Head loss through a Tarm 40 Boiler at 14gpm?

[oldmilwaukee]

I'm almost through plumbing my Tarm Solo 40 boiler (ha, I could be saying that two weeks from now too!) and I've already put a Grundfos 15-58 pump on the boiler (pumping into the boiler, per the tarm instructions). My boiler loop is completely plumbed (I'm starting out with no water storage in my system), except I still need to splice in the expansion tank and make-up-water line and I'm debating on where to put it. Everything I've read says to pump away from the expansion tank, but that's not necessarily how the Tarm instructions show to do it. I'm leaning toward putting the expansion tank on the return line to the boiler, so the only thing between the expansion tank and the pump intake will be the Thermovar mixing valve. I suspect that mixing (tempering) valve has as much resistance as the boiler and my primary loop piping. I can find the Cv for the mixing valve (but those pesky unions that attach it are so restrictive, that I wonder if the Cv number from the mfgr. is valid for the Thermovar). What I'd like to know but can't find out is... how much head loss does the Tarm boiler itself represent at 14gpm? Seems like a simple enough question, but the tech I talked to today could not give me a number. Does anyone have even a rough SWAG? Seems like this would be a very handy number to have.

Thanks in advance for any guesses or real numbers!

 

[flyingcow]

I'm just a truck driver......so bear with me.........why? I just had a tarm system installed by a very finniky/pain in the ass heating contractor, and head loss was never brought up. we installed per tarm diagrams and their equipment.

 

[oldmilwaukee]

At the end of the day, it probably doesn't matter too much. But I'm running on solar panels (for electricity), so I'm trying to use the smallest pump (electricity consumption-wise) possible. Also, if I knew the head loss through the boiler, then I could guesstimate the pressure at various points in the line when the system is running, so I would know if the intended placement of my expansion tank is going to be OK. This is my first rodeo - I guess an experienced installer would know what to sweat, and what not to sweat...

 

[Hydronics]

With respect to friction loss in the piping, I'd be quite surprised if head loss through the boiler is worth considering. I can't imagine Tarm designing it with any small orifices between the sections.
Keep in mind that most head loss in a pumped system is created by friction along piping (major losses) loss is also due to fittings (minor losses). The exception is when pipe runs are very short.