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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?

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up vote 7 down vote accepted

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.

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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.

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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.

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