In smaller batches I recommend hand scraping for finish removal on large, flat expanses as you're faced with here. It's not as onerous as it sounds because of how efficient card scrapers are, and at least you're not having to deal with the boards in situ on the floor. (Backbreaking work!)
Chemical stripping is obviously one option, and while the 'green' products (which are slower but can still work well) are much less odoriferous the cost does rise and rise the more you have to do. For furniture-scale projects I'm a big fan of strippers, but they're a little hard to justify for very large amounts of stuff if you're buying your stripper retail.
Heat or flame stripping is an option. Using a heat gun or blowtorch, with paint scrapers in a scraping motion or a stout putty knife in a pushing motion to scrape off the softened finish. But ideally you'd want to work outside, especially if using a torch.
There's a really good alternative to any of the above that can sometimes work to your advantage: use the back of the board which doesn't have any finish on it.