Pump selection for gravity retrofit

James mo

I do not engineer boiler installations, but I am tasked with fixing them. I love working on these old systems, but I am having some problems with gravity retrofit applications. The sales pro reduces pipe size for gravity retro jobs, but I have come accross a few systems where some radiators will not heat. The one I am currently working with is a cast iron baseboard system with 3" mains. I originaly found the system piped with a taco 007 circulator and 3/4" supply and return at the boiler with bell reducers to get to 3". I summed up the problem as undersized pipe and circulator. The installers went back and re-piped with 1 1/4" pipe and installed a larger (don't know which one)cartridge pump. I was told that one long baseboard in the master bedroom still will not heat. I wanted a 3 piece circulator installed, but could not make a strong case for the expense. To sum it up, I could use some input on pump selection for these installations.

Robert O'Connor_12

Jmo'

As our host would say " It pays to wander off the wall".
Read this.

http://www.heatinghelp.com/newsletter.cfm?Id=125

Robert O'Connor/NJ

James mo

Happy Thanksgiving...I will be giving thanks for this site and helpful people like yourself. Many thanks Robert.

Mike T., Swampeast MO

Gravity

The one I am currently working with is a cast iron baseboard system with 3" mains.

Are you certain the baseboard is original? Gravity systems generally used standing iron. Is the structure especially high-styled?

system with 3" mains...taco 007 VERY common and usually works reasonably. 3/4" supply and return at the boiler sounds too small unless someone bastardized a standing iron gravity system by removing the rads and installing baseboard without bothering to repipe the entire system...

re-piped with 1 1/4" pipe That's the standard sizing for converting a gravity system WITH STANDING IRON to forced flow. one long baseboard in the master bedroom still will not heat I have no doubt...

I wanted a 3 piece circulator installed, but could not make a strong case for the expense "Bigger pump" is the most common proposition to "repair" an under-performing system. Were this a true gravity conversion you would be looking for a smaller pump...

Steamhead (in transit)

J'mo, Mike has a good point

take a close look at this system. I'll bet you find the runouts have been greatly reduced in size, which happened when the original radiators were removed and the baseboard installed. So all that water in the now-oversized main can hinder heat travel to the farthest rads.

If this is what you find, and a repipe is out, run a bypass line from the end of the flow main to the beginning of the return main. This will get all that cold water out of the way.

The one long baseboard that you have trouble heating could be split in two or three sections, each with its own supply and return connections to the mains. This would get more water into and out of those baseboards.

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