hot water radiator vent

digger

I just completed installing a new boiler, converting a circa 1925 gravity system to a primary / secondary loop with four zones. my question is why were the air vents located 10" from the top of these old radiators?

Timco

Sounds like a steam rad?

Tim

digger

The original installation was gravity hot water.(obvious because of the pipe size and configuration. It was also equipped with a Honeywell heat generator). The radiators I refer to are the originals. The qulity of the original installation says a very skilled fitter did the work.Could he have used the wrong radiators? Are these ok for water? If so what's the trick to getting the air out? The seven originals,with low vent are cold on top. The five salvage rads with vents up high are toasty.

Timco

Really sounds like steam rads. Is there a pipe across the top, or just the bottom. If the tops are cold, Steam they are. If there is a top pipe, you can tap & thread a vent in a plug or a top location, but if just a bottom pipe, you would need to tap each section. I have a rad I salvaged where it only had a bottom pipe, and someone tapped each section, and it heats great! Rads may have been replaced.

Tim

digger

I have already tapped one and moved the vent to test a theory. It is now in the toasty column. I am still sure they are original. Lots of evidence. They are oversized for the application when you figure 180 degree water. With steam they would have rocked!

Timco

If the whole rad heats with one vent, it must be a 2-pipe rad for steam or HW. If it was a steam rad, just the section you tapped would heat all the way up. the rest would still have air in them...usually about half way up.

Brad White_9

You are wonderfully situated

to take advantage of outdoor reset with all of that cast iron bathing you in incredible heat. Tap for high vents as you have. Install TRV's on the radiators of you at all can.

If your boiler is a conventional cast iron one, primary-secondary with a 4-way mixing valve is a great way to achieve OD reset and superior savings and comfort.

Paul_31

maybe they served as the expansion tank

maybe the original system had no expansion tank, but the tops of all the rads served the purpose...