# Can I use a Polypropylene Solar hot water storage tank for my thermal storage?



## Gasifier (May 9, 2011)

Can I use a Polypropylene Solar hot water storage tank for the storage of hot water from my boiler? They have a hot water maximum temperature of 200 degrees. 265 gallons is 994.50. Expensive. Cheaper than a 200 gallon thermal tank at $2000. Can insulate myself or have them insulate it. Unfortunately I would not have the higher temp capability of what a used propane tank could handle. How high of heat can a propane tank handle? Thanks for your time guys. No fire needed tonight. I think spring might be here. I suppose I could always protect it with a mixing valve like I did for the heat going into my radiant heat in the garage floor. Right? What do you guys think?


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## tom in maine (May 9, 2011)

A polypropylene tank will still need a heat exchanger or two and insulation.
The bigger issue with them is the fact that when they are hot and are insulated, they are apt to stress crack
at some point in time.


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## Gasifier (May 9, 2011)

So the tank can not be sealed and contain the pressure of the boiler water?


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## tom in maine (May 9, 2011)

Gasifier said:
			
		

> So the tank can not be sealed and contain the pressure of the boiler water?




That's right.


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## jimbom (May 9, 2011)

Under some circumstances, it might be possible to achieve a water temperature greater than 200 Â°F and have it sent to the tank.  The safety factor for such a circumstance would be less than one.  Perhaps 200 Â°F /212 Â°F ~ .94.  Anything less than one is a matter for concern.  

This is without knowing what the design factor of safety is for the tank.  In other words, the tank might be rated at 200 Â°F, but really be able to handle a higher temperature.   

In this case, I would fall back on the fundamental rule for success in engineering.  The Prudent Man Rule.  Therefore, I would consider other storage tank materials.  Many gallons of scalding hot water inside my house = Design Factor of Safety(target value) for me ~ 3 or greater.  That way I can be assured the Safety Factor(actual operational condition) will always be greater than one.


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## afblue (May 9, 2011)

Propane tanks are all steel so they can accept temps way up into the steam range, so in a hydronic systems it can be said there is no temp you will ever create with your wood boiler that will affect a propane storage tank. they are pressure tested in the 100-200 PSI so with a pressure relief valve, you are well below that. Essentially a propane tank both temp and pressure is way over engineered for this purpose, so if you can fit it into space, fit them cheap, and insulate them they are the best situation going. Smokelessheat.com  sells 250gal vertical propane tanks cleaned, with aditional fittings welded to them, so that would be a better option if you cant find them locally.


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## Gasifier (May 10, 2011)

Thanks for the information guys. I will look locally for a propane tank. If I can not find one, I will see what smokeless heat has in stock. I think they told me it would be $300 to deliver it to my house the last time I called them to see what they had. That would make a total of $1000 into it. Ouch.


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## PassionForFire&Water (May 10, 2011)

afblue said:
			
		

> Propane tanks are all steel so they can accept temps way up into the steam range, so in a hydronic systems it can be said there is no temp you will ever create with your wood boiler that will affect a propane storage tank. they are pressure tested in the 100-200 PSI so with a pressure relief valve, you are well below that. Essentially a propane tank both temp and pressure is way over engineered for this purpose, so if you can fit it into space, fit them cheap, and insulate them they are the best situation going. Smokelessheat.com  sells 250gal vertical propane tanks cleaned, with aditional fittings welded to them, so that would be a better option if you cant find them locally.



I do agree, they are over-engineerd for this purpose.
Normal working pressure in a wood boiler application is 10 to 20 psi.
Put a 30 psi SV in and a 75 psi/200F T&P vlave.
Should be more then OK


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## Gasifier (May 10, 2011)

Put a 30 psi SV in and a 75 psi/200F T&P vlave.
Should be more then OK 



Okay, can you explain what this is to a boiler/plumbing impaired/inexperienced person. And where do I get find this stuff?

Thanks.


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## afblue (May 10, 2011)

SV is Safety Valve, the normal valve that should be on the boiler. T & P is Temp and Pressure Valve, like on a hot water tank.  I am not really sure why you would need a T&P when you already have a SV, unless you are talking about on the the actual hot water tank itself.


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## PassionForFire&Water (May 10, 2011)

PassionForFire&Water; said:
			
		

> afblue said:
> 
> 
> 
> ...



30 psi SV = 30 psi pressure only safety valve ($10 - Watts @ FW Webb)
75 psi/200F T&P valve = combination safety valve 75 psi pressure safety valve and 200F temperature relief valve. ($15 Watts @ FW Webb - the 75psi is special order, normally they are 150 psi set pressure)
The 75 psi is just an additional safety pressure level in case the 30 psi fails for what ever reason

These are very inexpensive safety accessories to protect your tank(s), especially used tanks.


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## Singed Eyebrows (May 10, 2011)

I would use the steel propane tank. A standard ASME air compressor tank is rated for 450 degrees F working temp & the propane tank is at least this & some have a thicker shell, no worries there. I don't believe the plastic tanks are pressure rated at all. Another concern is that if for some reason your water gets above 212 F with a power outage etc ,say 220, & because of pressure it isn't boiling & the plastic tank lets go, your boiler could possibly flash to steam. This is something to be avoided!  Randy


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