Primary loop

[Elegance]

Do I need to install primary loop on hydronic system with only one infloor manifold? I know that always good to have it and manufacture recommend it, but I always saw recommendations only for bigger system(infloor and rads together) and never for this small system or boilers up to 50 000.

[scarey8]

I've seen it before, and it might work, but boilers are such a flow sensitive appliance I would look at your flow rates before doing it.   

I would only do this orientation if the in floor manifold design gpm was equal to that of the flow rate of the boiler. 

GPM is naturally sized based on BTU, the general rule I've always referenced is 1 gpm per 10 000 btu, water tube boilers are generally more sensitive to flow than fire tube boilers, so you can also look at adjusting your equipment if you absolutely want to avoid the primary loop.


you should have an infloor loop design which details the flow rate, if it matches the boiler pump design criteria, you might be good. 


example of potential problem...

if your infloor system is sized at 10 gpm @ 10 000 btuh, but your boiler minimum modulation rate is above that, you will run into delta T issues or short cycling, primary loop / hydraulic separation would be needed then,

spend some time, look at the numbers and the boiler piping in the install manual, you can't ever go wrong with installing the boiler as per the piping drawing in the manual. 

and remember.... A short cut is the longest distance between two points.