something awry

bovide_4

boiler: Burnham V74, 140 mbh
heat loss of house: 60,000 btuh
12 loops of 1/2" pex, not exceeding 250 feet.
1/2 house is in slab, other half is staple-up w/plates.
boiler piping: 1 1/4" primary loop w/Taco 007 on primary loop.
Taco RMB-1 off primary loop w/closely spaced tees.
I made my own supply and return manifolds.(12-1/2" outlets soldered onto a piece of 2" type K copper.)
Problem: on a cold day, the mixing supply lags behind the target mixing temp. by at least 20 degrees and does not catch up.
Anything obvious as to where I went wrong, aside from my homemade manifolds?(can't send pictures-it will win the "ugly" contest from a few months ago.)

Al Letellier_9

whats wrong

Not enough info here.....only 12 loops? Insulation, controls, loop layouts, flow control, these all play a part in how the sytem works. Did you do a heat loss? What is delta T on the loops? How are you controlling the flow to the loops?

bovide_4

more info

the house is small: 2400 sq. ft.
heat loss of house: 60,000 btuh
the house is insulated well. the staple-up w/plates have R-19 fiberglass in the joist cavity.
flow control: 1/2" globe valves on the homemade manifold supply (should be on the return)
control: Taco RMB-1 with outdoor reset, and conventional thermostat inside.
loop layout: 8" o.c. (wirsbo thin plates, I know not the extruded)

McKern

Outdoor Sensor

Is your outdoor sensor exposed to and able to read the true outdoor temps?

Weezbo

Dave, how do you control the zones?

are all the loops ,both staple up and medium temp lashed into one headder with the idea you can meet the heat loss with the same water temps in both and zoning is a non issue?

Jed_2

Also

Is the outdoor sensor shielded from direct sun, are the system sensor and boiler sensor well insulated around the pipe?

Jed