Honeywell thermostats are top notch in my opinion. You can adjust the amount of times it cycles per hour (CPH). Set this to 2 or 3. The thermostat's job is to maintain the temperature as best as possible, and Honeywell's thermostats are designed to do this. My preferred thermostat is Honeywell's TH8320. Most likely you just have to change the CPH on the TH6110 to 3. It comes standard at 5 (which is what you're experiencing), which is too much--I don't know why this is standard. 3 should be used for heating and cooling.

I have a Honeywell TH3210D used with geothermal heat pumps and my Inside Temp and Set To temps are rarely different by more than a degree. In most cases, the heat comes on when the diaplayed Inside temp is the same as the Set To number. I wish the tstat displayed fractional degrees (at least tenths) so I could prcisley at what temp the heat is kicking on.

I looked at the CPH settings and mine are set to 3 for the compressor and 9 for the Aux Heat and Emergency Heat. Here is the question I have. When you set the CPH to 3, does the tstat then allocate those 3 cycles equally across the hour? Or - does it allow 3 quick on/off cycles say in the first 30 minutes and then no other cycles for the rest of the hour? If the CPH's are divied up evenly across the hour - then you can use that to control the short cycling problem. If it isn't an equal dustribution, then you might have Aux Heat coming on more frequently if you set the number too low. Imagine 3 quick cycles and then the tem dropping in the room by more than 2 degrees while the CPH keeps the system from coming on. The when you get to the next hours, the tstat sees a big temp differential and throws on Aux heat - that is what I don't want to have happen.

I also discovered a special case for CPG setting for my second floor heat pump where I have a zoned system with 1 thermostat in each of 3 bedrooms. The HVAC guys set the tstats in each room correctly as desribed in the manual (compressor CPH = 3). But I noticed that this heat pump was cycling quite a bit in the very cold part of the winter. I figured out that each tstat has an allocation of 3 CPH - adding up to a total of 9 since the tstats are not synchronized. This explains why this one unit comes on a lot more than the two units I have in the basement. I believe that I need to set these back to 1 or 2 CPH per room - but I would like to understand the distribution of cycles a little more before I do that.

The Honeywell recommended CPH settings of 9 for Aux heat and Emg heat in the manual lead me to believe that the cycles are evenly divided, but I would really like confirmation. If there is a call for Aux Heat, you would want a short boost to help the heat pump catch up - but you would not want Aux heat on for very long because it is basically a toaster that will run up your electric bill. A setting of 9 would mean a 6.66 minute on/off cycle - which I would assume to be 3.33 minutes on and 3.33 minutes off. That would make sense to me. Does it work this way?

One last thing I have learned is that when you touch the tstat temperature setting - it may clear the CPH counters for that hour. I am not sure what happens with a tstat with day/night timers but it is something to be careful with when you are testing. I also found during testing that when I push the tstat Set To up by 2 degrees or more, the tstat will call for Aux heat. The Aux heat will com eon for about 3 minutes and then turn off.

Interesting topic. I wish Honeywell would put these details in their manuals.

I would lower the aux. heat CPH to 5. The CPH is an average value and is applicable to more mild temperatures where the thermostat is trying to maintain temperature. The thermostat will spread the cycles out throughout the hour (so, with CPH 3, approximately 15-20 minute cycles). Sometimes this value will be more, sometimes less. If it's very hot or very cold out, the system may and should run constantly. Hope this clears it up.

Yes it does clear it up - thanks very much!

There is a setting for cph and mine is on 5 as recommended for 80% efficient furnaces. On the first call to Honeywell residential technical questions, I was told that changing to 3 cph was not recommended and would not make any difference. The tech could not tell me the reason. I called a second time and talked to someone else, who also told me that changing the cph would not help. She said that initially it would reduce the cph, but that the tstat would soon revert back to 5 cph.If so, it is too smart for my liking. Even though Honeywell advertises a 1 degree accuracy and differential, the tech admitted that it would cycle on as little as 0.2 degree temp change.

My experience is the same as Sniffdog in that the temp readout does not change from the set temp before the furnace comes on. That was when the tech said it cycles on as little as 0.2 deg temp change. Now, another puzzling thing is that my tstat manual says if you have a furnace with above 90% efficiency, the standard setting is 3 cph. The tech explained this is because the run time is longer on the higher eff furnace. The blower starts sooner and runs longer. Someone else also said that most 90+% furnaces are sized more closely to the requirements and thus run longer to heat the house.

I am still not sure that the tstat is smart enough to revert back to the standard cph setting. Guess there is one way to find out and this is changing to 3 cph seeing if that is true.

I would still like to use a tstat with an adj temp differential for the upstairs. One reason is the newer furnaces are generally noisier due to the draft fan starting early and the ignitor noise. For my comfort a 1 to 2 degree differential is fine.

I disagree with the Honeywell techs. Changing the CPH will make a difference. I have seen this first hand with an 80% furnace. It does not revert back to my knowledge. The value is not a maximum CPH; the thermostat actually uses this algorithm to control cycling.

Agreed Ryan, the H/W "tech" is a CSR that answers phones and refers to install manuals for questions asked.

Been there before

Decreasing cycles per hour will definately increase run time, increase time between operation and thus increase temp swings.

Ryan and zl700, I agree that most CSR's refer to the manuals or make up answers and do not have facts to back up their answers. To get the right answers one has to talk to someone like yourselves or the engineer who designed the product.

I am still not clear on the relationship of cph to temp differential. Aren't there conditions of outside temp, insulation, etc. where the differential determines the minimum cph? If the differential is 1 degree and you set the cph to 2, if the temp drops 1 degree in 10 minutes, wouldn't the cph be greater than 2 in order to control the temp drop to 1 degree maximum?

It would seem there is greater flexibility if the differential could be adjusted above 1 degree.

Wallace, the CPH is only applicable to when the thermostat is trying to maintain temperature within 1 degree. I think I see what you're saying, but a properly sized system presumably won't drop 1 degree in 10 minutes. Again, the CPH is an average, so it may not cycle 3 times an hour. I'm not sure if any of Honeywell's upper-end thermostats including the one you have or the TH8000 series have the ability to adjust the differential as their goal is to maintain temperature as accurate as possible (

Cycles per hour (CPH) on digital stats replaced the old heat anticipator which was truly a little resistance heater that was powered when the stat was activated during a call for heat. Without a heat anticipator or a programmable CPH, the stat would ultimately turn on and off continuously because it cant read a differential. This is mainly because if the stat waited till it could actually sense a 1 degree difference, by the time it does the room could be 3-10 degrees warmer before it had reacted. In addition stats when mounted on a wall must average the wall temp with the air temp that reaches it.

Regarding CPH settings, the lowest being for slowest reacting systems such as steam or gravity hot water, to hot water baseboard systems and hi-efficiency systems that are medium to low, on up to electric furnaces that tend to have quick responses and higher temp discharges. Thus the lower the CPH setting, the longer the burner will stay on expecting the heat delivery to take longer. So if a lower number is selected and not appropriate, the heat is delivered quicker and longer resulting in overshoot.
One must find the perfect balance for their comfort, temp differential tolerance and system efficiency.

On many stats including the 8000 series Visionpro, besides CPH settings, there is a selection for "heat & cool temperature control", program # 0680 & 0690 that is designed to offer further temp control to adapt for over and undershoot of set point temps. Most often a reason to use this is if the stat is in a bad location such as near a discharge.

I changed the cph from 5 to 3 and that reduced the cycling initially. However, yesterday I noticed it was cycling same as when set to 5 - on every 10-12 minutes. Unfortunately, it seems Honeywell was right that changing it will not help.

Going to try a Robertshaw 9600 with adj differential.

I have done some recent testing with my Honeywell tstats and the CPH adjustment definately changes the cycle rate, but it takes a while for the settings to reach a steady state. I lowered mine from 3 to 2 and the average number of cycles per hour dropped accrodingly, but it took at least 2 hours to see a rotuine, repeatable cycle per hour rate. When the cycles decreased the ON time for each cycle increased. I also measured the swing in the various room temperatures: they increased from a +/- 0.5 degree swing with CPH=3 to a +/- 1.5 degree swing with CPH=2 which I did not like, so I eventually reset the CPH back to 3.

The techs you talked to at Honeywell must not understand the software running in the tstat. I found a nice description of the Honeywell P+I algorithm way in the back of the Vision PRO documentation - and I believe that same algorithm is used in the other PRO tstats (I have 3210 PRO non programmable digital tstats). If you read the description of this algorithm, you can see that it is a combination of room temperture/set temp differential and long term room temperture trend that the tstat uses to decide when to call for heat and how often. In your case it may be that even with a lower CPH change the tstat will still come on more frequently beacause the differential between room and set to temperature is also a factor. How are you measuring the room temperture?

One thing I noticed is that it takes quite a while for the stat to reach normal operation when you change the settings - and this makes sense after reading the manual on the P+I algorithm. I let it run with the new settings for 12 hours, and took 2 sets of measurements: one set at night and the other in the early morning for 3 hours worth of cycling each. I evaluated both sets of readings, and made one GW post for advise, before making any decisions on re-adjustment of CPH.

The other thing I learned is that the Honeywell "Room Temp" has quite a range on it - something like +/- 2 or 3 deg. So while the tstat was showing a room temp of 65 even when I lowered CPH to 2, the actual temp swing I measured in that room was 64 to 66 which I verified with a standalone thermometer that i placed on a stand right next to the wall tstat. Prior to the CPH chnage, that room alawys stayed in the 64.2 to 65.2 range. This room temp display range is also described in the Vision PRO manual - and with the Vision PRO device you can actually change the tstat so that it displays the actual room tempertaure, which I cannot do that with my tstat. That alone was a good discovery for me.

I don't know how you did your testing. Even with the decision to change to a different tstat, i would still test the Honeywell unit throughly so you have a good baseline from which to compare. Use independent thermometers in a few rooms to measure the temp at the on and off times with the CPH at the recommended manual setting and then again with the change to a lower CPH. Make measurements at night and in the early morning when the outside temps are lowest,and do this for a few hours of cycling. It is a pain to do but the data will be useful when you compare the results with the new tstat.
After chnaging to the new tstat, I would repeat the tests and compare.

There is a lot happening behind the scenes in these digital tstats. You have to get into the details of not only what algorithm the tstat uses for contolling heat ON/OFF, but also what algorithm it uses for displaying the room temp.

best of luck.

Sniffdog, I did not accurately measure the room temp as you did, only observed that the room temp reading on the Honeywell tstat did not change one degree before cycling. A Honeywell tech mentioned that it could cycle with as little as 0.2 deg room temp change. I have two manuals, operator and installation, and there is no mention of the P + I alogorithm.

I have been waiting to reply until the new upstairs furnace and A/C were installed. It was installed a couple of days ago with the Robertshaw 9600 tstat. In the setup, I set the temp differential to 2 degrees and that is the result. It seldom cycles. I know it runs longer between cycles, but I much prefer that to 6-8 times per hour on the downstairs Honeywell unit. Programming is very easy, similar to the Honeywell tstat. The only negative so far is that the display does not light up like the Honeywell. I can live with that.

Thanks to everyone for your input.