Best practices for thermostat settings

Alex146

I live with several roommates in a 2 story house in Texas. Our electric central heat system has two thermostats and allows for separately heating the downstairs vs. upstairs. Recently we've been debating the most cost effective methods to heat the 2nd floor to 63 degrees. The temperature downstairs is considered unimportant except in terms of how it relates to the total cost of heating the upstairs as well as the stress on the heating unit.



One group contends that it makes more sense to set the downstairs thermostat to 63 degrees and let rising heat warm the upstairs. The primary reasons given are that heat produced from the upstairs vents will escape more quickly, and with closed bedroom doors, heated air will be less likely to reach a thermostat in the upstairs adjoining hallway.



The opposing argument is that using the downstairs vents to heat the upstairs will use more electricity than setting the upstairs thermostat to 63 degrees, simply because much more of the house is being warmed. The contention is that although running the upstairs heat may warm the bedrooms faster than the hallway, the air being blown out of the vents must result in air being pushed through the vents and gaps at the bottom of the doors, and thus it is a mistake to think that doors are preventing heat from reaching the thermostat. Also, since the heater doesn't run as hot when it runs for short periods of time to maintain a steady temperature, the temperature in the rooms tends to equalize with the hallway as the fan blows air out of the rooms.



And so the question in a nutshell is, does it make sense to use the downstairs thermostat to heat the upstairs, or should that primarily be the job of the upstairs unit?

Zman

What type of heat

It sounds like you have a forced air heat pump?

Are the ducts in an uninsulated attic?

Alex146

heat pump with ducts in attic

Yes, it's a forced air heat pump. The attic is insulated, though it certainly gets cooler than the house. I should probably add that the heater is turned off completely at night, so the attic temperature typically gets some help from sunlight during heating hours. Thanks for your reply.

Gordy

Speaking of two resolutions

Running both thermostats in conjunction will be less stress to the heating unit. Forcing the downstairs thermostat to heat the whole house is only making the heat source run longer.



A btu is a btu so I really don't see a matter of cost savings being more by only using one thermostat regardless of upper or lower floor saving money on the electric bill.



Shutting the heat off at night is only increasing the load in the morning, and decreasing comfort.



Setback only saves money if you are gone for extended periods....days weeks not hours. Or when the dwelling is so poorly insulated it cools rapidly.



Remember when a house cools so does any objects with mass that retain heat also. The furnace may get the air temp up to set point, but objects that have cooled during setback will lag in their recovery causing air temps to cool more rapidly making the furnace cycle more until an equilibrium is reached. We call this MRT (mean radiant temperature) this term is what defines comfort.



Your best bet is to maintain a set temperature, and let it ride.



If you think about it if the downstairs contributes to heating the upstairs depending on how open the floor plan is the upstairs thermostat will be satisfied causing the upstairs zone to turn off anyway.



If you are looking to save money, and sacrifice comfort turn the thermostats down to 60, and grab a blanket or a sweater, and live with it.

Zman

Agreed

What Gordy says is especially true of heat pumps. They are very inefficient when overworked. I would go with a lower fixed setting.