The short answer is: not always—and for an odd reason that, for me, was not immediately apparent.
My area of the country had an extreme cold spell this winter along with several other factors. Most notably, there was no electricity and no water from our local utility for 5 days. I was certain when power and water was restored, I would have many repairs to make to my outdoor plumbing. That was not the case. I had no problems with burst pipe and was curious why I did not.
I have three (3) outside faucets around my house. One of which is on a stand pipe with a faucet 3½ feet above the ground and 15 feet of exposed PVC pipe exposed on top of the ground. These faucets are connected to utility water. I have a water well with two (2) faucets on a stand pipe also. None of the total of 5 faucets and supply piping to each had any insulation. The only freeze protection afforded was a Freeze Miser installed on each faucet. Obviously, the Freeze Miser did it job, by releasing water that was close to freezing as long as I had water pressure. But when the power was off and the water utility cut off the flow of water for 5 days, I figured there would be many repairs to be made.
Given the ambient air temperature was well below freezing, the Freeze Miser remained in the open position, albeit there was no water to be released.
Or was there?
Curiosity got me to thinking: "Just how did I not have any pipe damage?" So I set up some simple tests and used a big glass doored freezer for observation.
In the first experiment I used 21 feet of ¾” plastic tubing. I filled the tube with water and left both ends about even and the water level 8 or 9 inches from the open ends. I marked the water level with a magic marker. The freezer was started and soon the ambient air was below freezing. It was not long before I saw the water rise slightly about the marks, however I attributed the initial rise in the plastic tubing constricting.
As the air temperature quickly got down to well below freezing and ice formation developed in the tube, the level of water rose fairly steady. When the water was almost completely frozen, the liquid was actually over flowing the tube ends!
It came to me then that it makes sense that water in a pipe or tubing freezes from the outside towards the middle of the pipe.
My observation was that as the water froze, it grew in size (water to ice = 9% growth) and as it did, it forced the water left in the middle of the pipe to move to the path of least resistance which was the open end. Another observation that seemed logical was that as the diameter of the remaining water got smaller, it eventually was so small that when it finally froze also, the growth factor was so small it didn’t affect the integrity of the tubing.
In the second test I used a 3-foot piece of polycarbonate (hard) pipe, capped on the bottom end and filled almost to the top with water. Again, the water level rose as the water turned to ice and overflowed the pipe until the remainder of water in the tube was completely frozen with no damage to the pipe.
My thought is that my personal faucets at home, equipped with Freeze Misers that stayed open in the freezing conditions left a path for the liquid to escape (path of least resistance) and as a result, that saved my pipes from damage.
The Freeze Miser was designed to release pressurized water that is close to freezing, period. But in some cases, mine and some of my neighbors were spared damage to our pipes in an unsuspecting way that was never a thought in the development of the product or one that could be reliable with certainty.