New Programable Thermostat SHORT CYCLES

Amy FitzGerald

I'm a home owner. We recently installed the Honeywell Vision Pro 8000 (TH811OU1003) along with a WIRED sensor C7189U because our thermostat was poorly located. We live in a 3-family home and we kept the thermostat in our unit but located the sensor in the coldest apartment. The sensor and thermostat were installed properly and function well. The problem is the differential on our old programmable thermostat was probably off 2 degrees. The newest programable thermostats have 0 or .5 degree differential. Even though we are more comfortable as the thermostat provides more consistent heat I notice that it short cycles. The thermostat comes on for 10 min or so and then off and then back on to keep the room at a set temp. The outside air temperature has been too warm to really gauge if we are using additional gas. So, is all the SHORT CYCLING REDUCING THE BOILER LIFE BECAUSE OF ADDED WEAR AND TEAR AND WILL WE USE SIGNIFICANTLY MORE GAS THIS HEATING SEASON? Any suggestions? FYI: We have an older Weill Mclain gas boiler on a one pipe steam system that was originally put in our brick home in 1928. Thank you in advance for any helpful comments!

Mike Kusiak_2

CPH setting

Have you adjusted the Cycles Per Hour (CPH) setting? Most new thermostats come out of the box set for 5 or 6 CPH, which is suitable for hot air systems but not steam.



Try setting it at 1 CPH which is the recommended setting for steam. Running a cycle every 10 minutes on a steam system will definitely drive up your fuel bill !

D107

Hot water system

What's the recommended CPH for hot water systems? does it vary for convectors versus over-sized cast iron rads?

Eric_32

had similar case with Honeywell..

They are a great thermostat when set correctly. Had a similar experience with mine, Have a mix off cast, radiant, and fin all on different hot water zones of coarse, and would short cycle and drove me nuts while the CPH was set to 5.

Changed it to 3 and it's like a whole new thermostat. Look in the manual or if you don't have it, can find it on Honeywells site to get to the setting.

Jean-David Beyer

CPH for mixed system.

For my system, heated with hot water, I have two zones. One is radiant slab at grade, and one is Slant/Fin Base/Line 2000 (oversized); The Slant/Fin zone is two rooms which are about the same size and heat load. About 3100 BTU/hour each when it is 0F outside. Design day is 14F. Each room has 14 feet of that baseboard. I used that much so I could use lower temperature water to get more condensing. At design temperature and above, it calculates to condense all the time.



I have two reset curves, one for each zone. Mine is set so the outdoor reset causes the boiler to circulate hot water just barely hot enough to make up for the heat loss (I calculated each room separately).



To run the radiant slab zone, my thermostat is set for one cycle per hour. It does not make sense to go any faster. For the baseboard zone, the thermostat manual recommends 3 cycles per hour, but I found that not ideal, and have it set to 1 cycle per hour also. The higher cycling rate might be appropriate if I were using 180F water to that zone, but I am not.



If you do anything "unusual" with your system design, you may wish to use cycle rates other than what the thermostat manufacturer recommends. I think the thermostat manufacturers have their greatest experience with forced hot air systems. By "unusual", I mean systems with outdoor reset with severe reset curves, modulating boilers, lower temperatures of circulating water, and so on. In my case, with the slab zone, it was pretty obvious that 1 cycle per hour was the way to go. If I could go lower, that would make sense too, but I did not have that option other than running the circulator 24/7, and I did not want to do that.



I am just a homeowner, not a heating professional. I would expect emitters like cast iron radiators, to be somewhat in between 1 cycle per hour and 3 cycles per hour, depending on their mass, size, and the temperature of the circulating hot water. In other words, it depends, and you may have to experiment to find the best rate. You sure would not want 10 cycles per hour (probably appropriate for electric resistance heat).

Jean-David Beyer

My Honeywell CT/3600 and PRO TH4110D thermostats

have very different manuals. The older CT/3600 (a great thermostat, but no longer available) has everything you need to know in the manual.



Unfortunately the PRO TH4110D has two manuals, and the manuals are a pain because some of the information is in the Operating Manual and the important stuff is in the Installation Guide. The installing contractor gave me only the Operating Manual, and the setting of the Cycles per Hour is only in the other manual (available on line). Setting Cycles per hour requires the Installation Guide.

D107

CPH/Anticipator Setting

As far as I understand CPH is shorthand for anticipator setting, yes? Usually anticipator settings are set according to the line voltage of the primary control, at least as a starting point, then readjusted if required. If the t-stat doesn't have anticipator adjustment, and the CPH setting is three,then the heat would come on 3x an hour even if it was 45 degrees outside but for very short--and perhaps unnecessary--cycles. If it was 0 outside, cycle could be on for 15 min, off for 5, on 15, off 5, etc. ??