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Converting one hot water zone from fin tub to cast iron radiator. Am I over pumped?

The scenario:
I am converting one zone of a two zone system from copper baseboard to cast iron radiators as part of an apartment remodel. It is in the basement level and the remodel has reduced the finished square footage to 700ft and greatly improved the insulation.

The zone is currently plumbed at the boiler (leftover from previous copper baseboard) with a taco 007-f5 pump and a B&G flow check valve. I have calculated the heat loss at 12,000 btuh and plan to use two cast iron radiators, one rated at 10,000 btuh (that I currently have) and another one at 2,000. They will be served with a split loop of 3/4 copper since that is what is left from the copper baseboard. The loops will be much shorter, since the first radiator is approximately 10 feet from the boiler and the other is 25.

I am not sure how to calculate head loss but following the calculation guide from Taco the best I can it appears I am over pumped with the new layout. I am more of a carpenter by trade and I originally though I could just hook up the new layout with cast iron radiators to the old near boiler plumbing and it would work. Now I am not so sure.

Now some questions:
What would be the best thing to do now? Install a different pump? Is there a low flow pump for a small zone such as this? Change size of the piping? Do I need to provide more information for a better answer? Do I just keep it as is?

Any recommendations are welcomed. Keeping the cost down is a high priority.

other system specs:
HB Smith 8 Series S/W4 Boiler Rated 133 -150BTUH With domestic hot water coil, currently set with a high temp of 180 degress and a low of 160 degrees.
Taco 007-F5 Pump for each Zone (floor)
Each zone has a B&G flow check valves
Taco air scoop with expansion tank
Other zone (main level) is 1,500 sqft living area with split loop of copper baseboard. I have not calculated heat loss for this zone but current system appears adequate.


  • icesailor
    icesailor Member Posts: 7,265
    Use the Taco 007-F5. But you can NOT series loop the two radiators. Use some form of parallel reverse return to get them to heat evenly.