Does every radiator need an air vent?

Robert_H

Restored C/A rads, home run system, TRVs.

All the first floor Rads have about a 4' rise above the boiler to them.  I understand its probably not the best practice but I would like to not put vents on a few of them. There is one column rad that is 60" tall that will for sure have a vent on it.



Thanks

Robert

Robert_H

I forgot to say

these are in a hot water system

140 max temp and I'm referring to the first floor rads ther will be three more on the second floor.

hot_rod

how are they piped

top and bottom connections? Or both bottom connections.



A small hydroscopic vent works nice for cast iron rads. They function as a manual vent for start up purging, then automatic. Some styles have a built in check should you ever need to remove and replace them.



They are not sensitive to debris in the system, no float or needle valve inside.



it's fairly easy to drill and tap a cast iron radiator. I use LocTite bolt sealent to assure they seal well in the radiator.

Robert_H

Sweet!

Those look perfect Hotrod!



The rad are a mix bottom to bottom, top to bottom same end and top to bottom opposite end. They were in steam use so I plugged the old vent ports and drilled and tapped the bosses at the top of the rads.



Thanks

Robert

hot_rod

still

you want a good central air elimination device back at the boiler. With old iron systems I would go with a combo dirt/ air separator, maybe one with a magnetic function also.

Robert_H

What document is that

HR, what document is that from, I cant read the text completely. It looks as if it may contain more good dope.

hot_rod

links

a good read on air elimination in general



http://www.caleffi.us/caleffi/en_US/Site/Technical_library/Idraulica_magazine/args/detail/~Details~Magazines~magazine_detail_0000057/type/magazine/index.sdo

jumper

no is short answer

With enough effort you don't need vents on any radiator. Sufficient air elimination also makes heating system noticeably more efficient.

RobG

What?

What are you trying to say Jumper, vents or no vents? Your answer seems to say yes and no. I just want to understand your post. I know a radiator can act as a form of expansion device, but eventually the air will be absorbed into the system potentially causing problems. An air separator and a bleed valve should be on any bottom to bottom feed rad in my opinion.  



JMHP



Rob

jumper

calculate pressures yourself

You want to remove free air,entrained air and dissolved air. During the summer when water is not heated apply vacuum to high point with circulator going. Eventually most air will be removed. Very old Amtrol Handbooks explain the formulas. Then you have an air free system without stinking radiator vents. Just a high point system vent.



The old open expansion tanks on gravity systems eliminated air during heating. Unfortunately air dissolved when water cooled.

RobG

Is that

Is that ever done in this day and age? People don't call you in the summer to work on their systems to remove air, they call in winter when something breaks, and if you are Lucky, you contact them for annual maintenance and they agree that service should be performed. People will bring their car in for oil changes every 3000 miles, but won't have their boilers serviced once a year! I still think a rad vent and air separator should be installed.



JMHO,



Rob 

jumper

RobG is correct

People wait for a problem on cold winter night and then they want it fixed. But Robert H wants to avoid some radiator vents. My point is that there are ways. Fill and pressurize your hot water heating system properly and you won't need to vent rads in winter.

Mark Eatherton

Old systems tips and tricks...

In my professional opinion, YES, you need manual air vents, or hygroscopic vents as HR pointed out on EVERY radiator. The exception to this rule is radiators that supply from a bottom tapping and return from an upper tapping.



I once came across an old gravity system that had NO air vents anywhere on ANY of the radiators.



So, being the newby efficient hydronician that I thought I was at the time, I went through the whole house, and installed manual coin key vents on ALL of the radiators, and bled the air out of the system..



The very next morning, we received a call that the pressure relief valve on the boiler was leaking profusely…



Upon further investigation, I determined that there was NO expansion tank on the system… Seem that the dead men decided to turn every radiator into an expansion tank by not putting any air vents into them. All radiators were bottom tapped only, so they were roughly half full of air, which was acting as a cushion for the expansion/contraction of the system fluid.



But unless your system was designed this way, (abnormally tall oversized radiators and no evidence of an expansion tank of any type) you will want to vent each radiator to give your radiators the opportunity to have as much wetted surface as possible.



We ended up "donating" the time and materials necessary to install an expansion tank in the basement… An expensive lesson, but one I will not forget, and now, one that you can use to pay it forward :-)



ME

Robert_H

Great discussion

Im installing manual vents (coin vents) on all the rads and good air separator on the output of the boiler. The LLH also provides some air separation as well.

Thanks

Robert_H

Great story Mark

I will be sure and install the expansion tank!

Robert_H

makes sense

"a bleed valve should be on any bottom to bottom feed rad in my opinion"

that makes sense as with Bottom to Bottom there will be more air likely to be trapped at the top.