Main Vent Location Question-slightly more complex

Brad White_203

A lot of systems have the vent at the end of the dry return, often over or near the boiler. That works fine but you wind up venting the volume of the dry return too and making it de-facto a steam-carrying pipe.

Until that (main)vent closes, the system is still very close to atmospheric pressure. Once that vent closes, pressure, even in the desired ounces, can build. But you also want to keep the venting burden off of your radiator vents as you know.

I have vented some systems where I added "end of main" vents and kept the original venting locations at the end of the dry returns.

As a less than scientific experiment, I timed it each way, venting mains only, venting the dry returns only and then both mains and dry returns, from a hot start/recently fired and timed to steam felt at the furthest radiator.

Having kept/replaced the dry return vents made a difference expressed in minutes, (about 3-4 minutes less time) than main vents alone.

Of course, the new main vents were a set of four (4) Gorton #1's where only a capped nipple existed. The old Vent-Rite dry return vents were replaced with single Gorton #1s.

The basic improvement profile looked like this:

"As-Is" (No main vents, old and probably plugged dry return vents): At least 30-40 minutes of firing with little steam to radiators. Heavy hissing at radiators. Burned a lot of fuel for nothing...

"New Dry Return Vents" (no main vents yet): 20-25 minutes. Still heavy hissing at radiators.

"New Main Vents" (4 Gorton #1's), no dry return vents: 15 minutes.

"New Main Vents plus Dry Return Vents": 12 minutes or so. I suppose this just got the air out that much faster but it also made that dry return a steam-carrying pipe versus mostly condensate. Left it that way and insulated it better.

Anyway, a snapshot of different venting strategies, not scientific really.

If your main steam line ends and drops to a wet return, indeed, that is where the vent must go, held back from the drop of course.

SusanC

Slightly More Complex Main Vent Location Question

I realize the recommended main vent location is about 15 inches back from where the return drops to eventually become a wet return. What is the downside of having main vents (or an auxillary main vent) slightly beyond the last radiator riser of the main - thus near the beginning of the return rather than near the end?

Unknown

Susan - It should be fine to do it that way. The main object of the vent(s)is to get the air out of the way so that the steam can get to the radiators. So as long as it is installed after the last radiator on the main, it can do its job.

SusanC

Thanks for your response; still a few questions

My major interest is in the Main Vents plus Dry Return Vents situation.

There was one statement I’m not completely sure I understood correctly: on first reading I thought you were saying that having vents in both locations makes the return more a steam-carrying pipe than with only dry return vents, which wouldn’t have made sense to me, but now I’m thinking your steam-carrying statement probably was meant only in comparison to the main vents with no dry return vents scenario described just before. Do I understand that correctly now?

I’m particularly interested in the reverse situation from the two location situation you described; i.e., I’m interested in a situation in which the major venting is still where (15 inches back) the returns drop to become wet returns and the one Gorton 1 is an auxiliary shortly past the last radiator riser. Do you feel there are advantages or disadvantages to such a scenario over only dry return venting?

Lastly, I’m not sure I understand your last sentence fully: are you saying that if your return (no matter how long) drops to a wet return near the boiler, one can put main vents only at the point (15 inches back, of course) where the returns drop to become wet returns and could not have an additional Gorton 1 shortly after the last radiator riser with the major venting at the end (almost end) of the dry return or were you just reinforcing the location of the majority of venting?

Once again, I appreciate your help.

Brad White_203

Susan-

Hi Susan- I probably ran off at the keyboard a bit there

If you do not have dry returns (and reading now, I see that maybe you do not), disregard those conditions.

I am not 100% clear on your last paragraph. If I understand it correctly, you are proposing to have one vent at the end of your main but you also have another location, a different one, which is further along but off of a dry return?

At the very least, I intended to reinforce the ideal venting location. Sometimes this venting opportunity is before the last take-off. This is really fine, for the speed of steam to that point is faster than if no vent existed at all. That last riser has little more to do that the run-out pipe and radiator volume.


I far prefer wet returns. Even if they tend to collect stuff over time, they carry more condensate for a given size (full of water versus competing water-air-water). Plus it forms a positive seal. Venting back a bit from the end of the main, just before a drop to the wet return is ideal and in fact is the last opportunity. Once your return is wet, it ceases to be a vent, as you know.


To your first question:


There was one statement I’m not completely sure I understood correctly: on first reading I thought you were saying that having vents in both locations makes the return more a steam-carrying pipe than with only dry return vents, which wouldn’t have made sense to me, but now I’m thinking your steam-carrying statement probably was meant only in comparison to the main vents with no dry return vents scenario described just before. Do I understand that correctly now?

Yes, I was just commenting that when the dry return vent (near the boiler) was plugged but a new venting tree was added, the steam time was certainly shorter and the dry return was at best, "warm". Once that dry-end return was vented, it sped up by a few more minutes but that return pipe was HOT. More radiation to the basement which called for thicker insulation than otherwise would be.

I hope this helps and does not add to any confusion! Let me know if I can clarify things better.

SusanC

Thanks, but now unfortunately I’m really confused..

I definitely have dry returns as noted in my stated interest in vents both on the main shortly after the last radiator riser and vents also in the usual position at the end of the dry return 15 inches back from where it drops down to become a wet return. The only difference between what I was asking about and your scenario of “New Main Vents plus Dry Return Vents” is that I’m talking about having the 3 or 4 Gorton #1’s in the usual position at the end of the dry return (15 inches back, of course) and the 1 Gorton #1 on the main after the last radiator riser, while you were talking about having the 4 Gorton #1’s on the main and the 1 Gorton #1 at the end of the dry return. My question is, would there be an advantage or disadvantage to having an auxiliary 1 Gorton #1 on the main and the 3 or 4 Gorton #1’s at the end of the dry return (15 inches back from the drop) vs. having only the dry return venting?

nicholas bonham-carter

vent location

i think it is better to have all the vents at the end of the dry return. lets assume for simplicity that the capacity of the main is 50%-50% dry return-supply, and that you have 1 vent on the supply after the last rad, and 3 on the dry return. as soon as you have vented 50%, that vent closes, and you are left with only 75% capacity to finish the job. just as "you can never be too rich or too thin", you can never have too much venting. a good goal would be to get the air out before the pressure rises above 3 oz.--nbc

SusanC

Thanks; still a question

The Gorton #1 on the supply would be an EXTRA vent so in addition to what was calculated to be enough venting (located at end of dry return). The aim would be to cut down on radiators trying to vent the mains even with plenty of venting at ends of dry returns (15 inches back, of course). Is there a downside to that?

On a different, but related topic, I find that Gorton #1’s tend to leak steam more than Gorton 2’s; the latter close and that’s it. So a menorah of Gorton #1’s may lose more steam than a Gorton #2. I realize with dry steam this would not be a problem, but in the real world not all steam is as dry as it should be.