Push or Pull Circulators

[TimCee]

I am new to the forum but have gotten a lot of good advice here as a lurker but I need to know what I should do in my situation. I replaced an old (from the 70's) boiler with a new Westinghouse WBRCNG140W 140k BTU Condensing Natural Gas Combi Boiler. It has a inline circulator on the supply side and I am wondering if I should place my new second circulator on the supply side as well. My system has the zone valves on the supply side and the old boiler had the circulator on the return. I purchased a new Taco VR1816-HY2-FC2A00 variable speed pump and I was going to place it back on the same return side but the installation manual says I should place it on the supply side. The two circulators would only be 3 feet apart, I am not sure if this would matter but two pumps that close just doesn't make sense to me. I would think placing the Taco pump on the return would work better. It appears I have to place closely-spaced-tees as well with this setup (or do I) so I am going to place that near the boiler. I would like to pipe this as much as possible because I would like a certified tech finish this up. Any thoughts or opinions would be greatly appreciated, thanks.

 

[Dana]

That combi boiler doesn't need another primary pump, but it does need to be plumbed primary/secondary rather than pumped direct- the flow for the secondary pump driving the radiation needs to be hydraulically separated (by closely spaced tees is one way) to keep the flows from interacting too much. It should never be pumped-direct on a system that uses zone valves. The internal primary pump it came with can handle the primary loop, even if if the hydraulic separator is some distance away.

Where in the manual does it indicate a preferred direction for the secondary pump flow?

 

[Sponsor]

 

[TimCee]

Thanks for your reply, makes so much sense to me now, I cant thank you enough because this has been driving me nuts trying to find an answer to this. I attached an image file of the directions indicating where and how the circulator should be placed. Thank you Dana for your answer and helpfulness.

 

[Dana]

There is nothing in the verbiage that indicates a preferred direction, but pumping away from the return manifold (instead of toward the supply manifold) on the secondary might affect the operation of the differential by pass valve.

No matter what, the orientation and relationship between the expansion tank & secondary pump needs to be preserved- if the pump moves, so does the expansion tank, and putting it on the return side would limit the amount of cavitation mitgation the tank could offer the primary (internal) pump.

Is there a reason why you don't want to or can't set up the secondary pump to pump away from the closely spaced tee hydraulic separator, and toward the supply manifold? If space near the boiler or supply/return manifolds are tight, the runs between the boiler and tees can be quite long (tens of feet, but not hundreds) and it'll still work.

 

[TimCee]

So I thought I should take a pic and sketch out my plans. It's not to scale of course but I placed some measurements by the closely spaced tees and if I have the room, I might extend that tee branch (supply side) from 10 inches to 12. Yes, thanks to this forum and members like yourself, I understand the importance of expansion tank near and behind the circulator. I really would like to keep everything on the return side where it is cooler just to get more life out of the parts. As you mentioned, I do have limited space but I will have a lot of cutting and re-piping to do but I'm certain I can make it work. Thanks again Dana for your help and quick replies (I can tell, you know what your talking about).

 

[Dana]

I really would like to keep everything on the return side where it is cooler just to get more life out of the parts.

That argument may have had something to it for systems running 180-200F water on the supply side with a cast iron boiler, but with condensing boilers the seasonal average temperature on the supply side is several tens of degrees cooler than the return side of a high-temp-only boiler. You won't be cooking the windings, seals & bearings nearly as much with the condensing boiler, and it will experience far fewer large temperature swings & associated mechanical stresses from expansion & contraction. Put it on the supply side and fuggedaboudit.

Thanks again Dana for your help and quick replies (I can tell, you know what your talking about).

I just make it up as I go along- but just lucky enough to get it sorta-right sometimes.

 

[TimCee]

OH!! OK that would work out great then keeping the pump and tank on supply side, but I would be pushing into the zone valves but I am guessing that would be OK then? I cant thank you enough Dana, thanks for your help and replies.

 

[Dana]

OH!! OK that would work out great then keeping the pump and tank on supply side, but I would be pushing into the zone valves but I am guessing that would be OK then? I cant thank you enough Dana, thanks for your help and replies.

Pumping on the supply side, toward the zone valves is how it's usually done these days.

 

[Fitter30]

That taco pump has a temperature limit of 230* so it doesn't matter was side of the system. Does the boiler have a outside temp sensor and is it on the north side of the house? With just a sensor you can have a boiler reset control that will very heating water temp based on outside temp to save energy. Heres a install manual.

https://images.homedepot-static.com/catalog/pdfImages/85/85f91a7b-2a4e-4deb-9331-8ac1ffc23d5e.pdf

 

[DrS1]

Hi @TimCee , I'm considering this exact boiler. I'm seeing mixed info online, does yours have a 10:1 turndown ration (min BTU 14k)? How did the install go?