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New Lochinvar combo questions

I’m about to install my Lochinvar noble Combi boiler. I’m using it for in floor heating in my shop and apartment. The PEX is already in and I have two questions. One we are in Montana in sub freezing temps right now. What should I keep the air pressure at in the tubing? We won’t be getting our propane tank installed for a few more weeks.
My second question is do you suggest filling the tubes with glycol or water or a mixture of both? We have very hard water here coming from the well. Is that ok to use ? 


  • GroundUp
    GroundUp Member Posts: 1,735
    After the slab is poured, there is no need to keep air pressure on the lines. Many will poo-poo the glycol idea, but I won't install a garage/shop system without it. There is a common misconception that glycol is glycol and that is false. You would want to end up with a 30-35% total concentration typically- so you can buy it premixed to that level, or you can buy it at a higher concentration and mix it down with water and add the appropriate inhibitors. If you have hard water, I would not use it. DI or RO water can be purchased pretty reasonably, otherwise maybe just buy it premixed to eliminate any "what-if" scenarios
  • hot_rod
    hot_rod Member Posts: 20,725
    No harm in leaving the air pressure on, especially if walls or equipment will be anchored into the slab

    Glycol or not depends on what you have for backup in event of a power outage or boiler failure

    I run my detached shop on constant circulation, plain water. With the water moving it would take a few days for the tube to come close to freezing. I have an electric boiler back up and a generator so I feel I could handle an extended power outage

    Glycol brings some baggage, cost, maintenance, additional pumping power, tends to leak around threaded joints more easily

    But piece of mind is the trade off. If the home is left unattended for days in winter, factor that in.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream