Circulation Pump Too Small?

DerekLH

We recently converted to a NTI Combi Boiler from a cast iron boiler upon purchasing this house built in 1925. Two story home with approx 2500 sq ft and 14 hot water radiators. The two pipe piping runs in a u shape with the boiler in the center of the U and going outward and is one zone for the entire house with the thermostat in the center hall first floor. The longest pipe run is about 75' across the house and up to the second floor, the second longest run is about 50'. There is one Taco07 pump on the system (supply line after the expansion tank). Radiators at the ends of the loop are luke warm while rads closer are overly hot. Installer has bled all rads and tried valve adjustments but no significant change is happening. I believe it is a circulation problem and that the pump is undersized and only getting the flow to go to the 4 or 5 rads closest to the boiler. I have to run the thermostat at 74+ to get any noticeable heat to rooms at the end of the pipe run.

GGross

take a picture of the boiler install please, and what model pump was removed from the old system?

Grallert

You might need to severely restrict the flow to the radiators closest to the thermostat

EdTheHeaterMan

What size is the pipe from the boiler to the system?

What is the model number of your NTI boiler?

Is this the pipe connections on the bottom of your boiler Fig. 10-2 (c)?

LRCCBJ

jesmed1

We live in a 100-year-old building with original cast iron radiators and a converted gravity hot water system. We have 11 radiators on 2 floors, 2400 sq ft, heated by a cast iron boiler. There's one Taco 007 circulator that does fine. Because the pipes are so big, there is very little flow restriction, and the 007 was pumping 19 GPM before I installed a controller to turn the flow rate down.

So it is possible to run a significant number of cast iron radiators off a single Taco 007, but only if you have big pipes and a big boiler. If you do have the original big pipes, I'm guessing the problem is the flow restriction through your new smaller boiler.

PC7060

I think the issue is the lack of flow control at the radiators which can be addressed by TRV at the radators.
I have a similarly configured heating system on 1928 home. The main supply / return lines are 2” with radiator pipe parallel series. The first floor radiators are serviced with 1” pipe, second level is 3/4” pipe.
The boiler is a low head FireTube with a single alpha 2 15 series circulator.

Works perfect running at low speed.
If the NTI has high head, you will need to pipe primary secondary and will need pump on both.

jesmed1

https://forum.heatinghelp.com/discussion/comment/1826719#Comment_1826719

We have similar pipe sizes, 2-1/2" near the boiler, then stepping down to 2" and 1-1/2", then to 1" risers for the first floor and 3/4" for the second floor.

But we don't need any TRV's, etc. The system is perfectly balanced. Not everyone is as fortunate, especially if their original old piping has been modified.

EBEBRATT-Ed

Agree with @PC7060 mod con boiler are restrictive to flow by design. If the Taco 07 is the only circulator in the entire system that could be your issue.

Not familiar with NTI and weather that boiler has its own internal circulator or requires primary secondary piping but that could be your fix if it does not have an internal circulator and requires primary secondary piping it has to be installed in accordance with the MFG instructions to work.

What is the model of your boiler NTI makes many.

GroundUp

Sounds like a balancing issue more than anything, but we'd need to see the piping to determine this for sure.

hot_rod

you can direct pipe some of the firetube models, everybody has them now. The manual may show you the available pumping capacity, beyond the boiler

Hydraulic separation is always an option, buy you get some temperature blending as flows vary

NTI, FTN model piping example

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