Steam Heat Cycle

Matt_11

When considering the various elements in a steam heating system (pressertrol settings, main vents, anticipator setting, etc.) what is a healthy time-range of a heat cycle when the system is in balance (with the outside temperature around the freezing mark)?

Matt

Fred Harwood

Cycle time

I tend a 140,000 BTU one-pipe in Western Mass. that balances around freezing at two minutes 15 seconds on and 10 minutes 15 seconds off. Never builds pressure, thermostat is a Honeywell Round. Heat to all rad sections similar (Gorton #1 on main, variable vents on the 8 rads, last one with a Gorton D), with more sections heating on each rad as the temp falls.

Matt_27

What about at a cold start? How long does it
take to come to full heat?

Matt_27

What about at a cold start? How long does it
take to come to full heat?

Doug_25

firing time comparison

For general comparison:
1920's house in NY

336 EDR (80,600 BTU) radiation, 9 rads
one pipe steam
1987 Boiler: 108,000 BTU net; 143,000DOE
combustion eff: 82%
Outside temp 31*-33*, inside 68*
all rads get first section heat in 10-12 min.

Constant 68*: boiler fires for about 25-30 min, no pressure, off for about 2-2.5 hours then repeats cycle.
Overnight after 6* setback, fires for 40-50 min, cutout on pressure and then the pressuretrol controls for another 7 or 8 cycles that are 2-2.5 min on, 4-5 min off (oversized boiler)

Fred Harwood

Cold start

Boiler also has direct DHW, so it never goes below 180. From there, steam to end of main in about 5 min.

Fred Harwood

Doug

With boiler off for 2 to 2.5 hours each cycle, how do you keep house temp steady? Also, with each call you must reheat all the piping, which delays heating the rads. The system you describe should be able to keep the house within one degree with 15 minute cycles. You don't burn any more fuel with more frequent cycles, and you achieve more even heating.

Doug_25

I've wondered about that as well. The temp stays pretty constant inside (HW CT3500 programmable thermostat will constantly read 68*) until it gets in the teens (last winter). That's when the boiler fires, the thermomostat reading 67* and the off time will be closer to 1 hour. The upstairs will cool off a little during the day and be cooler at night but heats up well on morning start.

Only been a HO here for two previous seasons and this system needed help. The first winter - no main vents, steam always out of all the air vents, pressuretrol was set to cutin at 2.5, diff at 3 (additive), missing pipe insulation, thermostat wasn't compatible with steam...and on and on. After reading up on it with Dan's books, made some changes but always looking to improve - one reason I posted to see comments. I had a system check by local heating pro but it was less than what I had read from Lost Art. Right now I have one cycle per hour on the thermostat but that may need to change. I think the CT3500 averages out the temp and it actually falls a little more than it reports so sometime my better half likes it set a little higher (I'm buying her a sweater for the holidays)

btc

cycle time and thermostat relationship

I like the concept Fred has about constant temp and short cycles--to what extent does thermostat adjustment (calibration) have to do with cycle time? I have a Honeywell T8090--it seems to have a +/- 2 degree swing. If I leave stat on 68, it kicks on at about 66 and kicks off at 69, the raises to 70 on latent heat. What adjustment can I make to the stat to tighten the lower end [cut in] of the cycle? Believe I can control cut out with anticipator?
Thanks Brian