System taking unusually long to build pressure

mookie3333

I have my pressuretrol set at 2 psi. On a warmish start (off for about 8 hours) In about 11 minutes, (wet) steam gets to my big mouth main vent, and it shuts. When they shut, my 0-5psi gauge reads 0. The pressure continues to build, as the radiators vent. However, this continues for around 35 minutes, until the boiler kicks off on pressure. 35 mins from cold start to 2 psi.

Why does it take so long to build pressure? Problem with radiator vents? All of my rads do get hot eventually.

For steam to reach the main vents within 11 mins off of a warm start (90 degrees?), is this unusual? The mains are ~ 20-25 ft long. Overfiring?

Can water quality cause this? (i.e. oil in the water, poor ph, sediment, etc)

Wet steam is a result of poor near-boiler piping - something I hope to address, but not for this season.

For what it's worth, I seem to recall the cold to 2 psi cycle being SHORTER with my gorton #2 (27 mins?? If I remember correctly - going to swap back today and see what happens).

Thanks guys.

KC_Jones

You don't want pressure. What do you think you will get with pressure? Pressure is slowing down the delivery of steam to heat your house. What you are seeing is what you want. Actually what you really want is to never shut down on pressure. The presuretrol is a safety limit device, not really a "control".

Jamie Hall

If it ain't broke, don't fix it. As @KC_Jones said, it's doing what you want it to do! For reference, the system I care for usually takes about 45 minutes to an hour to shut itself off on pressure -- at 12 ounces.

mookie3333

But what if it takes 1.5 hours to satisfy the thermostat? That's 1.5 hours of natural gas usage?

I thought the ideal situation was to build up some pressure (few ounces, if you have a vaoporstat) and have it radiate to the rads and condensate while the boiler is off for a few mins. Then after the pressure drops, boiler kicks back on to create more steam.

Question - in an ideal situation, proper sized boiler, no short cycling, how many minutes should the boiler be off (at max. pressure - 12 oz, or what not) between firings?

BobC

How many sq ft of steam is the boiler rated for and what is the connected EDR of all the radiators?

Have you clocked the gas meter to make sure it's burning the correct amount of gas?

Bob

KC_Jones

Once the burner shuts down the steam collapses fairly quickly and you aren't really getting much heat out of it. The steam in the mains (in general) will stay there, collapse and go back to the boiler as condensate having not heated your radiator at all. You want low pressure and long burn times.

To put another perspective on the situation. Why would the steam keep moving after the burner shuts off? The burner is the "engine" that is driving the steam. In low pressure heating, it's the expansion that moves the steam.

The pressure in your system is from air not being able to escape fast enough to get out of the way of the steam so it pushes back (slows down) against the steam production. Turn off the engine and the air pressure wins, steam doesn't move much if at all and you wait for things to settle then back on again.

Jamie Hall

In answer to the question "in an ideal situation, proper sized boiler, no short cycling, how many minutes should the boiler be off (at max. pressure - 12 oz, or what not) between firings?":

The answer is that in an ideally balanced system, it should never shut off. The objective of the exercise, after all, is to take the heat released by burning the fuel and transfer it to the heated spaces, and so long as the burner is running and the water is boiling and the steam is condensing in the radiators, that's exactly what happens.

In the practical world, most boilers are slightly oversized, so on very long runs in moderate weather the radiators can't condense all the steam, and the pressure starts to rise -- which is when you want the burner to shut off, because once the pressure starts to rise your heat transfer goes way down (all you are doing is squeezing the steam, which never warmed up anybody).

mookie3333

KC_Jones said:

Once the burner shuts down the steam collapses fairly quickly and you aren't really getting much heat out of it. The steam in the mains (in general) will stay there, collapse and go back to the boiler as condensate having not heated your radiator at all. You want low pressure and long burn times.

To put another perspective on the situation. Why would the steam keep moving after the burner shuts off? The burner is the "engine" that is driving the steam. In low pressure heating, it's the expansion that moves the steam.

The pressure in your system is from air not being able to escape fast enough to get out of the way of the steam so it pushes back (slows down) against the steam production. Turn off the engine and the air pressure wins, steam doesn't move much if at all and you wait for things to settle then back on again.

Good explanation, thanks KC. It's a little over a year that I've been dealing with a steam system, still very eager to learn anything I can. Think I got a good visual now.

Regarding radiator vents - any way to test them? Is there such a thing as "kind of broken" ?? or either they work, or they dont. I have an old vent, looks like a hoffman, that will hiss - pause - hiss - pause continuously.

Fred

As has been said, the Thermostat is your control device. Not your Pressuretrol! The Pressuretrol is a safety device that should only kick in when the pressure gets high enough that it has an adverse affect on moving steam (typically never over 2PSI, preferably under 1 PSI). The higher the pressure, the slower steam moves. You are working towards the wrong goal.
You say it takes an hour and a half to heat your house but you also say the heat was off for eight hours. How much were you trying to raise the temperature? That is what will determine how long the boiler needs to run to satisfy the thermostat. Yes, it used an hour and a half of gas at whatever the input rate is for your boiler but what about the eight hours it didn't use any gas?? Get Dan's books on steam heat and read them. They will explain the principals around steam systems.

mookie3333

Fred,
I was just using an hour and a half as an example. As it's been warm/cold/warm/cold here in New York, It's hard to keep any "regular" setting on the thermostat. As the temp drops, I will probably keep 72 degrees daytime, 70 at night. I know steam isn't good with large setbacks.

As for the books, I did purchase Dan's book The Lost Art ... last year a few weeks after we closed on the house. Unfortunately, given my current setup, I don't get much time to sit with a book at home in the evenings (a 1 and a 3 year old) , so I do most of my research online during the day. Wish the book included a PDF for portability - although I understand the piracy concerns.

Fred

Do try to find some time, here and there, to read that book. It will help you understand a lot. I understand your situation, with kids and all but the time it takes to read a few pages a day probably isn't any more than searching the site for specific issues and the info you will get is straight from the horses mouth and reliable.
Regardless of the temp swings of the weather, set the tstat and leave it there. A programed 2 degree setback at night is fine but don't physically shut the boiler down for eight hours and then expect it to recover 6 or 8 degrees. That will just cause a lot of short cycling and extended boiler runs. Not what you want.

mookie3333

Sounds good, thanks Fred. I could also just bring the book to work and hide it from my boss

Part of the problem is also the WEALTH of information here in the forum - I usually run here first to find what I'm looking for than consult the book.

Jason_13

Another thought, is the steam mains insulated. If not steam condenses quickly and takes much longer to get to all the radiation. Another problem better chance of flooding the boiler and creating water hammer.

RomanGK_26986764589

You mentioned that it takes 11 minutes for steam to arrive to the end of your 20-25 foot main. Sounds like you are under vented. For the reference, it takes about 3 minutes for the steam to reach the end of my 2 inch 55 foot cold main.