Opinion on EDPM Lined VS Stainless Steel Milk Tanks

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Mar 28, 2018
3
Buckland MA
Hello Hearth Folks,

I have been reading the forum for a few years and appreciate all the information you folks share. Thank you. Currrently we live in a 1300 sq ft ranch (poorly insulated) which we heat exclusively with a Blaze King wood stove. We use 2.5-3 cords a year. In the next year we will be building a new house (2 full stories, about 2400sq ft total, on walk out basement). The house will be very well insulated and have a small heat load. We intend to install a boiler in the detached garage and store water in the basement of the house.

We recently bought a Tarm MB Solo MKII 60. The boiler was installed in 2005 but only used 3 years. It comes with a 950 gallon STSS tank. It is a big boiler for our house but going days between firing at times sure would be great. My question is regarding the STSS tank. As the liner is 15 years old I really don't think it would be wise to reuse it. As this is new construction, access is not an issue and I could put a large insulated milk tank in the basement before construction starts. I tap maples for syrup and currently have a 1500 gallon tank I could use. These tanks can be found for $1/gallon. As a nearly permanent solution do you think a stainless tank such as this would be a better option than reconditioning the existing tank....knowing that the liner would have to be replaced again in 15-20 years. I am not interested in having pressurized storage inside the house.

Thanks for any thoughts you might have.

Jack
Western Mass
 

Bad LP

Minister of Fire
Nov 28, 2014
1,790
Northern Maine
I’d jump on the SS tank if the plumbing is going to work.
I personally would not own any open system.
 

peakbagger

Minister of Fire
Jul 11, 2008
6,604
Northern NH
No sure what an STSS tank is. American Solar Technics (AST) sells a popular open lined tank rectangular tank but they use PVC (except for few experiments). I also agree that a closed system is the way to go which means you would need to alter the milk tank to be able to install a heat exchanger. With a heat exchanger oxygen does not get inside the boiler and rot it out unless you provide proper dosing and analysis for the water. With a heat exchanger you fill the tank once and top it up every few years . Definitely do not use EPDM for a liner, its not rated for continuous immersion at elevated temperatures. The AST tanks are superior for insulation as unless you get the mil tank sprayed it would be difficult to match the AST design. I do not think there is any warranty on an open system for a Tarm.

One thing to consider is what do you have for heat emitters in the house. If you swap slat fin type radiators for lot temp emitters you can get up to double the storage time for given tank. It only makes sense if you are remodeling as low temp emitters are not cheap.
 

3fordasho

Minister of Fire
Jul 20, 2007
1,005
South Central Minnesota
Also not sure what a STSS milk tank is - if the liner was leaking, would it leak out the stainless shell? You want any water touching that Tarm to be a closed/pressurized system. That means a heat exchanger in the STSS tank to separate the closed system from the non-pressurized water in the storage tank. I just did a similar system with a 550G stainless tote that can not be pressurized and used a heat exchanger from American Solar Technics. The same exchanger can be used to heat storage and remove heat from storage for your emitters.
 
Mar 28, 2018
3
Buckland MA
I did not explain as well as I could. The Stss tanks are the ones Tarm sold up through some time in the 2000’s. The used tank has the heat exchangers (not that I am confident they are good). If going with a milk tank I would of course be using a heat exchanger. As the tank would be in the basement inside the thermal envelope I would not worry that it is not insulated as well as a AST tank.
For the price of $1/gallon the milk tank seems like a great option...I am just curious am I missing something? I have read all the discussions regarding open vs pressurized storage and understand most of the limitations with the unpressurized.

Yes we will be planning for low temp emitters to maximize effective storage.
 
Mar 28, 2018
3
Buckland MA
I just did a similar system with a 550G stainless tote that can not be pressurized and used a heat exchanger from American Solar Technics. The same exchanger can be used to heat storage and remove heat from storage for your emitters.
Interesting. I was not aware you could use just one exchanger. I thought you had to have a primary for the boiler loop and a secondary for the house loop.
 

peakbagger

Minister of Fire
Jul 11, 2008
6,604
Northern NH
I have one coil with a couple of valves that uses the same coil to heat up the tank and to heat the house.