installing vaporstat - which one to use

what did you "turn down"?

vapor systems are mostly 2 pipe.

how is the boiler fired and with what type of controls? a standing pilot gas boiler without a vent damper will deal with very short cycles better than say an oil burner.

I have a 30% oversized boiler and it never needs to go over 8oz unless I don't control the recovery. I think we can assume that the 4psi vaporstat would give the OP adequate control at a cutout less than 16oz if he cares to.

Several comments here…

first, I agree that the system will run nicely, most of the time, at a few ounces. However, unlike a vapour system, a pound and a half won't hurt anything — and the rise, once all the vents close, will be very quick.

Now on the three pressuretrols.

Pressuretrols (and vapourstats) don't wear out, but the do occasionally — very occasionally — break. If a pressuretrol is not tripping near its set pressure, odds are excellent that it isn't the pressuretrol — it's the pigtail from the boiler is clogged.

Bo. Before you plunk down your hard earned cash for a new control, try cleaning out the pigtails… no parts required.

On three pressuretrols in series — no problem there. In fact, all the safeties need to be wired in series. That's how it's supposed to be.

first, I agree that the system will run nicely, most of the time, at a few ounces. However, unlike a vapour system, a pound and a half won't hurt anything — and the rise, once all the vents close, will be very quick.

I agree with you, a pound and a half won't hurt anything, but it's annoying, and it means you are burning fuel for no real gain and will be much more likely to overshoot.

A system will run nicely, all of the time, at not a few ounces, but rather, less than 2" of water column, even less than 1" of water column. And the beauty is, it's self-regulating—the pressure will rise, if it needs to, in order to push the air out of the system. I know we aren't really arguing here, we are saying the same thing, it's just a matter of degree. A few ounces is way more than any residential system needs in order to deliver steam to every radiator and although I can't speak from personal experience, I am quite sure the same is true for large buildings.

@holograham I agree with your desire to reduce the maximum operating pressure of your system.

And let me clarify something I said that was not clear:

My friend has a large home (mansion) with one pipe and it doesn’t wiggle the needle on a 3psi gauge until the radiators start to fill.

I meant "it doesn't wiggle the needle until some radiators are completely full"

You don't need any pigtails except on that riser that currently has the large gauge on it. The other ones are on a water trap but yeah I don't like the way the water trap is built—but they won't see steam. A water trap setup like this for the controls and gauges is common on larger systems and on some smaller systems when the installer hates pigtails, like mine.

Do you have a plan for keeping your water clean? I hope it includes raising the ph.

the blowdown once a week only is beneficial with a float type lwco. if your lwco is a probe type the blowdown just adds minerals and fresh oxygen to the boiler.

As far as not hurting anything id say it's more likely to blow debris into the vents.

And they most certainly will be annoying. I start noticing mine at 1/4 psi.

Not familiar with water trap. So you think I shouldnt change it?

The pigtail is also a trap—yours is made of pipes and has a low spot that collects condensate, do you see that?

They both make a low area filled with water that prevents steam from touching the control, protecting it.

I like the trap built with pipe because it’s far less prone to clogging and it’s easy to clean out without having to remove the controls.

A float type LWCO is a large external float mechanism. The probe type has an internal probe in a port with an external electronic box. Send some more pics.

Oh yeah I had seen it and forgotten it haha. Might still have a float one for redundancy

He's asking about the vaporstat, not the pressuretrol I think.

The 16 oz vaporstat is what you want, the 4psi one would never be used in a residence, you'd just use a pressuretrol.

Or if you really want low pressure you buy a low pressure switch from Dwyer and use a timer relay module to make it shut off your boiler for some minutes after some low pressure is reached. That's how mine and some others are set up but some people might say it wastes energy somehow or something.

The vaporstat is the way that won't get you in trouble with your insurance if the place goes up.

Yeah, thanks @ethicalpaul. However what is really the big difference between a 4 psi Vaporstat and the PA404 ? You can split hairs on a 1.5 PSI Cut - Out ? I bet you can set the 4 psi Vaporstat at the same settings as the minimum of what a PA404 has and it looks like he has two PA404s already. So the question (to me) is kind of irrelevant. If he wants to experiment with lower pressures controlled by a Vaporstat the 16 oz version is the way to go. I just don't like spending money on dysfunctional equipment.

Yes you did but I added 'dysfunctional equipment' and using a timer for frequency control without adding a Vaporstat or any low pressure switch. Some folks like to know the options.