Pex tube and a frozen floor...

[SPIKER]

Rusty,

An automotive system is the same as a radiant system. The "coolant" in a car absorbs heat from the hotter interior surfaces of the engine block and gives it up to the cooler interior surfaces of the radiator tubes. In a radiant floor, the "coolant" absorbs heat from the hotter interior surfaces of a boiler and gives it up the cooler interior surfaces of the radiant tubing. Same thing. In both cases energy is simply being transported between two objects that are at different temperatures, by a fluid. The energy is being absorbed and released by conduction.

Principal is the same but the conditioning elements (physical make up of the coolant) in a cars system has different conditioning (anti corrosion inhibitors etc) materials for the engines and mixed metals (copper, aluminum, rubber hoses, cast iron, plates brass materials all in cars) while PEX and usually Steel/Iron/Copper for fittings and the water in a boiler is designed to last 10 or 20 years vs 5 years or 100K miles in car...

The thermal efficiency of the Copper, Steel, Iron & Aluminum in cars is much better than those in the Home Boilers as well & PEX is pretty poor at transmitting the heat from the boiler to the floor. BUT it lasts much longer in the concrete vs Copper or Aluminum which would corrode and leak in no time buried inside a concrete slab...

The Freeze Thaw should be OK on the PEX the Concrete however maybe develop some cracks or loose areas and if it was real good concrete the PEX may have compressed some thinning the walls at weak spots in the concrete as it lets the PEX expand MORE to those weak areas.
Mark

 

[Raspy]

The thermal efficiency of the Copper, Steel, Iron & Aluminum in cars is much better than those in the Home Boilers as well & PEX is pretty poor at transmitting the heat from the boiler to the floor. BUT it lasts much longer in the concrete vs Copper or Aluminum which would corrode and leak in no time buried inside a concrete slab...

Some interesting assumptions there. I don't know how you arrived at these conclusions.

Once again the word "efficiency" needs to be defined before the argument can be made. Copper is copper and iron is iron. Cars have no priority on special iron, that I know of, and Copper has been buried in concrete for radiant heating since at least the 1940s. Copper's biggest enemy in concrete is cracking, not corrosion. It's not enough to simply say PEX conducts less than copper. PEX systems are not the same as copper. Typically PEX systems have much better flow rates and more surface area, so you can't directly cross reference a copper system with a PEX system and generalize about overall heat transfer. Besides, the point was the transfer media, not the tube material.

No matter how you break it down, water is absorbing energy from a warm surface and transferring that energy to a cooler surface. It's the particular chemistry of the water mixture that makes it slightly more or less affective, compared to pure water.

 

[aczlan]

If you extend that math to cover a rise from 32°F to 72°F you'll have the increase just to room temperature. This phenomenon is exactly why torches should never be used to thaw pipes.
I believe the typical PEX lay line says something like 160 PSI at 73°F, and it drops off as temperature increases. I would guess that actual burst pressure would probably be at least double that #.

From the Home Depot install manual for heating pex:

Do not allow the fluid temperature to exceed:
200.0°F (93.3ºC) at 80 psi (5.5 bar) for Heating PEX.
200.0°F (93.3ºC) at 100 psi (6.9 bar) for Heating PEX-AL-PEX.

The heating PEX in my basement says 200PSI at 73F and 100PSI at 200F (IIRC, its Heating PEX-AL-PEX).

Aaron Z

 

[crazyal]

You should be fine. The first winter I wasn't living in my house so it wasn't heated. I got as much water as I could out of the lines but not as much as I wanted. 6 years later and everything is just fine. Trust me, my basement got a lot colder than anything you'll see down there. As for the lines that are still frozen, you'll have to heat the cement around them to thaw them. With no water flow you're not going to get any warm water into the lines to thaw them. Depending how well your manifold is balanced even if partially thawed water may not flow down those lines simply because there's not enough resistance from flowing down the other lines. this could be why it's taking so long to get them unplugged. I installed 1/4 turn shut off valves on each line so I can fine tune the system. If you have them you could shut off a couple of loops to build up a little more resistance but I would be careful not to go too far. Also if the system was balanced with the valves you'll throw it out and need to rebalance it afterwards.

 

[mx842]

You should be fine. The first winter I wasn't living in my house so it wasn't heated. I got as much water as I could out of the lines but not as much as I wanted. 6 years later and everything is just fine. Trust me, my basement got a lot colder than anything you'll see down there. As for the lines that are still frozen, you'll have to heat the cement around them to thaw them. With no water flow you're not going to get any warm water into the lines to thaw them. Depending how well your manifold is balanced even if partially thawed water may not flow down those lines simply because there's not enough resistance from flowing down the other lines. this could be why it's taking so long to get them unplugged. I installed 1/4 turn shut off valves on each line so I can fine tune the system. If you have them you could shut off a couple of loops to build up a little more resistance but I would be careful not to go too far. Also if the system was balanced with the valves you'll throw it out and need to rebalance it afterwards.

I haven't gotten far enough into the project to worry about balancing any of the loops. Right now I have everything wide open at the manifold and am using a valve at my circulation pump to restrict the flow through the system. I haven't been able to get the boiler up to much more than 90 degrees at the output pipe and by the time it gets to the manifold it has already lost almost 10 degrees. For the most part I'm looking at on average 75 degrees in and about 55 degrees on the return. I have had to shut the control valve off to almost 3/4's closed to get that much heat out of it because the floor temps were so low causing the return water to be so low it was flooding the boiler with so much cold water the boiler could not keep up. Burning wood that is not as seasoned as it should be is not helping matters either but it's all I have at the time.

On a good side note.....The boiler gods seem to be shining favor on me because the weather man seems to have missed again when he said mid 20's today. It didn't get into the 40's yesterday, only about 37 but it's going to be in the 50's today so the immediate threat is for now over and already I can report that there is now water flowing through all the loops and there is no signs of water leaking up through the floor anywhere. So for now I guess I dodged the big one this time. Thanks guys for putting up with my pitiful cries of dismay and frustration. Now with tail tucked firmly between my legs I will now go about my task of sealing up the building and big door to keep as much air movement in and out of the building as possible so I will be ready for the next arctic blast of global warming which is sure to come. LOL

 

[Fi-Q]

Do you have a mixing valve at your boiler ? Are you returning 55 degree water to the boiler ? If so i think your goin to kill it. As far as i know ( i do not have a wood boiler yet, but it is the plan ) you beed to keep the boiler tenp at a certain level to avoid major creosote issue and boiler corsion. But i do understAnd that if you are in a timing bind, it may not be the perfect set up yet. It would judt be bad to destroy your boiler or to burn the cheminy down due to lot of creosote building.

 

[Raspy]

mx842,

Here are a couple of things to consider:

The smaller the temperature differential across the floor, or through the loops, the more energy you are delivering. Always go for the highest flow.

Since some loops are flowing, restrict those loops only. Leave the pump open and try to get the maximum head pressure to the blocked ones. Reduce flow in the loops least likely to freeze and farthest from the frozen ones. Keep the flow highest next to the frozen area.

Another trick might be to put a heavy does of RV antifreeze in now. Then it will mix and begin to melt the ice block, where the ice meets the liquid at each end of the blockage, in addition to you adding heat.

 

[MacLawn]

Oh me, this floor heating is a lot more complicated than I thought! Kind of putting me off of it. I don't know.

Anyway, I hope none of ye pipes busted.

 

[quicksandfarmer]

A couple of belated thoughts on this:

PEX is considered "frost-resistant" because it will stretch the 9% needed to accommodate freezing water without exceeding its burst pressure. It is also slippery on the inside so a frozen plug can slide and relieve pressure. Concrete, on the other hand, is brittle. So I would worry more about the concrete cracking than the PEX bursting. The only exception is where the pipe exits the slab, the pipe can get damaged where there is a transition between being constrained by the concrete and unconstrained. It's good practice to sleeve the PEX where it exits the slab.

Water freezes from the top down, as ice floats. Liquid water is densest at about 39F and becomes less dense as it approaches freezing, so the top is the coldest water when you're near freezing. When it's cold out anything touching the ground is going to be warmer than the air. So if the boiler is above the floor, there's a good chance that the floor itself didn't freeze, only the exposed pipes.

It's a good idea to put antifreeze in any pipe you can't drain. I use this: Boiler Antifreeze I don't have any expertise to judge it really but it has worked for me so far. It's mostly propylene glycol, the same as RV antifreeze. However, propylene glycol is corrosive, so in a heating system you have to use a formula with corrosion inhibitors.

As for efficiency, there's a couple of things at work here. The conventional wisdom is that hydronics are 100% efficient, all of the heat that the boiler puts into the radiator water goes into the building envelope, one way or another. When people say that adding antifreeze lowers efficiency they're talking about something different. Antifreeze lowers the heat carrying capacity of the fluid. To move the same amount of heat you need to move more fluid. You don't need a bigger boiler or bigger radiators, but you might need a bigger circulator pump or piping to move the fluid faster. In the extreme case you could have the boiler or radiators working at less than full capacity, limited by the capacity of the circulation. If you paid for a certain boiler capacity and don't get to use all of it, that's inefficient.

 

[mx842]

Fi-Q..... I don't have a mixing valve on the system anywhere yet. At this point a mixing valve would be useless as I'm not able to get the water hot enough out of the boiler to make any difference. This morning when I went into the building it felt warm when I opened the door but room temp was only 38 degrees. I guess the 38 degrees felt warm compared to the 9 degrees outside temp.LOL The floor was from 38 to 45 degrees all over with the coldest right at the big door. I now wish I had put a shorter closely spaced loop about 10 feet out right where the big door is to put more heat in that area but it's too late for that now.

The next time It warms back up for a few days I'm going to change the direction of water flow. Right now I have one of those blue 55 gal plastic barrels sitting next to the stove that is catching the return water. I did it this way thinking it would help bleed out any air in the lines and also help to keep an eye on water levels. I wanted to be certain my circulation pump didn't run dry like the first one did.........That was a quick flush of $425.00 when a big air bubble worked it's way into the supply line. I guess one of the loops that was frozen had a large section of air in it somewhere and when it thawed out all that air worked it's way to the pump and fried it. Hopefully I can get a kit to rebuild it.

The way I have it now is plumbed out of the bottom of the barrel to the pump so the whole barrel would have to run dry to destroy the pump and hopefully I would catch a low water condition before it did cause a melt down of the pump or the whole system. I want to eventually feed the manifold out of the hot water tank rather than directly out of the boiler and have the return dump back into the tank. Then have a smaller circulating pump cycle the water through the holding tank and back to the boiler.

And yes creosote is a problem because of the low temps the system is operating at but right now I will just have to keep a close eye on the stack. When I built my connector pipe that connects the inside pipe to the outside I made it with a sq bottom so when it was plumbed together it is tilted downward slightly to the outside so that I could drill several holes in the end to let the goo drain out. A day or two ago I couldn't figure out why the stove would not put out any heat and didn't seem to want to draw. I also noticed black watery looking goo running down the outside of the stove pipe and down onto the stove then on to the floor. When I saw this I remembered I never drilled any holes in the end of the connector and when I did almost two gallons of really nasty water came streaming out of the hole and all over me, my drill, then splashed all over my brand new siding job. That stuff is really nasty and it takes a lot of soap and water to get it off your hands and cloths once it gets on you. It's hard to believe that much water and sap is still in that wood that blew down two years ago from a big storm. It looks dead an dry on the outside but it still has a lot of water inside on top of that the poor stove not only has to deal with all that moisture it first has to thaw it out so that it can start to try and burn whats left. Not ideal conditions for sure but at least it thawed out my floor and hopefully it will keep it that way without burning the whole place down in the process.LOL