Heating Cycle ???

brucewo1b

you will probably find 2 or maybe 3 cycles at most for steam to be about right

BAB

Heating Cycle ???

I have an old Honeywell programmable thermostat that works ok but may be turning the steam boiler on or off more often then necessary. The face of the unit swings on the left & then clips on & off. When the face is off there is a slot with two screws that can be adjusted for a "Hot Water Tank" or a "Forced Air Furnace" or "Others" and some other choices. By adjusting the two screws in or out the stat then has it's "heating cycle" changed from 6 times per hour or to 4.5 times per hour or 3 times per hour, etc. Is this heating cycle feature turning the boiler on or off when I do not want it to, ... what is the purpose of this feature? I am home & the stat is at work.

carol_3

You're on the right track. 6 means the boiler has the opportunity to come on 6 times per hour (60 minutes divided by 6 = every 10 minutes; 60 divided by 3 = every 20 minutes). This is called cycle rate, and any decent thermostat has adjustable cycle rate.

The purpose is to even out the amount of heat in the living space so that the temperature doesn't vary more than a couple degrees.

The reason for various cycle rates is that different convectors deliver heat at different rates. Cast iron radiators radiate heat for a long time, so longer cycles (3 20-minute cycles) give the radiator a chance to give off all its heat. For fin tube ratiators, 6 cycles per hour is good because they give off heat quickly.

Unless you have cast iron radiators, the higher number cycle rate will probably give you the least variation in temperature, which is the definition of "comfort."

BAB

Old Stat fine tuning

Thanks for the quick answers. The steam Smith boiler is only two years old. The commercial building was built in 1934. It is solid concrete & I beam construction. The big industrial single pane glass & iron windows leak like an open barn door. The radiators are cast iron, many are 15 feet long. Each winter I replace 10 to 15 steam traps. There are five heating zones with a stat & modulating valve controlling each zone. I have been repairing & updating the zones, … one zone is shut off as not active, two zones function properly, one zone is tweaked manually & left partially open for now & the longest or furthest zone from the boiler is turning the boiler on & off. You said if the radiators are cast iron I should use the “6” cycle? Or did you say if I have cast iron radiators do not use "6"? Can you explain again on the "6". I have it on 4.5 now & am not sure that is correct. I have the program drop the control temperature down 5 degrees every night from 11 pm to 7 am.

BAB

Thanks for the quick answers. The steam Smith boiler is only two years old. The commercial building was built in 1934. It is solid concrete & I beam construction. The big industrial single pane glass & iron windows leak like an open barn door. The radiators are cast iron, many are 15 feet long. Each winter I replace 10 to 15 steam traps. There are five heating zones with a stat & modulating valve controlling each zone. I have been repairing & updating the zones, … one zone is shut off as not active, two zones function properly, one zone is tweaked manually & left partially open for now & the longest or furthest zone from the boiler is turning the boiler on & off. You said if the radiators are cast iron I should use the “6” cycle? Or did you say if I have cast iron radiators do not use "6"? Can you explain again on the "6". I have it on 4.5 now & am not sure that is correct. I have the program drop the control temperature down 5 degrees every night from 11 pm to 7 am.

carol_3

Go with 3 since you have cast iron radiators.

BAB

heating cycle

Thanks again for your prompt response, I have set the stat at 3. However, during morning startup of the boiler, after the programmable stat had been turned down 5 degrees for the evening (11pm to 7am), it sometimes takes 45-60 minutes to heat up the whole building. Does my setting of 3 limit this long morning heatup? Does the boiler turn "on" for 20 min. then "off" for 20 min. then "on" again for 20 min.? What is meant by three(3) 20 min. heating cycles?