不是合同问题，是消费者保护的问题，我用英语回答。

It appears there is no problem with the contract, you get what you paid for.  The problem is that the product is not suitable for your need.  

I am not sure if your issue is related to this http://www.chimneysavers.com/chimney-flue-coating.html  Be aware that you cannot rely on this information completely. You have to talk to the manufacture of the product and somehow find out if that is suitable for your need.  For exxample, get the product manual, your case turns on professional opinion.  

If you have evidence that they used wrong product in your situation, you can rely on your state's "unfair and deceptive business practice act", maybe find local state attorney's consumer protection office for more information.  

$2500 is small amount in big scheme of things, so it's not worth it to hire a lawyer.