Help me understand and improve my main venting

straubtm

I own a 100yo 4000+ sqft 3-story tudor. Very minimal wall insulation as that’s only happened during renovations. So best to assume plaster walls throughout.

My boiler has two main runs. 2” off the boiler, quickly jumps to 3” and then to 2.5” .

• Long run (LR) is ~88’ (4’ @ 2” + 9’ @ 3’ + 75’ @ 2.5” = 2.819 ft^3). 237 radiator EDR.
  
• Short run (SR) is ~63’ (4’ @ 2” + 24’ @ 3’ + 35’ @ 2.5” = 2.414 ft^3). 273 radiator EDR.
  

Previously each had a Hoffman #75 (0.75 CFM @ 2oz) at the end. After steam was produced at the boiler it took 7m45s for the steam to reach the end of the SR, and 10m for the LR. I then created a manifold on each and added a Gorton #2 (1.75 CFM @ 2oz). This reduced the time to 6m and 7m30s respectively. These are on ¾” pipe (so maybe 6.8 CFM @ 2oz). So each run now has 2.5 CFM of main line venting.

My overall goal is to balance the system. In addition to adding the Gorton #2s, I’ve changed a number of radiator vents over the last 2mo (had 5-6 crappy box store air vents) and overall I would saying things are very good. Every radiator gets heat. At this point I’ve really enjoyed learning about one-pipe steam heat and I am geeking out and deciding how crazy optimized I should get.

So a few questions…

1. Based on volume of the main and the vents, I would assume I should be able to vent much faster than the 6m & 7m30s I am seeing. Is my understanding that I’m probably venting the radiators too fast and therefore the main is taking longer? If I slow down the radiators should I see a decrease in time to vent the mains? Is this what you would do?
   
2. Should I add more main venting to my LR (Currently, 2.819 CF w/ 2.5 CFM venting)?
   
3. If yes to #2, I can either add onto the manifold at the end of the line, or I can easily add it ~34’ away from the boiler (where a radiator was removed). Is there a certain length that one would recommend a vent mid line?
   
4. Based on my radiator capacity, I have a BTU need of 122,587. My Columbia boiler is tagged as “Capacity 219,000”. Am I correct that this is gross capacity? Then taking the 1.5x factor from The Lost Artbook and comparing to gross, I’m still oversized (~184,000 v. 219,000 // 19%). Everything seems to be running fine. I’ve never seen high pressure / pressure cut-out. Everything seems to generally run and heat well. Granted I’m a total amateur. Anything I should keep an eye out for?
   
5. Lastly, a maintenance question…I drain some water every 2 weeks in season, do you do anything with the water at the end of the season? Complete drain or anything of the sorts?
   

Looking forward to learning some more here.

Thanks,
-Tim

EBEBRATT-Ed

You may be oversized but if the boiler is not building pressure excessively it's fine. If you are building pressure adjust the pressure control to cut the burner off at 1.5-2 psi and back on at 1/4-1/2 psi. You may need to install a 0-5 psi gauge to see this accurately. Add this and keep your 0-30 psi gauge. Take the pressure control off once a year and make sure the pigtail and connecting pipe is clear. Your main venting sounds ok at 7 min. Don't reduce any radiator venting unless you are having issues

Jamie Hall

First and most important question: are all the mains insulated? If they are not, that will slow down the movement of steam to the ends of the mains, no matter what venting you put on them -- even a wide open pipe.

That said, based on your distances you may be doing just about as well as you can, assuming your timings are with the system cool. It simply takes time for the steam to move into those mains and heat them up so it can move farther along.

There is a common thought that the steam should move along the main at the same rate as air might, given the pressure difference -- but it doesn't. It has to heat the main up before it can move on, and that just plain takes time.

Not that there's any much harm to putting more vents on -- except, perhaps, to your pocketbook -- but there may not be much improvement, either.

I can't tell whether your figure of 219,000 BTUh is the rated gross capacity of your boiler -- the rating label should have several figures on it, not just one. Nor can I tell whether the boiler is actually being fired at that rate. That said, if that is the gross input, and it's actually being fired at that rate, it's actually not significantly oversized. Assume -- being an older boiler and, perhaps, not as well cleaned inside and adjusted as it should be -- that the efficiency is between 75% and 80%, then the net BTUh output would be around 164,000 BTUh at 75%. Applying the 1.3 pickup factor, that gives you a rated output for steam of around 520 EDR -- which if your BTUh estimate for your radiation is correct, is remarkably close to your estimate of 514 EDR load.

straubtm

@EBEBRATT-Ed I have a 0-3psi gauge above the 0-30 gauge that typically bounces around 2-4oz. Cut-out set to 8oz. Thanks for the advice about cleaning pig tail and piping.

@Jamie Hall boiler sticker only have two numbers: Input 262,000 BTUh and Capacity 219,000 BTUh. I'm sure I can find the manual and/or Google and get more details.

Minus the first 4-5ft, the mains are fully insulated. These times were early AM coming off of setback...so cold pipes. I totally didn't think about the steam needing to warm up the cold pipe along the way. Duh. We've be in the house a bit over 5 years. Boiler was replaced the year prior...so 6-7yo.

Thank you both for the insight and info.
-Tim

Jamie Hall

Found it -- the "net AHRI rating steam" -- 685 square feet/ So you are oversized, unless the boiler has been downfired (which if might be -- ask your tech.). But -- it's not that serious. You''ll get some pressure cycling coming out of a setback, but that's livable.

dabrakeman

Says 685 sqft rating on the boiler tag. But, your pickup factor may be a bit bigger than the assumed 1.33 by the sound of the main lengths, particularly during a recovery. If you are not building pressure even during recoveries from setbacks then I wouldn't worry about being oversized. IF adding more main venting could reduce your total cycle time to get the same amount of steam to each radiator then then so many seconds a month is so many hours per month and then from your BTU/hr input and cuft of gas to BTU conversion you could calculate your potential monthly cuft gas and $ savings. Problem is I don't know a good way of testing the potential for improvement you have left without trying more venting. Assuming your pipes were same temperature to start for your previous testing it would give you an idea but improvement from further venting would not be linear but diminishing returns. Also you should try to time steam from header to radiators as well because the improvement in time from header to main won't translate directly to time from header to radiator because with the slow main venting some of the runners might be partially full of steam before the mains closed. Good main venting will help the runners start filling more concurrently. So, it depends upon how geeked you are and whether you can sneak a couple hundred dollars for a couple more Gorton #2's past the spouse.

KC_Jones

When you look at the venting rate charts, especially for main vents, you should look at the 1 ounce rate and assume you are getting less than that.  Remember when the boiler fires you are at zero pressure.  The only way to get any pressure to achieve those venting rates is to purposely under vent the system to build pressure, this just slows the steam down which is the opposite of your goal.

The best test you can do is remove the main vents to an open pipe, fire the boiler and time the steam.  That is your maximum speed, then put vents back on until you get close to that speed.  There is a point of diminishing returns which is why I say close.

question

Copied from Balancing Steam Systems- Using a vent capacity chart


Take the vent off the end of the main and fire the boiler. Once the header pipe gets hot, time how
long it takes for steam to get to the open pipe where you removed the vent. Let’s say it takes
three minutes, for example. If it takes three minutes to get steam from the header to the open
pipe, then you would need to install as many main air vents as it takes, to get steam to the same
point (the open pipe), in as close to three minutes as possible, but with the air vents installed. For
example, if it takes three minutes with an open pipe, and it takes six minutes with a Gorton #2 air
vent in place, you would add another Gorton #2 and time it again. If it now takes 3-½ minutes to
get steam to the end of the main with two Gorton #2 air vents in place, that’s only 30 seconds
more than what you’d get from an open pipe. At this point, you have to make a decision as to the
cost of another main vent verses a 30-second increase in speed.
Why would you get only 30 more seconds speed if adding another vent, when adding a second
vent gave you 2-½ minutes of speed increase? Because you will not be able to vent any faster
than the open pipe did, irregardless of how many air vents you use at this point. You would be
venting the main as quickly as possible with the existing tapping. The only way to increase the
speed beyond this point would be to increase the diameter of the tapping, say, from ¾’’ to 1’’, or
to add another tapping and start all over again.

I hope this helps.

I personal use the Barnes and Jones Big Mouth vents for the mains They have the largest venting capacity at 3.60 cfm at 3 oz of pressure. I use the Gorton #2 for venting the risers .

straubtm

@Jamie Hall & @dabrakeman - Thanks for the help reading the sticker. I was so focused on the big font I totally missed it had the sqft number there.

@KC_Jones & @question, thanks for the responses. I'll definitely do the open pipe test. Ironically, I read about the Big Mouth hear after I had already purchased and installed the Gorton #2s or else I would have bought them. If needed after testing, Big Mouth was what I was thinking.

If I ended up adding another main vent to the 88' run , does anyone have any thoughts on whether the 88' main run would benefit more from adding the vent to the manifold at the end vs. adding it ~34' away from the boiler? Or is this one of those, you don't know until you try sort of things?

-Tim

dabrakeman

Best is at the end of the main so the total venting capacity will be active for air removal of the entire main.

nicholas bonham-carter

Is the waterline steady during the firing?
your improper boiler piping could be blowing a lot of water up into the system.
if you look at the boiler installation manual, you will see that having the take offs between the risers is not correct. Is there an equalizer?
Set backs of more than a couple of degrees, and less than 24 hours can also be a problem. When the boiler attempts to raise the temperature back up, the gas meter will spin quickly, like a roulette wheel, with equally unhappy financial results.
Try a consistent lower setting, with no setback, and see if that is more comfortable and economical.—NBC 

straubtm

Hey @nicholas bonham-carter thanks for the response. Couple of question as I'm still learning here.

Regarding...

nicholas bonham-carter said:

Is the waterline steady during the firing?
your improper boiler piping could be blowing a lot of water up into the system.

The waterline moves about 1-1.5" while firing. I'm guessing this would be considered not steady, correct? Should it, more or less, be still?


Regarding...

nicholas bonham-carter said:

if you look at the boiler installation manual, you will see that having the take offs between the risers is not correct. Is there an equalizer?

I don't think I have an equalizer. What would I be looking for? Just so I understand, are the take-offs in my pic above where the insulation starts? The risers are the vertical piping coming off the boiler?


Regarding...

nicholas bonham-carter said:

Set backs of more than a couple of degrees, and less than 24 hours can also be a problem. When the boiler attempts to raise the temperature back up, the gas meter will spin quickly, like a roulette wheel, with equally unhappy financial results.
Try a consistent lower setting, with no setback, and see if that is more comfortable and economical.—NBC 

Currently, the thermostat is set as follows:
- 8a - 6p @ 66*
- 6p - 10p @ 68*
- 10p - 8a @ 60*

You think if I move the setback to 64* it may save a few $$$? Is this a general rule, or b/c of the improper near boiler piping?

Thanks!!
-Tim

Jamie Hall

Well, it looks as though you do have an equalizer. Of sorts. As I look at your boiler picture, I see from left to right, a riser, then two takeoffs for your heat, then another riser, then hiding off at the right end a pipe which goes down which, I hope, connects to the top of the Hartford loop. If that is correct, that pipe that goes down is the equalizer.

Given that type of boiler and that piping, you are going to have wet steam. Can't help it.

An inch to an inch and a half waterline movement when firing is a bit excessive, but not enough that I'd worry about it all that much. The lamentable header piping is much more of a problem.

With regard to the setback, in general that much night time setback is not going to save energy. I'd suggest trying it at 64. That gives you a two step rise, each of two degrees, which the system can probably do without too much fuss.

SteamingatMohawk

I just got done commenting in "A Rude Awakening" about risks and low pressure gauges. I have also commented in other discussions on this subject

Please, if you intend to keep the low pressure gauge installed permanently, install an isolation valve so it can be protected from any pressure surges. My contacts with gauge manufacturers revealed they are only good for about 130% of their full range. 3 psi times 1.3 = 3.9 psig. Better safe than sorry.