Two-Stage Heat Pump
What is a two-stage heat pump?
A two-stage heat pump, also called a dual-stage heat pump, utilizes a two-stage compressor. It has 2 levels of intensity – high (100%) and low (typically 70%). The heat pump will cycle on and off at low speed — first stage — for the majority of the year, until it gets really cold or hot out and needs to jump to high speed — second stage — to keep up. The heat pump will automatically jump between stages in response to the temperature that you set on the thermostat.
How efficient are two-stage heat pumps?
Two-stage heat pumps are highly efficient: they consume less electricity at lower speeds and run for longer periods of time. Long run times circulate air throughout the home, eliminating the likelihood of hot and cold or humid and dry spots.
Once your home has reached your desired temperature, the system will switch to the first stage and continue to run. This fluctuation allows your home to efficiently maintain a steady, even temperature and humidity level.
SEER Ratings
All central ACs were required to have a minimum SEER rating of 10 in 1992 and by 2006 that minimum was raised to 13. In certain regions of the country, like the south and southwest, that minimum standard is raised even farther to 14.
In 2023, regulations will require a minimum SEER of 14 for the northern U.S. and 15 for the southern U.S.
Year North South & SW 1992 10 10 2006 13 13 2015 13 14 2023 14 15
SEER ratings are compiled using standard formulas to help you determine how much you can expect to pay annually in energy costs. This lets you compare air conditioning units and pick the one that best suits your needs.
"Aux Ht" and "Em Ht"
Aux Ht or Auxiliary heat is the backup heat that turns on to help the compressor for first stage maintain your temperature setting. You know if the auxiliary heat is running when you see "Aux Heat On" in the thermostat's display. During this time both your Auxiliary heat and your compressor may be on at the same time. The thermostat will only run the Emergency Heat when the thermostat’s system switch is moved to the Em Ht position. When the thermostat is in this position the compressor does not run, only the Emergency heat runs. It is common that the Emergency heat and auxiliary or backup heat is the same source of heat (electric heat strips or fossil fuel).
How to Install a Rheem and Ruud Thermostat
Using a voltmeter, check there is no power still flowing to the thermostat. Your wires should have been labelled according to their position in the old thermostat. Color can also help signify the correct placement of wires.
The return wire is usually red and labelled R, VR-R, or V-VR. This connects to the R terminal on your Rheem and Ruud thermostat. The stage one heating and cooling wire is typically yellow and labelled Y, Y1, or M. This connects to the Y terminal. The reversing valve wire for cooling is typically orange (but is occasionally blue) and labelled O or R. This connects to the O terminal. Your thermostat may also have the reversing valve wire for heating, labelled B, which should be connected to the B terminal. If you don't have this wire, cap the terminal with a wire nut. The fan control relay wire is typically green and labelled F or G, and should be connected to the G terminal.
There are also second stage hearing a cooling circuit wires which need connecting. The cooling circuit wires are typically blue and labelled Y2. The hearing wires are usually pink and labelled W1, W2, or W-U. These must be connected to their terminals.
Next, you'll need to connect the LED system monitor wire, which is usually labelled X and can be blue, brown, tan, or gray. This wire needs to connect to the L terminal. Then, connect the emergency heating wire, which is almost always labelled E and can be blue, pink, gray or tan.
Finally, connect the 24-volt transformer wire, which will be labelled C, X, or B, to the terminal labelled C. This wire may be blue, brown or black.
You can now install your new Rheem and Ruud thermostat cover and turn on the power to test your thermostat. If it does not work, disconnect the power and repeat the steps above, checking each wire and each terminal.