Hi BigBlaze,
This is a very common scenario in e-Commerce. For example, microphone and speaker cables come in hundreds of different lengths. Writing Pulitzer-quality content for pages like these is absolutely not necessary in order for pages like these to do well. In addition to that, people shopping for items like these do not expect to land on a page filled with paragraphs of content with flowery hyperbole. They want to find what they need, put it in their cart and checkout.
For this reason, your site isn't as bad as you might think. The fact that your titles are all the same I don't consider to be a problem at all because you have made them unique by including the furnace filter size. Same with the meta descriptions. As long as they are unique and do a good job of describing what's on the page, these aren't really duplicate content either.
If you want to work on unique content creation or go after longer-tailed search, you might consider adding some robust FAQ pages or even a blog.
The bottom line is your site isn't about content so much as it is about selling furnace filters. Even if you spent a lot of time re-working your product descriptions so they were all "unique," they are still going to be substantially similar in Google's eyes (and to users) anyway. I mean, it's really not realistic to wax poetic about furnace filters, although I'm sure someone's tried!
I'd concentrate on making the sizes easy to find and purchase process quick and painless. If you get good conversions and a lower than average bounce rate and good customer reviews, you'll be sitting pretty in the SERPs I think.
Dana