Main air vents - how many, where, what

SWEI

Fred said:

I would say fuel savings is driven, more by other factors in your home. A two stage gas valve will save some fuel costs because it essentially reduces the fuel input requirement and consequently the energy output.

When properly implemented, two stage firing can reduce fuel use by more closely matching the firing rate to the load. Doing so increases the cycle length, which reduces standby losses and increases comfort.

emk2badknees

I have an update to my hissing issue.

I removed a 3/4" plug at the end of the main and relocated two of the Gorton #2 vents and the Hoffmann 75 vent to that location maintaining 3/4" piping. Two other Gorton #2s I left at the end of the dry return with 1/2" piping.

While it appears that the pressure stays lower now for most of start up and there is less hissing, for some reason there is still a pressure spike up to 1-1.5 psi during start up. It happens for every cold start. At that time, several things happen:
- The water level in the sight glass rises beyond the top of the glass
- The who system seems to groan and shake. Sometimes there is a bang or clunk.
- The radiators hiss for about 3-5s (despite the fact that the pressure is below 2.5 psi)

This is the only time when the hissing is an issue. Just to see, I ran a test without the 3/4" plug and it did exactly the same thing, which suggests to me that more venting will not fix this issue.

Has anyone seen this behavior before? What could be causing it?

Chris_L

I recently saw the same behavior after increasing my main venting. But I doubt that had anything to do with it.

In my case, the banging was water hammer in the Hartford loop. My loop has an 8 inch nipple instead of a closed nipple, and I had let the water level in the boiler drop to around the height of the bottom of that nipple.

That caused water hammer, but only on a cold start. I didn't actually see it, but pressure surge was enough to trip Pressuretrol, as the boiler would shut off for a few seconds.

The fix was easy: adding water to the normal water level.

emk2badknees

I just wanted to share some experience as it relates to the main venting rule of thumb hiscussed on this thread, after having lived with my system running with three different main vent configurations now for a little time.
- One Gorton #2 at the end of the dry run: loud hissing in several waves every time the system would fire up.
- 4 Gorton #2s and 1 Hoffmann 75 in a 1/2" vent tree at the end of the dry return (@Fred indicated that the 1/2" pipe was restricting flow and this setup was equivalent to running 2 Gorton #2s.): hissing was still observed in a couple of waves, although it was less.
- 2 Gorton #2s on 1/2" vent tree at the end of dry run and 3 vents (2 Gorton #2s and 1 Hoffmann #75) in a second 3/4" vent tree located at the end of one of the mains: about 1/3 of the time, no hissing is observed. The other times there is one brief hiss, which is softer than it used to be. My family is much happier now, especially when the boiler kicks in at night.

Now, comparing with the rule of thumb (one Gorton #2 per 20' of 2" pipe):
- I have measured 100' of 2" pipe on mains
- Per @Fred's rule of thumb, that would require 5 Gorton #2s
- I have the equivalent of 4.5 Gorton #2s

My conclusion from this non-scientific study is that the rule of thumb appears to be just about right (at least for my system).

As I said in my previous post, I still that I still have a 1 psi pressure spike, which coincides with the brief hiss and a clunk. I will try adding water as @Chris_L suggests. Easy enough to do, right?. Out of curiosity, any idea what the theory is behind this solution? It isn't intuitive to me.

Steamhead

I bet the pressure spike and surging water means your water is dirty. Flush and skim the boiler and see if that helps.