Optimum cycle-on time for steam

Drod

That sounds really good; but where do you live and how cold does it get. I live in Chicago and on many days that are very cold, my system (which runs economically and heats well) could run for 11 or 12 hours out of 24.
With your settings, do you find the 4 degree temperature swing (64 to 68) uncomfortable at all? I could easily live with it, but my wife would be bothered.

E. Holtman

optimum cycle on time for steam

Can anyone recommend an optimum run time for a steam system. I can recognize short-cycling, but what should I aim for to 'right-cycle'.
Thanks,
Eli in Philly

Al Letellier

cycle time

Wow. Talk about a loaded question, Eli. Every system is different and has it's own "cycle time" It's whatever time it takes to get the system up to selected pressure settings and cycle off the pressure device.
Best suggestion is to have a quality steam contractor evaluate your system to make sure every single component is functioning properly (vents, traps, boiler, pumps, controls) and set the pressure to get steam to that furthest radiator. The system will then cycle to meet the demand. If you're using a reset or outdoor reset control, it will take time to find the proper cycle rate through trial and error (after you do all the above evaluation and repairs as needed.

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btc

cycle time

My best achieved results for our single pipe steam system is to:
1. Leave Tstat set at 66 degree
2. Set Tstat anticipator at .85
3. Dont touch it.

At these settings, system kicks on at about 64 deg. then runs "on" for about 40 minutes and kicks off at about 67--latent heat pushes tstat to about 68. Depending on outside temp, 4-8 hours before hitting 64 and kicking on again...
40 minute "on" cycle sends heat about 3/4 across rads and system seems to peform quietly. System kicks off on temp before pressure limit reached (1 1/2 psi cut out).

btc

cycle time

System is in Washington, DC, which is pretty mild compared to Chicago! However, this winter has been pretty cold...We depend on our storm windows (townhouse) and I bought girlfriend a bunch of sweaters--and we have a glass of wine with dinner each night--for medicinal purposes :-) and to forget about the temp setting! What I like about leaving tstat on one setting is the quiet operation of the system. If cycle is too long--above 45 minutes or so--system seems to act funny and sometimes rad vents would stay shut and boiler would not even start upon the next heating cycle without me adjusting the pressuretrol upwards to get it started(normal setting of .5 and 1.5 psi) --which is a whole different post...I would say on a cold day-- 20 degrees--, the system might cycle on 6 times over 24 hours. Gas bills have been about $100/month this season...

David Efflandt

Sounds like the pigtail the Pressuretrol may be gunked up if vents stop operating after prolonged operation and system fails to start next time without cranking up the Pressuretrol. Adjustable vents only operate properly up to 1.5-2 psi.

I am just another Chicago area (Elgin) new home owner of old 1-pipe steam system learning the ropes. My RobertShaw thermostat with no anticipator or system adjustments had too much swing: -1 on, +1 off, plus 1-2 degree overshoot. Honeywell CT3500 usually keeps temp within 1* and rarely overshoots 1* (changing weather) set for gravity/steam (1 cycle/hr max). I should have gotten CT3600 which can monitor actual run time.

I have no main vents yet (just D on most distant radiator), but house is tight with added insulation and heats evenly. Oversize boiler typically runs 25-35 minutes every 90 minutes to several hrs depending upon weather, but starts cycling on pressure (1.5 psi) every couple of minutes after 20-25. So I only use setback in mild weather to not run all day (which works well ramping up, except for the frequent pressure cycling which give my vent damper and ignitor a workout).

Gas bills for 1200 sq/ft @ 67 degrees (excluding unheated porch and basement) Oct-Jan ran $37, $75, $95, $144 (w/o deducting $15/mo other gas use). So payback for doing anything about the oversize 2 yr old boiler would be a very long time. But I will likely have main vents added to shorten run time and throw a bit more heat into the basement from dry returns.