Carboy temperature readings

[beerisyummy]

Question for the hive mind. I ferment in glass carboys. I have the stick-on thermometer and another thermometer to measure the ambient temperature of the room. After the fermentation slows down or stops, I consistently get a temperature reading about two degrees colder on the glass than in the room. Anyone conversant with applicable thermodynamics in this situation & can tell me what is going on?

• Do the stick-on thermometers suck?
• Is my other thermometer likely mis-calibrated?
• Is the glass a different temperature than the air or the liquid?
• Do glass carboys "hold the cold?"
• Should I just use the temp. probe all the time even if I'm not using the heating pad?
• Should I just relax and have a home-brew?

 

[Birrofilo]

My Stick-on thermometers are quite in agreement with my room thermometers,which are two and quite in agreement between themselves.

So it is possible that one of the thermometers is imprecise (or both!).

 

[day_trippr]

Solid glass is an excellent conductor, and the mass of wort/beer will dominate whatever temperature reading is taken.
I once did a series of comparisons between strapped-on probes vs thermowells and never found the two disagree by more than 1°F, even as the chamber was ramping up or down. I didn't include the stick-ons as it wasn't pertinent, but an accurate one should fairly mimic a strapped-on sensor (aside from resolution, of course)...

Cheers!

 

[Jim R]

I wouldn't even worry about it unless you are prepared to control the temperature with cooling / heating.

 

[Transamguy77]

Not sure I’d be concerned about 2 degrees, and if I was going to worry about accuracy I’d be concerned about the carboy and not the room temp.