I currently have a forced hot water heating system with 3 zones, all of which have the circulator pump on the supply side of the line. I need to install a 4th zone and am being told that putting the circulator on the return side is more efficient.

What are the pros and cons of the circulator's location? Are there issues having some on one side and some on the other?


Water pumps pump water, not air, so putting it on supply side makes water allways available for circulator to pump. If you put that circulator on other side it could be hard to fill system with water and avoid air pockets. And basicly you can't pump air with water pump as it makes them break.

  • Actually, putting it on the return side can create pockets of air, if you have a strong enough pump. – Brad Gilbert Oct 28 '11 at 5:12

I'm making a bit of a guess here but I would speculate that there are two factors at play:

1) Hot water going through the circulation pump is more "active", and thus could shorten the lifespan of the pump (active meaning more likely to cause corrosion); and 2) When you push water through pipes, the path of least resistance will get the greatest water flow. When you PULL the water through the pipes, you'll create suction on all the flow paths, which I guess would mean the water flows more evenly through them.

All of this is sheer speculation on my part, however.


The location of the pump would all depend on ehat kind of a heating system you have. If you have multiple zones and the zone valves are on the supply, then the pump can go either on the return or the supply. If you have multiple zones but with circulating pumps the i would put them on the supply. However, if you do have multiple zones but with circulating pumps and the pumps are on the return, then you would need to have zone valves on the supply so that one of the pumps only heats up the area where the thermostat is calling for heat.


Fluid dynamics is a field of engineering that is very intense and complex. However simply put, it is a game of pressure differentials and not a path of least resistance or "last river" concept. Pumps "pump" because they create a lower pressure on their suction side, and a higher pressure on their discharge side, and flow is created. The higher pressure will always seek the lower pressure. Every time the flow meets resistance, ie pipe friction, turns, coils, heat exchangers, the pressure gets a little lower on the other side of that resistance.

Now depending on how you pipe your boilers, if you put your pumps on the supply side, my personal preference and the preference of reputable heating contractors, you keep the higher pressure at the air removal portion of your piping and you have a greater chance of getting the air out of your system.

The other school of thought is to have the highest pressure of the system at the boiler as it is the greatest resistance to flow. Also most boilers come with some kind of rudimentary air scoop in their exchanger, and if that is all you plan to use to remove air, then the return is a good option. I also wonder if its sheer laziness as the boiler usually comes out of the box with the pumps mounted on the return side.

To sum up, it sounds like you had a good heating contractor design your piping system and I would stick with keeping it on the supply side!!!



Flow Dynamics dictate that you should have it on the feed not the return also try adding so glycol to the system as it will extend the life of your circulator

  • Also you don't need the flow check's they are obsolete there is a ciculator with an internal check or you can buy the check and insert it yourself just remember to get a new flange gasket – Bruce Miller Sep 22 '18 at 16:52

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