Type I, type II, and type III pumping units covered by this specification are intended for use in steam heating and process systems in which the condensate cannot be returned to the boiler by gravity. Class I, type II units are intended for use on systems in which the returns are under a vacuum, class 2 is intended for use on sub-atmospheric system in which the supply piping, radiation, and returns are all under a vacuum.

Capacity shall be based on the actual output of the boiler or steam heating system expressed in gpm (L/s) of condensate based on boiler hp or Btu/h (W). Some manufacturer's make units to the standard hp ratings of the American Boiler Manufacturers Association. Branch lines of steam heating systems should be based on Btu/h (W). When the capacity is expressed in Effective Direct Radiation (EDR), the EDR rating should be converted to Btu/h (W) by multiplying the EDR by 240 (Btu/h/square foot) (W/m²). The EDR is not applicable in specifying the capacity of the condensate return units since the Hydronics Institute has changed its method of rating radiators for baseboard and convection heating systems to Btu/linear foot (joule per metre (J/m)). The 480,000 Btu/h (140 674.1 W) for gpm (L/s) of condensate has been established on the basis that there are approximately 1,000 Btu (1 055 kJ) in 1-pound (0.45 kg) of steam at 212 °F (100 °C), and water at 212 °F (100 °C) weighs approximately 8 pounds per gallon (958.6 gram per litre) and for a time of 60 minutes. The 0.06974 gpm (0.004 39 L/s) of condensate for one boiler hp (3.281 08 W) was established by dividing 33,475 Btu/h (9 810.55 W) for one hp by 480,000 Btu/h (140 674.1 W) for gpm (L/s). The 0.558-pound (0.2531 kg) per minute for one hp (W) was established by multiplying 0.06974 gpm (0.004 39 L/s) by 8.00 pounds per gallon (958.611 2 gram per L).

Receiver capacities given in the manufacturers' catalogs are generally the actual volumes of the receiver and not the net working volumes required. In calculating the cycle time of the pumping unit the net working volume should be obtained from the manufacturer. The cycle time requirements of 3.10 should be adhered to in order that adequate life can be obtained from the motors and other components of the electrical system. Units with smaller receiver capacities, such as type I, style A and type II, class 1, are suitable for compact heating systems having short return lines where condensate will be returned to the receiver within 5 minutes for the smaller units and 2 to 3 minutes for larger units. For systems with longer return lines and higher pressures, such as multi-story buildings or multiple building installations, other units having a larger storage capacity, such as type I, style C, should be specified. When type I and type III units will be equipped with feedwater make up valves (see 3.15.9) and controlled by water level sensing elements on boiler, a receiver capacity equal to not less than 1 gallon (3.79 L) per boiler hp (9.803 kW) is recommended.

Condensate pump capacities specified herein are based on the pressure at the pump outlet. In selecting the appropriate discharge pressure for the intended installation, the static head and friction losses in piping from the receiver to the boiler must be considered in addition to the boiler operating pressure.

Whenever possible, it is recommended that the receiver be procured without insulation. It is preferable that the unit be lagged at the site after the unit is in place, connected, and tested. Not only is the insulation susceptible to damage during shipment and handling at the job site, but should any leaks develop in joints or fittings due to strains and jars incident to shipment and handling, the lagging will be damaged to an extent normally requiring complete replacement.