No pressure, no leaks, plenty of air vents!

AnthonyV

Fred said:

@AnthonyV , there are any number of factors that can make a difference between those mains:
- The difference in length and diameter of the mains. Longer and or bigger mains have more air in them.
- The size and/or number of vents you have on each main.
- The amount of time you let the boiler build pressure before you open any of the isolation valves.
- The actual pressure in the system at the time you open anyone of those valves
- The number of radiators connected to each main. The more radiators, the more vents to dissipate the air.
- The size of the radiators connected to each main. Bigger radiators can act as a larger "buffer" to the impact of sudden exposure to pressure.
- The size of the radiator run-outs on each main.
- The list just goes on and on.

Your right, there are many many factors. You've been a great help, your ability to digest what Ive said is fantastic. Its almost as though you've seen my cellar! Many diff size, lengths, radiator sizes etc...I learn more each day.

Jamie Hall

On latent heat. You are not entirely amiss -- at least you have the term, which a lot of folks don't! But one has to remember that the there are different kinds. The latent heat in the cast iron radiators themselves -- which is very real is determined by the specific heat of iron, which is 0.11 BTU/lb/degree F, and the mass of the iron -- and the amount of heat which you can extract from that iron is related to the temperature change. Suppose, for instance, that you have a 400 pound radiator sitting at 212 Fahrenheit (just after the boiler quits) and you let it cool to room temperature -- say 72. That's a temperature change of 140 degrees, which will release about 6000 BTU into the space in the process. Not, I agree, insignificant in and of itself. However, now consider the steam. Here the heat we are talking about is the heat of vapourization, or the amount of heat which it takes to boil one pound of water (or which is released when it condenses). That figure is about 1000 BTU per pound of steam. So it would only take condensing six pounds of steam to release the same amount of heat as the cooling of all that iron -- and that is the heat which is heating that radiator and the space around it. So long as you keep supplying the radiator with steam, the steam will keep condensing and heating the radiator, and the radiator will keep radiating (and convecting) the heat into your room. Once the steam stops, the radiator has only that 6000 BTU left.

Mark N

@AnthonyV, your system seems to be running quite a long cycle to satisfy the Tstat. You state 1 hr on then 20 min off. Mine is just the opposite 20 to 25 min on and then 1 hr off. I do have an event logger hooked up to the boiler. I log boiler on and boiler off and I also have thermal switches at the end of the mains so I know when the steam has arrived at the main vents. From that info I can calculate the efficiency of a heating cycle. For example say the boiler ran 20 minutes total and the steam reached the main vents in 5 minutes. I would consider that cycle 75% efficient because 15 minutes of the 20 minute runtime was spent heating the rads. Only 5 minutes was preheat, the time to make steam and get it to the end of the main. When its cold like this the efficiency goes way up. The boiler stays hotter and the pipes stay hotter in between calls for heat and you get steam to the rads much quicker.

Jamie Hall

The relative lengths of the cycles depends on a number of variables -- size of boiler related to radiators (and @AnthonyV 's is just about perfect) and outside temperature and infiltration and thus heating load in relation to radiator output -- which is also apparently pretty close for Anthony's system. Your system, @Mark N , may have more radiation output in relation to heating load.

clammy

Latent heat is change of state 212steam to 212water 32 water to 32 ice sensible heat is a heat u feel or read on a thermometer After your rads are hot and your boiler off they are giving off the latent heat there’s only a percentage of latent heat given off to your rads while steam enters that’s your edr no steam edr output drops I would agree on the nest and go simple non programmable thermostat . I think if the issue really make u crazy figure out your radiators total edr do a heat lose on your home Room by room compare to your rads edr x240 for each room also have u clocked your gas meter so you know what your input is just a thought if it makes you extra crazy Without boiler input and edr of system u will never know peace and good luck clammy

SuperJ

Pressure goes up when the radiation can’t get rid of the heat/condense the steam as fast as the boiler is producing it. So if you’re pressure isn’t going up but you have no cold rads/rooms your almost perfectly balanced.

Heat only enters the system when the gas valve is open and btu’s enter the system. There is a bit of energy in the steam in the pipes and rads but the pressure callapses very quickly after production stops.

The vaporstat or pressure controls only exist to deal with the imbalance between the rads and boilers that often occurs. If no pressure buildup exists then no need to cut off the steam since your system is consuming it as fast as you can make it.

Steam Boilers should be sized to the EDR or you may run of steam before all the rooms are heated leading to cold rooms, even if the boiler is running without stopping.
Steam goes where it can condense, hot water goes where it’s pumped. So an undersized hot water boiler will still usually equally heat a house even if it doesn’t get to set point. With an undersized steam boiler, some rooms may have heat (or overheat if the stay calls constantly) while other rooms may be unheated and cold.

Sounds like your boiler may technically be slightly undersized if you were to calculate its optimal size by standard means, but luckily your system appears to be perfectly balanced.

You are lucky to have such a well balanced and optimally sized system. When and if you replace the boiler it may be more efficient but it will be hard to exceed your current comfort.

Steamhead

AnthonyV said:

Mind you, the system is a texaco Fuel chief, converted to gas from oil in the 1970's according to paperwork found. Boiler was estimated to be from the 1950's according to one gentleman. I was quite surprised to see 75% efficiency for that old girl.

I bet the boiler was actually built by Dunkirk or maybe Utica. What burner is in it now? Can you post some pics?

SeanBeans

Some people come to this site wanting help getting rid of their built up pressure, some come wanting to build pressure!! LOL

mikeg2015

AnthonyV said:

Gary Smith:

Gary Smith said:

The main criteria is, is your house heated comfortably? If so and if your boiler does that without building pressure, then you are in the best situation you could be. If you try to make your boiler build pressure when it doesn’t need to, you are just wasting fuel and money. It takes energy, which costs $’s, to build pressure. Be happy sounds like you have a perfectly set up heating system.

Im wasting fuel by satisfying the stat ONLY, the boiler won't stop running unless the stat tells it because i never get to 8 oz of pressure which would allow the rads to give their heat to the room without the stat satisfied. My situation is unique because i get great even heat, dry steam, no water loss etc....BUT I need a way to get the rads to their job before the stat tells the boiler enough...

mikeg2015

IN a hot water or steam system, if designed perfectly, the temperature and pressure controls on the boiler are a back-up and not needed if the load is matched to the boiler.

Having a boiler cycle on a pressure control makes as much sense as a refrigeration system cycling off a pressure control (commercial walkwalk ins excluded). It would be like having a 3 ton evaporator and condenser but installing a 4 ton compressor and evaporator and just cycling it off the high pressure.

The reason to build pressure in a steam system is to save money and space on piping. A vapor system will use a 3” header whereas a 8-16oz system might get away with a 2-1/2” header with the same connected load and downsize all laterals and radiator valves. You could cut costs by maybe 20% and save head room in the basement and can run longer laterals and achieve the pitch required.

Fred

@mikeg2015 said: The reason to build pressure in a steam system is to save money and space on piping. A vapor system will use a 3” header whereas a 8-16oz system might get away with a 2-1/2” header with the same connected load and downsize all laterals and radiator valves. You could cut costs by maybe 20% and save head room in the basement and can run longer laterals and achieve the pitch required.

Mike, I don't think you have this right. I can't think of any good reason to build pressure on a residential steam system. Pressure is typically built by producing more steam than the system can condense. Smaller pipes may increase velocity and possibly produce wet steam but as long as the system can condense what the boiler produces, excessive pressure won't be the issue.

ChrisJ

@Fred overall I think Mike has it correct.

Gerry Gills system needs some pressure to operate with the smaller tubing.

KC_Jones

My first floor rads are piped with 1 1/4” feeds all my second floor is 1”. I have a 0-15 ounce gauge and I never see any pressure. You don’t need pressure except to overcome piping losses which, in an average house are almost immeasurable.

You don’t need more pressure (measurable) for smaller pipes unless you are talking mini tube, which is really small and a completely different discussion.

Fred

ChrisJ said:

@Fred overall I think Mike has it correct.



Gerry Gills system needs some pressure to operate with the smaller tubing.

I don't think we are talking about Gerry's system which is not the typical steam system and certainly not this OP's system. I also doubt that Gerry built his system to save 20% in installation costs or headroom. If that is what Mike was referring to, he should probably qualify his post.

Jamie Hall

Have to wave my oar around a bit here...

First off, it is quite correct to say that if the boiler steam output is perfectly matched to the condensing capacity of the system -- mostly radiation, but a bit in piping -- then the pressure should never rise beyond what is required to overcome the head loss of the steam in the mains. That head loss is usually pretty small -- on the order of ounces per square inch -- but is influenced by the size of the mains, of course.

The joker is in that "perfectly matched" comment. We often, and mistakenly, assume that the condensing capacity of the radiation is fixed at 240 BTUh per EDR. Unfortunately, that's not true. The condensing capacity of a given radiator will be influenced by a number of factors, some of which (like paint colour) are relatively fixed over time, but others of which, predominantly the ambient temperature in which the radiation is located, are not -- and may vary significantly (one of the minor beauties of steam is that in a well balanced system a radiator in a cold space will automatically give out more heat -- no valves needed). Thus we are faced with a situation in which at times -- in fact, normally -- the boiler is not perfectly matched with the rest of the system.

Then we have another factor: it is very common on residential systems to have one device -- a pressuretrol -- serving two functions: control of the boiler output and as a working safety limit. This is, in control theory, a rather poor idea, though it's simple.

All of which is why my own preference -- and others are welcome to differ, no harm done -- is to make sure that the boiler is large enough to be able to start and run the system from a cold start to the full capacity of the radiation on a design day. That means, however, that on a warmer than design day, or coming from a hot start, the boiler will be bigger than the rest of the system can handle. At this point it is necessary to modulate the output of the boiler; this is a control function, not a safety function. There are many ways to do this modulation. The ideal would be to actually modulate the firing rate as a rather steep function of pressure. This could be done, and is, in fact, done on large power boilers. The necessary controls are neither inexpensive nor simple, and pretty well require attentive maintenance -- none of which is attractive to the average homeowner. Another -- particularly with gas -- is to use a two stage burner. This does require an additional pressure control, but works quite well. The simplest approach, though, is to use a sensitive pressure control, properly set to turn the burner off and on with a duty cycle (ratio of on time to total cycle length) which produces exactly the amount of steam, average over many burner cycles, that the system can condense. That sensitive pressure control -- it may be a vapourstat or a pressuretrol, depending on the system requirements -- is functioning as a control device and should be used for nothing else.

A second pressure control -- usually a pressuretrol -- set at a pressure somewhat in excess of any expected operating pressure (3 to 5 psi is a good range) is then used as a safety control.