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Raytherm boiler piping diagram from Raypak (C) Raypak 2009 and InspectAPedia.com 2009Heating System Circulator Pump Location & Mounting

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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- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

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 Friedman 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, but the can occur, often accompanied also by water leaks. .

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.

Watch out: from a service-life viewpoint, however, traditional best practice puts the circulator on the cooler side of the boiler's heating loop where many technicians opine the lower heat gives longer equipment life. We say more about circulator pump location below.

But at least some manufacturers say it doesn't matter. Here is Taco's position on circulator pump position:

All of the "00" pumps can be used on the supply side or the return. It is preferable to put a circulator on the output of a boiler, but the expansion tank should be between the boiler and the pump section. Most of our "00" iron pumps have a max water temperature of 230ºF.

The max for the bronze is 220ºF. 160ºF is cold. No matter what the water temperature is, the motor housing will be hot. There will be no change in performance or life. - Taco FAQ

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 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.

See details at CIRCULATOR PUMPS & RELAYS - home

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-01-31 - by (mod) - importance of circulator pump location & position

Very informative, Marty, thank you.

Standard good practice among heating techs is to install the circulator pump on the return side of the loop where cooler temperatures can extend its life.

On 2020-01-30 by Marty - The good science on this is to pump away from the area of no pressure change

I certainly wouldn't say that the circulator position is inconsequential.

The good science on this is to pump away from the area of no pressure change which is wherever your expansion tank is piped into the system. If you follow good practice the expansion tank ought to be on the supply side and as close as possible to the hottest available temperatures which is also (and for the same reason) where your air separator should be located.

This also happens to be a great location for your water make up to enter the system to allow any make up water to heat up through the system before it gets to the boiler return side.

The circulator operates on a pressure differential and is sized to deliver A: the correct amount of flow (GPM) to meet the heat demands of the system and B: overcome the head losses through the system created by pipe, fittings, valves etc.

If this principle is understood then it makes the most amount of sense to pump away from the expansion handling device as it's job is to regulate pressure in the system which means it controls pressure fluctuations created by expanding and contracting water as it moves through the temperature differentials.

So in short, the pump is designed to create enough pressure on its outlet side to overcome the inevitable pressure losses it will experience throughout the system, so pumping into the area of no pressure change (expansion tank) would defeat the work of the pump. Put simply, always pump away from your expansion tank.

So if you've correctly positioned your expansion device on the supply side of the system then your circulator will always be on the supply side as well, albeit downstream.

There are several other factors to consider in the myriad of piping possibilities but generally speaking if you follow this rule then you won't go wrong.

On 2019-10-19 - by (mod) - best to put circulator pump on return side of heating loop

That's the correct installation position

On 2019-10-18 by dennis

my burnham oil boiler has the circulator pump on the return pipe with the arrow and flow going toward the boiler will it work ok

On 2017-12-08 by David

my old boiler had the cold water supply. going in the supply side. the diagram for the new boiler has it on the return side. is this a big deal and needs switched, or can I leave it as is?

On 2016-12-19 by Anonymous

Dear sirs can you please send me a piping diagram of a three zone hot water heating system using circulation pumps. thank you Greg MacPherson

On 2012-11-06 - by (mod) -

Noise from Raypak

Rather than wild guessing, I suggest tracking down the noise to the offending part. Use someone with good hearing, notice when equipment is turning on and off and just what's running; try a mechanic's stethoscope.

Details about noise track down procedures begin at NOISE / SOUND DIAGNOSIS & CURE (article links at page left)

On 2012-11-06 - by (mod) -

Mike A:

take a look at AIRBOUND HEAT SYSTEM REPAIRS (article link at page left near top) for the procedure to add water manually to your system and fix an air bound hot water heating boiler problem.

On 2012-11-06 by Noise from Raypak Hydronic Boile

Hello -
I recently purchased a house with an outside hydronic boiler which I guess heats my faucet/shower water as well as my heating system via hot water radiators.

As of right now - there's a noise that sounds like a humming/whistling noise which every 5 minutes.
it usually last about 1 or 2 minutes and then after several minutes I hear it again.

My circulating pump is inside one of my kitchen cabinets and its hard to tell if its the pump or if the boiler unit has its own pump inside the housing.


The boiler I have is a raypak (raytherm) which has a sticker that says it heats up to 108,800 BTUH.
I believe the model is a the 133 size boiler from what I can tell from the internet but I'm not 100%.

Can someone please help me determine what this noise might be? and about how much will a plumber cost to replace the pump... if its trully that piece thats defective?


On 2012-10-13 by Mike A

Question: I know I need to add water manually to my loop, Air bound. Boiler at temp, circulator pump is on, system is at 15psi. There is two values, one input the other is the drain, I do not know which is which. One is above the circulator pump the other below. The one above has a value directly below it controlled by a screw driver. My question is which value is the input (house water) and which is the drain. Both have a garden hose adapter.
Thank you, Mike.

On 2011-07-13 by (mod) -brown water coming from the water heater

Harley:

First we need to understand what setup you have. Is this an indirect-fired water heater? if so then the circulator pump would be cycling heating boiler water through a coil that is heating physically separate water heater water and you'd only get brown dirty water (from the heating system where that is normal) leaking into the domestic hot water (in the water heater) if there was a leak in that coil. (Usually leaks go the other way - from the higher pressure water heater water into the lower pressure heating system water).

If your system is using a circulator pump to provide "instant" hot water at all plumbing fixtures by constant cycling of water heater hot water through the building piping loop, then if your outcoming hot water is dirty you need to drain the water tank, probably clean it, and probably replace a deteriorated sacrificial anode.

On 2011-07-13 by harley

if so what can be done to fix this problem?

i have brown water coming from the water heater which has a circulation pump on it. i have opened all related facuet and let them run for long periods of time but doesn't go away. is this a circulation pump issue?


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