A Guide to Thermostats


Thermostats are finely tuned sensing devices. It doesn’t matter if you’re using a smart thermostat or a thermostat from the 1950s, it still has to convert a physical measurement, temperature, into an electrical control signal. Mercury switches, coiled springs, and bimetallic switches are all viable methods of measuring the current temperature. As a room warms or cools, these metals expand and contract, respectively. When you set a thermostat, you’re physically placing the point at which an expanding strip of metal will make contact with that switch closing a circuit and sending an “ON” signal to your central unit.

On the other hand, electrical thermostats work differently. They include a suite of electrical sensors which generate or dampen electrical signals based on weather conditions. A microcomputer interprets the signals from the sensors and then sends a control signal to the unit for finer control based on current time, temperature, and humidity for more accurate climate control.

Type of Climate Control System

Thermostats are designed to operate different kinds of heating and cooling units.  While there are many different styles, types, and makes of HVACs and furnaces, they can be broken up into three simple categories:

  1. Single-Stage
  2. Multi-Stage
  3. Heat Pumps

The differences here are in how the systems operate.


A single-stage unit needs what is roughly an “ON/OFF” signal, while multi-stage systems have a more relative switch.  The difference is in the design. Single-stage heating and cooling units have only two states, on and off.  When active, they run at full intensity.  This is why setting your thermostat past where you want to the actual temperature will not actually heat or cool your home any faster.


Multi-stage units improve on energy efficiency because of their operating cycles.  Initial startup, heavy fuel burns, and high RPMs on fan motors all use a large amount of energy for operation.  Multi-stage systems reduce this cost by using finer controls. Emergency heating and full power cooling are only triggered at large differences in temperature adjustment (the first time you turn the heat on for example).  Balances to keep temperature regulated are made with longer run-times at lower intensities.  This improves efficiency but requires a thermostat capable of sending more than just a simple “turn on” signal.

Heat Pumps

Then, of course, there are reversible heat pumps.  These double-duty heating and cooling units come in variants of single-stage and multi-stage systems.  If you’re using a heat pump for heating and cooling your home, make sure that you have a thermostat designed to work with the system.  Features such as emergency heating won’t work properly otherwise.

Service Legends Heating and Cooling has a team of experts who know everything there is to know about heating, which means we’re the best experts for heating and cooling.

Thank you for making Service Legends the #1 provider of residential heating and air conditioning in the Des Moines area. A live and friendly customer care representative is ready to take your call 24/7 at 515-COMFORT (515.266.3678).

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