Installing hydronic radiant floor heating during cold weather

robinsbd

Hi,
I am in the process now of finishing the work on the plumbing for my radiant floor heat in my new garage. The concrete slab had the pex tubing installed and the concrete was poured in early summer this year. I am just about ready to introduce water to the system and fill it. The only thing is that we have had several days now with lows around 10 degrees and highs in the 20’s. I am wondering if there are any precautions I need to take as far as starting up the system. Is it ok to start running hot water through the slab? Does it need to be gradually heated first or is there a recommended procedure because of the cold temps? Does the air temp in the garage and pex tubing need to be warmer or pre-heated before starting? I just want to make sure I follow correct procedure don’t cause an issue with slab. Thanks!

Zman

Filling a very cold slab like that with water is a risky proposition. The water is very likely to freeze. I would suggest premixing a 30% propylene glycol mix and pumping it in. As far as heating it up, I would keep the supply temps below 130 to minimize the risk of thermal stress.

nibs

Like Zman says, antifreeze is a good move, even if you dump it out later and use plain water.
If you can bring the slab temp up quite slowly, the concrete is pretty much cured so you should not get any edge curl, but you could get cracking.
Concrete has thermal expansion so it is important to keep the slab at an even temp throughout as you warm it, covering it with blankets or straw helps also. Warming the space above the concrete would be a good idea
If possible set your supply water temp low and increase it by a degree or two per day until you are up to temp.

robinsbd

Thanks very much for the quick responses. This is exactly what I was concerned about.

Do you have any recommendation for how to mix the antifreeze and how to pump? I was looking at Cryo-Tek at Menards.

Zman

https://www.supplyhouse.com/Axiom-MF200-MF200-PRESSURE-PAL-Hydronic-Mini-System-Feeder-6-Gallon?gclid=Cj0KCQiAk7TuBRDQARIsAMRrfUYxanFlKT64l4pXviJhqBmjw4VAE9dWJ5ZeWizGDFLLFyFaxGrZG50aAuM3EALw_wcB

GroundUp

The Cryo-Tek -100 is a 55% concentration in the bucket, so if you mix 5 gallons of it with 3 gallons of water you'll be at 33% total concentration and would be safe to pump in at that ratio. A transfer pump is best for filling, I now use a Milwaukee M18 but any regular old cast iron unit (Wayne, Simer, etc) will do the job just fine. I have even done radiant floors with $10 drill pumps but it takes forever. As for temp, I would limit your SWT to 80 degrees for the first 6-8 hours and then raise it to 95-100 if you have to. Odds are you will never need any higher in a garage if you have a decently installed system. Most of my slab homes run 100-105 at -40F outdoor temps here in MN while garages seldom exceed 90. The most efficient slab heat you can get is at the lowest SWT possible with constant circulation, so unless you plan to keep it 80 degrees in the garage there will be no reason to ever exceed 110

robinsbd

I see there is a Cryo-Tek 45% mix available. Would this perform OK, or is it too high of a concentration?

HomerJSmith

You can try Zoro online for cryo-tek 100. It comes with a mixing guide sticker or you can buy a inexpensive Refractometer from DHgate.com or Amazon and measure the propylene glycol mix.

I use AG (90%) or 100 (50%) rather than original. If there is aluminum in the system you need an anti-freeze compatible with aluminum. The higher the concentration of propylene glycol, the more pumping energy is needed as it is thicker than water.