Thermostats With Adjustable Cycle Rate Differential

By | January 17, 2020

Thermostats With Adjustable Cycle Rate Differential

Thermostats with adjustable cycle rates are something any home owner can install to lower power cost and help an HVAC system last longer.

What is a Adjustable Cycle Rate Differential Thermostat?
All thermostats have a set temperature that will turn on and off a heating and cooling system.

The temperature difference that a thermostat turns on and off a HVAC unit is called Differential.

For example, a thermostat with a +-1 degree differential that is set at 70 degrees will turn an air conditioner on at 71 degrees and off at 69 degrees.

It is also sometimes referred to as the cycle rate since it is the cycle that a unit such as an air conditioner turns off and on.

When HVAC units are turned on and off constantly it takes a toll on the equipment leading to parts wearing out and needing to be replaced.

A unit that cycles often can also lead to larger electric bills.
 
Why is there Higher Electricity Cost?
When an air conditioner first turns on is when it has the biggest power consumption.

This is mainly due to the compressor which needs a large draw of power to start running.

After a compressor has been running for a few minutes the power draw drops.

This is the reason that short cycles can run up a power bill.
 




 
Wear on Equipment
When an HVAC unit first powers on is the hardest time on parts.

A units that cycles frequently causes wear and tear on parts which leads to a shorter life span.

For example, an air conditioner must pump refrigerant through a cooling system which takes more work at the start then it does after it has been running.
 
How to Get a HVAC Unit to Have Longer Cycles
Using a differential thermostat that has an adjustable cycle rate is a quick and easy way to solve this problem.

Your current thermostat may be capable of changing the cycle rate which can be seen in its manual.
 
Buying a Differential Thermostat
Most thermostats have a built in differential of +-1 degree, while others will have a +-3 degree differential.

For example, a thermostat with a +-1 degree differential that is set at 70 degrees will turn an air conditioner on at 71 degrees and off at 69 degrees.

With a +-3 degree differential it would turn on at 72 degrees and off at 67 degrees.

Most thermostats are rated for +-1 degree differential.

Thermostats that have “Adjustable Temperature Differential” or “Adjustable Cycles” in their product description will usually have a +-3 degree differential.

*This post contains affiliate links.
Adjustable Cycle Rate Differential Thermostats

 


 




 

25 thoughts on “Thermostats With Adjustable Cycle Rate Differential

  1. Jenifer Kennedy

    I had a new 14 seer Maytag HVAC system installed in February of 2020. I live in mooresville NC & it gets quite humid here. The temp inside is set to 75 degrees in the summer. The installer set the differential to 1/2 a degree. This unit runs for 45 minutes, turns off for 5 minutes the back on again. We are being told by the installer that this is normal running time for these new energy efficient units. I’m worried my power bill is gonna be $300-400 because it runs for 50 minutes of every hour. Is this normal? We have a 3 ton unit for a 2300 sq ft house.

    Reply
    1. David Midlick

      A 3 ton unit is not enough for a home your size. 400 – 450 square feet per ton is max. A5 ton unit would be pushing the limit unless your home was supper efficient.

      Reply
  2. gabriel

    I just had to jump in on this, the 1 degree differential is in reference to the set point, as in +/- 1 degree from the set point. In your example of the water vat set to 33 degrees the unit turned on at 34 degrees (+1) from set point and turned off at 32 degrees (-1) from set point, which I would call “operation swing” and not differential.

    Reply
  3. Billly Searle

    So, how do we remove or turn-off the 1 degree differential to keep the temp at what i set, not something different from what i set?

    Reply
  4. bill ghera

    we just had a new carrier performance series furnace 70 thousand btu installed in our townhome . The thermostat that the installer provided is a honeywell T6pro programmable thermostat. The problem is that the furnace cycles on for 5 minutes and off for 15 minutes day and nite. the furnace is rated at about the same as the unit we replaced.
    The installer turned off the program which supposedly senses the room temperature change before it actually goes down. This didn’t help. Still goes on an off every 5/15minutes. The thermostat has a built in swing cycle of -1/+1. He says this cannot be changed. He is going to find a thermostat that has the ability to set the cycle to a wider range ie
    -3/+3 . Any suggestions as to what would be a sutable replacement to use. Our old thermostat (12yrs old) would be set at 70 degrees and fire u[p when temp dropped to 69 and run til it reached 71. Any help would be appreciated

    Reply
    1. Steven Jeannides

      press and hold the menu button on the thermostat down for five seconds or until it takes you to the programming menu. The screen will say “device setup.” Hit select then use the right arrow on the touch screen and press until you see “auto differential.” Press edit, then put the auto differential at “00.” Then click “done” to save your changes and then click back 2 times (I believe) to get out of programming.
      Hope this helps

      Reply
      1. Charles Miller

        Is this a tip for a Honeywell Thermostat? And if yes, what does it make the differential?

        Reply
    2. Ann Ho

      Robertshaw RS 5110(5+2 days Pro) , Robertshaw RS 6110 (7 days Pro), Robertshaw RS 4110( None Pro). All of them 1H/1C. Differential 1 to3 F.

      Reply
  5. Doug Kon

    I leave in Winston Salem NC – often very humid in the summer. My home is often at 52% RH and I use a dehumidifier in the basement to keep it below 50%RH.
    Will the Fast cycle be better at lowering the RH than the other Cycles?
    I own a new Sensi WIFI thermostat UP500.

    Reply
    1. Jeremy Livingston

      No the faster cycle will not allow enough air to be dehumidified during the process. So longer cycles will greatly accomplish more work than shorter cycles

      Reply
  6. Ali

    Does anyone know whether this model supports Adjustable Cycle Rate Differential (+/- 2 Fahrenheit)?
    Emerson Sensi Wi-Fi Thermostat for Smart Home, ST55

    Could you please update your list for supported devices?
    It seems the list is from 2015.

    Reply
    1. Gretchen

      Ali, I have the Emerson Sensi WiFi thermostat & yes, it offers both A/C and Heat cycle adjustments. You can program them easily and separately to your preference (a/c and furnace). The cycle rate, on the app is under settings, system settings, underneath the humidity & temperature offsets. I absolutely love this feature and am thankful my cheap Honeywell thermostat (extremely basic & somewhat outdated model) that came with my hvac broke! Fast will turn it on and off w/in 1 degree, medium 2 degrees (my preference) and slow 3 degrees. It is definitely personal preference, although where I live the fast cycle kept my A/C turning on and off, on and off with little delay between, to be expected w/ 1degree differential.

      Reply
      1. Leona Malo

        Actually, the Sensi WiFi unit doesn’t have a 3 degree differential. I contacted Sensi to understand why the Slow/Medium/Fast cycles are all basically the same and they explained that the Slow cycle is only a 0.95. So, it’s just barely below a +1 differential. It’s the biggest fault with the otherwise wonderful Sensi, as I have to manually change the range each time. I’ve run spreadsheets on actual energy usage and the manual range changes are far more cost-effective than the tiny built-in cycles. The Ecobee Smart will likely replace my Sensi, as the Ecobee allows for a +3 differential, which is huge in super-hot desert heat. Maybe other people want their air conditioners to run 4-8 times an hour, but thanks to my manual changes, my A/C averages just 1-2 CPH (cycles per hour), which is a tremendous cost saver and I’m still comfortable.

        Reply
  7. Troy Hupp

    The difference is a 1-3 degree offset of the desired temperature. If the differential is set at +/- 1 degree, and the temperature is set at 70 degrees. The thermostat will wait 1 degree over the desired temperature (70) before turning on. Then once the desired temperature is reached(70), it will wait an additional degree(69) before shutting the unit off. This way the unit isn’t constantly turning on and off due to temperature changes in the home.

    Reply
  8. midimagic

    On a mechanical thermostat, the anticipator setting adjusts the hysteresis.

    Reply
  9. mean chicken

    Controlling thermal hysteresis is the correct approach. It seems obvious many control systems engineers (Presumably those who design thermostats?) are confused by the most basic of subjects.

    Reply
  10. ALVIS JENKINS

    The differential explanation does not make sense. What is a differential of 1 degree if a unit is set at 70 and comes on at 71 but turns off at 69, as that is a difference of 2 degrees?

    Suppose I had a vat of a water solution that I wanted to maintain 1 degree above freezing. My setting would be 33 degrees for the desired setting. Now, I would like for the cooling unit to come on with a 1 degree differential. It would come on at a 1 degree change at 34 degrees, correct? Now, I ask, why would the unit turn off at 32 degrees which would be making the solution freezing? To me, that is a 2 degree change since the unit came on at 34 and then cycled off at 32.
    What is confusing me here when we speak of a 1 degree differential?

    Reply
    1. RPRPRPRPRP

      You’re kidding right? Ok, the unit is set at 70, turns on at 71 and goes off at 69. That’s a 1 degree differential from the 70 degree setting. The overwhelming majority of thermostats have this type of differential setting (some have up to 3 degrees).

      Reply
      1. Rebecca Davis

        But which is the most energy efficient? 1 degree or 2-3 degree differential? It seems with only 1 degree it will cycle more often than 2-3 degree, but in the Deep South where, like today, it is 90 degrees outside with feel-like temp of 104 Because if high humidity. Wouldn’t the unit stay on for hours at a time With 2 degree diff? Thanks for your help

        Reply
        1. Leona Malo

          A +1 degree differential doesn’t do much, it’s basically fast-cycling your A/C. You want to have a range, so the +3 differential is best. I have to manually set mine as the Sensi’s pre-set cycles have tiny differentials. For example, we had 112 degree temps with dew points of 72 degrees just a week ago. If I had kept the Sensi stat at the Slow cycle (which has the widest differential at 0.95), my A/C would have been cycling on and off constantly. By using a manual range, my A/C only ran 1-2 cycles per hour.

          Reply
          1. Cathie Baith

            I just installed a Sensi. How did you manually change the cycle rate? Not finding a way to do that.

    2. Robbie Morgan

      WELL DAM, ITS AMSZING HOW SOMEONE CAN MAKE THE EASIEST THING HARD

      Reply

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