HVAC Near Boiler Piping Components - HVAC near boiler piping is very important to a good hot boiler loop circulation of the water. Hot water loop piping is key to maintaining good water flow throughout the system. The placement of valves, the circulator pump, and other loop controls are generally installed near the boiler.

HVAC Near Boiler Piping Components

HVAC Near Boiler Piping Components
In the photo one can see the circulator pump, the expansion tank, the flue that exhausts the gases from the combustion process, an automatic air vent just to the right of the hot water loop circulator pump, a PRV or pressure reducing valve where the boiler make-up water comes into the boiler, and some unidentifiable controls. These loop components make up the near boiler piping which is very important to a good installation. If the near boiler piping is not installed properly several problems can occur that will cause issues with the heat and efficiency of the heating system as a whole.

HVAC Near Boiler Piping Components - The Circulator Pump

The circulator pump keeps the water moving through the system and is an essential component in the loop system. In the photo above the circulator pump is in the pipe and colored green. The pump is controlled by an aquastat. The aquastat is located on the boiler and controls the circulator pump based temperature. Typically it is the thermostat that sends a signal to the aquastat and a relay in the aquastat engages the circulator pump. If there is a problem with the circulator you will not get heat through the loop and into the baseboards or radiators. For more on this see our other article boiler circulation problems which is about circulator problems and other related problems that prevent circulation in the loop.

HVAC Near Boiler Piping Components - The Expansion Tank

The expansion is another component in the photo above. It is a bladder type expansion tank and it is important that the air pressure inside the expansion tank. Inside the tank is a bladder. On one side of the bladder is a pressurized air pocket and on the other side is the water from the loop. The expansion tank keeps the pressure in the system at a reasonable pressure. When water heats and cools it also expands and contracts. The expansion tank absorbs the expansion and contraction of the water in the system and prevents too much pressure in the system. Too much pressure in the system and the pressure relief valve will vent causing a water spill from the pressure relief valve. Another type of expansion tank is the steel type of expansion tank. It is cylindrical and does not have a bladder inside the tank. For more on how a steel type expansion tank works see our article on steel type expansion tank water levels.

Additional Components

In addition to the expansion tank in the near boiler piping, there should be some type of air management system to expel air out of the loop system. Air can prevent the circulation of water in the system and needs to be vented. The air vent system is most likely near the expansion tank and where the makeup water comes into the loop. Air in the system can cause hydronic air lock. It is essential this works properly to keep air out of the system.


Other components close to the boiler are valves. Shut off valves that will isolate the pipe system in the event a repair needs to be made to a component in the system.

Thinking of Replacing your Boiler? Check out our boiler review pages.

High Performance HVAC

HVAC Near Boiler Piping Components

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