Some indoor plants (cyclamens, cactus, some orchids, etc.) actually prefer cold night temperatures during the winter: 33–50?F (1–10?C). But how can you find which spots in your house really are the coolest … without spending the night sitting in each one to test it out?
Here is one case where modern technology can really make your gardening life simpler! Most modern digital room thermometers display not only the current temperature, but the maximum and minimum temperatures of the spot where you place them. Leave one in a location that you think is appropriate for a few nights, jot down the temperatures, then try a few others. Soon you’ll have a much better idea of the true growing conditions in various spots throughout your house.
By the way, most digital room thermometers also give you the relative humidity, something you also need to know. Most houseplants prefer a relative humidity of 50% or more.
You can easily find an inexpensive digital room thermometer in any hardware store.