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Where to put the circulator pump on hot water heating systems: Here we explain where the circulating pump can or should be mounted on a hot water or hydronic heating boiler.
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This article series discusses hot water heating system circulator pumps: how to find, inspect, diagnose, and repair problems with Hot Water Heating System Circulator Pumps or circulator pump relay switches and controls. This article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs. The heating boiler piping diagram at page top, courtesy of Raypak® shows the heating system circulator pump assembly (red in our sketch) on the return or inlet side of the heating boiler. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
We often receive the question "Where should the heating boiler circulator pump be mounted: on the supply or boiler outlet side (the hot side) or on the return or boiler inlet side (the cool side) of the heating piping loop?"
Read the instructions: The short answer is, mount the circulator and arrange all other piping and controls according to the boiler manufacturer's installation and operating instructions and you won't go wrong. A sample boiler installation and operation manual that is particularly clear and easy to follow is provided by Raypac® but of course you should obtain and follow the instructions from the maker of your particular boiler maker.
On the boiler return or inlet side: most but not all residential heating boilers and probably most commercial heating boilers mount the circulator pump on the return or inlet side of the heating boiler.
This location is a traditional one preferred by some old-school boiler installers and service people, dating from a time when a boiler came from the manufacturer without the circulator pre-installed on piping attached to the unit.
Some heating service technicians (including the web publisher) opine that the cooler heating water temperature on the return side of the boiler means that the circulator pump and its bearings may have a longer life than if installed on the hot side.
Typically heating water returning to a boiler after circulating through a building is about 20 °F. cooler than water leaving the boiler. The heating boiler piping diagram at page top, courtesy of Raypak® shows the heating system circulator pump assembly (red in our sketch) on the return or inlet side of the heating boiler.
By piping convention the triangle (which we surrounded in red for emphasis) points down, showing the direction of water flow.
On the boiler supply or outlet side: as we explain just below at Air Exit Tanks, in some heating boiler installations that use an air exit tank to combine the Expansion Tank function with the Air Bleeder Valve or air purge valve function on a heating system, the air exit tank is mounted on the header piping on the supply side of the boiler and the installer may prefer to place the circulator pump below that tank to improve the air purge function of the system. Air exit tanks are not common on residential heating systems.
It does not matter which side of the boiler gets the circulator pump: ultimately, from a functional viewpoint, it does not matter one bit which side of the heating boiler has the circulator pump mounted, supply side or return side.
That is because in a hydronic heating system the circulator is pushing water around a closed loop: the boiler and boiler piping are filled with water and there is (or should be) no air in the system. (If a hot water system piping or boiler contains more than a few bubbles of air the system is likely to become Air-bound and heat will be lost or missing in all or part of the building.
The circulator pump is only a water mover, not a water lifter. The hydronic heating system is relying on the starting water pressure in the heating system to provide enough lift to get hot heating water into baseboards, convectors, or radiators in the upper floors of the building.
Typically the cold starting pressure in a heating system is 12 psi, provided by the Water Feeder Valve on the boiler. On tall buildings higher pressures are needed - we provide a chart of pressure reducer/water feeder valve settings at WATER FEEDER VALVES, HYDRONIC BOILER.
Circulator pump position: Watch out: as we explain at our home page for this topic (CIRCULATOR PUMPS & RELAYS) be sure that the circulator pump is installed as the manufacturer describes. While most circulator pumps can pump heating water in just about any position, there are some positional constraints. For example, quoting from B&G:
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
Other heating system controls related to hot water circulator pumps - three alternative ways to control hot water heat circulation