New Boiler Never Cuts Out on Pressure

Tom_42

I have a year old Peerless Boiler that seems to be working as well as the old 50 year old boiler that it replaced. I have no problems heating the house and all my rads get steam. I spent a lot of time when I first bought my house balancing the system and the radiators. And with the new boiler I saved almost 250 gallons of fuel in the first year. However, I have one concern. My boiler never seems to cut out on pressure. There are a few occasions if I set the thermostat too high from the current house temp it will just run and run. Eventually it will reach temp and turn off the boiler. A few minutes after that happens you can hear a giant sucking in sound from some of the farthest radiators. What I am assuming is happening is that the steam had pushed all the air out but the boiler kept running building up pressure. Then when the thermostat reaches it's set temp and the boiler cuts out the pressure in the system drops (probably from something much higher than 1.5 psi) back to 0 causing the air to come rushing back into the system. So my question is should I leave it alone or change from a pressuretrol to a vaporstat? I have attached an image of my current setup. Would really like to get the wall's opinion on this.

BobC

What pressure does the system reach? You could just be lucky that the installer sized the system just right and it will never build significant pressure.

What kind of vent do you have on the steam main(s) and how long are those main(s)?

Bob

Jamie Hall

What -- if anything -- does the pressure gauge read at various times? I'll grant you that a 30 psi gauge is pretty useless (but the insurance companies like it!) but it may say something helpful...

Also, what is your pressurestat set for?

Tom_42

I have two mains off of a single branch out of the boiler. Each measures about 20 to 30 ft long. I have Gorton #2 on the end of the mains (see pics). The pressuretrol is set for a cut in of 0.5 and a differential of 1 psi. In looking at the pressure gauge I have seen it reach about 2psi but it's really hard to tell how accurate it is. I have not observed it when I have heard that giant sucking sound after a long cycle. I did order a small 0-3psi gauge I am planning to add to the system to see if I can get a more accurate reading.

Fred

Aren't you the lucky one! Sounds like the installer got the boiler very close to the connected EDR. However, it also sounds like maybe the Pressuretrol isn't accurate enough to shut the boiler down at 1.5PSI. They never are that accurate but they can be re-calibrated, once you get your 0 - 3 PSI gauge on there and can see exactly how far out of adjustment it is. We can provide the Re-calibration procedure, if/when needed.
The sucking noise you hear, at the end of a cycle, especially a long cycle, is the result of a vacuum that is created when the steam collapses and that space in the pipes/radiators is being filled with air. That, is typical, on a one pipe system.

EBEBRATT-Ed

This is a perfect example of what I have been complaining about. The customer sounds like he has the right size boiler and it seems to be working fine but after reading posts here about pressure controls, vapor stats and low pressure gages he is concerned that he should be building pressure or that "the boiler never shuts off on pressure"

we are sometimes sending the wrong impression. House boiler shouldn't build pressure

Tom_42

Just to be clear. I am not a dissatisfied customer at all. I have Dan's book (haven't read it in about 7 or 8 years). My main concern was simply the occasional "giant sucking noise" at the end of some cycles. I was always under the impression that this was due to overly long cycles that built up too much pressure before the thermostat reached it's temperature. This would be where I thought the pressuretrol would come in to play, cutting out the boiler at around 1.5 psi. But as I said in my original post that on my old boiler or my new one I don't believe the pressuretrol has ever stopped it from steaming.

As Fred said maybe my new boiler was just sized correctly. I would hope so since I gave the installer the total EDR of all my radiators plus a pickup factor of about 25%. Most of my steam pipes have been insulated except for the elbows and unions. Put all new vents on the radiators when I moved in (mostly vari-valve) in an effort to balance the system. There are a couple of things I would have preferred in the new installation. For example I don't particularly care for the automatic water feeder. Before the new boiler was put in I was pretty religious monitoring the water level on a weekly basis. I would use the LWCO to drain the rusty brown water out of the boiler once every week or two. On the new boiler the installer said there is no need to do that (nor with the probe type LWCO that is installed is there even an easy way to actually do it).

Fred

You have a bypass valve on the water feeder so you could turn the water feeder off, if you wanted to and manually add water like you always did. I manually feed mine too. You can drain a quart or so of water out of the drain valve on the bottom of the boiler once a month or so. That is where any mud settles. I too have the old MM #67 LWCO and I blow down a quart every week during the heating season. There's a lot to be said for the newer water feeders and the probe LWCO's but there remains a lot of value in the older methods too, like keeping a Homeowner visibly aware of what is going on with the boiler.

EBEBRATT-Ed

@Tom , sounds like you have done your homework and the installer it would seem did a decent job.

The sucking sound is probably the steam in the mains condensing. When water changes to steam the volume increases 1700 times. When it changes back it shrinks 1700 times. The difference between steam at 0 psi or 1 or 2 psi in this case won't make much difference, it's the change in volume from condensing that you are hearing.

If you think your main venting is adequate and the noise is bothersome you can always add a check valve piped like a vacuum breaker. You can put it on the boiler above the water line, a dry return or on a steam main or tee it in with a main vent wherever you have a spare tapping. Use a good quality Y pattern check valve. It will break the vacuum faster. 1/2" ips would be fine

ChrisJ

Yes,the system sounds sized well. As others have said the sucking sound is a vacuum being pulled when a lot of vents are closed and it's normal.



@EBEBRATT-Ed I sure haven't sent that message. My opinion is the system should limit pressure and the vaporstat is safety limit that should never actually do anything during normal operation. Sadly most on here are often against me especially when it comes to sizing boilers.

EBEBRATT-Ed

@ChrisJ IMHO you should never see pressure on a 30lb gage in a house job if vented well and the right size boiler.

Vapor stats and low pressure gages are fine if someone insists on knowing what pressure they are running at.

My problem with all the pressure discussions is that it sends the wrong impression. People start tinkering with their pressure controls and are thinking if they don't see pressure on the gage or are not cycling on pressure that something is wrong. This is an example of that as @Tom said:

"I have no problems heating the house and all my rads get steam. I spent a lot of time when I first bought my house balancing the system and the radiators. And with the new boiler I saved almost 250 gallons of fuel in the first year. However, I have one concern. My boiler never seems to cut out on pressure"

Canucker

I don't know @EBEBRATT-Ed I'd say if they think their boiler has to cycle on pressure they haven't read enough of the information on this site.

Jamie Hall

This seems to be perennial discussion. If it's not whether a steam boiler should cycle on pressure under certain conditions, it's how many cycles per hour should be on the thermostat or what should the aquastat be set at or how should the outdoor reset curve be set or...

I think we all need to realise that in our real world we have to operate heating equipment over an extraordinarily wide range of loads -- at least 50 to 1 and perhaps in more northern climates as much as 100 to 1. Perhaps worse, the actual load which we are attempting to feed is both ill-defined and astonishingly difficult to measure accurately; outdoor reset, for instance, measures the outdoor air temperature more or less accurately in one place near a structure -- but doesn't account for wind loads or solar loads at all, which can be significant. Nor, except in some very sophisticated systems, does it adjust the commanded water temperature for changes in the demanded indoor temperature, nor does it account for changes in indoor heat generation (that wild New Year's party, for instance!). And yet it is about the best we have.

Then, of course, even the best systems I have seen referenced rarely seem to have an internal firing modulation range of more than 20 to 1 (there is an exception, of which more below).

We are left with both a mismatch in modulation capability and in measurement capability.

The result of all this is that -- with the exception to be noted -- somewhere in the system we have to have the capability of determining the desired result condition; that is, a certain space temperature, and adjusting the BTU input rate to the heating system to achieve and maintain that space temperature. Since the load on the system changes by more than the available modulation in the system, that can be done in only one way: the system has to be turned off an on at such a rate as to match the load to the average input rate over time. Hopefully this can be done with a minimum loss in efficiency and, at the same time, with a minimum dead band (temperature swing) in the output. The debate rages largely over the merits (or lack of them) of the various approaches which can be used to do this, and the way various controls can or should be set.

I mentioned that there is an exception. Electric resistance heat with full computer controlled modulation. The efficiency, of course, is horrible if any fueled fired power plant is the source of the electricity, but that is another -- and fraught -- topic. There is no particularly good reason -- other than money and time -- why a suitable computer could not be equipped with sufficient sensors both inside and outside the structure to determine, within very small limits, exactly what the load conditions are, and it would not be at all difficult to then program that computer to respond to those load conditions by altering the power input to the heating grids essentially instantly.

I doubt very much that anyone would be interested in the cost of such a system, and as I noted the efficiency would be much less than what we can achieve now, routinely.

mikeg2015

I don’t see often mentioned either that EDR assumes 70f ambient and it’s not very precise. Lots of factor effect it and if it’s 65f indoors your Connected EDR is higher. I think it’s a great target but I wonder if sizing closer to the DOE number with less pickup is better and stay away from building significant pressure. Then keep venting as slow as needed to stay balanced.

I think the problem with sizing smaller is that too large of vents are used and steam goes “wild”. If it switched one of my Maid if most orifices from a 4 to a 6 another radiator will likely go completely cold. Similarly, if it turn a ventrite set at 5 down to 3 it could suddenly loose almost all its steam because now another radiator is over vented too much and robs all the stem.

But that’s just observations on my system.