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  • Tech Discussion Installing an Internet connected thermostat
    The old, standard thermostats commonly installed on central heating systems in homes operated on just two wires.

    [Image: 2iRIE.gif]

    The first generation of "smart" thermostats that allowed for setback programming and temperature scheduling required batteries installed in them to power the electronics.
    But Wi-Fi enabled thermostats draw too much current to allow them to be powered from batteries.
    They need to connect to the 24V AC power available from the central heating system transformer.
    That requires a third wire, the transformer "C" (common) wire as shown below.

    [Image: Htu7d.gif]

    In addition, if the thermostat is used to control central air conditioning as well, then a fourth wire is required for the cooling relay.
    Controlling the fan in a forced air system separately (it will come on automatically when heating or cooling is called for) requires a fifth wire.
    There is no standard color code for these wires, but the list below is quite typical.

    R - Red - 24V AC transformer hot lead
    G - Green - Fan relay
    W - White - Heating relay
    Y - Yellow - Cooling relay
    C - Black or Blue - 24V AC transformer common lead

    The letter designations are the standard ones used on thermostats in North America.
    Some thermostats have multiple R terminals. They may have separate ones for heating and cooling. These are typically just jumpered together on the thermostat.
    That will work as long as the heating and cooling system relays connect to the same 24V AC transformer, which they generally do.
    If they do not, connecting together the common side of their respective 24V AC transformers in the furnace room will solve the problem.

    Before you consider installing a modern Internet thermostat, you must first address the wiring issue.
    If all you have is an old style two wire thermostat loop between the thermostat on the living room wall and your central heating system, then you will need to fish in a new replacement cable inside the wall.
    It should have a minimum of five color coded conductors.
    All the Internet connected thermostats with Wi-Fi radios in them will require the "C" wire connection, since they use the 24V AC furnace transformer as their power supply.

    I purchased a Honeywell RTH8580WF thermostat last year.
    It has a touch screen and it connects to the Internet via 802.11n Wi-Fi.
    It cost me $150.

    [Image: sY1gWTT.jpg]

    I picked that particular thermostat for several reasons:

    1. It is remote controllable and programmable via an Android or iPhone app.
    2. It is remote controllable and programmable via a web page.
    3. It is less expensive than the Nest thermostat or any of the other Internet thermostats with color LCD screens.
    4. It control the temperature more accurately than the Nest thermostat does.

    Review: --> http://thermostat-reviews.com/wifi-therm...uchscreen/

    The Nest thermostat, designed by former Apple employees, and now in its second generation, has become very popular.
    The Nest sells for $250.

    [Image: Screen-Shot-2012-12-08-at-3.02.40-PM.png]

    Review: --> http://www.wired.com/geekmom/2012/12/nes...at-review/

    Here is a review comparing the two: Honeywell WiFi thermostat Vs. Nest - a notable review

    There are other high end Internet connected thermostats available besides these two, typically with color LCD screens, but they are even more expensive.
    Most homeowners who are going to install a smart thermostat these days that they can control and program from their smart phone or tablet will likely pick either the Honeywell or the Nest.
    Both of them will automatically update their installed firmware over the net when the manufacturers have new versions of the code available.

    Note that while the two picture above show the temperature in Fahrenheit (72F = 22C = room temperature), both thermostat models can easily be configured to display degrees Celsius instead.
    (This post was last modified: 01-14-2014, 08:21 PM by velvetfog.)

    Never underestimate the power of human stupidity.
    - Robert A. Heinlein
    The latest networked thermostat is Honeywell's new Lyric Smart Thermostat.
    It comes with a smartphone app that accesses the phone's GPS radio, so that the app knows when you are approaching your home,
    and is able to take the temperature up before you get there.

    [Image: BN-DD930_LYRICT_G_20140609212916.jpg]

    Honeywell Lyric Smart Thermostat Knows When You’re Coming Home

    Smart Thermostats: Honeywell Takes On Google’s Nest
    (This post was last modified: 06-13-2014, 06:49 PM by velvetfog.)

    Never underestimate the power of human stupidity.
    - Robert A. Heinlein

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