Circulator pumps are designed to circulate liquids in open and closed heating systems, such as radiant floor heating, hydronic heating, hydro-air coils, water to air heat exchangers, and domestic hot water recirculation. These pumps can be used in a variety of residential and light commercial systems, and are sized according to specific system requirements.
Circulator pumps come in a variety of housing materials: bronze, cast iron, and stainless steel. Generally, cast iron pumps are used exclusively for closed-loop hydronic systems, where no oxygen gas is present to cause rust. Bronze and stainless steel pumps can be used in either closed or open loop applications heating and domestic hot water recirculation applications.
Many manufacturers of circulator pumps also produce optional timers and aquastats, which turn the pump on and off either on a pre-set schedule, or at a pre-determined temperature range.
Grundfos Circulator Pumps
Grundfos is a global manufacturer of water pumps for domestic, commercial, agricultural, and industrial applications. Grundfos offers circulator pumps in cast iron, bronze, and stainless steel. Cast iron pumps are intended for closed loop applications, such as radiant heating, baseboards, and fan coils. Bronze Grundfos pumps can be used in open and closed loop heating applications, such as radiant heating, fan coils, radiators, baseboards, and solar applications. Stainless steel circulator pumps are especially useful in applications where extra corrosion resistance is necessary, such as open loop radiant and hydronic heating.
Grundfos circulator pumps are available with or without integral flow check valves (denoted by an IFC in the model number). All Grundfos pumps come standard with two gaskets (O-rings); flanges must be purchased separately.
Taco Circulator Pumps
With over 80 years of HVAC experience, Taco is a reliable source of pumps for residential and light commercial use. This company boasts a field-serviceable design that allows cartridge replacement without the need for a brand new pump. Taco circulator pumps are available in cast iron, bronze, and stainless steel. Cast iron pumps are designed for closed loop radiant and hydronic heating systems, whereas bronze and stainless steel circulator pumps can be used in either open or closed heating, as well as domestic water recirculation. Stainless steel pumps are lead-free and corrosion resistant, and can handle a wide variety of applications. As such, stainless steel Taco circulator pumps have been steadily replacing their bronze equivalents.
Types of circulator pumps
Circulator pumps come in a variety of materials, as well as speeds.
Single speed circulator pumps function at a constant factory-set speed, and are selected for a specific application based on the system’s specification (eg, pipe length, flow, elevation).
A 3-speed circulator pump features an external switch, which allows the pump to be set to Speed 1, Speed 2, or Speed 3, or to Low, Medium, or High speed, depending on how the pump is labeled. A 3-speed pump is equivalent to three single speed pumps, and can be best fitted to a specific system by repositioning the switch, giving the user much more flexibility.
Variable speed circulator pumps automatically adjust to the system’s requirements. The Grundfos MAGNA series of pumps uses AUTOADAPT technology which keeps track of and “remembers” the system’s usage patterns, and vary the flow rate accordingly, saving on pump operation costs.
To size a circulator pump, it is necessary to calculate the system’s flow requirements in gallons per minute (GPM) and head range (feet of head or pounds per square inch), and match them to the pump’s capacity. The pump’s GPM is dependent on the heat load (BTU) for a specific zone (the sum of the areas of the walls, windows, doors, and roof multiplied by the heat transfer coefficients for each, multiplied by the temperature difference between the outside). The conversion is 1 GPM = 0.002(BTU)/(Temperature Drop). The Temperature Drop is the difference between the system’s supply and return temperatures. So if the temperature drop is 20F, then 10,000 BTU/hr give 1 GPM of flow.
To calculate the pressure drop (feet of head or psi, where 1 psi = 2.31 ft of head), it’s important to know the friction of water through the system’s tubing; to calculate this, it’s necessary to know the number of outlets and the tubing length. It’s also important to know the pumping height, which is then added to the friction. For instance, if there are 6 outlets in the system, and the system gives off 100,000 BTU, then 100,000 BTU/10,000=10 GPM; 10 GPM/6 circuits = 1.7 GPM per circuit (if all circuits are equivalent).
The next step would be to consult a pump curve chart specific to the manufacturer. Sometimes the pressure drop is given in pounds per square inch (PSI), in which 1 PSI is equivalent to 0.434 feet of head.
It is also important to note the circulator pump’s connection to the water line, as different pumps come with a variety of connections; flanges provide flexibility in using the connections, without buying a separate pump.
Baseboard/radiator heating requires constantly circulating hot water from the boiler (or other heat source) through the baseboards or radiator series. In closed loops, cast iron circulator pumps may be used, but in open loop systems, either a bronze or a stainless steel pump is required.
Snow melting operations require circulating hot water from the heat source (boiler) through the tubing. As boilers are not meant to come into direct contact with the glycol used, these systems must be separated from the boiler by way of a heat exchanger.
Hydro-Air Fan Coils
Hydro-air fan coil systems require a water to air heat exchanger, which heats air moving through the heat exchanger to a certain temperature, and then shuttles it through the ducts to a given room within the building.