How Do I Choose the Right Control Valve Size?


Select Pro software

If you browse Boston Aircontrol’s online shop for HVAC valves, you will find dozens of options in a wide range of sizes. So, how do you know which control valve size is right for your job? 

Valve Flow Coefficient Calculations

One tried and true method is to calculate the Valve Flow Coefficient (Cv). Valve manufacturer Belimo helpfully defines Valve Flow Coefficient as, “…the volume of water (GPM in the US) at 60°F that will flow through a fully open valve with a pressure differential of 1 psi across the valve.” They provide the following equation to determine Cv for a given system: 

Valve Flow Coefficient equation
  • Q = Flow in Gallons per Minute
  • G = Specific gravity of fluid (estimated as 1 for water systems)
  • ΔP = Differential pressure over valve (delta P) – stated in psi

Once you’ve calculated the Cv, Belimo recommends rounding down to the closest valve size unless a maximum ΔP is exceeded. 

SelectPro Software and Web Apps 

If you want to move beyond pencil-and-paper calculations, Belimo now offers a free downloadable software for Windows called SelectPro™. SelectPro will guide users through a step-by-step process to select the right valve components for their project. The program is also available as a free web app for valves, actuators and sensors

SelectPro will walk you through each stage of product selection and allow you to input all the appropriate specs to narrow down your choices. It includes calculations for Flow Rate Coefficient when needed, and it will show you actuators and accessory options to include with your selection. Once you’ve chosen your products, you can export the list to CSV or add them to your project list if you have a Belimo account. 

Choosing which products you need for your next job is a time-consuming task, and solutions like SelectPro help make the process smoother, quicker and more efficient. These solutions are one of many reasons why we at Boston Aircontrols are proud to be a Diamond-level distributor for Belimo. If you are looking for the best forward-thinking HVAC technology, contact us or browse our online shop today

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