It does not look like an umbrella, but I can explain…

As I start writing this in the evening, it is -2.5C outside the neighbor’s house.  I know this because the neighbor has a thermometer that broadcasts its measurement.  And I know this again because I have a thermometer in two parts, probably the same model, which does the same.  The part that was meant to be outside, I placed in the bedroom instead.  Much to my surprise, the temperature in my bedroom stubbornly stayed well below the freezing point, except it did not feel that way and when I went and looked at the thermometer it showed plus grades.  (Each part has its own LCD display, just in case you want to look at it directly.)  So I changed the channel and continued to get the freezing temperature on the old channel.  Evidently my base station picked up a signal from outside that overrode the signal that had passed through a few walls, so it is probably my nearest neighbor.  Even so, it is a couple good stone throws away, so it was a bit of a surprise.

Anyway!  It may be -2.5C now, but it was -12C in the morning.  And who can my neighbor thank for that shift?  Today in my lunch break I went and bought yet another space heater.  Because as Wikipedia correctly points out, air-to-air heat pumps are less effective than plain space heaters when you have freezing temperatures outside.  This is because it takes a lot of energy to extract the little heat from the freezing air, but also because you frequently need to stop and defrost the outside unit so it doesn’t get covered in ice.  (Even cold air holds some water that is deposited as ice when it is cooled even further.)  The frequent periods of defrosting outside were felt inside as rapidly dropping temperature, especially at my feet.  Even with thick socks, it became quite unpleasant to sit in the home office.  And it was chilly enough that even my fingers grew cold. Not to mention having to wear an outer jacket inside.

Now that I have the space heaters, temperatures are up almost to the freezing point outside and I don’t actually need it.  But that is the umbrella effect for you. If you don’t bring an umbrella, it rains. If you bring an umbrella, the sun comes out.  Obviously it is better to have an umbrella and sun, even if you look stupid.  The real problem is that you forget your umbrella in town.  But that is unlikely to happen with the space heater.