Help With Venting

PhilKulkarni

I have a newly installed one pipe steam boiler. The front part of the 3 floor house has 4 rads all of which keep venting throughout the heating cycle. The piping for the front consists of:

2”X25.5’ counter-flow, dripped
2”x13’ parallel flow with 3 risers
1 1/4”X22.5’ parallel flow measured till it turns down into a wet return

At the end of the dry return there is one 3/4" Big Mouth and another 1/2" compact B&G Vari-Vent whose venting capacity I cannot find but vents pretty fast.

The front and back are separate mains and the back is also part counter-flow and dripped. The back has a single Hoffman 75 and the back rads heat up fully and the rad vents close.

The boiler runs at 0.5psi and shuts off on temp.

How much more venting do I need and where should I place it so that the front rads vent completely? Would it help if I installed any additional vents at the end of the last riser on this mains?

All the slow venting front rads have varivents, fully open, while the rads on the back mains have Hoffman 4A and Gorton 4/5.

Thanks in advance.

ethicalpaul

How much more venting do I need and where should I place it so that the front rads vent completely?

This is an odd question. This boiler is tiny. Surely the big mouth can vent every cubic inch of air as fast as the steam is pushing it.

The main vent isn't there to make rads vent completely. It is there to let the steam start to get to all/most the radiators at about the same time.

How fast the radiators fill with steam is determined by the radiator vents. But you don't want them to fill with steam fast. You want them to fill with steam relatively slowly so that steam gets into all the radiators.

PhilKulkarni

I had Gorton 4s on 3 rads and a Gorton C on the largest rad on this loop. But the previous boiler was oversized and the rads would vent in approx 4-5 mins. The new boiler is ‘right’ sized: 308sq’ output for 295sq’ radiation. But with those vents, the rads barely got warm leaving the front of the house, especially the living room pretty cold. After I replaced them with the Varivents they get hot but not fully, since they keep venting. The only time they close is when the boiler is recovering from a 1 degree setback at night, and when they do it is only for about 5 mins before the temp is reached. Today it is cold in NYC and the boiler cycles often, the rads are hot but never stop venting. The rads on the other mains are just fine.

To be clear, the situation is much better with the Varivents than the smaller vents. Otherwise it would have been miserable on a day like this. It would be nice if I could get those rads to operate at their full output.

ethicalpaul

It is a combination of slowing the too fast radiators and speeding the too slow radiators.

But always start with all of them slow and only speed up the ones in the rooms that end up cold, is my opinion on it.

If the radiators are not getting hot enough fast enough in a room that is too cold, slow down the hotter ones.

PhilKulkarni

My living room + dining room is the only place where I have a fast and slow heating radiators. They are on different mains. The faster heating rad has a hoffman 4A while the largest rad which is on the same mains as all the others supplying the front of the house has the fully open Varivent. The 4A is really a small vent and is the same one that was there with the old boiler.

Which vent size would you recommend I replace it with?

All other slow rads are in separate rooms which face the front of the house thus there is no faster radiator to throttle down.

The boiler runs for 65mins to go from 69 to 70 in the morning. Subsequent run times to maintain the 70 degree temp take 30 mins and the rads get hot during the last 5 mins while still venting. Assuming the same outside temp, it takes a certain number of BTUs to increase the temp by 1 degree. If half the radiators in the house are not functioning properly then the only way I am going to get the same BTUs is to run the boiler longer. Wouldn’t the run times be shorter if the slower rads were to be vented faster so they could put out more heat simultaneously? Am I missing something like improper near boiler piping?

PhilKulkarni

This morning I plugged the main vent on the faster heating loop. Now the slower venting rads on the other mains are venting faster. Three of the four Varivents close in 17 mins or less of a 30 mins heating cycle; they seldom closed before. The Varivent on the largest rad closed about 26 mins into the cycle; it never closed before.

On the previously faster venting mains, one of the rads with the Hoffman 4 isn’t getting as hot like before but on balance the front of the house is a lot warmer than yesterday even though the outside temp is hovering near 3 degrees. I am still hoping someone on this forum can suggest how I could make the mains vent optimally. I still suspect there isn’t enough steam in that mains and using brute force(plugging the main vent on a perfectly working part of the system) is the right remedy as it might cause other problems down the road.

Thanks for your input ethicalpaul.

Jamie Hall

Two distinct problems -- and therefore, two distinct solutions.

First, the mains. The objective of main vents is to allow the steam to get to the end of the main as quickly as possible. Therefore, one wants to vent the mains liberally. However, no matter what you do a short main will fill faster than a long one. So this is a situation where, if there is a really significant difference, it may be advisable to slow the venting on the shorter main.

Keep in mind that for mains all bets are off unless they are insulated. From a hot start, that doesn't make that much difference. From a cold start, insulation can make a difference of several minutes to tens of minutes, depending on the main.

Now assuming that the mains are adequately vented and insulated, one uses the radiator vents to balance the heat output to the load placed on the radiator. The most satisfactory way to start is by slowing down the venting on radiators in spaces which are getting too warm. Don't worry if the radiator doesn't get hot all the way across -- it may not need to, to keep the space warm. Slowing the overenthusiastic radiators will help steam get to the others. If you find a situation where a radiator does get hot all the way across, and the space is still not warm enough -- you've just found out that that radiator isn't big enough. More venting isn't going to help, although longer cycles may well help (and slowing too fast radiators helps there, too).

dabrakeman

Obviously you have verified that the Bigmouth on the originally slower venting main is a actually working (not stuck closed)?

PhilKulkarni

Thanks Jamie, your points understood. There is an endless list of people on the forum that have some radiators partially or not at all and venting turns out to be the culprit in a majority of cases. My case is no exception.

With the main vent on the shorter mains plugged, the pressure has gone up by 1oz or thereabouts to 9 oz on my 0-5psi gauge. Though nonlinearly, the increased pressure is causing the Big Mouth to vent faster. Therefore I see an improvement, a substantial one with the always venting rads, but far from before. With my previous oversized boiler operating at 1psi, I had a single BigMouth on that mains and the Hoffman 75 on the shorter mains. Now I have none on the shorter one but have added a second vent, comparable to the Big Mouth on the longer mains and then have fully open Varivents on all the rads to boot, and still can’t vent fast enough. That is where I have a disconnect.

As for the insulation, all the mains have 1” fiberglass and the returns 0.5”. I am less sanguine about the condition of the risers but the original piping had asbestos insulation.

Other changes in this install were better matched boiler output to radiation load, elimination of a bullhead distribution tee, using the full 3” boiler tapping for a taller header, and addition of 1” drip legs to the two counterflow mains. Boiler skimmed properly.

Thanks in advance.

PhilKulkarni

@dabrakeman : TheBig Mouth vents slowly but closes completely and does not leak. @ 44 degrees ambient, it closed in 22 mins from a warm start. The shorter mains took 9 mins to close the Hoffman 75 from a warm start but I plugged it yesterday.

I would appreciate if someone took a look at the two drip legs and determine if they are installed correctly.

PhilKulkarni

Still trying to troubleshoot this venting problem....

On the slower(longer mains) I removed the Varivent from the largest rad and it still keeps venting.The remaining rads feel warmer, but still vent air during the heating cycle. The stat is being satisfied by the rads heating on the shorter mains.

I want to check the pitch of this counter flow section, but because one end of it is in the crawl space where the surface is rocky and uneven, it is difficult to measure the ht correctly.

Can anyone suggest a work around to check the pitch?

Checking the pitch to eliminate the possibility that water standing in the counter flow section could condense the steam and prevent the rads from venting entirely. I hear no hammering in the pipes and the water level goes back to the ht marked on the boiler in under 3 mins after the boiler shuts down.

To recap the situation, I have blocked the main vent on the faster mains to slow down the steam and have Hoffman 4A vents on all the rads and all of them close and the rads get hot but the other(longer) mains doesn't.

Jamie Hall

Can you sight along the steam main? Use a laser level.

PhilKulkarni

I can see both ends. In the last few days I have called a couple of heating companies to see if they can determine and correct the pitch(if needed). They told me that a laser level is not needed until I explained the situation and then they passed. However, one intrepid boiler guy came around to look yesterday and said he can't tell if the pitch is correct but can increase ht at one end by using a 1" pipe as a lever and use straps to hold the mains in place. He may have to rotate an elbow at the low end of the pipe, and all told achieve an inch greater ht at the higher end. Since the pipe is already pitched up adding an inch more(assuming it is possible) should help keep water out of the pipe and return it to the boiler via the drip.

I wish I could see a 2.25" diff in ht, since the counter-flow section in question is 22' long. Is this worth trying?

Another option I am considering is inserting a tee just before the 2"mains transitions to a 1.25" pipe and moving my current Big Mouth there. I am thinking this should vent the air faster since the pressure drop from the boiler to this point due to friction should be less than the pressure drop where the main vents are now(at the end of an additional 22.5" of the 1.25"dia mains). Is this worth the expense?

Yesterday, when the temp hit 62 degrees, the slower venting rads were still slow but the vents closed faster than when the temp was below freezing last week.

Thanks in advance.

PhilKulkarni

I am continuing this dated thread to keep the conversation thread intact. Per Jamie Hall’s suggestion, this past summer, I added 2” to the pitch of the counterflow section of the slower mains and additional clevis hangers as well to ensure the pipe doesn’t sag. With the added pitch, both the front and back mains heat evenly, and 40-50% faster to boot.

A minor problem. Now there is more crud in the boiler, though the water in the sight glass is clear. I did a blowdown upon noticing that two #5 MOM vents had stopped working and that a lot of rust particles fell out when I cleaned them. The remaining vents are either adjustable Ventrites and Hoffman 40 with tongues, that are working normally. The wet returns are in good condition and while a small amount of rusty water does drain out, the amount of rust particles are a lot less than from the boiler.

Should I replace the MOMs with Ventrites or add some rust inhibitor to the boiler? If the crud is coming from the counterflow pipes, will the inhibitor be effective?

The boiler runs at 0 psi for the first 15 mins then at 0.3psi for another 8-10 mins before shutting off on temp.

Thanks in advance.

EBEBRATT-Ed

Probably some rust from disturbing the pipes. I would just blow it down once in a while and it will probably settle down. As long as the water level is stable while steaming I wouldn't skim. The rust will probably settle at the bottom