re-visit of Thermostat Question

norb

i have a another question regarding the Honeywell rth4100d thermostat. My original question, some time ago, had to do with the setting of #1 for steam heat systems. The answer was that this setting causes the furnace to cycle one time per hour.
My new Questions is: What if the thermostat is set to , say , 74 degrees. If the room ( thermostat) is maintaining 74 degrees, will the furnace still kick on in roughly one hour? the room where the thermostat is, my living room, seems to be maintaining 74 and the furnace is only going on about once every TWO hours----thus my upstairs bedrooms are cooler than normal. I did change out the living room valve to make that room warmer, and so I will mostly likely go back to the valve I had---a Gorton #4. However, if you still could answer my new question: Should the furnace kick-on roughly each hour at the mode setting of #1 or only of the temp drops below 74? Also, is it possible that I knocked out the setting of #1 somehow when I was programming it for Daylite Savings Time, maybe I accidentaly did something ?

delta T

I believe it acts as more of a limiting factor, so that it will not cycle MORE than one time per hour. Less cycles is better. The settings should all be maintained, unless the batteries (if any) were removed for a long period of time (more than 10 or fifteen minutes, there is a capacitor on board to allow you to change batteries without losing all the settings.) Changing the clock should not affect any of the settings.

adambnyc

Boiler will only kick on when the thermostat temp dips below what you have set.

Fred

If the thermostat falls below the set point, by some increment, the tstat will call for heat and the boiler will run a heat cycle. My understanding of the number of cycles per hour (CPH) is that the cycle setting changes that increment, much like an anticipator in the non programmable tstats. I'm not sure what those increments are or even if there is a standard across all tstat manufacturers. For example, a setting of "1" might program the tstat to wait until the room temp falls by .9 degree before calling for heat, a setting of "2" might cause the tstat to wait for the temp to drop by only .75 degree before calling for heat and so forth with settings of 3, 4 and 5. If your room temp should drop by the increment you have by setting the tstat to say "1", before the hour, the tstat will still call for heat and the boiler will kick on. In your case, if the boiler doesn't cycle for two hours, it simply means the tsats is still satisfied with the room temp.

ChrisJ

Best I can tell Honeywell's CPH setting is kind of like an anticipator and kind of not.

I feel it does widen the temperature range between on and off, lower number meaning a wider swing. I believe it also causes the thermostat to change it's predicting behavior, I.E. shutting the system down before the setpoint is reached, expecting it to be reached after shutdown.

Overall, the higher the CPH, the tighter the temperature swing, assuming the system can keep up.

The CPH setting actually seems to have little to do with cycles per hour, it'll still run 2, 3 cycles per hour when set to 1 if the conditions require it. But, the programming of the thermostat is aimed at 1 CPH running approximately 1 cycle per hour. It may take time to settle in after you change the setting. You'll find it's behavior will change greatly over the first few cycles.

norb

thanks guys for the information