How many feet of head? Boiler design

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MikeG88

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I've attached a scan of the blueprint section showing the location of my HWBBs and I penned in the approximate runs of 3/4" PEX that connect them. The HWBBs are typical slant fin type stubbed through the floor. The system plumbed primary/secondary - with the primary loop being 1" and this secondary loop is 3/4". (There are two thermostats shown in the print, but only one was ever installed (at design time- two zones were an option)). I've seen formulas and different rules of thumb for estimating feet of head but would appreciate an educated/experienced opinion.

I'm interested in using this information to plot my GPM on the curve chart for my current pump on the secondary loop. I have a problem most likely caused by a low Delta-T and it has been suggested (see my other recent thread) I reduce the volume through the loop either by changing out the pump or installing a flow restricter. I'd like to get an idea of what my flow is now and what the range of adjustment would be with other pumps, as well as how drastic the change would be using a flow restricter.
 

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MikeG88

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I'm figuring 144 feet around the perimeter (I know it actually a bit smaller on the inside), plus 14 extra feet to get the HWBB on the interior wall and another 17 additional feet to pick up the HWBBs in the kitchen. So that equals 175 feet of 3/4" between the pex and baseboards. So if I use the common rule of thumb to multiply x 1.5 to account for elbows and other common connectors then multiply by .04 to represent 4 feet of head per 100 feet of 3/4" copper (assuming pex is reasonably close to copper), I get 10.5 feet of head.

I'm running a Taco 00R-MSF1-4IFC on the slowest speed. Checking 10.5 feet of head on the performance chart puts me at 4 gpm.

I'm hoping somebody can validate my rough calculations or point/correct out my error(s). I'm assuming that the 4 gpm is a bit too fast and the main cause of my low Delta-T...
 
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