Teeing off last month’s column on antifreeze, let’s chat about one of the most exciting (sarcasm) and critical (not sarcasm) components featured on certain hydronic installations: the system feeder, sometimes referred to as a “glycol feeder.”

Despite being called a glycol feeder, these devices are valuable in hydronic applications with or without glycol.

A system feeder is a self-contained unit including a pump, pressure control and liquid storage vessel. It’s installed in place of a system’s fill valve. This way, the system isn’t drawing water from the building’s potable water supply but rather from the system feeder’s tank. 

These devices were designed almost exclusively for use in hydronic systems with antifreeze. The tank is filled with the correct ratio of water and glycol so that when the system leaks, the glycol levels won’t be diluted by adding fresh water.

Isolating Hydronic System from Plumbing System

Over time, installers and building owners have realized that system feeders serve a function beyond glycol applications, whether for boiler systems, chillers, solar-thermal or geothermal applications. As water quality across the country continues to fall, feeders also provide an opportunity to remove the hydronic system from the well or utility supply. 

In this scenario, conditioned water can be added to a feeder to ensure that a hydronic system only receives makeup water from a source free of chemicals, minerals or harmful pH. 

A properly installed system feeder also avoids damage in case of a catastrophic leak. Because the presence of a system feeder means that the hydronic system is isolated from the building’s plumbing system, a system with a major leak can only lose the volume of liquid within the heating appliance, pipe and the feeder’s reservoir. This way, the system leaks a few gallons, the low water cut-off trips and the boiler shuts down. 

The homeowner will no doubt figure it out when the house starts getting cooler instead of going downstairs to find the basement flooded up over the boiler’s burner. Or better yet, if the feeder is equipped with an alarm contact, someone will be notified about the low water status. 

Most system feeders feature a translucent tank, so a service tech or maintenance staff can monitor fluid levels, easily determining if there’s a leak. Also, if a liquid cleaner or corrosion-inhibiting product — such as Rhomar Pro-Tek or Fernox Protector F1 — is used in a system. In that case it can easily be added to the feeder tank during fill. Much like filling the tank with glycol solution, this will ensure that as feed water is added, the treatment chemical in the system won’t be diluted. 

Heating system regulations are changing on both the commercial and residential sides. Code in certain areas now require installing an expensive dual-check valve in addition to a pressure-reducing valve any time a hydronic system is connected to a potable water line for makeup water purposes. 

In this case, or even in the average residential hydronic system where only a PRV is present, the cost of a system feeder is offset by the components it replaces. 

Not every job needs a feeder, but many could benefit from one. You can typically find models ranging from less than five gallons in capacity to 100 gallons, so finding a feeder to fit any application isn’t difficult. 

I’m big on annual maintenance, and feeders make boiler maintenance easier. With a system feeder in place, my technicians can immediately determine if the system has been losing water with a glance at the vessel. We also can ensure that the makeup water being consumed is of high quality and is treated with the same chemicals circulating within the system. 

Feeders are a relatively cheap insurance policy, whether glycol is included in the system or not.