Slab heat anti freeze

kody

We have a slab and truss mounted pex tube heating system. In the event of freezing temps affecting our system we have used a 50 % solution of water and propylene glycol. I am wondering if the propylene glycol based RV solutions could be used if the 50 % ratio could be maintained using pure propylene glycol ?  I will be checking with the RV anti freez manufacturers to find what percentage their product consists of glycol and what other additives are present and what effect they may have on a heating system.

Jean-David Beyer

I would not do it that way.

I am not a professional, but I have a relatively new mod|con boiler with an aluminum heat exchanger. I do not happen to have anti-freeze in it, because the contractor that installed it recommended against it. I have since gotten a new contractor, but they did not recommend anti-freeze either. I am in New Jersey where the design day is +14F which is only a little below freezing My downstairs zone has its reset curve set so the circulator runs most of the time in very cold weather. Furthermore, my boiler's control board will turn on the boiler at low fire if the water temperature in the boiler gets below 40F and runs until it gets up to 45F. The piping is primary-secondary, and the boiler circulator and the circulator for the downstairs zone (radiant in slab) are turned on. This should handle everything except long-term power failures or unnoticed boiler failures.



I have had this house for 34 years now, and the only long-term power failure was about three days, when the transformers at a local power substation burned out. This was at the height of the air-conditioning season. The power company had replacement transformers on the property because they were going to replace the ones that failed, but at a later time. I have had 6-hour power failures sometimes, but that would not freeze the system around here.



Were I to put anti-freeze in this system, I would  use what the manufacturer specifies. In my case this would be ALPHI-11 from Weil McLain, Aluminum Safe Propylene Glycol from Chemical Specialties Inc, or Rhogard from Rhomar Water Management, Inc. They say not to mix it any stronger than 50%.