Sizing Circulators

#2Fuel

I am trying to find the GPM so I can size the circulator I need for my hot water system. I am looking at the chart is Dan Holohan's new book. The problem is that I do not know which pipe size to use. I have 2" at the boiler and circulator. 1-1/2" mains running in the basement. 1" and 3/4" risers running upstairs. What pipe size do I use? What is my GPM?

Thanks.

Steamhead

Did this system run by gravity

when it was installed, that is, without a circ? If it was installed before about 1930, it probably did.



In that case, use this chart:



http://www.heatinghelp.com/article/343/Circulators/238/Sizing-Circulators-for-Hot-Water-Heating-Systems

AlHeating

Old thumb rule

Hi,  You're talking about the actual pump size, and with the small pipes you're talking about, it would be surprising (but not impossible) that the system was originaly a gravity system.  Can you tell us what was the pump model installed?  How old is the building?



Normally, we simply go with the simple 10GPM per 100 000 BTU/hr.  If your boiler is 200 MBH, then 20 GPM would do the job.



Probably that your boiler is a bit oversized for the building.  If the system was designed with 1 1/2", 2" boiler connections and pump is probably too big.  I would use the 1 1/2" in the charts, but again, I would refer much more to the MBH of the boiler in your case.



You need to be as much careful about the HEAD of the pump than the GPM when selecting the new pump.  You can compare with the actual pump GPM and HEAD.  I see a lot of mistakes in pump replacement situations.  Many people change their old "high flow low head" pump for a "same flow but much more head" pump.  Selecting a pump only with the GPM is a big common mistake. 

#2Fuel

I think I get it

It sounds like I should decide my GPM based on the most COMMON pipe size in the system. In other words, If I have 2" at the boiler and pump but 1-1/2" mains running throughout the entire basement, I should use the GPM of 1-1/2" pipe. Also, I should check that with the BTU of the boiler. 10 GPM for every 100,000 BTU.



Thanks for your help.

Jason_13

Pipe size

If the boiler pipe size is bigger than the building pipe size I am concerned the boiler is oversized. What size is the new boiler and what size was the old boiler?