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NAVIEN

Paul SPaul S Posts: 503Member
Hey everyone....tomorrow I will be installing a navien combi boiler tomorrow for a customer of mine...this is for radiant in slab job....the customer ran the pex himself and buried the tubing....my question is at what temp should I be supplying to the zones....? The navien boiler will just be doing two radiant zones and dhw....I know I'm giving very little info but anything would be of help....I don't do pretty much any radiant jobs.......all I really know is from dans books.....also about the water temp can I control it with mixing valves or can I set the boiler to maintain the temp.....I will get more info tomorrow when I get the manufacture literature.....should I use manifolds? Zone valves or pumps?...I will be piping this primary secondary....thanks Paul s
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Comments

  • SWEISWEI Posts: 4,541Member ✭✭✭
    edited August 2013
    I hate to sound like a broken record, but...

    a room-by-room heat loss is your first step.



    For a job like this, it's literally unavoidable -- since you don't know if the original design (aka the tubing layout) was at all correct.
    Post edited by SWEI on
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  • Paul SPaul S Posts: 503Member
    swei

    I know I really shouldn't of taken this job but even if I do the heat loss....how would that give me the temp....? Like you said I do not know what's buried....Paul S
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  • SWEISWEI Posts: 4,541Member ✭✭✭
    What tube spacing

    and loop lengths are you dealing with?



    Assuming the owner has good records, start with those and run the numbers.



    If it's literally a case of "I don't know," you need to charge an appropriate fee (or outsource the work required) to determine the capacity of the installed loops.
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  • heatpro02920heatpro02920 Posts: 989Member
    math math math

    Does he know how much tubing is in each circuit? I always keep my loops very close in length and record them {some tubing still comes with counters, so oyou may be able to figure it out}.



    I would do a heat loss for each manifolds space, then figure the minimum temp needed to meet the zones requirements.... then go with the highest number for all the zones as the baseline... so if one zone calls for 91 and the other is 96 go with 96....



    Did he have a drawing made by the materials supplier, I did a boiler for a customer who installed his own tubing, but he was smart enough to bring his prints to the supplier and let them make a parts list and drawing with all the temps and flow requirements printed rite on it...



    When all else fails go 95 degrees and call it a day... :)
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  • Paul SPaul S Posts: 503Member
    95

    You mean 95degrees supply to the radiant loop...?
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  • HomeOwner1HomeOwner1 Posts: 134Member
    I own one - good so far

    Just a homeowner, but my two cents.



    The manifold makes this easier to pipe up and will save you a bunch of time, if you have the clearance available.



    In my home, it was a rip a replace of existing very well balanced loops already. Glad that was the case, otherwise it could have gotten complicated very quickly calculating flows in each loop, pump size and other stuff.



    If you buy the outdoor temp sensor and hook up to the unit, this will modulate the loop temperatures automatically and then you don't have to set them. You just have to calculate the setting of the curve on the control unit for the design day temperature in the region of the country.



    Make sure you install it correctly!



    Our unit was done by a guy who has done many of them prior. Things like monoflow Tees, pumps on the supply side pushing to the loops, the makeup has an internal pressure control and sizing the primary loop and feeds are very important. It was surprising to me how much different this was from my previous cast iron boiler configuration.



    We have zone valves and multiple thermostats in the home. There are dip switches to configure external thermostats and other settings.



    We set our hot water temp to 130 degrees by the way. More of a consistent temperature to what we were used to with our previous setup. We have three baths and works good for us.



    Another tip, set the unit up for the external well water setting. Works better that way for some reason.



    Also, we were advised to stay away from the 180 unit and only stick with the 210 or 240 larger ones.



    Good luck.
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  • ChrisChris Posts: 2,869Member
    edited August 2013
    Do The Heat Loss

    Suggest you do a complete heat loss and radiant design for what should be in the floor. Then weigh the water in the loops. There is .92 gallons of water in 100' of 1/2" pex.. Now you have your loops lengths! Adjust the loops lengths in your design to find your water temperature.
    Post edited by Chris on
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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  • ChrisChris Posts: 2,869Member
    Boiler Cannot Modulate The Loop Temeratures

    Impossible when piped pri/sec or LLH when the system flow rate exceeds the boiler flow rate and in the case of the Navien that's 5gpm! Reason it's impossible is that the Navien does not utilize a downstream temp sensor and when the system flow rate exceeds the boiler flow rate your mixing in colder return water temp into the supply water temp.



    (Sys Rtn Flow - Boiler Flow) * Sys Rtn Temp + (Boiler Flow)*Boiler Supply Temp/Sys Rtn Temp = System Supply Temp
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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  • HomeOwner1HomeOwner1 Posts: 134Member
    Confused

    My boiler modulates the main loop temperature. This is the main 1 inch loop. This feeds any sub-loops.



    It keeps heating until that main loop loop reaches the target temp. In my case, I have 6 loops in large home with 3/4 piping. I never noticed my loops not getting sufficiently hot with any appreciable delay even in the furthest sections even when all six loops are going at the same time. It performs just as quick heating up the loops as my old cast iron boiler did.
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  • Paul SPaul S Posts: 503Member
    customer

    Said both loops are 250 ft.....at 1/2 pex....thanks Paul s
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  • ChrisChris Posts: 2,869Member
    You Should Be

    Your a homeowner..
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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