub or pool store to get the chemicals.


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## danmitchell9 (Jan 23, 2009)

Neoprene looks good.  230F high end temp.  Now if only I knew someone with a wetsuit factory.


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## tom in maine (Jan 23, 2009)

There are a couple materials like Neoprene that are decent. They are expensive and are difficult to work with in sheet form.

All these materials have their pluses and minuses. There is always a balancing act between the cost/benefit of any given storage scheme or material.

As I mentioned, we have had good results with high temperature PVC's that we have custom run. It is more expensive than EPDM, but it is weldable, 
field repairable (that is, patchable, in case someone attacks it with an ice pick or drill!) and we have liners that are over 25 years old in thermal storage applications.

PVC's age by loss of plasticizer. When you have a storage tank that is not constantly be flushed out with new water, the plasticizer stays in equilibrium in the water and the plastic
stays flexible. Even if it aged, it would become rigid, which is not an issue unless you need to move the tank. That is not a usual situation.

There is a lot of art that goes into producing a decent tank liner out of any weldable material, that is why there are not tons of them out there and most people use EPDM.
We hope to change that.


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## free75degrees (Jan 23, 2009)

Hey Tom, would you be willing to sell a custom welded seam pvc liner if given a set of dimensions?


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## tom in maine (Jan 24, 2009)

Right now, no. We are in the midst of making some changes and are working only with stock sizes. 
If you have some time, we might be able to provide custom liners for folks in a couple months.


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## Ugly (Jan 24, 2009)

too bad resin has gotten so expensive... high temp acid resistant Vinylester Resin runs about 180.00 for five gallons.... a thin coating bonded to light fibreglass or other mat is all that's needed to protect against water on a built in place concrete reservoir...keep in mind resins like that don't like the cold much and shouldn't be exposed to temps below -10c too often or they will begin micro fracturing...


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## free75degrees (Jan 24, 2009)

Tom in Maine said:
			
		

> Right now, no. We are in the midst of making some changes and are working only with stock sizes.
> If you have some time, we might be able to provide custom liners for folks in a couple months.


Sure, I have time, probably a lot of time.  I currently have epdm, but I regularly hit 180+ so I'll probably have to replace it some day.  If you were willing to do it in a few months I would have to seriously consider doing it because I wouldn't want the opportunity to be gone when in a few years when I need a replacement.


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## bupalos (Feb 5, 2009)

How about aluminum flashing as a lining material? I once made a very simple wooden water trough lined with aluminum flashing. Each plank was faced with it and then silicone at the butt joints, screwed together, super simple. Could I make a tank this way, or is wood not suitable to take the heat?


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## bupalos (Feb 5, 2009)

Another kind of weird thought would be styrofoam board. Could you fabricate say a 3x3x10 ft interior box out of thick styrofoam panels with silicone joints, then build a wooden box around that? Of course fittings in there would be a little tricky. Flange and silicone perhaps. How does styrofoam do in high temp water?


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## tom in maine (Feb 5, 2009)

I would not use aluminum in any plumbing situation. I have seen way too many weird electrolytic failures when aluminum is used in contact
with water and copper.

If you want to think about metal, how about copper flashing. It is more money, but it is copper! 

I prefer polymer liners and copper heat exchangers. Both are serviceable and easy to work with and fairly easy to get.


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## tom in maine (Feb 5, 2009)

Styrofoam will start to melt at 140F. Looks like a blow torch hit it over those temps.


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## NHFarmer (Feb 5, 2009)

My tank is 7' in diameter, I used 4'x10' sheets of galvanized steel pop riveted together.The base is concrete and it is lined with EPDM. I feel that I will need to replace the liner at some point but I keep thinking that there must be a better way to make the tank waterproof without the EPDM.I am thinking that something like a spray on bed liner would work.I just don't want to be the Guinea pig


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## bupalos (Feb 5, 2009)

Tom in Maine said:
			
		

> I would not use aluminum in any plumbing situation. I have seen way too many weird electrolytic failures when aluminum is used in contact
> with water and copper.



I was going to use either pex-al-pex or corregated stainless (trac pipe) for heat exchange in the tank. But I don't know if wood would be allowed as the structural tank material. Any idea?


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## tom in maine (Feb 6, 2009)

I am not sure I understand what the wood is doing. If you are asking about wood supporting a HX, no, use CPVC.

Extending surface tubing generally does not enhance heat exchange enough to warrant its extra cost. And it does have some impact on flow.


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## tom in maine (Feb 6, 2009)

I would like to hear from people who have used EPDM that has been in service for five years or longer. Is there any degradation? What kind?
Effects on copper?

I suspect that everyone's fears about EPDM's premature failure are overstated. It does degrade, but no one is giving numbers.

My experience with EPDM is with solar products like Solaroll. It was a EPDM solar collector that deteriorated big time in service. It was permeable to oxygen.
Another one was Entran radiant floor tubing, which used EPDM. Similar failures.
This is not a similar use since  these uses  were under pressure and perhaps experienced some surface erosion.


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## bupalos (Feb 6, 2009)

I mean wood is the main material of the tank, whether lined with aluminum, edpm or whatnot. I saw suggestions to use titan Rboard between the liner and plywood backing, and that this worked out fine. I was just wondering if wood itself would have a problem at 180f.


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## Der Fuirmeister (Feb 6, 2009)

bupalos said:
			
		

> How about aluminum flashing as a lining material? I once made a very simple wooden water trough lined with aluminum flashing. Each plank was faced with it and then silicone at the butt joints, screwed together, super simple. Could I make a tank this way, or is wood not suitable to take the heat?




not good unless you used all PEX tubing for the hx.  Aluminum just reacts poorly with dissimilar metals.


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## tom in maine (Feb 6, 2009)

Wood should be fine against the liner. I would prefer to use the foam as a buffer to protect the liner against any stray splinters or fasteners.


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## thearvman (Feb 8, 2009)

This is my first post. This thread is fairly similar to my concern. I am installing a Tarm Solo 60 with 1200 gallon unpressurized storage. The tank liner is EPDM. The house is being renovated for infloor radiant heat. The basement is going to have a concrete over pour. We wanted to do this on the main floor also but the floor joists and hangers etc would not support the load. So we built the floor up with 3/4 plywood strips and aluminum transfer plates with pex running in the transfer plates. With concrete only the design water temperature was going to be in the 100 degree range now with the transfer plates it is going to be about 125 degrees. Planning to not heat the tank to above 175 and that a full load of wood in the tarm would raise tank temperature about 40 degrees then I only have a small window to fill the boiler again on very cold days. Is this a huge concern or not really because there are only so many super cold days and the tarm could be fired somewhere around 150 degrees ( in the storage tank ) safely because of the tank temperature continuing to drop while the boiler is being fired?


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## tom in maine (Feb 8, 2009)

Hi,
It depends on the heat load of your building. The heat output of the radiant floor will be a function of what the floor covering is. It is likely that the only pinch point could be on really cold days, as you said.  (Of course, we have had a whole month of this weather in Maine!)  And then, the house might underheat slightly.
Check out www.builditsolar.com and look at the heat loss calculators.

That will tell you a lot. If the radiant floor is inadequate for the heat load, it can be supplemented with high output baseboard or radiant panels, to help you stretch to a bigger temperature differential from storage.

Welcome to Hearth.com

Tom


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## thearvman (Feb 8, 2009)

Hi
Thanks for the quick reply. I have ductless mini split heat pumps also but the don't work when it is really cold. We are installing an electric boiler for backup ... It is not huge ... ie meant to keep house from freezing when on vacation. I am not sure if it could operate at the same time during really cold days.? I am not sure what you mean by high output baseboards and radiant panels. I do not really want to install any baseboard heat. What is a radiant panel? The guy doing the concrete over pour in the basement mentioned that we could do a 5/16 inch skim coat of some type of concrete product upstairs that would make the heat transfer better which would lower the design water temp of the system. I am not sure how much of a difference that would make.
Thanks


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## tom in maine (Feb 8, 2009)

A radiant panel is like an old fashioned radiator, but it is made of steel and is wall hung. It puts out a lot of heat, like a mini radiant wall or floor.
www.qhtinc.com has them. They are available at most plumbing houses.
I suspect a skim coat might not function that well in boosting heat output on the floor. It depends how much is in contact with the tubing. 5/16" is pretty thin.
Thin radiant slabs are usually about 1.5-2" and completely encapsulate the tubing. An educated guess is that it will not function much better than what you were planning.

Radiant panels are small enough that they can be discreetly used and are not as ugly or obtrusive as baseboards.


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## DaveBP (Feb 8, 2009)

> The guy doing the concrete over pour in the basement mentioned that we could do a 5/16 inch skim coat of some type of concrete product upstairs that would make the heat transfer better which would lower the design water temp of the system. I am not sure how much of a difference that would make.



A professional radiant designer told me to never let concrete or cement tile setting mortar contact the aluminum heat transfer plates. They will corrode the metal. I've seen aluminium that was in contact with concrete. I believe him.



> I would like to hear from people who have used EPDM that has been in service for five years or longer. Is there any degradation? What kind?
> 
> My experience with EPDM is with solar products like Solaroll. It was a EPDM solar collector that deteriorated big time in service. It was permeable to oxygen.
> Another one was Entran radiant floor tubing, which used EPDM. Similar failures.



I think it's going to be difficult to reach a concensus on EPDM and its suitability for tank liners. EPDM is another one of those industrial materials that have been outsourced over the last couple decades. Most of it is made in China and India now. EPDM can be mixed with lots of different materials for different properties. It can also be cut with ground mineral powder just to cut costs. Some stuff out there labeled EPDM is over 50% ground stone. 
What 15 or 20 year old EPDM did in service may not have a lot to do with what modern-sourced EPDM can be expected to do. Too many examples in the news lately of what a mess Asian quality control can be; and just how much some American corporations really care before they get caught.

I think there is probably still good quality EPDM out there but you'll need to do your research and ask for source certiticates if you can. You may not find it on Ebay.


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## tom in maine (Feb 8, 2009)

DaveBP,
Both excellent points. If you were using the skim coat, you should not be using plates, they would be extraneous.

EPDM has a lot of variants out there. I hate to think that much of it comes from overseas, but have found that is the case with a lot
of polymers that we have researched.ARGH.
I am very skeptical of this type of material that is produced overseas. Quality is questionable and engineering support is not immediate.
I am still waiting to hear back from a company that responded to my initial query in November 2008. They needed to confirm something with the engineers in Formosa.
I don't think we will be doing business!

Fortunately there are still some manufacturers of these product here in the US and we can reach the right people with a simple phone call and speak English to them.

My experience with Solaroll, was not good. It was pulled off the market, for good reason. Entran was a different case, but spoke to the issue of formulations and additives.

All that being said. EPDM does work. I am certain that there are better quality versions of it. Who that is and where they are, I am not sure.
Tom


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## pybyr (Feb 8, 2009)

Here are some leads I found - this product looks as if it is similar to Tu-Tuf, only a lot thicker.  

If it is up to lining landfills, which it apparently is, then it ought to be up to the use for a heat tank
http://www.geocheminc.com/hdpealloy.htm
and they’ll apparently fabricate it into a pre-shaped-to-dimensions tank liner:
http://www.geocheminc.com/tank.htm
looks hard to beat unless the cost is insanely high- which I tend to think it actually may not be if people are using it for the applications that they describe.

If I did not already have some gorgeous already-fabricated stainless steel that is worth about as much as a roadworthy used car in the cellar, I’d be pursuing this membrane like wildfire- and I think that the “homemade tankage” thread from "Smee" in Maine represents the most elegantly simple DIY membrane support structure that I have seen yet- just that I would not use either EPDM or PVC


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## tom in maine (Feb 8, 2009)

When it comes to plastic liners, you need to be over 20 mils thick. Anything under that is too permeable and water will migrate across the plastic. Add heat into that equation and it becomes more pronounced.

HDPE will not take the temperature. Polypropylene will, but it is rather stiff. These are both usually used as geomembranes and are used for large tanks, landfill or lagoon applications, which stiffness is a plus and handling is simpler than trying to do a small (500-1,000g) tank.

There are some options out there. They all have limitations. And unless you have used them for a very long time, you cannot necessarily believe everything that a salesman tells you! I am afraid I know that all too well.

At this time, even though there are some limitations, high temp PVC and some alloys utilizing it and EPDM are the ones that work well for this application.

As a DIY project, one can certainly site weld thicker PP sheeting  for a liner. 
I am intrigued but leery of truck bed liners. They could take the temp, but being sprayed on a tank and then exposed to the temps could cause differential expansion failures between the adhered liner and the shell.


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## Fred61 (Feb 8, 2009)

NHFarmer said:
			
		

> My tank is 7' in diameter, I used 4'x10' sheets of galvanized steel pop riveted together.The base is concrete and it is lined with EPDM. I feel that I will need to replace the liner at some point but I keep thinking that there must be a better way to make the tank waterproof without the EPDM.I am thinking that something like a spray on bed liner would work.I just don't want to be the Guinea pig



Well I'm going to be the guinea pig. I located a two part epoxy called water insensitive coating and if I can believe the sales person, it has been used on tanks at IBM and other industrial locations. It's rated for 320* wet. Check out the link below. This isn't the stuff I'm using but is interesting. I had a couple more links but I screwed something up when I posted them.

www.armorshieldlining.com/hot_water_tank.html


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## NHFarmer (Feb 8, 2009)

Looks interesting,any ideas on cost and is it a DIY project?Keep us posted


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## Fred61 (Feb 9, 2009)

NHFarmer said:
			
		

> Looks interesting,any ideas on cost and is it a DIY project?Keep us posted




It is a DIY project. Of course it will be some time before we know whether it works or not (hopefully). I was in the adhesives and coatings buisness up until 1999 and have a lot of faith in the chemistry. What I did is cut one end of a 500 gallon fuel oil tank and, at present, am preparing the surface to accept the epoxy layer. I will be using the tappings for probe wells, and return water to my flat plate HX. The guy I spoke with at the supply house felt that poly urea (like some bedliners, not Rhino and Bullhide) would work because the operating temp. is about 230* but I decided to go for the epoxy, which has a working temp. almost 100* higher for that extra margin of safety. It isn't cheap. About $250.00 for a 2 gallon kit. I felt a little vindicated on my choice after finding a couple hot water tank manufacturers online that offered epoxy coated liners.


http://www.hotwater.com/lit/spec/storage/AOSTT35200.pdf


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## Der Fuirmeister (Sep 23, 2010)

pybyr said:
			
		

> this is the reason I decided to launch into a one-off 409 stainless tank;
> 
> the delta -T between the max temp of your tank and the minimum effective output temp of your heating system defines the useful capacity of your storage
> 
> the closer to boil you can push your storage (which you cannot do with EPDM), the greater net effective heat storage you can acheive



pybyr, you used 409 SS.  How is it working for you?  Did you price other SS sheet such as 304 or 316?  

After a year of researching, looking for the perfect answer to the tank liner question, I've decided to use SS.  I'm gettin' too old to fool around with replacing EPDM in 5-10 years.  Long story - short, I'm using SS because a 1100 gal. SS tank will only run $900 more than EPDM.  And when it's done I will leak before it will.  I also plan to run at 190-200* on a regular basis.  This translates into getting ~30% more usable btu storage for the same size tank using SS vs. EPDM.

Your input or others would be appreciated.


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## pybyr (Sep 24, 2010)

Der Fiur Meister said:
			
		

> pybyr said:
> 
> 
> 
> ...




When I went to have the tank fabricated, 409 was substantially less costly than 304 or 316, and it apparently discolors but does not corrode, which is OK for this application.  My tank has water in it but has not really been put into use yet by actually being fully heated- need to finish some of the controls, and keep getting sidetracked with other projects.  Truth be told, if I were starting afresh and couldn't use a propane tank (which'd be my first choice) I would probably go with an American Solartechnics tank.


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## Der Fuirmeister (Sep 24, 2010)

Thanks for your input.  I can't use a propane tank in the area I have.  I've also looked at the American Solartechnics tank, but would like a larger tank.  900-1100 gal. would be the size.  Since I'm off work I can fabricate a tank for roughly $1200-$1400.  I'm looking at a grade 201 SS which is 15-20% cheaper than 304 (201 is $1.70 / lb in 12 ga. sheet), but have read some things about stress corrosion cracking above 60*C (140*F).  I've also just found a geomembrane product designed for high temps.  If that doesn't pan out I'll end up with SS.


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