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Radiant Floor potential issue

papetk Member Posts: 11
I finally installed an in-slab radiant floor heat system, much in part due to the sound advice I received here on previous threads. The system is fired with a Navien NHB-080 modulating condensing boiler operating on LP and the rest of the system is designed/packaged by Radiantec. It's 12 loops of 300' 1/2" pex, 2 zones, although I have them set the same. I have a 30% mixture of antifreeze as this is a hobby auto shop and I only intend to heat to 55-60 and it's been in the single digits at night here in VA. Here's my question:

The radiant heat controls package from Radiantec, includes the controller, the thermostat, and the digistat to measure input/output temp differential. Also, Radiantec designs their systems for a wall mounted tankless hot water heater, but it was this forum and other heating pros that recommended the boiler option. Everything appears to be working...however the Navien has a ton of options to set. I am wondering if all of the controls that Radiantec provided, are also included within the boiler and if I am confusing the boiler or not operating as efficiently with those added in. When the boiler turns on (Thermostat calls for heat), everything fires, the pumps run, etc. When the boiler cuts out, all the pumps stop too. Shouldn't the pumps continue to circulate for a determined amount of time, even with the boiler off? Also, do I want to enable Outdoor Automatic Reset? I have had it both enabled and then disabled. My HVAC guy, who is awesome at air handlers, but not that knowledgeable with boilers, thinks I want it off, as in this setup, the boiler is purely taking commands from the radiant floor controller.

Anyway, sorry for the long post, just trying to make sure things are set properly. I fear it may be short cycling. It is definitely keeping temps up, which is amazing.
Thank you!


  • GroundUp
    GroundUp Member Posts: 1,926
    In typical Radiantec fashion, the system is piped wrong, the pumps are grossly oversized, and the expansion tank is for a domestic water system- not a hydronic heating system. It is also in the wrong spot. Typically, there is a post-purge run time for the circulators to rid the boiler of any residual heat so yes they should be running for 30-60 seconds after the heat call ceases. Using the ODR will certainly help with your efficiency by lowering water temp on warmer days. I will never understand how Radiantec continues to do this to people.
  • HomerJSmith
    HomerJSmith Member Posts: 2,468
    To be truthful I have only worked on one Radiantec sys. Professionals in my area don't use that setup. It seems from their web site that it is geared for the homeowner, do it yourself, which was the case on the one sys that I worked on.

    I think that I would have installed a buffer tank and operated it as a primary/secondary sys, but what do I know.

    Outdoor reset is an energy saving option which I alway take advantage of. I don't know if the Navien regulates supply temp with a supply sensor. If it does I would use it.

    I think you are going to get short cycling with your setup.

    I would contact Radiantec for the answers on their controller vs Navien. They claim good tech support.
  • papetk
    papetk Member Posts: 11
    I appreciate the input! Where should the expansion tank be and how oversized are the pumps? The slab being heated is just shy of 2000 sq ft. What else is piped wrong? I want to get this correct for the long haul, even though it is heating extremely well so far.
  • hot_rod
    hot_rod Member Posts: 22,261
    edited January 2022
    Do you have the installation manual? I think that boiler needs to be piped primary secondary or with a hydraulic separator. The sell the piping kit as an accessory 
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • GroundUp
    GroundUp Member Posts: 1,926
    As Bob mentioned above, the Navien manual will show you how it should be piped and the expansion tank (a hydronic one, not that one) location. Those appear to be 26-99 circulators, which won't hurt anything if run on speed 1, but a 15-58 would have easily done the job with half the power consumption and would have saved you $600+ upfront. Honestly, it will probably be just fine as-is, but if there's ever an issue, Navien will take one look at the piping and deny all warranty.
  • jad3675
    jad3675 Member Posts: 127
    GroundUp said:

    I will never understand how Radiantec continues to do this to people.

    I'm just a guy who reads a bit on the internet, but their 'Open Direct Radiant' system doesn't seem exactly...safe.

    Also, this: