Nest thermostat: Fixed .7 deg temp swing (heating) uses more energy (gas & elec), excess HVAC wear

[ReedMikel]

Just “upgraded” from a Filtrete CT50 tstat to a Nest.  One shortcoming of the Nest is that the user cannot set their preference for the “temperature swing” (aka maintenance band).  Being fixed at .7 degrees in heat mode results in far more and frequent heating cycles.  Our Filtrete could be set anywhere from 1 to 2 degrees.  I had ours set to 1.5 degrees F.  The Nest tstat, being fixed at .7 degrees, means my system runs much less efficiently!  I have a propane furnace, so when a short heating cycle runs (e.g. 10 mins) - the first 2 minutes or so are just to heat up the furnace, after which blower will come on and blow out heat.  Compare that to longer heating cycles, where temp swing is say 1.5 degrees: in this case maybe the heating cycle lasts 20 mins.  Again, the first 2 minutes of cycle get the furnace up to temp, the remaining 18 minutes produce/blow heat.  It is more efficient to have fewer, and longer, heating cycles as opposed to many short cycles (no choice with Nest).  The extra cycles not only use more fuel (propane), they also use more electricity and wear the HVAC components faster (e.g. blower motor cycling on/off more frequently).

Granted, some folks might prefer less temperature swing in their homes -  but we’ve been happy with a 1.5 degree swing for many years.  But this important “temperature swing” setting really should be a CHOICE that users make, rather than have an arbitrary value forced upon them.

I was going to replace all 5 thermostats (2 homes) with Nest thermostats, BUT will go with another brand that allows configuring of the temperature swing setting…

[CoolingWizard]

The efficiency of your HVAC system has absolutely nothing to do with the so called temperature swing you speak of. The efficiency has to do with the compressor, refrigerant, the outdoor coil, the indoor coil, the total static pressure of your supply and return duct, to but some of the factors. What you are describing is the point at which the thermostat makes a call for heat or cooling.  So if you set the temperature desired to say 78°F, at 78.7°F the Nest Thermostat would call for cooling.  Or at 77.3°F the Nest Thermostat would call for heat depending on which mode the system is set on. 

If you set the anticipator to 2 or 3 degrees,  all that you are doing is allowing more heat or cold to infiltrate the living space.  Your system just has to work longer to remove the extra heat or cold in the house.  I hope this helps to clarify your misunderstanding of HVAC system efficiency.  

The AC Cooling Wizard

[ReedMikel]

I disagree with you.  Running shorter, more frequent cycles because the temp swing setting is so low (.7) actually is less efficient compared to a higher swing temp setting.  Why?  Because the lower swing scenario will result in more startup cycles (the first 2 mins or so where furnace is heating up, waiting to turn on blower motor).  Every time there’s a heating cycle, that startup period contributes nothing towards heating your house - and uses fuel (propane in my case) and electricity.  The more frequent cycles will not just consume more fuel and electricity, but will also wear out your HVAC components faster (e.g. starting up the draft inducer fan and blower motors).

Swing temperature can also affect one’s comfort, but everybody is different - so Nest choosing a fixed .7 degree setting is a poor design choice IMO…

To be clear, I am not saying that a higher swing temperature affects the technical “efficiency“ rating of one’s furnace - that’s a fixed value.  BUT the operational efficiency is affected.  This inefficiency was crystal clear when I looked at the history/graph display of the Nest…