Identifying hot water re-circulation systems

When you walk into a mechanical room and you see pipes and pumps everywhere, how do you spot the hot water re-circulation system or tell easily that there is one?

In the photo below, the electrician pointed out that the re-circulation pump was unplugged. Is it always plugged into a separate outlet?

The hot water recirculates back to the tank through a “T” or other junction with the cold supply. The cold supply pipe will always be hot after the junction as it carries the unused hot water back into the tank. The pipes will / should be well insulated for energy conservation purposes.

Look for a circulating pump such as a Grundfos in the re-circulation loop. It should be warm to hot from running and from moving the hot water; if its on the hot side of the installation, just make sure water wasn’t drawn in the last few minutes. Although they are a very quite pump, you can just here them running by putting your ear to the casing (if not too hot). Some pumps may be direct wired with an inline switch and /or a 24 hour timer (no need to have it running full time if no one is home to use it)

Correct me if I’m wrong. I’m looking for a return (cold) line coming into the water heater near it’s base, probably with a circulation pump not far back. In addition to the hot and cold lines coming out of the top of the water heater, there will be a third, which is the recirculating line. If the pump is on the return, it must be a closed system, eh?

The Hot Water recirculation system is for pottable water.

In some houses the water heater is located on the far side of the house away from the master bath or kitchen. The recirculation pump is normally attached to a water line close to the water heater. Depending on the system that is installed their may or may not be an additional water line running from the water heater to the farthest hot water faucet. The pump keeps the water circulating so that the water at the tap will not have to be turned on for several min. waiting for the water to turn hot.

Instead of instant hot water, it would be always hot water.

On the Metlund system, the pump is generally underneath a vanity or kitchen sink. The hot water circulates and is redirected back into the cold water side until the sensor detects the hot water reaching the pump.

This system operates on a “on demand” control system. There is either a door bell type push button switch or motion sensor that trigger the pump to start the circulation. The pushbutton is generally underneath the counter top by the sinks.

The things that I look for first are the pump (which does appear to be unplugged like the eletrician said) and the zone valves.

I identified them in the pic provided. There also appeared to be another pump visible on the right of the other pic as well.



I was assuming the zone valves were for the hot water heating system and were being fed from a boiler of some type to the right and rear of where the picture was taken.

what the heck is all that plumbing in the pic???

Hydronic zoned heating systems get complicated Mark.


Thanks for that pic.

From what I see:

The pump at the bottom of the photo, next to the water heater, is a pottable hot water recirculating pump. (It looks to be unplugged.)

The pump to the far right of the water heater at chest level looks to be a boiler circulating pump. (It circulates the hot water through the zones of the under floor, baseboard or other forms of radiant heating systems through the house.)

The valves & tubing (pipes) behind the water heater look to be the controls for all the zones in the house for the radiant heating system.

Paul you did a good thing by adding the arrows to this photo! Good thinking! :smiley:

Correct Brian, Boiler with radiant in-floor.
It’s a common scenario here, usually (but not always) in homes with boilers.

Typically, you walk into the mechanical room and there are all these pipes running off to feed the space heating system, plus home potoble hot water and hidden somwhere in this maze of pipes are two which are the loop for the hot water re-circulation system. The return pipe usually seems to enter the water heater near the bottom.
I think this system had 3 pumps.

That is helpful, Paul. What program do you use to do that?

Taking out the DHW re-circulation pump, leaves two pumps for the heating system.

This may be an injection pump design used to attain lower heating water (100-120 deg F) temps for the floors while protecting the boiler from the thermal shock of low temp water coming back from the floors (85-95 deg).
If this cooler water returned to the heat exchange areas of the boiler, it may cause enough stress by the steel contracting to cause fine cracks and leaks.

With the injection system, a main pump supplies the lower temp water that radiant requires to all the heating zones. There is also a pump that “injects” small amounts of hot (160-190 deg) boiler water in to the main pump system to keep it at the desired temp. As the injection pump injects into the main distribution system, it also takes a small amount out of the main sytem and brings it back to the boiler to be reheated and then re-injected. This system prevents the coolest water from reaching the boiler by having also a re-circulation element- a supply pipe from the boiler hot to the cool return so that not only the coolest water returns to the boiler but an adjusted mixture of the hottest and the coolest to suit the boiler.