Air Separator and Expansion Tank ?'s

Robert_25

Hello, I am looking for recommendations on an air separator for my boiler.  I just moved into the home and after examining the boiler I realized that there is no air scoop/separator on the system.  It appears that the boiler originally had a compression tank up in the ceiling that went bad and was replaced with a diaphram tank (60gal model).  There is a small tapping on the top of the boiler next to the main supply outlet, this tapping is connected to the diaphram tank with 1/2" copper.



The system has a few automatic air vents installed at the top of a few return elbows, but that's it.  I was just going to add an air scoop to the supply header but wondered if it is worth the cost to install a Spirovent or B&G EAS. 

I want to install something that will remove the air and last a long time.  I would love to hear some opinions and experiences with these different products,



Also, how much of a pressure increase should you typically see when the system goes from ambiant temp. to operating temp.?  The guage on my boiler reads 12 psi when cold, but when my main heating zone calls for heat and everything gets up to 170-180 degrees the system pressure goes up to 22-24 psi.  I haven't done the math to see how much water my system holds, but I did verify that the feed valve and diaphram tank are set at 12 psi.



-Robert

Jean-David Beyer

I am not a heating professional.

I think you would be well served by having an air separator in your system, placed pretty close to the output of your boiler. Some separators require a length of straight pipe on either side of the separator. And most require the flow through the separator to go in the correct direction, and not be too fast. I happen to have a Taco 4900 series separator (the small ones, mine is 49-125), but Spirovent should be fine too. The Taco does not require any straight pipe on either side, and the water can flow through in either direction. They can tolerate flows as high as 5 feet per second, though slower is better. Since you probably do not want flows in excess of 4 feet per second, that should be fine.



As far as pressure change with temperature, in my opinion, you are getting far far too much change. On my system, it barely changes from 80F to 170F. That is when it heats domestic hot water in the summer. So either your tank is too small, has insufficient air pressure in it, or piped incorrectly. In my system there is a T (on its side) between the expansion tank and the air separator. The tank is at the bottom of the T, the air separator is at the top of the T, and the makeup water comes in the side. The air separator has a 1/2" tap at the bottom of it for just this purpose. This is all pretty close to where the water comes out of the boiler on its way to the house.



In my system, I get what I consider false readings from the pressure gauge when the circulators run. The heat exchanger in the boiler holds only about 3 quarts of water, so the flow rate must be pretty high. The pressure gauge is at the output of the boiler. As long as the circulators are not running, I get a pressure about equal to that in the fill valve. When the circulators run, the pressure drops quite a bit. This is when running to the indirect hot water heater that has low resistance. It has not been cold enough to heat the house yet, so I do not know how that will be with the higher resistance heating circuits.

Steamhead

Depending on the boiler model

that small tapping where the diaphragm tank is connected might be a built-in air separator. What model is it? Also, a picture would help.



It's equally important that the circulator should pump AWAY from the air separator/tank connection. This will help flush air back to the separator.