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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.

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. Also you will see that this website 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.

© Copyright 2012 InspectAPedia.com, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use page top links to major topics or use links at the left of each page to navigate within topics and documents at this website. Green links show where you are in a document series or at this website.

Where to Mount the Circulator Pump on a 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.

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 degF. 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.

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Questions & answers about heating circulator pumps: diagnosis, repair, maintenance, replacement advice

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

BOILERS, HEATING
  BOILER OPERATION DETAILS
  BOILER CONTROLS & SWITCHES
  Air Bleeder Valves
  Air-bound boilers & radiators
  Air Scoops Purgers Separators
  AQUASTAT CONTROL Functions
  Boiler Pressure Controls & Settings
  CAD CELL RELAY SWITCH
  Circulator Pumps & Relays
    Circulator Pumps vs. Zone Valves
    Circulator Pump Trouble List
    Checks for Circulator Operation
    Single Zone Heat Tests
    Multi-Zone One Circulator Tests
    Multi-Zone Multi-Circulators Tests
    Individual Zone Tests
    Un-wanted Heat in Some Zones
    Leaks at Circulators
    Circulator Motor or Bearing Failures
    Where to Mount Circulator Pumps
    Other Circulator Controls
  ELECTRIC MOTOR OVERLOAD RESET SWITCH
  ELECTRICAL POWER SWITCH FOR HEAT
  Expansion Tanks
  FIRE SAFETY CONTROLS
  Gauges on Heating Equipment
  Limit Switches, Boilers
  Low Water Cutoff Valves, Boilers
  MIXING / ANTI-SCALD VALVES
  RELIEF VALVES - TP VALVES
  Reset Switch - Primary Control
  Reset Switch - electric motors
  SPILL SWITCHES
  STACK RELAYS
  THERMOSTATS, HEATING / COOLING
  Water Feeder Valves, Hydronic Boiler
  Zone Valves
WATER HEATERS
ZONE VALVES

• "Installation and Operation Instructions, Raytherm Residential Boilers," courtesy of Raypak®, and technical advisor Wayne Hoffman, personal communication 5/11/2009. Mr. Hoffman is a technical advisor with more than 30 years experience in the heating field. Raypak is a Rheem company that provides hydronic heating boilers for residential, pool, and commercial use. Raypak can be contacted at 866-583-0664 for technical support or for assistance in selecting the proper heating equipment for a specific application. Rheem Corporation is a manufacturer of water heaters and heating equipment including Ruud heating and cooling products.

Other heating system controls related to hot water circulator pumps - three alternative ways to control hot water heat circulation

• Individual High Limit and Low Limit relay switches on heating boilers: these may be provided on older heating boilers. See Limit Switches, Boilers
• Zone valves on heating boilers - heating water piping in a building, particularly where hot water baseboard heat is used, may be divided into separate heating zones (different floors, or different areas on a single floor) to permit more detailed control of heat distribution in a building.
  
  The control of heating water through these different heating zones may be accomplished by use of zone valves (one per heating zone or area or "loop" of heating piping) which in turn are connected to individual thermostats. When the thermostat calls for heat in a particular building area, the thermostat switch causes the zone valve to open, to permit hot water to flow through that zone.
  
  When the zone valve is fully open, an "end switch" inside the valve tells the heating system's circulator to begin operating, causing hot water to flow through the zone. Typically heating systems using zone valves will have two or more zone valves (usually but not always located close to the heating boiler) and a single circulator pump (usually located on the return end of the hot water piping close to the heating boiler).
  
  See ZONE VALVES for details.
  
  
• Circulator relays on heating boilers - an older and by some heating service technicians, a preferred method to control the distribution of heat to individual building areas uses a individual circulator pump to force heating water through each individual heating zone piping. This system too is usually found on hot water baseboard heating systems.
  
  Two or more circulator relay switches, one relay for each circulator pump, will be installed to turn on and off each heating water circulator if more than one heating circulator is installed. Individual low-voltage thermostats located in the living area will respond to a call for heat by switching on the circulator relay which in turns on the (120V) circulator pump.
• Air exit tanks on heating boilers and circulator pump mounting location - some heating boilers use an air exit tank mounted on the hot water header above the heating boiler to combine the function of an Expansion Tank with the Air Bleeder Valve or air purge valve to rid the hydronic (hot water) heating system of un-wanted air. Air in the heating system will often rise to a high loop of radiator or heating baseboard piping where it will block the flow of hot water, leading to an air-bound heating system and no heat in some or all of the heating system.
  
  The air exit tank captures and vents unwanted air from its location above the heating boiler on the boiler outlet or supply side. When an air exit tank is used instead of a simpler expansion tank at a heating boiler, the boiler manufacturer may specify that the circulator pump be mounted on the boiler outlet side to improve the function of this device. Thanks to Wayne Hoffman, technical advisor for Raypak, a Rheem company that provides hydronic heating equipment, for this detail.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

• Carbon Monoxide Gas Toxicity, exposure limits, poisoning symptoms, and inspecting buildings for CO hazards
• DUST CONTAMINATION FROM HVAC? An Investigation of Indoor Dust Debris Blamed on a Heating/Cooling System Reveals Carpet Dust
• Fuel Oil & Oil Heating Magazine, 3621 Hill Rd., Parsippany, NJ 07054, 973-331-9545
• Goodman Furnace High Temperature Plastic Vent HTPV safety recall US CPSC notice
• Home Heating System Should Be Checked [for proper venting and for CO Carbon Monoxide Hazards - DJF]
• Inspection Procedures for Oil-Fired Heating Systems Detailed step by step approaches for inspecting complex systems]
• Lennox Pulse Furnace Safety Inspection/Warranty Program: Carbon Monoxide Warning
• Oil Tanks - The Oil Storage Tank Information Website: Buried or Above Ground Oil Tank Inspection, Testing, Cleanup, Abandonment of Oil Tanks
• Oil Tanks Above Ground, UL Standards, guidance for home owners, buyers, and inspectors
• Plastic Heating Vent Pipe & Other Heating Safety Recall Notices
• Weil McLain Model GV Gas Boiler/gas valve CPSC recall/repair
• Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
• National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
• The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
• Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
• The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
• Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
• "Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• "Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
• Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
• Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
• Installation Guide for Residential Hydronic Heating Systems
• Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
• The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
• Links to our list of additional information on heating system inspection, repair, maintenance
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