Raytherm boiler piping diagram from Raypak (C) Raypak 2009 and 2009Guide to Heating System Circulator Pump Location & Mounting

  • CIRCULATOR PUMP MOUNT LOCATIONS - CONTENTS: Where to Mount the Circulator Pump on a Heating Boiler. Circulator Pumps: Hot Water Heating System Circulator Installation. Where should a circulator pump be installed on a heating boiler? On the inlet or on the outlet side of the boiler? Use of air exit tanks and circulator pumps on heating boilers
  • POST a QUESTION or READ FAQs about where to mount heating circulator pumps
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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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Where to Mount the Circulator Pump on a Heating Boiler

Heating zone circulator pumps mounted on the return side of the boiler - preferred (C) Daniel FriedmanAt left our photo shows the heating zone circulators mounted on the return-side of a Weil McLain heating boiler. If you click to enlarge the photograph you can see the supply and return piping in more detail.

[Click to enlarge any image]

Similarly, 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.

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.

Locating the Circulator Pump on the Boiler Return or "cold" or "inlet" side

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.

Locating the Circulator Pump on the Boiler Supply or "hot" or "outlet" side

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, the pump will work in either location and will move water through the heating piping loop(s).

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.

Typical Lift Capacity of Heating Zone Circulators is Limited

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 Mount Position - keep the shaft horizontal and observe flow direction arrows & wiring locations

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:

The Series LR Circulator can be installed to discharge up or down, horizontally, left or right, but the motor shaft must remain in the horizontal position, the arrow on the body must point in the direction of the flow, the conduit box must be positioned on the top or to the side of the motor housing. - "Instruction Manual, Bell & Gossett Series LR Circulators" [see References]

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.

Hot Water (Hydronic) Heating Boiler Circulator Articles


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