Freeze isn't technically the right term, but it won't vaporize anymore when it gets cold enough. Fortunately it rarely gets that cold, but if it were to and your tank wasn't insulated you could lose your heat.

This actually happened to people I knew back in the 1990's. We had a snap that set records, and people's propane tanks got so cold that it would no longer vaporize.

Here's what happens:

When the temperature gets down to -43.6 F propane turns to liquid and won't boil. That's the temperature when propane turns to a gas. If it's not at least that warm, the propane won't ignite in your furnace and you'll be left out in the cold.

That may seem so cold that it would never happen, but it has. Not to mention we have temps in the forecast for some of Northern Minnesota at -30 or colder this weekend. I know if I had a propane tank I would make sure I banked some snow around it to help insulate it just in case.

My grandpa has told me stories about back in the day where they had large propane pig tanks freeze up, and they had to crumple up newspapers to start small fires under the tanks to warm them up enough to get the propane gas flowing. I don't think I would recommend that, but that's what they had to do.