# Over-sized Pump vs. Undersized

How did I end up with a Taco 011 pump for the secondary system anyway? The project spreadsheet has the original calculations.

 Pressure Loss Zone Length Delta T 20 degrees Loss @ 20 Rear Bedrooms 1 50 0.03 1.50 Family Kitchen 2 355 0.03 10.65 Entry/ Dining 3 330 0.03 9.44 Living 4 290 0.03 8.29 Master 1 5 245 0.03 7.01 Master 2 5 250 0.03 7.15 Highest 10.65 Secondary Loop Zone 1 3/4″ pipe Zone 2-5 1/2″ pipe Loop corners 90 degrees 180 degrees Total Pressure Loss at delta 20 Rear Bedrooms 14 28 Family Kitchen 11 9 29 Entry/ Dining 11 13 37 Living 2 14 30 Master 1 22 6 34 Master 2 30 4 38 1 1/4″ pipee Highestp 38 Tee Side Port 5.5 43.5 Reducer Coupling to 1″ 0.6 44.1 Reducer Coupling to 3/4″ 0.5 44.6 1″ pipe Air eliminator valve (gate valve?) 0.3 44.9 Tee Straight 0.45 45.35 Ball Valve 4.3 49.65 Tee Side Port (Tee off primary loop) 4.5 54.15 3/4″ pipe 90 degree elbow 2 56.15 Zone Valve 10 66.15 Plus longest 1/2″ length 10.15 Equivalent Feet of Pipe Divided by .04 132.45 5.298 Total HEAD Loop plus piping 15.948 Room Zone BTU Capable Sq. Ft. Rear Beds 1 15729.00 565.00 Family/ Kitchen 2 7281.00 342.00 Entry/ Dining 3 9419.00 315.00 Living 4 15942.00 420.00 Master 5 9952.00 376.00 Total 58323.00 2018.00

Given a requirement of about 60,000 btu/hr, if 10,000 BTU/hr= Pump Speed of 1 Gallon per Minute, then the base pumping requirement is 6 GPM.
Given an effective 16 ft. of head, then the pump needs to be capable of 6 GPM at 16 ft of head pressure.

Taco and Grundfos Pump Curves

According to the Taco pump curves, the 008 would not be powerful enough, the 014 would do the job and the next higher pump is the 011. So since it is more common and more easily available, the 011 seemed like it was a reasonable choice.

The downside is that I have burned out two of them! I am assuming that the pump is too big for just one zone at a time. The rear bedroom radiators are only capable of about 15,000 btu/hr which may be a bit undersized for the lower temperature water in the radiant system. So it runs more often that the rest of the system.

ECM pumps (electronically controlled motor) are considered much more energy efficient, however the largest residential pump I could find is the Grundfos Alpha 15-55 which is roughly equivalent to the Taco 008. Notice on the graphs above that the fixed speed Grundfos 15-55 is just a little more capable than the 008 although it can only pump 6 GPM at about 14 ft. of head. The Alpha graph shows a lower capability of 6 GPM at 12 ft. head.

Grundfos Alpha 15-55

Grundfos Alpha Pump Curve

Most of the time the pump should be operating at below the maximum requirement. The Alpha has the additional feature of showing the watts being used and the flow rate. Since it is designed to provide a constant pressure that adjusts automatically as the demand adjusts, it should not burn out from not enough flow. So I ordered one from Supply House and took advantage of a three day 15% off coupon that came just when I needed it. With that the pump was only \$275 so hopefully it fits the taco flanges and I can install it when it arrives.

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