NEAR BOILER PIPING CHANGED...SYSTEM IS NOT THE SAME

Doug83

Hello All. I have a question related to near boiler piping and I'm disappointed that I didn't have a sketch or full pictures prior to work being started. I had a 45 year old American Standard atmospheric steam boiler that was recently replaced by an HB Smith with a Becket Power burner. The problem started at the beginning of heating season when I got a call from tenants saying that their master bedrooms and kitchens were getting no heat. The building is 5 stories, 5 full floor apartments with the living room and hallway accounting for about 40 % of the space, and a small bedroom , bathroom, kitchen and master bedroom accounting for the other 60%. There are 5 large radiators in the living rooms all on one riser. The bathrooms have just risers, and the kitchens and master bedrooms each have a riser with medium sized radiators. AS you can see from the sketch, I believe... from a picture that has obstructions, that the way the near boiler piping was configured was as is shown in sketch "A." When heating season started, and I received the complaints, I saw that the configuration they left is with was as was shown in sketch "B".... The boiler room is about 15 feet from the living room riser, and the bath, kitchen and master bed risers are 10, 25 and 40 feet from the boiler room. When i told the contractor, they sent a tech ( who was not the mechanic on the job) who pumped the pressure up to 6psi and killed most of my air vents. I replaced them all with variable heat timer vents ( 15 radiator, and one on the top of the bath riser.) The mechanic who did the work came the next day and said he would be back in a few days to reconfigure the piping. When he reconfigured the piping, he left the system as shown in sketch "C." When we fired back up, all the risers got hot, but there is still a balance issue. I got am infrared gun and shot the radiators and saw timing issues for heat and started adding additional air vents on the risers ( as per prior great advice from this site..) and I even added a second air vent on the master bedroom radiators. I Still get complaints from the last master bedroom saying they are not getting enough heat, long enough... and the room shoots at 69 to 70 degrees when the living room is getting 74 or 75 degrees. Should I ask them to fix this? Tie the two sides back together? add valve in the living room riser supply out from the boiler? I am afraid to do anything now while it is so cold.. but what is the best test to determine the right near boiler configuration. The plumber that did this 45 years ago either knew what he was doing, or, went through the same issues and piped the system to resolution.... your thoughts are much appreciated as always!

Ironman

No sketches posted.

acl10

Do you have main vents

nicholas bonham-carter

We always concentrate on “what has changed?” in these cases, so your pictures/diagrams will help a lot.
Was the new boiler correctly sized for the EDR of the radiation, and not what the old boiler was?
Was the new boiler piped according to the requirements of the manufacturer at a minimum?
Has the pressure been set higher than 1.5 psi, (basic function, 8 ounces economy, and comfort).
Were the main vents checked for capacity, and changed? You may need additional vents on the risers for a 5-story building, so as to fill all the horizontal, and vertical pipes first before the radiators fill. I would use Hoffman 40’s on the rads, as a higher resistance vent is needed. You could try a faster rad vent (only) at the top rad, like a Gorton D.—NBC

BobC

What pressure is the boiler operating at, it should be below 2 PSI. You need properly sized main vents and you should probably throw out all the heat timer varivalves - they are must too aggressive for single pipe steam.

Bob

newagedawn

another beauty from hackers paradise, "the pain of a poor install lasts far longer than the joy of the lowest price"

the_donut

You also mentioned 5 large radiators in the living room. Heattimer vents are notoriously fast vents. GW Gill ran into a case where one radiator would not heat no matter what he did. He even pulled the vent from the radiator and nothing. Issue was the heater timer vent on other radiator was so aggressive that the radiator was in a state of constant vacuum. Steam goes from high to low pressure always. Vacuum is a lower pressure than atmosphere.

Turn down the living room vents.

Doug83

My apologies for not seeing that the pic didn't post. It is there now. I copied your questions and answered them below, thank you!

Q:Was the new boiler correctly sized for the EDR of the radiation, and not what the old boiler was? Yes the new boiler was sized by the boiler engineer/filing engineer It was sized at the same EDR of last boiler in analysis, which was probably sized to heat with the windows open....

Q:Was the new boiler piped according to the requirements of the manufacturer at a minimum? Yes, as far as piping off the boiler to the header.

Q:Has the pressure been set higher than 1.5 psi, (basic function, 8 ounces economy, and comfort). It is set at 2psi, and i can tell you that at a set point of 72 degrees on the highest floor living room, with a sensor in the far corner of the room, the room gets to 74 degrees.

Q:Were the main vents checked for capacity, and changed?
There are no main vents on this system. It would be difficult to install them now due to distance to ceiling constraints... not impossible, but just very difficult. It never had main vents in the atmospheric system and worked fine.

Q:You may need additional vents on the risers for a 5-story building, so as to fill all the horizontal, and vertical pipes first before the radiators fill. I would use Hoffman 40’s on the rads, as a higher resistance vent is needed. You could try a faster rad vent (only) at the top rad, like a Gorton D. I placed a Gorton D on each of the 4 risers, right below the 5th floor. Maybe I don't need one on the living room riser??

Q:What pressure is the boiler operating at, it should be below 2 PSI. You need properly sized main vents and you should probably throw out all the heat timer varivalves - they are must too aggressive for single pipe steam. Yes, 2 psi, what would you recommend, fixed valves in increasing orifice size as I go up? I put the heat timer variables valves on so I could balance the system to recover from this disaster....So the each floor the opening is larger until the fifth floor where it is full open, and with two varivalves on the living room and bedroom radiators.

Q:another beauty from hackers paradise, "the pain of a poor install lasts far longer than the joy of the lowest price". Would you believe this was not the lowest price, and was through a large reputable contractor and a family connection....

Q:You also mentioned 5 large radiators in the living room. Heattimer vents are notoriously fast vents. GW Gill ran into a case where one radiator would not heat no matter what he did. He even pulled the vent from the radiator and nothing. Issue was the heater timer vent on other radiator was so aggressive that the radiator was in a state of constant vacuum. Steam goes from high to low pressure always. Vacuum is a lower pressure than atmosphere.

Q:Turn down the living room vents. This sounds like a good next step. Will do!

Here is my follow up question in relation to the sketches now being attached. Should I have the boiler engineer redo the EDR calculation based on the fact that steam production is now split in this un-engineered configuration? Or, since I am getting heat at all the radiators, just not balanced yet, play with the variable valves and Gorton D's to see if I can achieve it there first?? Thank you all again!

nicholas bonham-carter

I would get the installers to redo the piping in conformity will the manufacturers requirements, in case you have a warranty boiler replacement needed in a couple of years.
The mains still need lots of main venting, and it could be done at the tops of each of the risers with a couple of big mouth vents each. In these cases you are allowing the air in the pipes to escape at the lowest possible resistance, (back pressure under 2 ounces). The valve bonnets and stems could be removed, and tapped for a menorah of big mouth vents.
When the mains are full, then the steam will enter the radiators all at the same time.
Did you tell us how the system is controlled?—NBC

EBEBRATT-Ed

Need pictures. If it is piped like "C" it should be correct if the near boiler piping is sized correctly. Was the boiler skimmed?

You may just need to fix the venting. Need more information

KC_Jones

Actually if it is exactly like C it is still wrong as one of the system take offs is between the boiler risers which isn't correct.

Pictures are really needed here, sketches can't usually capture the subtleties.

Fred

I don't see any of those sketches as correct piping. The piping should be (1) Riser out of boiler, connected to the Header, (2) Second Riser out of boiler connected to header, next to the first riser, (3) Riser to Main #1 Connected to Header after Boiler risers, (4) Second Riser to Main #2 connected to Header, next to Main #1, and (5) Equalizer at end of Header, back down to lower most boiler tapping below water line, with Hartford loop properly tied into the equalizer about 2 inches below the Normal Boiler water line.

Doug83

You are right about pictures
.... I have attached a pitcture of the original configuration with the Tee shown, a picture of the risers coming out of the boiler and into the header, a picture showing the risers coming out of the header, both on the right of the risers coming out of the boiler and into the header. and a sketch showing the correct current configuration...sorry about that!

Doug83

The first picture is original install and shows the two pipes from a low header all connected together, with what appears to be a wye maybe on the left giving extra flow to the kitchens, baths and living rooms. The right pipe goes to living room.

The last picture shows current, two risers from boiler into header coming in horizontally, then two risers on far right of those coming in from boiler. Then they split from the header as shown in the sketch.

Gsmith

This is almost certainly a venting/balancing issue. The questions and advice of others earlier are almost certainly correct. Let's summarize:
1. old boiler, vents and piping worked ok, system was balanced enough that you didn't report complaints.
2. New boiler installed, slight problem with header, riser takeoffs which was fixed.
3. Before header/riser repaired, boiler run at 6 psi, destroyed all your vents. You replaced with Heatimer varivents.
4. Tenants still complain of unbalanced heat in apartments: too hot in living rooms with very large radiators, too cool in the other areas served by the two other risers.
5. Pressuretrol set at 2 psi, no report on whether this is cut-in or cut-out.

To summarize the suggestions above I'd suggest going back to "normal" one pipe steam arrangements and do the following:
1. Set pressure-trol to 1.5 cut-out, 0.5 psi cut-in.
2. Add main steam vents to the top of all three risers, if you need help in sizing post exact size of mains, risers and distances, but you indicated a 5 story building (say 40 feet from first floor to 5th floor) and horizontal mains in basement are 15 feet for the living room riser and 25 and 40 feet for the mains leading to the other two risers. Total distances are 55 feet to top of living rooms riser, 65 feet to top of center riser, and 80 feet to top of the bedroom riser. Because of this configuration you must consider the vertical risers as "mains" and try to vent all three so the steam arrives at the top of all three risers at pretty close to the same time. You can use your hand or infrared thermometer to tell when the steam gets to the top of each riser. If it were mine, I'd add the equivalent of one Barnes & Jones Big Mouth vent on each riser, with perhaps more venting on the furthest riser from the boiler (bedrooms you said). Add the vents to the piping BEFORE the radiator valve on the top floor.
3. Remove all the heatimer varivents. These are, as said by others earlier, probably too aggressive and if on the large living room rads are probably preventing steam from getting to the rads on the other risers (because the others are further away from the boiler and the path of least resistance for the steam is to the living room rads with very fast vents even at the lowest setting of the varivent). I'd suggest trying either Hoffman #1a or Vent-rite #1 adjustable vents (I like the vent-rite vents personnaly) these are easily adjustable and will help you enormously to balance the system. If you knew what make/size vents were originally installed at each rad you could probably use those, but that may be hard to determine now. Conversely to what you would think, adding fast vents to the radiators is often not helpful. As is said many times on this site, vent the mains quickly and then vent the radiators slowly and proportionately to their size and the comfort in each room you want. Maybe start all the adjustable radiator vents on a mid range setting (say 3 or 4), then slowly over a few days turn up (faster) the ones where the rooms are too cool and turn down (slower) the ones in the rooms that are too warm.

From all you described I'm pretty certain this will work for you. You haven't mentioned water hammer (banging) and the near boiler piping seems about right (doesn't have to be perfect unless you have some problem symptom like water hammer).

If you have trouble with the individual steps, post back and I'm sure someone will help with each step.

Steamhead

Assuming the pipe sizes are correct, the piping in your most recent post looks good.

Doug83

@Gary Smith @Fred @nicholas bonham-carter @eberbrat-ed , @the_donut " , @KC_Jones , @Steamhead , @BobC . You guys are incredible, and this blog is worth its weight in gold. Thank you again and I will perform and report back.

Doug83

@Gary Smith Some answers to questions, the piping lengths you have are very close, from basement we are 55 feet up to last radiator, elbowed right into the 5th floor rads, and as we said 15 feet to living room, 10 feet to bathroom, 25 to kitchen and 40 to bedrooms

The pressuretrol is set to 2psi for cut out and back in at 0.5, but i noticed it never comes back on after it hits the 2psi. Here is why, and maybe this is also contributing to the balance issue.... I have a system whereby the control is both a temperature sensor at the opposite end of the living room radiator with a set point of 73 on an ECOBEE controller in the basement, the ECOBEE is wired into a switch that allows it to work in conjunction with an EPU heat timer. So what happens in a call for heat, say when the temp on 5 hits 72 (and a call for heat), is that the boiler starts, and when the boiler hits 2 psi, it is at the same time the temp on 5 hits 73, but by the time the pressure comes back down to zero, the temp on 5 is already at 74, and actually settles at 75.

Maybe when i perform your balancing recommendations, it stays on longer, and actually steams the bedroom radiators longer?

Who knew that only 40% the battle was the installation, when in fact, knowing what you are doing on the balancing and control could be the other 60%....

Gsmith

Maybe someone who knows the Ecobee controls could chime in here?

Fred

The controls sound like they are working properly. Anytime any one of those controls reaches a set point, it should shut the boiler down until there is another call for heat or the pressure drops below cut-out, etc. It does sound like the issue is balancing but, out of curiosity, has the boiler been properly skimmed? Oils on the surface of the boiler water can do strange things. Main vents are also critical. They can be placed at the ends of the mains or on the top of risers after the last radiator on a main. They need to be generous in terms of capacity.

Jamie Hall

If you have a timer in the soup, it becomes more essential than ever that the venting be not just good enough, but excellent. All the above comments on vents are spot on, as well as insulating the dickens out of the mains -- and perhaps the risers, if you can. Uninsulated pipes slow the steam a lot, which venting won't help. Poor venting also slows the steam, more obviously, and you really need to get it so that the farthest radiators get steam within a very few minutes -- certainly less than a quarter or less of the timer lock out -- to get the system balanced.

Doug83

@Fred @Jamie Hall

so...interesting you hit on skimming... I didn't think it would play much into this issue, but the answer is no.... The contractor and then I did some skimming but probably not enough. What happens during the heating cycle is the boiler water starts at NWL, then rises two inches (say 10 minutes) , I guess until it steams, then it drops very slowly (next 10 minutes) until it goes 2 inches below NWL. BY the time it hits that low point, it goes out on Pressuretrol 2psi and I get 74/75 degrees in the living rooms.
The contractor was supposed to come and do a "boil out" he called it (chemicals), and apparently HB Smith recommends it. We are months into operation and now they are saying they want to schedule it ( its 30 degrees out)...I really like the idea of getting the larger main vents on the risers right before (4th floor) the last floor as the pipe elbows into the last radiators on the 5th floor. I drilled and tapped Gorton D's on all 4 risers on the 4th floor about 1 foot below the ceilings. I didn't think I could put bigger vents in those locations... mostly because they would be in their living space and would look funny...but I am not concerned about looks at this point.

These are 1 1/2 inch risers, what would you recommend for vents?

Jamie- I thought about insulating the risers.. but don't they act as radiators too? The mains are all required to be insulated as per NYC code. Thanks for the timing advice...so I should check for 200 degree temps (infrared) at the beginning of the 5th floor radiator inlets in a few minutes of when? When the heat timer says circulation has started? For me, this is when the drip leg with the internal sensor sees like 180ish degrees. I am glad you mentioned this point because I did not know when the starting point of that timing should be...
Thanks again all!

Fred

If the vents on those risers are the only vents on the system (shy of the radiators) ,Gorton D' aren't nearly enough venting to move the air out of all of the mains and risers. You probably need multiple Barnes and Jones Big Mouths to get the air out quickly. Why are you putting them on the forth floor instead of the fifth floor? The vents need to be at the top. If you can tell us how long and what diameter each main is as well as the risers, we can tell you how much venting you should have on each. Also, remember it is a waste of time to try to balance the system until the main venting is correct.
If there are oils on the surface of the boiler water, that oil makes it very difficult for the steam bubbles to break through and burst, releasing the steam. That means more turbulent water and less steam for your fuel dollars. It is critical that the boiler be skimmed well.

New England SteamWorks

The equalizer is not big enough, and do I only see a single 2" riser off the header to the mains?

Gsmith

1. Insulate the visible steam mains in the basement as Jamie Hall suggested.
2. Install as large as feasible vents at or near the top of all 3 risers. B&J Big Mouths or Gorton #2's at least. I realize the practicality and aesthetics may play a role here. Easiest place may be at the top of the 4th floor near the ceiling (its only a foot or so from the end of the riser on the floor above and won't make much practical difference). Better, but not essential to locate them at the top of the riser on the 5th floor, but if you can't, you can't (might require changing pipe work, adding a T where the rad valve is, getting new straight rad valves and accompanying spud, and moving the rad slightly sideways--a good amount of work. If you put them on the riser at the 4th floor ceiling you may have trouble drilling and tapping a 1-1/2" riser pipe for a 1/2" or 3/4" vent, if so, you can use a Romac service saddle, 101U or 101S from Romac Industries, BUT GET THE SPECIAL ORDER EPDM GASKET FOR STEAM SERVICE. These service saddles only require drilling an appropriate size hole in the riser and then adding a 90 deg elbow and nipple to the service saddle to mount the vent. The service saddle and elbow/nipple can be painted to match the riser. I happen to like the looks of the brass B&J Big Mouth vent, have one in one of my finished bathrooms, no complaints after a week or so. Like lots of things after it's there a while it disappears.
3. Get rid of the heatimer vari-vents, put slower vents on the radiators preferably adjustable vents. Adjust vent rte as needed to get balanced heat.
4. Turn the pressuretrol down a little if possible 1.5 cut out, 0.5 cut-in--just a matter of turning the top screw and dial inside to the correct settings.

The above 4 steps will be needed in any case, even if your boiler piping is not exactly right and even if you need skimming. You will be pleasantly surprised how much these 4 steps will go to balance the heating in your building.

Skimming never hurts, so do it if you can, but may not be essential. Does the boiler water line move up and down by large amounts when the boiler makes steam? (skimming probably needed if it moves up and down more than 1/2 to 1" or so, 1/2" to 1" movement is about normal.

You haven't indicated noise concerns like water / steam hammer so even if the near boiler piping is not perfect, it may not matter. Plenty of near boiler piping installs work fine if not perfect, including my own. So do the 4 essential items above then if needed move on to other more difficult items, like changes to the near boiler piping.

Doug83

Thank you all again... I obviously have some work to do on venting.... it will be a little work to get the right vents at the end of the mains...but it sounds like I have no choice. The risers end on the 4th floor and then elbow into the radiators on the 5th , so the 4th is the only place I can put the vents.... @Gary Smith , I will try your suggestions for riser venting, thank you for the Romac recommendation I will look at this! We have no water hammer in the system so that is good. I will adjust the pressuretrol down to 1.5 psi. My water line moves up like 1 3/4 inches (first 10 minutes) and then down 1 3/4 inches (last 10 minutes) before going out on pressure. So I will skim again this week. I gave the tenant in the 5th floor bedroom a space heater for the extra degree or two she feels. She was happy... So now I have some time to get this work done under a "no pressure" condition.. no pun intended. Have a Happy heating season!

Gsmith

post back as you move ahead. We're all interested in the results.

the_donut

We are asking about sight glass surging. This is the rhythmic sloshing of water up and down and back up again of water in the sight glass. A cycle of up down and back up again usually occurs in a 1-2 second interval.

What you are describing is boiler water line movement over a heating cycle which is normal. The unit boils off steam, the water level drops, steam condenses in the system and makes its way back to the boiler (water level rises).

Gsmith

One more thing, are these riser pipes through the apartments uninsulated and exposed? If so they too would help the system by insulating them, particularly the riser through the living rooms. You can get 1" thick fiberglass insulation for 1-1/2" pipes in 3 or 4 foot lengths and if you want a better looking finish you can get easily applied PVC insulation jacket. Here are two links to Grainger products, but I'm sure you can buy them plenty of other places as well.
https://www.grainger.com/product/JOHNS-MANVILLE-1-Thick-45NE17

https://www.grainger.com/product/JOHNS-MANVILLE-5-Max-O-D-White-PVC-Insulated-6ZKJ5?cm_sp=Product_Details-_-Products_Based_on_Your_Search-_-IDPPLARECS&cm_vc=IDPPLARECS

This is a pretty easy do it yourself project, and can be attacked in stages (not all at once).

Doug83

@the_donut , this is what I was trying to understand, it is not the fast up and down movement, my water line movement is very slow and specifically directional in pre steam and after steam phases... I was just astounded that it could move 1 3/4 inches for each phase,.. but maybe this is tied to that fact that we have not skimmed enough...At least I don't go low enough to go out on low water trip which is what was happening when they placed the feedwater valve at the wrong elevation ( prior post where you guys saved me from pulling the last three hairs out of my head....) @Gary Smith , yes the risers are uninsulated, I think this is a good idea because the living rooms are already overheated....and I was wondering where I could get the pvc jackets... the look great, they used them in areas around the boiler....I am really looking forward to trying the recommendations here and will report back (this coming Tuesday). I just wish there was an easier way to iterate here... each cycle could be as long as two hours if it stays above 40 degrees outside

Double D

I've had good luck with orders from Buyinsulationproducts.com
They deliver right to your door. http://www.buyinsulationproductstore.com/pvc-90-deg-elbow-cover/

nicholas bonham-carter

Somehow with the aid of an assistant, try to get the mains, and risers vented so that all the top floor rads receive steam at the same time. It would be best to jumper the control wires instead of trying to set up the Heatimer control.
I still think it would be possible to take off the bonnet off all the top floor lnlet valves, remove the stems, and drill and tap the bonnet holes for the 1/2 inch needed for the big mouth vents.
The risers which heat will need equivalent good venting so they also get steam at the same time. The rads need slower Hoffman 40’s so as to allow them not to short circuit on the lower floors.
The Heatimer, and it’s cousin the Tekmar can only function properly on a perfectly balanced, and vented system. This is ironic, as their sales force have sold them as a cure all for all symptoms of badly maintained systems, and they make the situation worse, judging from the many posts here throughout the years!—NBC

Gsmith

Here's a picture of a Big Mouth vent on a Romac service saddle on a 1-1/2" main in a finished bathroom. If you insulate the main the insulation will mostly cover the service saddle. You can paint the elbow and nipple white to match the insulation cover.

the_donut

No amount of skimming will change the water line movements between startup, steady state and cold boiler. Steaming removes lbs of water per hour that slowly returns via return lines.

Good luck on installing the vents. The Romac saddles are nice, but if you find them cost prohibitive, and are feeling adventurous you can tap the pipe and use fittings to adapt to vent size.

I ditto the recommendations on gorton #2 and big mouth. I also recommend Barnes & Jones vari-vent. You can adjust vent rate from 2.5 cfm (which is still more cost eff3ctive than a gorton #2) down until steam arrives at each riser at same time.

Doug83

Thanks again everyone for recent recommendations. You can't buy this type of help and advice, obviously! @Gary Smith , I looked at pictures of the installed pressuretrol. They installed an L404F (honeywell) which has a min of 2psi main and 2psi diff. I asked the contractor to swap with one with smaller increments so I can get 1.5 psi.

Gsmith

May not be that big a deal. Many times on one-pipe steam systems if you get the venting right, the boiler will never build significant pressure and will shut off on the thermostat being satisfied. My own system rarely see pressures of more than 1/4 psi, except on really cold days below design day temperatures.

I would concentrate on the pipe insulation and venting changes they will make the biggest difference to your balance and comfort. Don't forget to insulate the basement mains and near boiler piping as well as the vertical risers. Keep the steam as steam and get it to the top of all risers at as close to the same time as possible (don't get obsessed with small time differences, if the tops of the risers get to steam temperature within 1/2 to 1 minute of each other that's good enough usually), then adjust the radiator vents to make the rooms heat as evenly as possible.

KC_Jones

Doug83 said:

Thanks again everyone for recent recommendations. You can't buy this type of help and advice, obviously! @Gary Smith , I looked at pictures of the installed pressuretrol. They installed an L404F (honeywell) which has a min of 2psi main and 2psi diff. I asked the contractor to swap with one with smaller increments so I can get 1.5 psi.

I know every system has it's quirks, but I am having a difficult time understanding why on a brand new install you are hitting pressure like that. The pressuretrol is supposed to be a safety device not an operating control. In my opinion under normal operation you shouldn't ever shut down on pressure. If you are coming back from setback and running a vaporstat at low pressure I could see it, maybe.

The pressure should be set by proper boiler sizing and venting.

Are you absolutely sure they sized it properly? They went into every room and measured every radiator? They then compared that number directly to the manufacturers rating? That's the only way to get the sizing correct. Honestly unless you are running for an hour or more I am not understanding how you are hitting these pressures, unless the boiler is over sized or the venting is terrible.

Related to that this statement is actually concerning:
"It was sized at the same EDR of last boiler in analysis, which was probably sized to heat with the windows open..."

the_donut

Either a L408J1009 (0-16 oz) or a L408J1017 (0-4 psi) vaporstat would be good replacement choices.

Gsmith

@KC_Jones , I agree, weird to see such high pressures. That's why I think his problem is mainly in the lack of venting and relying on the radiator vents to vent all the risers and main piping. All steam boilers are oversized by a lot on all but the coldest (design) days and yet they will not build significant pressure--the rad's do not get hot all the way across to satisfy the thermostat--usually. My own house boiler (35 years old, 1-pipe) had no main vents and several rads removed with cast iron baseboard installed in place. Heated very unevenly, second floor 8 degrees hotter than first (where thermostat is). Once I installed main vents, insulated the mains and put in variable radiator vents, and removed all the heatimer vari-vents, all rooms are within 1 degree of each other. Same boiler, still oversized by a lot, never builds more than 4 oz (1/4 psi) pressure based on a good 0-3 psi gage. I do have a vaporstat in addition to the two original pressurtrols and it never shuts the boiler off--always off on thermostat. In my case I'm sure the radiation is oversized for the space, the boiler is oversized for the radiation, but once I insulated mains and with good venting, the boiler always shuts off on satisfying the tstat, never vaporstat or pressuretrols--they operate as you say as safety devices, the tstat is the control device.

Doug83

Now I am a little worried... I was under the impression that going off on pressure was ok, but now it seems like switching from an atmospheric boiler to a power burner has changed the operating dynamics of this system and it needs an expert to troubleshoot... Can anyone private message me with a referall for an expert on site review and possible resolution? The project is in manhattan...

Fred

@Doug83 , Don't let these discussions overwhelm you. There are some basics that you must take care of, regardless of the sizing of the boiler.
- a Pressuretrol set at a Cut-out of 2 PSI is fine. Don't spend money on one that can be set at 1.5PSI.
- Insulate all pipes as much as possible. Un-insulated pipes will cause the steam to condense faster and cause the boiler to run longer to get steam to the radiators. The longer the boiler runs, during a heating cycle, the greater the potential for pressure issues, especially if the boiler is over-sized.
- Get as much venting on the mains/risers as is necessary to allow the air to be expelled as quickly as possible. That will reduce the amount of time the system has to run pushing air out so that steam can get where it needs to be AND reduce the pressure that builds up during the heating cycle. This venting has to be done and correct before you can balance the heat to each radiator.
- Once you have these things done, if the boiler still shuts down, excessively, on pressure, then we can suggest a few ways to improve that, maybe down firing, maybe a two stage gas valve. Whatever the remaining issue may be, it can't be properly diagnosed until the basics are done.