Best vaporstat to use for home boiler

skimmer

I’m looking to change out my pressuretrol to a vaporstat. And I have a choice of 3 vaporstats that I acquired.

I want to use the 0-16 oz but I’m not sure if that would cause short cycling on my system. 1 pipe steam burnham IN4

What do you guys think? Am I wasting my time here? Is it worth it will i gain anything

Jamie Hall

If you can actually get your hands on a mercury switch 0 to 4 pound vapourstat, rejoice. They are much more reliable and bulletproof than the newer microswitch version. The 0 to 16 ounce version is not the range you really need for one pipe steam — the ideal range there is a cutout around 1.5 psig and a cutin around 0.5 psig, which the 0 to 4 pound version is well suited to.

It will not cause short cycling by itself — but if your boiler is oversized, it won't reduce it, either.

skimmer

Yes I have it in hand..

1.5 for the main?

Boiler is not oversized

Long Beach Ed

Your savings depend on your system. If your radiators are oversized and your radiator vents only close on the coldest day of the year, switching to a vaporstat will yield very little info savings. It won't pay for itself.

If your radiators are small and regularly fill with steam, building pressure in the system, the vaporstat will cycle the system sooner and theoretically save you money.

If your system is slow venting, and fast steaming requiring pressure to build before steam circulates, the vaporstat won't save anything because very low pressure won't get the circulation you need and the boiler will turn off before steam circulates.

As Jamie says, the mercury bulb vaporstats are better controls than most pressuretrols and snap switch controls made today.

skimmer

My radiators are copper tube fins.. Disappointing because the entire system is black pipe right up to the radiators and then its copper..

Heats up nice but it does not retain the heat like the cast iron standing rads.. These are semi recessed into the wall with a removable cover. As soon as the cycle is done they cool down pretty quickly

109A_5

Hello skimmer,

" I’m looking to change out my pressuretrol to a vaporstat. "

May I ask Why ? If you boiler is not oversized. What are you trying to gain ?

For example; My boiler is a bit undersized and the the pressure never goes over 2 Inches of Water Column (1.16 Oz). On a day to day basis my pressuretrol does nothing. It is just siting there waiting for someone to close off a lot of the radiators or if the system were to flood, neither of which will probably happen while I am here. It's just a safety device. As much as I do like Mercury switches, I would not spend the money on a Mercury switch pressuretrol or vaporstat for my system.

I'd actually first accurately monitor your system's pressure to see what it actually does, then go from there with real data.

BTW maybe I'm confusing you with another member but didn't you post (in another thread) your boiler pressure went close to or over 5 PSI ? If so how did this happen if your boiler is not oversized ? Does your system have other issues ?

Mad Dog_2

I hoard Mercury Pressuretrols & V.P.Stats...they don't go bad. Mad Dog

Mad Dog_2

If I were you, put in a 0-4 psi V.P. Stat, but make sure you're well vented and have dry steam. Mad Dog

Long Beach Ed

https://forum.heatinghelp.com/discussion/comment/1832081#Comment_1832081

Great minds think alike… But then I hoard a lot of cast iron too.

ethicalpaul

just to counter my friend Jamie’s opinion about the required pressure range, 1.5psi is far, far, far more than any one pipe residential system would ever need to quickly deliver steam to every part of the house.

We know this because if you watch a system on a call for heat, it is not until well into the call when many or all radiators are full that pressure starts to climb past a couple inches of water column (about 1 ounce per sq in)

So an 8 oz cutout is beyond enough.

Note that the above assumes a reasonably sized boiler. But with an oversized boiler cutting out is good, rather than build useless pressure. If you don’t like so-called short cycling, then implement a timer relay to pause the boiler longer when it cuts out.

Jamie Hall

Systems vary. There is a good method, however, if rules of thumb are dismaying, to determine the optimum pressure for the control cutout. It requires a decent low pressure gauge — but 0 to 3 psig is good enough; no need to go expensive.

As @ethicalpaul noted, when the system fires up from cold — we're going to assume adequate main venting here — when steam first rises you will note a relatively quick rise in pressure which will then flatten out — stop rising completely, or just rise slowly. That is your system operating pressure. It may be as low as a few inches of water column, or it may be a few ounces (Cedric's system runs at 4 ounces, for instance) or it may be even close to a pound. In any event, take note of that pressure. Once all the radiation is pretty well filled, the pressure will start to rise again — often fairly quickly. The optimum cutout will be about half again as much (no more than twice) the stable pressure noted. Going higher — up to a pound and a half to two pounds — is not a problem except for a slightly longer run time in one pipe or non-vapour two pipe systems.

In my opinion.

The question of "short cycling" is a rather vexed one. Some people don't like it because it makes them nervous or is just annoying, but there is actually some valid engineering relating to just what is, or is not, undesirable short cycling. I'm still working on some studies on the subject, although Cedric is perhaps not the best subject for them (nearly perfectly matched to the system he powers and also a good size boiler…), and the question also depends somewhat on the type of burner in use; atmospheric gas burners have some very different considerations from either gas or oil power burners. Stay tuned — but at the moment it looks as though if the duty cycle is at least 75% on (that is, the on time in a cycle is at least three times the off time) and the total cycle time is at least 4 minutes, the most efficient result will be to let the pressure control the cycle for power burners — the main consideration being avoiding electrical overload on the blower motor starting. For atmospheric burners the total cycle time can be much shorter, and the duty cycle as low as perhaps 25% to 50% — provided one doesn't run so short a duty cycle as to get into the low frequency acoustic range. There is one additional consideration for one pipe systems using thermostatically controlled vents: the off time must be long enough to allow the system pressure to drop to atmospheric so the vents can regain control. This is NOT desirable in other systems, however, if it can be avoided.

Forced off time delay will result in an efficiency hit which can be substantial — but may be unavoidable with seriously oversized boilers.

But there's more work to be done…

ethicalpaul

Thanks Jamie, I look forward to your conclusions. We definitely agree on so much. At the risk of going a bit off topic, but not much because this is still related to what pressure controls do:

Where do you see the hit to efficiency due to a forced off time delay? I'm aware the term "efficiency" is overloaded and can mean different things to different people, but I assume (please correct me if needed) that you are talking about the percentage of fuel that actually goes into heating the living space.

There is the firing time to get the boiler up to boiling, plus the time to fill the mains and runouts with steam. Those are easy enough to measure. Some of that heat does get to the living space, but it's difficult to say how much and it varies greatly by house.

That has to be compared against the futility or harm of letting it burn and raise pressure. I actually don't think there's much or any waste in building pressure because as the pressure increases, the temperature of the steam (and radiators) increase. The heat gets into the living space. Probably the biggest issue there is overshoot.

My system definitely never overshoots with its current cutout of about 6" of water column with a delay of 8 minutes, so the comfort benefit is nice. I suspect the cost difference either way is immeasurably small. I get great peace of mind from the low pressure as well.

Mark N

@skimmer, from what you’ve posted it sounds like you have convectors with copper fin tube elements. Not sure what type of thermostat you’re using but if it’s one that allows you to set the CPH I’d try. setting it to 2 or 3 instead of 1 as is usually recommended for steam. Maybe the pressure is going high because the elements are full of steam. They don’t hold much air as compared to cast iron radiators. At a higher cycle rate the boiler will turn off sooner.

Jamie Hall

I'm still working on the efficiency bit — and somewhat hampered in that my test subject has a fixed minimum off time (30 seconds — post purge and pre purge). What I'm seeing, though, is that — and again, remember that Cedric is a WM 5-80, which is a pretty hefty beast) — there is enough residual heat in the boiler metal to keep the water slightly above a simmer even as the pressure drops, so that when the boiler does refire it comes up to a full boil within literally seconds, rather than — once it has been off for say ten minutes — taking several minutes to get up to a boil again. At that minimum time, the pressure doesn't quite get down to atmospheric, so the mains and radiators stay full of steam (and again, Cedric is probably a lousy choice, since the system he powers is a Hoffman Equipped vapour system, so that the returns never get steam anyway).

And yes, the efficiency I'm looking at is how much of my money in the oil tank winds up as useful heat in the house…

skimmer

@Mark N im using the sensei st55 WiFi thermostat

I have it set for slow. The choices are slow medium and fast

”Faster cycle rates provide tighter temperature control and shorter on/off cycles. Slow cycle rates allow for a wider temperature swing and longer on/off cycles”

I’m believe I was advised to set it for slow here a few years ago

Mark N

How long does the boiler run on a call for heat when you’re just maintaining temperature? Maybe try the medium setting.

skimmer

I don’t know I have to check. It runs fine from cold start until it shuts off on pressure usually from what i remember. Once it’s on a pressure it cycles on and off. Until the thermostat is satisfied.

I do get heat before it shuts off on pressure. If I raise it 2 or 3 degrees then yes it always shuts in pressure first

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1832188#Comment_1832188

Do not confuse the cycle rate for the thermostat with the cycle rate for the boiler. Completely different.