Water flow sounds in radiators of circulating two loop system

Robert Wilcox

I am a relatively new home owner in Connecticut (been in the house about a year and a half). Recently, I have been hearing water flowing through my baseboard radiators. It sounds as if the pipes are not full. What are the possible causes of this phenomenon and what, if anything, as a homeowner, can I do about it? My gut instinct is that there is air in the system from somewhere. What is the procedure for purging the system? I have a two loop system with pumps for each loop. The returns join at a Tee just upstream of the snubber. Any help here is greatly appreciated. Thank you.

Brad White_9

Sounds like

classic air entrainment. If it is, the causes and solutions are fairly pro-forma around here:

1. Make sure that your circulators (pumps) are pumping away from the point where the expansion tank connects to the system. I suspect that the circulators are at the inlet to the boiler (common but incorrect location) and the expansion tank is on the outlet from the boiler if not from the boiler itself.

Solution: Move the circulators.

2. The expansion tank is likely the horizontal kind (often green sometimes red) up between the joist of the basement. This is an air cushion type and has air inside it above the water. That is a rich source of air that can find it's way into your system.

Solution: Replace with a sealed diaphragm type and connect it to the suction side of your circulators.

3. There may or may not be an air separator. I like the Spirovent kind. For $100-$150 depending on pipe size it is worth every penny. Really scrubs the air out.

4. The final picture:

Preferably the order of flow from the boiler outlet will be: Air Separator, expansion tank (may be connected to the air separator), circulators off of tees and a flow-check valve at the discharge of each.


Lastly, once the piping is set up this way, fill your system to the appropriate pressure. Generally 12 psig when the system is off/cold for up to a 2-story house. 16 psig for a 3-story house. Vent the radiators and let the Spirovent do it's thing. Sleep well.

Brad

Plumbob

A continuous rushing-water sound, as opposed to a gurgling/bubbling sound, is velocity noise, i.e. your pump is too powerful.

Robert Wilcox

Air in the system

OK, I checked the system layout. The circulators are on the outlet side of the boiler, rather than the return side. The return is a common return at the boiler. The returns from the loops feed into a Tee fitting upstream of the snubber, which is a vertical installation. The water then feeds into the boiler. The sound is a gurgling sound rather than a rushing one, so high pressure/volume on the pumps seems to be ruled out. Thanks for the heads up. I appreciate your help.

Brad White_9

Where is the expansion tank connected

in all of this? It should be on the suction side of the pump. And what type of tank is it?

Glad at least that the original installer took the leap to put the pump there.

I would not ordinarily think velocity noise because you would have always noticed that; this seems to be a more recent development.