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[GCTerpfan]

I question the 9 foot head estimate.  Does that take into account elevation, pipe length and every possible flow obstruction?

I did screw up the head calc.  I have a 370' loop of 1 1/4" pex with 10 elbows, 4 ball valves, 2-5x12 plate Hx with 1 1/4" ports, and a 6' elevation difference. Disregarding the Hx the 'correct' head number is 15.6' (unless I screwed up again). 

With the Taco 009 this should mean I have a flow of about 7 gpm.  (http://s3.supplyhouse.com/manuals/1350986824086/84486_PROD_FILE.pdf)

So, I had supply temps of 180 and return temps of 127 for a difference of 53 degrees, lets take away the 4 degree drop I see with no load and that's a difference of 49 degrees.  Assuming I am getting a flow of 7gpm that means by turning all three thermostats up from 70 degrees to 75 degrees at the same time on a warm day, my system required 171,500 BTU?

Am I missing something or doing something wrong? These numbers just don't make sense based on what I know (or think I know).

Am I over thinking it?  We had temps in the 30's this weekend and when I fixed the fire I never saw return temps below 165. 

[LittleJohn]

I would assume since you did not account for the HX, your flow rate is a bit lower, so BTUs are also a bit lower. 

What is you application, cause 171k BTU/hr might not be out of the question, but without know what your load is or how big your structure is its hard to say?
...I do think a delta T of 50f seems a bit high, but my longest run is 100' one-way

[GCTerpfan]

What is you application, cause 171k BTU/hr might not be out of the question, but without know what your load is or how big your structure is its hard to say?
...I do think a delta T of 50f seems a bit high, but my longest run is 100' one-way

It's a well insulated house with an 1,100 sq. ft. floorplan and a partially finished basement for a total of about 1,800 sq. ft.  The previous winter which we had very low temps including a two week spell of subzero temperatures I used less than 500 gallons of fuel oil to heat my home. 

The three zones in the house feed a total of about 100 linear feet of hydronic baseboard.

So another way would be to assume 600 btu/hr per foot of baseboard and I'm stiil only at 60,000 btu/hr.  I just cant figure out where all of the btu's went unless I am getting significantly less flow than I think. But I admit I have no idea what I am talking about either