WEST MIDLANDS, England — Mikrofill Systems Ltd. recently brought its thoroughly time- and application-tested Mikrofill 3 hydronic system pressurization unit to the North American HVAC market. Originally unveiled in the mid-1990s in the U.K., the product made its debut on this side of the Atlantic at the 2022 AHR Expo. 

As a result, U.S. and Canadian mechanical engineers and contractors are now able to experience firsthand what their U.K. counterparts have known for the past quarter-century: that the unique Mikrofill 3 is an advanced, “direct-type” pressurization unit available for sealed, low-pressure hot-water (LPHW) and chilled-water (CHW) commercial and multifamily residential applications. Able to fill any heating or chilled water system from empty without the use of a pump, the product also delivers commercial backflow protection with no RPZ valves, while also providing comprehensive electronic pressure management.

  • The Mikrofill 3 has been tested and approved in accordance with ASSE LEC 2009-2021. 
  • The Mikrofill 3 connects directly to a commercial building’s incoming water supply (main or boosted), leveraging that line pressure to fill any heating or chilled water system — again, completely dispensing with a conventional circulating pump. By eliminating the pump, the Mikrofill 3 not only helps building owner-managers avoid the expense and hassles of periodic maintenance, but it also saves them substantial energy costs. 
  • The Mikrofill 3 consumes only 30 watts per hour when filling a LPHW/CHW system and only 10 watts per hour when monitoring the system while on standby. That performance results in an energy savings more than 95 percent, compared with pump-type pressurization units.
  • The Mikrofill 3 integrates American Society of Sanitary Engineering (ASSE)-approved, commercial backflow prevention, eliminating the need for reduced pressure zone (RPZ) valves to avoid contaminating a building’s potable water supply. Once the required system pressure is achieved, the internal solenoid valves default to the closed position. This automatic deactivation drains internal waterways, resulting in commercial backflow protection (Fluid Risk Category 4).
  • The Mikrofill 3 continuously monitors system inlet and operating pressures through a series of pre-commissioned sensors that automatically maintain system presets. By recognizing a change in cold-fill water pressure, these sensors open the Mikrofill 3 valves to top off the system, stopping the fill once the required pressure has been reached.

This comprehensive electronic pressure management protects the system and the building by alerting owner-management to potential issues and providing leak and flood protection: 

  • Small leaks will prompt continual topping off. Once a preset number of refills has been reached (say, 25 refills over a 24-hour period), the integral color-screen display on the top-front side of the Mikrofill 3 will indicate a problem.
  • Larger leaks may prevent proper replenishment. If the Mikrofill 3 does not detect the expected pressure increase over a preset period, the unit will shut down to prevent further water damage.
  • In the case of catastrophic leaks, the Mikrofill 3 will quickly close off the main water supply to prevent further damage.


The fill rate for the Mikrofill 3 is 3.8 gallons per minute, based on an incoming pressure of 30 pounds per square inch (psi). The built-in fill volume indicator aids water-treatment calculation.

The base requirement is a water-supply pressure 4.5 psi greater than the cold-fill requirement. For example, a cold-fill requirement of 22 psi would need a main-supply pressure of 26.5 psi to completely fill or top off the system. Maximum inlet pressure is 100 psi, allowing a maximum cold-fill pressure of 95.5 psi.

The wall-mounted Mikrofill 3 weighs only 11 pounds and measures 9¾-by-10½-by-4½ inches. This compact design facilitates installation by a single, trained technician. No on-site commissioning by the manufacturer is required.

“The ready-to-install Mikrofill 3 is essentially plug-and-play,” said Dominic West, managing director, Mikrofill. “The product’s highly innovative approach to monitoring and maintaining hydronic systems has served the commercial mechanical market in the U.K. exceptionally well for more than 25 years. We see no reason why it cannot do the same in North America.”

For more information, visitmikrofill.us.