It's not impossible or "free energy:" the issue is that the way your space is heated is completely different and it's hard to understand/explain for people new to the tech. The heat pump is not producing heat like an oil or gas furnace do, hence why their efficiency percentage can never go above 100%. It's circulating colder air out of your house and warmer air in (yes, the design of the evaporator/condenser is such that it can do this even when it is below freezing outside). So the 200% number, or even higher for top-rated models, is accurate. But you're right that the efficiency rating can drop in colder temps and also depends on how well your house is insulated. My heat pump heats my 1980s condo-boom condo very nicely (and more evenly than my Rinnai gas heater) in fall and spring and on warmer winter days, but when temps get down into the teens I start to notice a dropoff in performance so I switch to the Rinnai. Improved insulation and a newer model would probably improve that to the single digits or even just below zero.