How does cycle per hour setting work on programmable thermostat

Joe_134

How does cph work. I understand 6 cph is a 10 min.cycle (5 min on-5 min off = 10 min.).When does the cph come into play? I read from honeywell it at 50% of load.Does it work in setback mode? If programmable thermostats work off of temperture your furnace might not need to run 5 min on and then 5 min off. Is a book out that explains the process in detail?

David Nadle

It's max cph

The thermostat CPH is a maximum. 6 CPH means the thermostat will call for heat not more than 6 times per hour. But once it does, it will continue to call until the room temperature meets the setpoint. It's not going to shut the furnace off after 5 minutes if it's still too cold.

Joe_134

Ok, I think i understand but why have it? If it still going to call for heat after it past its max cycle what the need for it?

k

Cycling is designed to match different types of systems. For example an electric hot air system heats the space very quickly so to keep temperature constant you cycle it on and off frequently. If, however, you have a conventional cast iron boiler you'll want to set the cycles to the lowest setting. With cast iron you want really long cycles so the system can work at it's most efficient level.

While it may seem illogical that a thermostat would call for heat when it needs none you need to realize that with each passing second you lose heat. The cycling is designed to best match your heat output with the heat loss you experience to create an efficient heating system.

rich on heat

Joe, some systems can cycle faster than others. Hot air gets made quickly and transfers its heat to the room quickly. Steam takes a while to make, then it heats cast iron radiators that stay warm a long time. The natural cycle is longer. So if you've just had a steam cycle and the thermostat is satisfied, you wouldn't want to start another one within the hour. But if you've just exchanged cooler air for warm air and satisfied the thermostat, no matter how long that cycle took, you might need to do another one in ten minutes. Or maybe not. The CPH setting isn't going to turn your heat on if the room temp is over the set point.

Digital thermostats are sensitive to half a degree. If you didn't have a CPH limit normal room fluctuations could have the thing turning on and off every miunte. There's no limit to how long the on cycle will be, that's determined by how long it takes to reach the setpoint. On the coldest day of the year it might be on all day and night. CPH limits how frequently a new cycle can begin.

Does that make it clearer?