A:Answer Both are about the same height but the 311 has a smaller footprint than the 211. We moved the 211 from the bedroom to the living room and put in a 311 in the bedroom. The 311 may be for a smaller space than the 211 but it's quieter and its front light isn't as bright, so it's better for sleeping. If you're looking to purify a room that can be closed off such as a bedroom or an office, I'd recommend the 311 (or even the 411 if the room is small) and for a larger space or open floor plan, the 211.
