I spent a week in warmer climes recently. While I was gone I left the heat completely off. I turned off the water and drained the pipes to prevent damage. I put all the houseplants in a small room in the basement with a tiny space heater.

I know that while I was gone, temperatures at a nearby airport were below 32F (0C) for some amount of time, but when I returned home, the temperature was back up to 40F, and had been for a day or so.

How can I tell whether the inside of the house reached sub-freezing temperatures?

Is there anything in my fully stocked pantry that might be a giveaway? Or in the toiletries cabinet?

5 Answers 5


If it was only once, and only for a "couple of hours", you probably did not reach freezing temperatures. Especially if you did not let any windows open.

You can search for any glass-made bottle of water. If it is broken without other reason, the house reached freezing temperatures.

While I am not an expert, I think that an occasional 27 F is not enough to fix a problem with an ants colony.

Even if the air in the rooms went down to 27 F, the inside of the walls surely remained significantly warmer. Of course, I assume that your house has at least a minimum of decent thermal and sound insulation. I also assume that the colony is (partially) inside the walls / floors.

However, there are better ways to deal with ant colonies. You should discuss with a specialist. The solution can be anywhere from trivial to a nightmare, depending on type of ants, extent of the colony, areas where the colony spread... Just pray that the bulk of the colony is not under your house.

  • Thanks - The ants are not really the point of this question, so I edited it to remove them. Nor is the likelihood that the house reached freezing. I am just curious whether people know of indicators of freezing temperatures (along the lines of your second paragraph)
    – Adam
    Feb 23, 2019 at 7:11

The reliable and accurate way to keep a record of the minimum (or maximum) ambient temperature for any time is by using a recording thermometer.

There are several different makes and models. Some keep a running record of the temperature with a pen trace on a roll of paper for over a week. They typically work with a wind-up spring-activated movement. This elderly style starts at ~ $100

Recording thermometer

Some record the minimum and maximum temperatures with a magnetic ball inside the tube with solutions that expand and contract with temperature variation. The magnetic indicator remains at the limit of the liquid travel until it is "reset" by pulling the indicators back to the liquid surface with a small magnet. The thermometer can be a liquid as with this model for ~ $20. …

Min-max recording thermometer

… or in a bi-metallic aneroid dial format that can be reset by gripping the tabs on the moveable temperature-recording arms also for ~ $20.

Min-max recording dial thermometer

Then, of course, there are many electronic ones. (They start at $ 15 and can go waaay up.)

Thermoco recording digital thermometer

Any of these will indicate whether your weather temperature was acceptable.


If you expect the weather to turn cold, you can leave a plant (specially bought for it) in the room(s) you want to be sure about.
It has to be a kind of plant that can not stand any frost. When the temperature drops below freezing, the leafs and stems of the plant will show that, going soft and drooping. Good for this are herbs, living or cut for direct use. (But check online which kinds can not stand any frost at all.)
Easier and more clear, but not a lifehack, is to buy a minimum/maximum thermometer, which will show the lowest and highest reached temperatures since the last time it was reset.

I have lived, till reaching adulthood, in a house where the temperature would drop to below freezing in cold weather, without heating in the upstairs area.
Most plants, even from tropical climates, can stand a bit of frost.
You could not tell if the inside temperature had been below 0C, freezing point, unless you caught the water in your glass or bottle still frozen.
For colder nights, like -5C or lower, there might be frost (often in the shape of flowers) on the inside of the glass of the windows, more likely on a single layer of glass, less likely on double or triple layers of glass, and that will thaw away slower and may leave water on the sill even when all has been melted. But from your description I would say that your house has not been cold enough to get frost flowers on the windows.


When you say "turn off the heat completely" I assume you just lowered the thermostats to the lowest level. If they are electronic thermostat the lowest temperature that they engage at is 5 C. Mechanical thermostats are 10 C minimum. In both scenarios your place was maintained above freezing therefore no issue. Most houses these days are largely air tight and well insulated and probably maintained a habitable temperature for a week if the exterior temperature was only down to 0 C. If it was -20 C for a week that would be different story.


I don't know about ready-made hardware (there probably are a few), but you can build a device that logs temperature (and other stuff) to an SD card, a remote server, a computer, or anything you like. I've built one, and it was cheap, but as IoT and home automation gets more and more popular, you can probably find something like this.

Buying a plant (or a plant per room) just to test temperature sounds unnecessarily cruel to me. I can accept experimenting with animals if there is a good reason, but I don't like the plant solution. It's also unreliable.

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