Very low pressure questions..

NJ08534

Hi y’all! Hope you are nice and warm as winter is here!

I have a low pressure question….
1 pipe steam.
Crown Bermuda BS172 steam boiler, 446sq ft EDR, 3.5 hrs years young.
Nice drop header in near piping, Single stage burner, Honeywell pressuretrol
set to 2 PSI, -.5 subtractive. No obvious leaks, VXT reports 6 gallons of water use per year.
I reset it this Fall, an no new VXT water reported since then (three wwwks still zero).
92 year old pipes to rads likely age. Good, new main vents. Elevation 250’ above sea level (NJ).

So, it had a boring old useless 30PSI code pressure guage which I never saw move, so I finally added a new 3 psi guage on a whistle clean pigtail and clean port to the steamchest. It doesn’t move either. So, I rechecked the new 3PSI guage, I rechecked the new pigtail and re assembled and steamed, —still it doesn’t move at full steam. I put it on an antler with the pressuretrol pigtail (also clean as a whistle). I even tried a second 5psi guage —it does not move either.

My all rads are great, nice cozy house.
Nice radiant heat.
No steam coming out the chimney (no hole likely in steamchest).
Unit lights about 6-7 times a day

So…. Question for the Wall…
Why don’t I read any pressure when at steam? What am I missing?
…There is some missing insulation on the mains in the basement….
Is my rad and pipe EDR too high for my units output?
Maybe I try turning off a rad at its service valve and reducing my EDR temporarily to test?
Maybe I find a third guage?
???

Cheers and thanks for reading this far!

-perplexed in NJ

Jamie Hall

And you are complaining? Your system is working remarkably well. Steam systems don't have to generate much, if any, pressure to operate just fine. Some -- I know @ChrisJ 's -- never show any pressure. Cedric, the big one I tend among others, shows maybe 1 ounce until the end of a very long run.

If the radiators are getting as warm as you need them to be, and doing it in a reasonable length of time, be happy.

EdTheHeaterMan

This is the only thing I could think of when I saw... VERY LOW PRESSURE QUESTION

Although the Chicken in this cartoon may think otherwise!

delcrossv

Get an 0-16 OZ gauge. 3psi is way too coarse for a low pressure system.

NJ08534

Hmmm. That makes a great deal of sense! I’ll give it a try..

I guess my underlying question, is…. Am I losing any fuel efficiency if my rad and pipe EDR is higher than my EDR capacity from my boiler? If everything is truly working but my pressure never rises, the EDR ratio must not be met?

Jamie Hall

NJ08534 said:

Hmmm. That makes a great deal of sense! I’ll give it a try..

I guess my underlying question, is…. Am I losing any fuel efficiency if my rad and pipe EDR is higher than my EDR capacity from my boiler? If everything is truly working but my pressure never rises, the EDR ratio must not be met?

Well, no. If it were the case that your boiler's EDR is significantly less than the system EDR, the only thing that will happen is that parts of the system will heat late, unevenly or not at all, depending on the particular system.

However, in your concern about EDR ratio you are, perhaps, overlooking two factors. First, that the EDR rating of the boiler takes into account the necessity of heating all the piping at startup, as well as the radiation -- called pickup factor. As a result, if the two numbers are equal, the boiler is actually capable of powering more radiation. Second, and perhaps more important, while there is a need to overcome the pressure losses in the piping leading to the radiators, these are very small. There simply is no need for pressure to build up otherwise.

EBEBRATT-Ed

I find it unfortunate that because of all the oversized boilers incorrectly installed that we spend a lot of time discussing pressure controls and pressure gauges and "pressure" or the lack of "pressure"

A lot of home owners reading these posts think the lack of "pressure " means something is wrong when in fact they are the lucky ones with a good working system.


Oh to to back to the coal burning days

No pressure control
no low water cutoff
no thermostat

yet the old boiler made steam for 50, 70, 100 years or more

and the pressure gauge is just an indicator.... it doesn't control anything

Hap_Hazzard

There has to be some pressure, because the steam is moving out of the boiler, and (all together now)…

High Pressure Goes To Low Pressure

Always.

Jamie Hall

Quite true, @Hap_Hazzard -- but the pressure in question in most residential systems is on the order of an ounce or two...

Hap_Hazzard

That's right, @Jamie Hall. Mine rarely registers at all on my low pressure gauge, but the steam gets out of there in a hurry. I wonder if it's possible to estimate the steam velocity and work backwards to the pressure. 🤔 But I'm not curious enough to actually try it. It sounds hard.

ChrisJ

Jamie Hall said:

Quite true, @Hap_Hazzard -- but the pressure in question in most residential systems is on the order of an ounce or two...

If you look at my piping diagram, the pressure assuming no vacuum created by steam is something like 0.005 psig on a 30' run from the boiler. Much less than an ounce or two to compensate for friction losses.

But, steam is also very good at creating vacuum even on a single pipe system with wide open vents so really, at times it could be even lower.

Hap_Hazzard

Losing 99.94% of your volume will do that.

mattmia2

You could make a manometer out of a piece of clear tubing filled with water, you will see something, it won't be much. What you are seeing is the ideal condition as long as it is enough heat for your house. You can play with venting to balance things if you need to. Any pressure above 0 represents heating the steam to a higher temp than needed and reduces the transfer of heat from the fuel to the steam some, the greater the temp difference between the water/steam and the products of combustion, the more heat is transferred rather than going up the flue.

NJ08534

Thanks so much to all of you for the discussion!
Not surprisingly I see a wee bit of pressure when I close off a rad service valve or two on a new 1 psi guage.
Plan:
I will reopen the rads I just closed off for my little test
I will replace to missing sections of insulation on the basement mains to lower the pickup losses and get a bit more of the heat upstairs.
I will re-check the rad vent sizes to ensure all the rads are heating appropriately. (I have one that’s a lilt too slow/intermittent)
I will sit back and enjoy the miracle of central heat with a coffee and a newspaper…

cross_skier

My winter experiment --
If my vaporstat sees more than 2 ounces (rarely happens) new controls driven by signal from vaporstat  will shut down system for fixed time period.  I will try time periods between 20 minutes and one hour.

Hap_Hazzard

NJ08534 said:

Thanks so much to all of you for the discussion!
Not surprisingly I see a wee bit of pressure when I close off a rad service valve or two on a new 1 psi guage.
Plan:
I will reopen the rads I just closed off for my little test
I will replace to missing sections of insulation on the basement mains to lower the pickup losses and get a bit more of the heat upstairs.
I will re-check the rad vent sizes to ensure all the rads are heating appropriately. (I have one that’s a lilt too slow/intermittent)
I will sit back and enjoy the miracle of central heat with a coffee and a newspaper…

Also, see what the cycle length is set to by the thermostat. This can be set in several ways, depending on the thermostat. Some have a heat anticipator setting, some have a cycles per hour setting, some have a differential setting, others call it "swing." Whatever they call it, it's a way to contol how many degrees the temperature has to fall before the thermostat calls for heat again. If the thermostat is designed for all kinds of heating systems, this may not be set to the optimal setting for steam heat by default. Steam heating works best when the cycle is longest. If it's too short, the system barely stays on long enough to get the pipes hot and warm up the living room, so your basement stays warm and toasty, the living room stays warm, and the upstairs is chilly. You might find you can keep your whole house confortable on a slightly shorter cycle if your radiators are well balanced, but if the thermostat came set up for forced air or electric baseboards, that won't do.

hank66

What is a reasonable cycle time for a well balanced, low pressure ( less than 1 psi) system?  15 minutes per hour?

Jamie Hall

There really can't be a single answer to that, @hank66 .

The cycle time -- so and so many minutes per hour -- will depend entirely on the boiler output power and available radiation vs. the heat loss of the structure. If it is warm out -- I'd expect 10 minutes per hour or, if a better thermostat is being used, something more like 15 to 20 minutes every two or three hours. On the other hand, on a really cold night or coming out of a setback, the boiler may be on almost continuously.

The total on time of the boiler, taken over say a day, must be exactly enough that it supplies the same amount of heat the structure loses. How the cycling on and off is divided over that time span depends much more on the thermostat's characteristics than on anything else.