Programmable Thermostats

Reviews of digital programmable thermostats

Swing Control Explained

Swing control is a very important function for a programmable thermostat. Swing control is adjustable on all good programmable thermostats. Usually you can alter swing control in 0.25 degree Fahrenheit increments.

The purpose of swing control is to set up a range around the set point temperature and within this range the thermostat DOES NOT activate the heating or cooling. So for example, if the set point temperature is 78 degrees and the swing control is set to 1 degree then the thermostat won’t cycle the cooling until the room temperature rises past 79 degrees and it won’t cycle the heating until the temperature in the room falls below 77 degrees. Of course, in most cases you will only use either heating or cooling not both. So for the example above if the temperature reaches 79 degrees it is more likely that the HVAC won’t cycle and instead the cold weather outside will naturally cause the temperature to drop to the desired 78 degrees.

On  first consideration swing control might not seem important. After all, you want a house that stays at a constant temperature not one with a fluctuating temperature. However, in reality it is bad for your HVAC equipment to try and keep an exact temperature because it means a lot of short cycling. Short cycling is when the heating or cooling comes on for a few minutes. If a heater or cooler goes on and off many times in an hour the equipment can wear out quickly and lead to expensive parts replacements. This is particularly true of furnaces.

Another factor is noise. It can be very irritating to hear the HVAC constantly clicking on and off. It is much more energy efficient to let the temperature rise and fall a degree or two and then run the heating/cooling for a longer time. This is what swing control does.

All Lux Products thermostats come with swing control as does the Hunter 44550 Auto Save. What is a mystery to those looking at thermostats is why there is no swing control on Honeywell thermostats. It is not a simple oversight on Honeywell’s part. Honeywell is one of the earliest makers of control technology for the home and they have deliberately done away with the idea of swing control.

Honeywell’s Alternative to Swing Control

Honeywell instead of letting you input a number to represent the parameters of the swing control give you the option on their thermostats of letting you set the number of cycles per hour for your HVAC equipment. In the Honeywell instruction manuals you will find the relevant information in the part entitled “Configuration Menu”.

How does this different system work?

When the heater is bringing up the room temperature to your programmed set point temperature the heating cycles per hour function is alerted when the set point is nearly reached. Say it you set the temperature at 70° an anticipator circuit cuts off the heat at a predetermined point say 69° to stop the heating overshooting the mark. The idea is that the residual heat will raise the room temperature to the desired 70°.

The problem comes if your room is poorly insulated or a window is open or your furnace is too small. It might be for one of these reasons that the residual heat in the room doesn’t nudge the room temperature up to 70°.

What happens now? This is where Honeywell’s alternative to swing control comes into play. If you have set your cycles per hour for the heater to 3 then the heater cycles 3 times in an hour. Each cycle is 10 minutes long or until the room reaches 69° and again the anticipator will cut the heat. If after 10 minutes the temperature is still not 70° the heater will start up again.

This system works fine if your house is well insulated or the outdoor temperature is mild. The problem is if the weather is really hot or cold or your house fails to adequately keep its warmth or protect you from the heat. It can be that at 69° the heating keeps cutting out and that 70° is never reached leading to many cycles per hour of the heater.

This issue of Honeywell thermostats and their absence of swing control is sometimes mentioned in reviews by people who have bought a Honeywell thermostat. Some reviews report very poor performance and complain of constant short cycling and others report that their Honeywell programmable thermostat manages to keep the room temperature at the same point with only a couple of cycles per hour.

One thing to remember about setting the cycles per hour program on your Honeywell thermostat is that different types of heating and cooling require different cycle rates to be effective. Hot water that sends hot water to radiators requires longer cycles because it takes time for the heat from radiators to raise the room temperature. It is very energy inefficient to have hot water only cycle for a short time. The best setting for hot water is 3 cycles per hour.

In contrast a wall heater is much faster in raising room temperature. They only need a short burn to reach our hypothetical 69° at which point there should be enough residual heat to make 70°.  The best setting for electric heat is 9 (9 cycles of 6.7 minutes per hour).

Summary

To sum up: Honeywell thermostats don’t allow you to set up a swing control range around your set point temperature. Instead you have to input a number to indicate how many and how long the heater or cooler should cycle to maintain the set point temperature. This number depends on the type of HVAC system you use. Hot water needs less cycles per hour (3) and electric heaters need more cycles per hour (9). This system seems to work best in houses  that have good insulation and in areas where the weather is temperate. It is not advisable to use a Honeywell thermostat in the tropics or in Alaska.

Sat, February 26 2011 » Functions, Honeywell, Hunter, Lux Products

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