If a house drops from 80F to 30F within a couple of hours then it is poorly insulated, and likely has a lot of air exchange. http://www.winnipeg.ca/epp/pdfs/CoolingRatesOfHouses.pdf looked at how houses cooled during a power outage in Quebec in January. "The mean outside temperature during this period was between -7 and -8°C, with daytime highs of up to 3°C. ... The temperature was as low as -23°C during that period."
12-17 days after the power failed, the contractor measured temperatures in houses that had had neither power nor occupants during that time. "None of the air or surface temperatures in the 31 houses inspected had fallen below 0°C."
There is a proviso: "In very cold temperatures (for example, -30°C), high winds or houses without basements, the rate of cooling will be much faster than observed in the southern Quebec houses of this study."
Now, I lived for a year in a house which was poorly insulated, and where you could feel the draft through the window frame. When it was -15F outside 2L pop bottles would freeze on the floor of the pantry even when the heat was on, and when the furnace went out during Thanksgiving weekend the inside temperature quickly dropped. Even then, it didn't match the freezing outside temperature over a couple of hours. I can well believe that your experience is true, but it is atypical.
On the other side of things, Passivhaus designs (see http://en.wikipedia.org/wiki/Passive_house ) give an example of what can be done with good design, for houses designed for freezing weather. They need only 10W/m² of heat, which can often be met by normal activity (people, computers, screens, coffee makers, etc.)
It's possible to have south facing windows in Germany which let in more solar energy in winter than is released by heat loss.
12-17 days after the power failed, the contractor measured temperatures in houses that had had neither power nor occupants during that time. "None of the air or surface temperatures in the 31 houses inspected had fallen below 0°C."
There is a proviso: "In very cold temperatures (for example, -30°C), high winds or houses without basements, the rate of cooling will be much faster than observed in the southern Quebec houses of this study."
Now, I lived for a year in a house which was poorly insulated, and where you could feel the draft through the window frame. When it was -15F outside 2L pop bottles would freeze on the floor of the pantry even when the heat was on, and when the furnace went out during Thanksgiving weekend the inside temperature quickly dropped. Even then, it didn't match the freezing outside temperature over a couple of hours. I can well believe that your experience is true, but it is atypical.
On the other side of things, Passivhaus designs (see http://en.wikipedia.org/wiki/Passive_house ) give an example of what can be done with good design, for houses designed for freezing weather. They need only 10W/m² of heat, which can often be met by normal activity (people, computers, screens, coffee makers, etc.)
It's possible to have south facing windows in Germany which let in more solar energy in winter than is released by heat loss.