Where to place the circulator pump - on the Supply or Return?

[rickh1001]

I am ready to start cutting pipes and put together the near boiler plumbing loop for an EKO 60, with a 500 gal LP storage tank. I can't figure how to draw a decent picture and post it, but the fundamentals are pretty simple. The supply comes out of the top of the EKO 60 in 2" - but I will be reducing it to 1.5" black iron. The primary loop is the "normal" configuration, going to the tank in the top, and out the bottom for the return. There will be a pipe connecting the supply to the return, with a balancing valve, to a Danfoss 3-way thermostatic valve, controlling the return water temp. So this primary piping would look like two adjacent rectangles, the supply on top, the return on the bottom, with the balancing valve/piping being the shared vertical line.

Every book I have read, including the I=B=R guide, Holohan's book(s) and Siegenthaler all strongly recommend the combination of the placing the expansion tank (the Point of No Pressure Change), and the supply and air scoop, before the circulator, on the supply side out of the boiler. I understand their reasoning, and it makes sense. Based on that, it seems the worst thing to do would be to place the circ pump on the return side, and the expansion tank/supply/air scoop on the supply side, separated from one another. Yet, most of the diagrams I have seen, as well as the one supplied by the vendor who sold me the EKO, recommends placing the primary circ on the bottom, return run, and the expansion tank/air scoop on the top, just out of the boiler supply (along with the low water cutoff, venting valve and pressure relief valve).

So, if I plumb it "by the book", I would place the primary circ high up on the upper supply line run, after the expansion tank combo. If I follow the other advice, I would place it on the bottom return piping. One reasoning I have heard for placing it on the bottom return piping is that is will be the last thing in the system to run out of water if there is a leak - but the low water cutoff should have stopped everything long before that.

Should I go ahead and do it by the book, which means placing the primary circ on the upper piping run, after the expansion tank, or go ahead and put it on the bottom return run?

The head pressure on this 1.5" primary loop is very low - 4 feet of head or less, and the return line is 37" or so below the top of the water level in the 500 gal storage tank, so the suction side of the circ has little danger of seeing any starvation.

I know this has been discussed in previous threads, but I am still at a bit of a loss as to why it would be "wrong" to put the circ on the top supply side, as all the books recommend? Is there something different about having a storage tank, that changes the reasoning here?

 

[Dune]

One simple reason is that the circ will run cooler on the return side.

 

[Nofossil]

Unless you have a big pump and big head loss, I don't think the whole issue about pumping away from the PONPC makes much difference. At my plumber's advice, I put my Taco 007 in what would have to be almost the worst possible location and orientation according to the books you mention: Just before the boiler inlet, pumping downwards. It's worked fine since I installed it in 1989.

 

[BrownianHeatingTech]

Primary loop circulators don't need to "pump away," unless you have a very odd primary loop.

It's zone circulators that need to pump away - those going to high-head zones.

That's the general rule, anyway. Each install is different.

Joe

 

[rickh1001]

Thanks for the responses. I am using 1.5" piping with a short straight run (less than 10 ft each way) for the primary loop through the storage tank, so the head is minimal - estimated at less than 4 ft. The point is well taken that it won't make any practical difference if I put the pump on the return side in this system. The pump will run cooler, and being at the bottom level of the storage tank, it will actually have a positive inlet pressure.

The only advantage that has occured to me is that there would never be any debris getting into the pump when it is mounted on the top supply side. I am not adding a sediment trap, as the tank alone should act as a huge sediment trap, plus the upward run through the boiler, should keep any particulates to a minimum. Other than that, it will be much easier to mount it on the lower return, and it won't be subject to starvation if any air temporarily works into the system before the scavenger can remove it all.

Thanks for the help, and I need to get the pipe cutter fired up.

 

[EricV]

I put a 007 on each. Mainly for backup if one fails. I had them so it didn't really cost more except for the flange set. They are wired together. I figure on a system that cost me alot of money spending another couple bucks for a backup was worth it.

 

[Willman]

They are wired together.

Eric, how do you control (switch on/off) the backup circ ? It can't be running with the other can it ?
Will

 

[EricV]

Yes, they run together, in opposite directions of course.