Question: what is the difference between 16 seer and 21 seer?
Answer: One difference that you may find between 14 SEER and 16 SEER units is that the 14 SEER units generally have a single-stage compressor while the 16 SEER units often have a two-stage compressor. ... Not only does the two-stage compressor make your HVAC unit more energy-efficient, it also allows for longer run-times.