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Joined on September 15, 2010

Last Post on July 15, 2014

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Boiler cycling

@ January 21, 2011 9:25 AM in Steam a "Dying Art"?

A steam boiler will cycle on pressure until the thermostat is satisfied. If the system is sized just right it will run almost 100% of the time on a design day (Zero F in my case) because the radiators will condense the steam as fast as the boiler can make it.

My system usually fires initially for about 14 minutes before cutting out at 12 oz of pressure. It then cuts back in at 4 oz and that continues (60 sec on and 90-120 sec off) till the thermostat is satisfied. My boiler is oversized but I'll live with it till it's time to replace that 15 year old V75 because the fuesl savings would take a very long time to pay for the replacement costs.


Your right

@ January 21, 2011 9:16 AM in Steam a "Dying Art"?

Your absolutely right about that, I remember Dan's article from a couple of years back where he argued for matching the load as close as possible to the boilers rating.

My only concern in the Boston area is the gas companies habit of mixing air into the gas lines to keep the pressure up in really cold weather. Some of my neighbors have complained about low heat and the flames not being blue during really cold weather. I'm still on oil so it doesn't bother me until they fill the damn tank! Does anybody know if there is a limit to the amount of air they can mix in.

time to go out and shovel,


Pressure too high!

@ January 21, 2011 8:06 AM in Steam a "Dying Art"?

It is not easy to find good steam men anymore and that is why this board exists. People have realized they have to become knowledgeable so they can tell the plumbers what has to be done if they don't understand steam systems.

Converting a steam system to hot water can be an expensive proposition because steam works at 1-1/2 PSI and forced hot water runs 10X that. You might find some areas that don't like that pressure after 80 or 90 years of low pressure. If you do convert, be prepared to remove all the radiators and piping so you can install everything new.

You said the boiler was running at 5.5 PSI that is MUCH too high, it should be 1.5PSI. All steam systems have air vents and some have steam traps (2 pipe); these do not work at anything over 2-3PSI and that makes your gas company very happy because they get to sell you a lot of fuel. Turn that pressuretrol down (0.5 on the front tab and 1 on the dial inside the front cover). Post some pictures of the boiler and the piping around it from a few different angles, also a picture of your pressure gauge and pressuretrol.

A steam boiler is sized to supply the connected load (EDR). The boiler has a plate on it that tells you how many BTU's and how many square feet of steam it can supply at a given fuel rate. The boiler sq ft should be 15-20% higher than the sq ft of radiation you have attached. Any take offs for domestic hot water have to be considered as well as if the piping in the basement is insulated, etc.

You can figure out what each radiators sq ft by printing and filling out this chart. just figure out what kind of radiators you have and then how many columns they have. The chart will tell you how many sq ft each section of a radiator has according to it's height. Then count the number of sections (rows of 2 or 3 columns) and multiply that by the sq footage per section to arrive at the square footage of that radiator.

A properly configured steam system can be very efficient. If your going to live with steam heat you have to understand it, you can buy a copy of "The Lost Art of Steam Heating" under the shop banner of this site. That book will give you a better understanding of steam heat than most service people. It's well written and has a huge amount of information in it. It will pay for itself 10X over.


Turn the pressure down.

@ January 20, 2011 8:47 PM in 2 pipe system-banging noises

That pressure is much too high, if they can heat the Empire State Building with 2-3PSI an apartment building will do just fine with 1.5PSI maximum. Higher pressure makes everything worse but it makes the people supplying your fuel very happy.

Has this system been noisy forever or did it start after some work was done on it? Have they checked the main air vents to be sure they are working? A lot of main vents do not take kindly to anything above 3PSI - in fact they lock shut and they can't work as they were designed - and then you pay the fuel company in spades.


Run it back along that return

@ January 20, 2011 4:37 PM in Got Book Now need main vent!!

It would be nice to get a foot or more back from that drop down so the new vent lasts a good long time. Maybe a short nipple and an elbow so you can go back along that return, Come out of the elbow with a reducer to get down to a smaller pipe and then another elbow to screw the new vent into. The Gorton #2's are large so you want to make sure you have room for it and that #2 wants to go into a 1/2" fitting -

That book is going to pay for itself in spades!


degree days, radiator venting, tstat

@ January 20, 2011 2:26 PM in Steam Main Venting (Residential)

Here's a link to Boston degree day data -

Now that the mains venting has been addressed it's time to see how well the reast of the system is balanced. The goal is to have all the radiators start to heat at about the same time and for that to happen the venting on the radiators has to be proportionate to its EDR (square footage of radiation). larger radiators require more venting than small ones do. Just putting huge vents on all the radiators does not work.

Print and fill out this form for all your radiators and note the type of air vent and if it is 100, 50, 25, or 10% open. there are pictures and charts that should enable you to figure the EDR of each radiator.

Also what kind of thermostat do you have and is it set up for steam?


EDR seems small.

@ January 20, 2011 10:14 AM in Pressurtrol needs help

Those numbers look awfully small. A typical radiator in my single family 1920 house is a 38" tall, 3 column, and has 6 sections; per the chart each section (of 3 columns) for that height is 5 sq ft and since I have 6 sections that radiator is 30 sq ft - 5sq ft per section X 6 sections = 30 sq ft. In my 6 room house I have 190 sq ft of radiators (EDR), yours will be different. Please check your number again to be sure because a total EDR of about 75 sq ft seems very small.

make sure your thermostat is set up for steam, the newer digital ones need to be adjusted to 1 CPH (cycles per hour). You should also insulate as much of the piping in the basement as you can, start around the boiler and work your way outwards.


Pressure, calcium deposits

@ January 18, 2011 1:46 PM in Spitting Air Vents

First, do you know what pressure the boiler is running at?

It sounds like calcium deposits are probably preventing the Hoffmans from closing all the way. Knowing what the Hoffmans cost, I'd replace them with Gorton #1's and then try to reclaim the Hoffmans as spares by boiling them in white vinegar for 15-13 minutes.

Last year my Ventrite 35 did the same thing and the vinegar boil allowed me to reclaim it and use it as a spare after I replaced it. just make sure everything is relatively cool and shut the boiler off before getting out the wrench.

Take some pictures of the boiler, the piping around the boiler, and those vents from a couple of different angles and post them here so we can see what you have.



@ January 18, 2011 8:20 AM in Is this a crazy idea?


i agree with Dave that adjusting the radiator venting down might help this system a lot. Also his comment about venting the steam main fast should be followed.

Another item is insulating all the piping in the basement, any heat your losing in the basement is not available for use upstairs and that might just be enough to make it all work.

If you could post some pictures of the boiler and basement piping it might help us visualize what your dealing with.



@ January 17, 2011 7:54 PM in Steam Pipe Fiberglass Insulation versus Asbestos air cell insulation

I have no clue what R factor asbestos pipe insulation is. However I've removed it from pipes and installed 1" fiberglass pipe insulation in it's place,  and my intuition is that the fiberglass insulation is at least as good as an equivelent thickness of asbestos.

All the exposed piping in the basement should be insulated with a minimum of 1" fiberglass pipe insulation.


main vent location

@ January 17, 2011 10:59 AM in Removing air valves in one pipe system

On the steam main in the basement there should be a short pipe nipple and a main air vent near the end of the main (usually a long 2 or 2-1/2" pipe); it can also be near the end of the dry return which comes off the end of the steam main.

The main air valve may look like a larger version of your radiator vents or it may be a large copper or green in color. that is there to handle all the air in your steam main and the boiler, the radiator vents then just have to handle the ar in the radiator and the pipe that feeds them.


Main vent

@ January 17, 2011 9:04 AM in Removing air valves in one pipe system

Do you have an air vent on the steam main and is it large enough? It sounds like your radiator vents are venting the entire system, they are only supposed to vent the radiator and it's feed pipe.

Also if the thermostat has a selectable CPH setting, Select 1 or "Steam and gravity hot water". A lot of these come preprogrammed for hot air and that doesn't work at all well for steam.


use a voltmeter

@ January 16, 2011 6:59 PM in problems with pressuretrol not coming on

In domestic boilers the pressuretrol is usually wired in series with the oil burner, once it opens (or breaks) the oil burner shuts off.

If you have a multimeter you can measure the voltage across the pressuretrol when the boiler is running, you should read 0 VAC. If the system shuts off because it reaches the pressure setpoint you should read 120 VAC. That indicates the pressuretrol opens (or breaks) on rising pressure.

Note that if the boiler shuts off because the thermostat is satisfied the pressuretrol will still be on (in make mode) because you have not reached the pressure setpoint.

The spare PA404-1033 that i have on the shelf (just in case) opens on rising pressure.


Installation manual pipe diagram

@ January 16, 2011 11:29 AM in having a problem with a steam boiler

i assume things worked reasonably before the new boiler?

What make and model is the boiler/ Post some pictures of the boiler and the piping around it from a few different angles so we can see what your dealing with. Also look in the boiler installation manual and see if your piping agrees with the piping diagram in the manual.


Insulate - skim - vent

@ January 16, 2011 9:08 AM in Short Cycling on Pressure? Downfire? Air Vents?

i agree with all the comments above on skimming and possible downfiring after you have been through a couple of design days to see how the system performs when stressed.

Start by getting all of that piping insulated with 1" pipe insulation. Start at the boiler and work your way across the basement. Check the pipes with a level as you go to make sure they are pitched correctly. While doing that you could be cold skimming so you would get two things done at once. Skimming takes hours so putting up the pipe insulation would be a good use of that time.

Install those Gorton #2's as soon as you can and then see if the steam is reaching all the radiator valves at about the same time; the checking of steam reaching the radiator valves should be done after insulating the basement steam pipes. Put a level on the radiators and make sure they are all pitched back towards the input valve so water can find it's way back to the boiler.

All the above can be done by the home owner so your not shelling out for labor.


Pipe size

@ January 15, 2011 12:44 PM in What is my Pipe Size

A pipe with 2.37" outside diameter is a 2" pipe.


Is this single pipe steam?

@ January 15, 2011 8:04 AM in What constitutes Short Cycling?

When a boiler initially fires up it takes it a while to come up to steam, 8-15 minutes? As the steam builds the steam mains have to be vented so the steam can travel down the pipes, the radiators should be venting also. If the boiler is only running for a minute or two during the initial firing period you probably have main vent issues, can you tell what kind of main vents you have?

It is normal for most boilers to cycle on and off after the initial burn if it's not frigid outside. There is a control on the boiler (Pressuretrol) that sets the pressure range the boiler operates at, usually from 0.5 to 1.5 PSI. Once all the air vents close pressure will build until the upper pressure limit is reached; then the boiler shuts down, the steam condenses inside the radiators and the boiler starts up again until the thermostat is satisfied.  Are the air vents on your radiators all working? What kind of vents are they?

Tell us what make and model of boiler you have and post some pictures of the boiler and the piping around it from a few different angles. Also take a picture of a sample radiator showing both ends.


header is too low

@ January 14, 2011 9:05 PM in Drop Header Q


Your header is too low but exactly what symptoms are you experiencing? How well did the system perform with the old boiler?

Once you post the next set of pictures I'm sure we can find a solution to your problems. In the meantime do you have the installation manual? in that you will find a suggested piping diagram, that is the MINIMUM ACCEPTABLE PIPING. Anything above that just makes the steam dryer. From looking at your pictures that header is much to low.

If you don't have the manual, give us the model number of the boiler and we will find it for you.



@ January 14, 2011 1:01 PM in pipes knocking

How much of a setback is the system coming back from? steam systems don't respond well to deep setbacks.

What pressure is the system running at?


Couple of things to check

@ January 14, 2011 12:59 PM in New Steam Boiler Options

Picture #3 shows the main air vents on the returns, they look a bit small. If those two mains (actually a split main) aren't more than 20 ft long I'd replace them with 2 Gorton #1's so the mains vent nice and quickly.

Make sure the mains and radiator leaders all have the correct slope. All of the radiator vents should probably be replaced unless they are new. Other than that just make sure the installer follows the installation piping diagram and that he agrees to skim the boiler until the water i clean (usually a couple of days after the install).


no main vents

@ January 13, 2011 9:53 PM in I thought we did everything right. What do you think?

I'm not a pro but my feeling is that this is a counterflow system and it would benefit greatly from some large steam main vents after the last radiator takeoffs (or as close as you can get from a plumbing point of view).

Steam is a harsh mistress and she is choosy about what violations she will accept without protest. (sorry for that)

As I said, just my initial feelings.


Longer burn

@ January 13, 2011 8:27 PM in cycles/hour

It's just below 20 with a light wet wind right now. My steam boiler comes on about every two hours and runs for 6-7 minutes to get my radiator vents hissing (Gorton #! on the 15 ft steam main), the system cycles off on pressure initially about 3 minutes later. It cycles on and off a few more times till the thermostat is satisfied 15 minutes after the initial call for heat.

This is with a thermostat that maintains the temperature within a degree or so. I would follow Mikes advise to lengthen the burn time by adjusting your anticipator since you don't have a CPH adjustment.

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