Many folks contact us wanting to know why we don't use EPDM liners in our tanks. We have been building tanks for a number of years, and have encountered problems with EPDM.
The first tank we ever built used EPDM. It smelled strongly of skunky rubber and we smelled just as rubbery when we finished building it. It was a hassle to fold it into the container that we had built on site, but it worked very well initially. EPDM is a very strong material when it is new.
However, after being exposed to hot water for a while, EPDM starts to break down. The hotter the water, the more the EPDM degrades. This has been seen with EPDM based radiant floor tubing as well.
The other problem with EPDM is the way it affects copper heat exchangers as the liner ages. The by-products created by EPDM rubber as it breaks down will not allow the copper tubing to create a proper layer of tarnish. Copper naturally produces tarnish as a protective layer that acts as a corrison inhibitor.
There have been some postings online that say stainless steel tubing can also be affected by EPDM breakdown by-products.
We have tested a number of polymer liner materials over the years. The material we currently use is custom manufactured for us. It is field repairable, in case it is ever attacked by an ice pick wielding mainac (unlikely, but possible!). To date, we have seen no aging failures in tanks using our material. The normal type of failure for similar polymers would be embrittlement; as this type of plastic ages, it can become brittle. However, we have not seen this type of aging with any of our liners. The oldest tanks we have been into that use this material, some of which are over twenty five years old, are as flexible as they day they were installed. Even if one of our liners were to become brittle, it would not be an issue unless the tank needed to be drained and moved to a different location.
While EPDM is a less expensive material and EPDM liners are a lot less time consuming to produce (there is usually no welding involved in producing a liner made of EPDM), we feel that the extra cost to offer a fitted liner provides our customers with the best heat storage solution on the market today.
I had a conversation was with an old friend out west who has been using a tank from a competitor (who is now out of business). They used EPDM liners and stainless steel heat exchangers in what was a very expensive tank (more than three times more than ours).
The stainless steel heat exchangers have been failing. I haven't seen pictures of the failure yet, so I cannot be positive of the cause, but I can make some good guesses. First, EPDM breaks down in hot water. When this happens, it can attack copper heat exchangers. It seems possible that it can also attack stainless steel. I have no direct experience since we do not use EPDM, but it is common knowledge that it breaks down. Hotter water accelerates the process.
Second, in tanks that heat up and cool down, you need to design for expansion and contraction - of EVERYTHING! That includes the actual tank and any hardware installed inside of it. This includes coiled heat exchangers of any material; metal, plastic, or whatever. There are a number of metal coiled heat exchangers that are solidly tied to metal support structures. This is apt to cause an abrasion failure. Any failure in a tank is a bad thing (I learned that a long time ago).
Heat exchanger failures are particularly troublesome and can be costly.
It is my experience that a properly designed stainless steel heat exchanger can outlast us. In Europe, they are the standard. In Europe, they do not use EPDM liners. Maybe that is not a coincidence?