I have two of the above thermostats controlling two furnaces zoned to the main and second story of my home. The furnaces are 20 years old 80% *** (singles stage) units (Lennox).
I've noticed over the years the furnaces seemed to short cycle and run frequently. I finally decided to do something about it and set up a monitoring system to track the furnaces for a few days. I found that the main floor furnace was running for less that 5 minutes 55% of the time and the second floor was running 24% of the time less than 5 minutes. My thinking was the heat exchanger is just getting warmed up and its being shut off only to turn on again in 10 or so minutes.
So I explored the CPH setting in the secret parameters mode of the thermostat and found parameter 240 set to 5 meaning the furnace should attempt to cycle 5 times per hour with an 80% furnace. So I changed the setting to "3" which is recommended for two stage and more efficient furnaces. I reran the data collection for a couple days. Here are the results:
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So I am thinking the run algorithms in the Honeywell thermostats are flawed. While seeking to achieve a tight temperature control and trend to the set CPH level they don;t account for short cycling and the inefficiency that creates. The algorithms (in my opinion) should have some notion of shortest heat cycle time and whenever there is a heat call they run at least that long. Sure you'll get some temperature overshoot but the cumulative wear and tear on a furnace caused by the current algorithms and the related fuel inefficiency is a bigger problem in my mind.
Anyway despite the users manual saying otherwise I recommend anyone using these thermostats on a single stage gas furnace to set parameter 240 to "3" and not the "5" Honeywell recommends. That's my 2 cents on the subject.
I've noticed over the years the furnaces seemed to short cycle and run frequently. I finally decided to do something about it and set up a monitoring system to track the furnaces for a few days. I found that the main floor furnace was running for less that 5 minutes 55% of the time and the second floor was running 24% of the time less than 5 minutes. My thinking was the heat exchanger is just getting warmed up and its being shut off only to turn on again in 10 or so minutes.
So I explored the CPH setting in the secret parameters mode of the thermostat and found parameter 240 set to 5 meaning the furnace should attempt to cycle 5 times per hour with an 80% furnace. So I changed the setting to "3" which is recommended for two stage and more efficient furnaces. I reran the data collection for a couple days. Here are the results:
So I am thinking the run algorithms in the Honeywell thermostats are flawed. While seeking to achieve a tight temperature control and trend to the set CPH level they don;t account for short cycling and the inefficiency that creates. The algorithms (in my opinion) should have some notion of shortest heat cycle time and whenever there is a heat call they run at least that long. Sure you'll get some temperature overshoot but the cumulative wear and tear on a furnace caused by the current algorithms and the related fuel inefficiency is a bigger problem in my mind.
Anyway despite the users manual saying otherwise I recommend anyone using these thermostats on a single stage gas furnace to set parameter 240 to "3" and not the "5" Honeywell recommends. That's my 2 cents on the subject.
