Grundfos variable speed heating zone circulator pump UPS 15-58FC (C) Grundfos InspectApediaVariable-Speed Zone Circulators
Brands & features of heating circulators that can vary circulating speed

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Variable speed heating zone circulators:

This article describes brands & models of forced hot water heating system circulator pumps whose motor speed or circulating speed can be set to varying rates.

We describe both older obsolete variable speed circulator pumps and modern currently-available models including manufacturer brand, model, and circulator pump sources.

Green links show where you are. © Copyright 2017, All Rights Reserved.

Variable Speed Hot Water Heating Circulator Pumps, Motors & Controls

B&G UpStart circulator with variable speed motor (C) Daniel FriedmanVariable speed heating zone circulators provide an additional level of heating zone control and can be used to solve heating problems amenable to either an increase in circulating water speed (get more heat in a zone) or a decrease in heating zone circulator speed (less heat or continuous, more even heat).

Older Variable Speed Heating Circulator Pumps

At left is a Bell & Gossett UpStart hot water heating zone circulator pump produced - a B&G product no longer distributed. This circulator pump included a variable-speed circulator motor (see that gold knob on the electrical box atop the motor?).

This hot water heating zone circulator used a four-speed motor whose output rate could be set by the consumer or heating service technician.

By changing the circulator motor speed on this pump or on the next model shown below, we could slow or speed the flow rate of hot water through the zone managed by this circulator. The result: this control provided another way to balance heat flow among multiple zones (and circulators) in a building.

This circulator, the Bell & Gossett SLC-25 Upstart Circulator was sold during the 1980's and is not currently available. But B&G offered similar replacements (such as the NRF-22).

At below is a newer but also obsolete product, the B&G NRF-VS variable speed circulator is shown.

B&G NRF-VS variable speed control with circuator pump - InspectApedia Bell&Gossett Xylem

Currently-Available Variable-Speed Heating Circulator Pumps & Controls: Taco BumbleBee & Grundfos Alpha Series & MixiMiser™

Other variable speed circulators include the Taco BumbleBee High-Efficiency Variable-Speed Circulator HEC-2 and Variable speed circulators from Grundfos.

Quoting from the company's product literature:

The Taco Bumble Bee (model HEC-2) represents the very latest in variable speed wet rotor circulator technology. Its high efficiency ECM motor uses up to 85% less electricity than a standard circulator, and its out-of-the-box settings and 360 ̊ swivel flange makes it a breeze to install. Most importantly, the Bumble Bee’s Delta-T variable speed technology maximizes the overall efficiency of your heating system. - Taco Catalog q#100-101 retrieved 1/24/2014 [on file] see References at the end of this article

Taco BumbleBee HEC-2 variable speed heating circulator pump (C) Taco InspectApedia

Alpha Series pumps by Grundfos also provide variable speed hydronic heating water circulation control. Quoting [with minor adaptations] from product literature from Grundfos, including the UPS15-58FC and the Grundfos Alpha series.

Grundfos variable speed heating zone circulator pump UPS 15-58FC (C) Grundfos InspectApedia Grundfos Alpha variable speed heating zone circulator pump (C) Grundfos InspectApedia

The Alpha Series pumps [above right] (e.g. ALPHA 15-55F - ALPHA 15-55SF/LC) have permanent magnet motors designed for circulating water through domestic hot water systems, heating systems, or cooling and air conditioning systems.

The Alpha pumps can be used in systems with either constant or varying water flow rates. example of a Grundfos ALPHA pump The Alpha pumps incorporate a frequency converter, an integrated differential pressure control, and an electronic processor to automatically adjust pump speed based on the system demand and flow rates.

The AUTOADAPT™ software recognizes changes in the system like opening and closing valves or faucets that can cause a change in the head-flow requirements of the system. AUTOADAPT™ monitors the motor current versus the pump hydraulic or pressure conditions and automatically adjusts the motor speed to minimize the pumps energy consumption and at the same time maximize your system needs for your comfort level.

The Grundfos MixiMiser™ is the only pump and controller system of its kind. The mixing-reset control automatically calculates and controls water temperatures according to outdoor temperatures in primary and secondary heating systems.

The MixiMizer™ can be installed into a thermostatic or zoning control system for maximum design flexibility.

A fully serviceable check valve is installed into the pump housing to eliminate unwanted, uncontrolled, flow when the pump is not on and will not inhibit water flow when the pump is on. LED indicators located on the terminal box indicate pump performance and help diagnose possible faults without the use of tools.

Question: what is the best speed to use for my variable speed circulator pump?

Taco Delta T 00(R) variable speed circulator pump - at cited in this articleCan you tell me if there are any studies or articles that may guide me to the best speed (RPM) that a circulation pump should have ? We all know that when an Oil Boiler "kicks" on after a call of heat that the circulation starts however we all also know that the slower (and longer) that water stays in the boiler the faster and hotter the water will heat.

Also, as the boiler reaches a temperature to shut off and the circulation is still on, there must be a best speed to let off heat within the baseboard, radiator, etc. - Anonymous by private email 2018/01/31

Reply: how is the desired circulator speed determined & set?

I too have asked service technicians and manufacturers about the "best" speed for variable-speed circulator pumps and I've gotten answers that were all over the place. I suspect that that the bottom line is that there is some subjectivity in deciding on the circulator speed.

If we need more heat in an area we can send more BTUh through the piping by upping the circulator speed.

Manually-set variable speed circulators are then adjusted to increase the heat output of an individual zone as needed.

Variable-speed self-adjusting hydronic circulators like the Taco Delta T 00® (described in more detail just below) monitor temperature across the zone and adjust the circulator speed to a desired heat delta T setting. That design is particularly useful for radiant heat flooring systems.

You might already realize that in many boiler set-ups, especially in the U.S. the thermostat turns on the circulator and the boiler temperature is what turns the burner on or off. So the circulator will run until the thermostat is satisfied.

The link given below describes a more-sophisticated "Delta-T" circulator from Taco

The instruction sheet for this circulator explains:

Variable speed pumping to maintain a set differential temperature (delta T or ∆T) between two sensors allows for automatic adjustment of the pump’s performance to match the load of the system or zone, eliminate velocity noise in zone valve systems and conserve energy.

Since delta T is directly related to flow rate, the pump’s speed continually adjusts to the required BTU per hour. In almost all applications the design of the system was based on being able to maintain a certain delta T and figured by using the universal hydronics equation of BTU/hr = GPM x 500 x ∆T.

Given that, any time there is a change to the heat load (i.e. warmer day or greater heat loss from a structure) then the GPM should change to match the required BTU/hr.

This is achieved when the variable speed 00-VDT Circulators automatically and continually adjust their GPM output (by varying speed) to match the required BTU/hr output of the system, no matter the changes in heat load, while always maintaining the designed delta T between a supply and return sensor.

The company includes a video on how to read circulator pump performance curves.


Continue reading at CIRCULATOR PUMPS & RELAYS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see these

Hot Water (Hydronic) Heating Boiler Circulator Articles

Suggested citation for this web page

CIRCULATORS VARIABLE SPEED at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman