How to properly set boiler PSI

SamEnergyPlus

Hi I have recently upgraded an 8 story 110 unit 2 pipe gravity return steam system.

We have repair all 160 in-unit steam traps, all shutter valves were replaced with Thermostatic radiator valves (TRV) and all top floor Radiators have been fitted with a Gorton #1 air vent.

The basement steam lines has been completely re-insulated with 3" thickness insulation, and the 2 end of the lines has been fitted with Gorton #2s, 1 end got 6 vents and the 2nd smaller end got 4 vents.

The boiler control has been changed to in-unit sensors.

My question is this building has been operating on 5psi which is obviously too high, but the building manager told me that he didn't have a choice, because otherwise he will get a lot of heat complains. So now that he did so much upgrades would anyone be able to recommend how to set his boiler pressure?

Just to enjoy see here some photos from this amazing project.

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Steamhead

Get a screwdriver that only turns counter-clockwise. That system was probably designed for less than 1 PSI on the coldest day of the year, so honor the Dead Men who built it.

Jamie Hall

It should run just fine on a pound and a half. In fact, you mention shutter valves, and that makes me wonder if maybe it wasn't once a vapour system — running on less than half a pound.

The presence of TRVs is going to make my preferred method of setting pressure problematic (and may lead to some rather interesting cycling problems, but that's another matter). However, if you can arrange a time when all the TRVs are open and stay open, and you are certain that the steam traps are all working correctly, then here is my approach — and it's rather simple.

Install, if there isn't one already, a reliable low pressure gauge, preferably on the header but on the boiler will do. 0 to 3 psig is fine.

Fire up the boiler and observe the pressure gauge. Meanwhile, have an assistant or two wander around the building. As the boiler is making steam, have them verify that all the radiators are heating.

Now what you will observe, assuming here that the boiler isn't wildly oversized, is that the pressure will rise initially, but that after an initial rise it will stabilise or at most rise very slowly over a period of perhaps as little as ten minutes to as much as an hour (how long that plateau is is very much dependent on just how oversize the boiler is). After that plateau, you will observe the pressure to begin to rise moderately to rather rapidly. Once that rise is apparent, that is the pressure you want to shut the boiler off at — or to give you a margin for the lack of precision of the control, a bit more than that.

Then the cutin pressure should be around half of that.

Now there is one other thing you can gain with this test: how much oversize the boiler is. An ideal boiler will not show that second pressure rise even on the coldest day — it will just sit there and run. Mostly one is not so lucky. However, if the plateau is much shorter than half an hour, investigate to see if the boiler can be downfired some. Some can. Some can't.

If you are doing this test and the assistant comes back and tells you that Apartment 6B isn't heating, stop the test and find out why not and fix that and then start over!

Last, don't be alarmed if the pressure seems insanely low. It isn't — if all the radiation is heating, you have enough pressure, even if it's only a few ounces.