Any pipe that is in an unheated part. A very common place is under the kitchen sink either directly under the sink or just under the floor. A gap between the foundation and the house or where the drain may go in the wall. Either place can be lacking in insulation and allow pipes to freeze. Any pipe that is in or against an outside wall should be looked at on an individual basis.
At least one degree above freezing?
It would drop below freezing during the night and then roast during the day
Not unless the drain and or tub is full of water and you have no heat on or it gets below freezing in the house.
By having the air conditioning set at 75, that means the air conditioner will come on only if the temperature in the house rises above 75. It will maintain the interior temperature at a temperature of not more than 75. If the outside air temperature is lower than 75 and you want the interior temperature to stay at 75, you will need to turn on the furnace and set it at 75. Now the furance will come on if the temperature in the house drops below 75 but will not come on if the temperature in the house rises above 75.
The freezing weather made icicles on my house roof.
That depends on the ambient temperature. A corpse will take on the temperature of the environment. If it's in a house that is 70 degrees, the corpse will cool to 70 degrees. If it's outside at 40 below, it will cool to 40 below.
What causes the cracks is rapid temperature changes--if you were to leave the heat off for a week, then come home and turn the furnace on for a couple days, then leave for a week and so on, you'd get cracks. But if you were to let the house sit over the winter, allowing it to gradually change temperature, you'd be fine. (This omits the effects of mold.) This actually happens all the time--if a manufacturer builds a manufactured home in December and parks it in the storage yard until it sells in April, it will sustain freezing temperatures for several months without damaging it.
Because of the thermostat. This will turn on the unit when the temperature gets below what ever degree it is set at and then will turn off when the thermostat gets at that temperature.
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You mean just sitting in the house? I've noticed that when the temperature in the house gets to be in the upper '70s, the chocolate in the snack bowl (normal snack-type chocolate, like Hershey's nuggets) gets soft and bend-y. Not hot enough to stick to the wrapping or fingers, but ver-r-r-r-y close. When the indoor temperature is in the low '70s, the chocolate is normal consistency. I always wondered why a 7-degree difference could cause that much of a change.
House temperature in Celsius (centigrade) is 20°C which is 68°F.
I've never heard that in my house, but the pipes could be freezing or something.