Definition of proper boiler cycling?

TomM

What is the definiton of proper boiler cycling?

My boiler will cycle for about 10 to 20 minutes, and then it reaches the pressure set point, and then will be off for about 1 to 3 minutes, then it kicks back on.  It will continue to cycle like that until it reaches the Tstat set point. 

What should be going on with cycling in a properly cycling boiler cycle?

(2 pipe air vent system)

(ps-  I think i'm getting a ton of wet steam b/c of ugly near boiler piping)

TomM

Correction

Correction:  I meant to say:  after the first long cycle, it will cycle on for about three minutes, and then off for about one minute, until it reaches the tstat set point. 

What is a proper boiler cycle in a properly running system?

Thanks!

jpf321

3on 1off seems about right...

3mins on and 1min off seems about right .. see this thread .. http://www.heatinghelp.com/forum-thread/128792/More-boiler-cycling-thoughts ... you may want to adjust your setback to no more than 3degF from normal .. steam doesn't like deep setbacks and apparently it actually costs more in recovery than it saves in setback time. you should try to have your t-stat satisfied just before the pressure controls kick-in .. or at least minimize the number of "pressure" cycles the system makes before the t-stat is satisfied. 

Unknown

Cycling

Your cycling times don't seem too bad..... Are your mains and boiler piping insulated? - Rod

SteamHeat

What About Motorized Flue Damper ?

I am surprised. I get cycle times like this with my leaking main vents and I thought that the off time should be much longer if I solve my leak problem. In my boiler there is a motorized automatic flue damper which closes off the chimney each time the boiler shuts off to keep heat in the block during off time. I hear that motorized flue damper running over and over again. Wouldn't it wear out prematurely with such short off times?

jim_72

Questions

Tom let us know   #1 boiler size  EDR rating in sq/ft and amount of radiation in sq/ft you have  connected to your boiler. #2 Are your mains insulated? #3 Do you have functioning main vents on each main.

jim_72

Vent damper

Steamheat  FWIW I have a 19 year old system that has cycled 3mins on/ 2mins off since installed( oversized). Motorized vent damper/ pilot ignition/ no winter setback  always 70 degrees and have not replaced a part except the LWCO. So either I am very lucky or wear and tear is overstated but I have to say products, eg. controls , back then were made much better then todays.

TomM

boiler cycling

Nothing is insulated.  That is only one of my many problems.  the building heats, so I think I can make it until spring ok.

I think the major problem is that water is being sent up into the mains because the near boiler piping is so bad.  The installer bushed down the 3" tapping to a 2" copper pipe, and sometimes you can actually hear it bubbling up the takeoff.  There is only like 12-15" from the boiler tapping to the header too. 

I was thinking that the burner was cycling on and off so much because of the volume of water in the system was making the pressure fluctuate wildly, causing short cycling. 

Problems:

1)   Bad near boiler piping.  Bushed down tapping, bullheaded T, copper pipe totally bent out of wack. 

2)  Union on the hartford loop 'closed nipple'.  Also, that area is about 10" long and it hammers at times.

3)  Condensate is taking a long time to return to the boiler.  I have a two pipe air vent system, and I think that one of the return lines may be partially blocked.  When I tilted the radiator towards the return line, it hammered some.  When I tilt it towards the inlet pipe, it works fine. 

4)  No insulation on anything.  Including pipes under the kitchen in a crawlspace which is at outdoor temp.  Hope that never freezes. 

5)  No main vents anywhere.

6)  I have a leaking hot water coil I think.  I drain about 5 gallons of extra water out of the boiler a day.  Keeps it a little cleaner, i guess.  OR, it may be the manual fill valve that's leaking.  I'm going to replace that over the holiday.

7)  The tankless heater coil Low limit control temp thingy is toast.  I only get hot water when the boiler is making steam.  When I shower, I have to turn the heat on to get hot water. 

Not that bad, i guess.

So, I want a duty cycle of 1 optimally?

jim_72

Fix

Tom because your near boiler piping needs to be redone,it's best to get a Steam Pro in there to fix as well as to assess your other issues

TomM

Steam Pro?

c'mon man, that's no fun!

TomM

Definiton of proper boiler cycling?

What is a proper boiler cycle though?

jim_72

Proper cycle.

Tom "proper" or shall we say ideal steaming is not cycling but rather one long uninterrupted burn without pressure increase until the tsat is pleased. This is done through a well balanced system where the boiler creates the same amount of steam that the piping and radiation can constantly condense. Most systems are over sized, some grossly, and a 3min on / 1min off cycle is what most over sized systems can expect short of doing anything radical such as downfiring.That's why it is important to let us know your boiler size and the amount of radiation you have.If you are not over sized then besides the repipeing there are other minor tweaks that can be done to help you possibly eliminate your cycling on pressure.

TomM

Definition of proper boiler cycling-

Thanks Jim!

Unknown

Insulation

Without insulation you have one huge radiator. Steam is condensing all over the place causing the system's pressure to drop rapidly and start the boiler again.

I'd worry about the constant addition of fresh water and attend to that right away, This is a problem as fresh water contains excess oxygen which can rapidly corrode your boiler. It's very important to bring any new fresh water to a boil as this drives off the excess oxygen. Assuming that the original steam system was put in properly I'd would try to determine exactly what that was and restore the system. As you have noted your close boiler piping needs to be ripped out and redone.

- Rod

mel rowe

Tom/Jim

Homeowner here with similar problems in past.  Oversized boiler, incorrect piping, poor venting, poor insulation, dirty system, cycling and poor controls.  Did I miss any?  LOL  



Anyway, after getting a copy of LAOSH and absorbing the info for a while, I went to work on my system myself.  Fixed all these problems, with the last, and most effective, being downfiring the boiler.  From the EDR of my rads, I calculated boiler was about 25 % oversized.  Downfired it a year ago by removing 4 of 16 burners and plugging the openings with 1/4 inch plugs.  Then got a tech to adjust the gas flow to get the right gas pressure in manifold.  Checked gas flow on meter and was actually 32.5% less than when installed.  Since then, no more wet steam problems, since  the steam velocity has dropped so much.  Also, my system now meets Jim's definition of an ideal steamer.  It fires up and runs with very little pressure ever showing on the gauge (0-3 psi), until it goes off on the stat.  Also, I am seeing a 5.1% decrease in gas usage, although I haven't taken the time to figure in any difference in degree days year-over-year.  My wife now says that I will have to find something else to keep me busy during the winter.    FWIW

jim_72

Fix

Mel well done. I have to say 25% oversized is a gift. I know many boilers in that range that have never been downfired and purr like kittens. Having said that it is impossible to find any licensed Pro in my area who would assume the liability of downfiring.Most steamers have a 10% fire reduction limit. I have to say reducing your fire 25% is a bit concerning .i hope your CO levels are safe. 

mel rowe

Jim

You're right.   If it was only 25%, that would not have been quite so bad.  I was using the boiler's EDR with a 1.3 pickup factor.  It was actually closer to 50% oversize.  

SteamHeat

I Hope I Am That Lucky.

Jim, if I get such good service out of my controls as you, I will feel like I won the lottery.  I thought I was beating the vent damper and gas valve to death.  I feel relieved now.  Thanks.



After I get my main vents to stop leaking and finish insulating my Tee's and Elbow's I'll post my cycle times for whomever is interested.



Many folks talk about the oversizing of boilers, but no one mentions that, short of tearing holes in your walls, if the pipes inside are uninsulated, like mine, there is going to be extra heat loss there. My walls have no insulation on the pipes or in the walls, period. My old oil burner took 50 minutes just to get my radiators hot and heating the house up took all evening. My new boiler with a pickup factor of 1.56 like they used back when the house was built, heats all my radiators in 20 to 25 minutes. It may not be as efficient mathematically, but it is a lot more comfortable to live in. :-)