Pex tube and a frozen floor...

[mx842]

I wonder what's going to happen to the pex in my floor now that it is all but frozen solid? Well, let me step back a bit......I guess it's frozen cause I checked the surface temp with one of those laser temp guns and it is reading between 26 and 34 degrees. I had been working on my woodstove/boiler stove and that took longer than I had planned and by the time I got it fired up we had a really cold spell that has had me between a rock and a hard place.

before I could get all the kinks worked out and really got it working to where it was making enough hot water it was so cold the floor froze and now there are only one or two loops that are passing water from one to the other and the rest are blocked. This morning when I went back out there I could see where several places had started to warm up a little....from around 34 degrees up to 44 but the parts in front of the big doors and my office, welding room and machine shop room are still frozen with no water passing through.

I don't have much choice but to keep chunking wood in the firebox and hope it will sooner or later thaw out without any of the tubes busting before this cold spell is over. It's supposed to warm up today to almost 40 but tomorrow night it's supposed to get cold again and not get out of the 20's next week.

 

[Dave M7040]

You need to be blowing warm air unto the floor for any hope of a timely thaw. Fans directing hot air over the floor is one way.
Another way is to elevate a tarp over the floor about 12" above the floor and blow warm air into this cavity.
Hot air rises and the floor is the last place to warm up.
Dave M7040

 

[milkman636]

I can't say for sure what will happen. Hopefully the concrete will help reinforce the pipe from bursting.

The highest risk of damage occurs as the ice in the pipe thaws. If a section of pipe begins to heat up and the water in it tries to expand against solid ice in both directions, the pressure can skyrocket and rupture the pipe wall. It is best to thaw pipes slowly and evenly making sure that the warming water has somewhere to expand to. Knowing that your tubing is in concrete, I don't know how to make sure that happens.

 

[jpaeye]

Pec is pretty resilient to freezing. You will probably be just fine

 

[CurlyDave]

Pex is claimed to be resistant to freezing, but those experiments were done with unconstrained Pex. Even if the Pex survives, I expect the bond between the Pex and the concrete will be disrupted. Your floor heat will probably not work as well as you might like.

The only thing to do now is to wait and see what happens.

If the floor survives without major cracks, it may well be less costly to abandon the Pex in place, and find a different way of heating the rooms involved. Blow out the Pex with compressed air to get all the water out if you do this, otherwise there will be tubes full of algae, bacteria and general unwholesomeness permanently in your floor.

 

[BeezFun]

The highest risk of damage occurs as the ice in the pipe thaws. If a section of pipe begins to heat up and the water in it tries to expand against solid ice in both directions, the pressure can skyrocket and rupture the pipe wall.

Unless you're talking about generating steam during the thawing process, the damage comes from expansion of the ice during the freezing process, not from water expanding. The coefficient of volumetric expansion for liquid water is tiny: 1.0002. So if you increase a volume of water at 50psi by 10C, the new pressure will be 1.002*50= 50.1 psi. If you increase it 100C, the pressure will rise to 51psi. So the pressure change is so small as to be difficult to measure with a standard guage.
On the other hand, the expansion of water changing to ice is quite large, a volume change of about 9%. So unless the pipe can constrain that increase in volume, or the system has some air entrained in the water to absorb that change, the pipe will break.

 

[cmyoung2]

Keep a close eye on the water level in your stove. If a pipe breaks it can drain the stove, which is not good. Don't ask how I know. I had one above ground PEX tube break, and then drained the stove again, so I guess I have a break in the concrete somewhere. It was below zero, inside a shop with no heat turned on. Just didn't think about that freezing, guess I should have.

 

[randy41]

for a 9% volume change a 1/2" pipe would have to expand by 4.5/100". that ain't very much.

 

[Raspy]

BeezFun is absolutely right. The destructive expansion occurs during the freeze process, not during a warming after a freeze. (Now imagine a somewhat wary eye, glanced toward the earlier post about thermal vs freeze expansion in post #3. Incorrect speculation.)

In your case I think you will be OK. The water froze near the doors first which meant it could possible displace out of that loop as it froze. Also, the interior of PEX is very smooth and you have no complicated passages to trap the ice like tees or valves or other fittings. The PEX might be able to expand, or force into the inside of the concrete passage, by the required amount before the concrete breaks.

Keep trying to heat the floor until it flows everywhere. Then do a leak a check at a stable temp. This means stabilize the temp over a number of hours, make sure there is no air in the system, pump up the pressure to 60 PSI or so with water (not air), shut off the supply, isolate the expansion tank and watch the gauge for an hour. If no loss you are good to go. If it does loose pressure you can find the area and make a repair. If the concrete pops from the freeze, it will be easy to locate the problem. DO NOT abandon the system!!!

If it is leaking with no apparent concrete damage (unlikely), keep the system pressurized and look for a wet spot. If that doesn't do it, blow out the water and pressurize with air. You can even hose down the area and look for air escaping up through the concrete to find the spot. Don't worry about how to fix it until you've proven it leaks. PEX is easy to fix.

 

[Gary Fowler]

I am not that familiar with in floor heating but the folks that I know that use them use a closed system with antifreeze in the water to keep this from happening. I was wondering why the OP didn't do the same thing. If he had, he could have not worried about lines freezing without heat.