Variable Speed Circulation


The topic of variable speed hydronic circulation has been something of a mystery for many in the industry.  In 2004, Taco introduced the world to a full line of residential variable speed circulators. Even though that was five years ago, some are still grappling with this “new” technology.


Taking a closer look at the concept of variable-speed pumping, Taco trainer John Barba and professional contractor Bill Riley explain when it’s best to apply the technology, where you’d use it and what the key benefits are.


The Universal Hydronics Formula


The purpose of a variable speed circulator is to automatically adjust its speed based on heating load demands, or how many BTUs are needed in a structure. To understand how it does that, let’s take a quick look at the universal hydronics formula, which states that GPM is equal to BTUH divided by delta-T, multiplied by 500.


Let’s define the terms. 


GPM is gallons per minute.  That’s the flow rate needed to deliver the required amount of BTUs.


BTUH or BTUs per hour, or the required amount of heat for a house, or zone, at any given point in time. We all know that outdoor temps or the number of people in a home will alter the BTU load. 


Delta-T (

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