Main Vents and Hartford Loops

wintermute

We recently moved into an old house with steam heat (old system, new gas boiler) and I'm trying to fix the knocking and spitting by picking low-hanging fruit (pitching radiators, insulating) and have two questions. The first one is about what appears to be a main vent on one of my two one-pipe loops. It's a Hoffman (see photo - not sure what model or size). Looking at the picture, there is one radiator to the left of the vent and the main pitches down to the right, toward the boiler. The return drop is to the left of the vent.



Now, the pipe to the left is inaccessible without sheetrock demo. In your opinion, does this vent appear to be a retrofit and I should expect to see a true main vent (inoperable) further down the line behind the sheetrock. The Hoffman does not vent - maybe too low in the pipe? SHould I bother trying to rehab or replace it, or should I plug it and look for the old main vent that's possibly further down the main?



Another problem I have is that a couple of feet of the return, just before the Hartford Loop, is copper, with no dielectric bushing or brass between it and the black pipe. At what point should the copper from the makeup water supply meet iron? Thanks.

Brad White

Location, Location, Location.

The vent is installed in the middle of Suicide Alley at a NASCAR race- steam and associated condensate coming in from the left has no choice but to hit the vent head-on before making the turn. Steam is not Dale Ernhardt. It is Michael Waltrip but with better thermal properties.



IF there is only one radiator downstream, you may decide to put a larger vent on that radiator (not ideal, but better than what you have), or install a vent just upstream.



As for the Hartford Loop, copper below the waterline is not a problem. I do not worry too much about dielectric corrosion but if any doubt, a brass or bronze ball valve between the two will serve you well. If you do any re-piping, consider a low point full-port ball valve in line with the horizontal to enable flushing out the ends.

crash2009

Can't see in there Huh?

  Try using a mirror first, or if you have to, get a $30 inspection camera from the hardware store. 

If there is a vent, it will be located after the last rad, and before the drop to the boiler.

If you can identify the vent, or the fitting, the vent is supposed to be in, then cut a nice clean access hole so you can install or repair the vent.  The hardware store has these DYS access panels that come with a template.  You just mark the hole and cut it and the panel fits right in.  No drywall repair needed.

wintermute

Going in Blind

Thanks - unfortunately I can't see in there and the top of the pipe is up against a floor joist running perpendicular to the pipe.  I'll have to cut some sheet rock to find the vent.  There is no drop at this point in the loop (because there's a door to a set of Bilco doors immediately to the right of this vent) - steam heads up to the left, condensate flows down to the right and hits the drop a few feet downstream.  I'm guessing with this configuration, the vent would be located immediately before the radiator, and not at a dead end after the radiator?

Brad White

End of the line (end of the line)

'"I'm guessing with

this configuration, the vent would be located immediately before the

radiator, and not at a dead end after the radiator?"



Not on a dead-end, but usually after the last radiator. Sometimes you have to admit defeat and go less than the ideal.



The key elements you want to preserve are:



1) Getting as much bulk air out of the mains ahead of the steam in a short time (proportional to other mains of course).



2) Use a location which prevents the vent(s) from direct impact of steam-borne condensate.



Sometimes this location is upstream of the last radiator. But too far upstream and the vent will close before air is released from the downstream portions of the main. But it may get you halfway there.