Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

A Cv calculator Excel sheet

hot_rod Member Posts: 22,476
When you size a valve or any device in a plumbing or hydronic circuit, the Cv number is important nto know.
If you have a 7 gpm flow, ideally you would use a 7 Cv valve. But it is not always possible to find a valve that exactly matches the requirement.

So the 3rd box allows you to plug in the actual flow rate you need to run through the valve, along with the known Cv.

It calculates the pressure drop across the valve. There is no exact answer to how much pressure drop is excessive, certainly a couple - 5' of head is not generally a concern.

The number needs to add into the pressure drop of the circuit to size the circulator, of course.

On the other end, you do not want to oversize a control valve. This forces it to run at a closed down position and could damage the valve and takes away it's authority.

While it is possible to run 22 gpm, on a sales sheet :) through a 3 Cv mix valve for example. Two things, the flow velocity in the 3/4" tubing connected to that valve would be excessive,,m in excess of 12fps. You would need a supersized circulator to overcome the pressure drop. In a DHW application, the same pressure drop penalty applies. You would lose 53 psi, 124' head, across the valve regardless of what is driving the flow rate.

A little info on valve authority below.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream


    EBEBRATT-Ed Member Posts: 15,839
    The b& G "system size" either the wheel or the electronic version will work as well