In article , Bubba wrote:

Okay, I'll buy that, based on your experience. I have not worked on
any residential systems for several decades, and don't recall ever
working on a residential boiler. Commercial boilers have such things
as automatic vents at the tops of the risers. I have always vented
from the top down without having any problems, but I accept that
residential systems are not the same.

Damn Gary, you were starting to scare me there. :-) I thought you and
I might be living on 2 different poles of the earth.........you know,
like South America where the toilet water flushes down the bowl in the
opposite direction as here in North America. I understand where your
coming from. With bigger commercial boilers and piping, a little air
isnt a huge problem. In residential though, a bubble of air 1/2" in
diameter is enough to stop a radiator (baseboard) from heating.
Bubba

You call those baseboard heaters radiators too? I've been picturing
the cast iron monsters that I have here. Also, do you use a single
riser for multiple radiators? On different floors even? Ewwwww...
Every radiator in my home has it's own riser ( 1" black iron pipe ).

--
"De inimico non loquaris sed cogites."