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Tuesday, October 14, 2014

Programmable Thermostat: How to Install a Replacement Thermostat and Save Money

Replace Your Thermostat and Save Money

Save Money with a Programmable Thermostat
Image Source: Dr. Penny Pincher

Heating season just started here in Iowa, and last week I noticed a problem in the middle of the night.  I was hot, and the furnace was running.  The problem was that this meant I was wasting money.  Why was the furnace running when I was hot?  Why was it so warm in the middle of the night?

The problem was the old thermostat.  It was still working fine, but it was primitive by today's standards.  The old thermostat only had one temperature setting.  The reason it was hot at night, is because we turned it to 70 to warm up the house and forgot to turn it down for the night.  Sometimes we left for the day and forgot to turn it down then too.


Old Lennox Thermostat
Image Source: Dr. Penny Pincher
Another problem with the old thermostat was that the temperature control was not very precise.  It had a sliding lever to set the temperature, and it was hard to make small adjustments.  Also, the old analog temperature sensor did not seem to be very precise.  This all adds up to wasted energy and wasted money.  I decided to look at a replacement thermostat options.

Programmable Thermostats

Modern thermostats are programmable and allow you to program different temperatures for different times of day.  For example, you can program a temperature you want the house when you wake up, and another temperature when you are gone for the day, another temperature when you get home, and another for after you are asleep in bed.  You can let the thermostat program run and it automatically adjusts the temperature for you.  You can override the program at any time if you want to adjust the temperature.

7-day Programmable Thermostat
Image Source: Dr. Penny Pincher

You can get thermostats that are 1-day, 5-2 day, 5-1-1 day, and 7-day programmable.  A 1-day programmable thermostat has a single program that it follows every day.  A 5-2 day programmable thermostat gives you a program for Monday-Friday, plus a program for Saturday and Sunday.  A 5-1-1 day programmable thermostat allows you to set a program for Monday-Friday, Saturday, and Sunday separately.  A 7-day programmable thermostat is the most flexible and allows you to set a different temperature program for every day of the week.

At our house, the schedule varies quite a bit, so I was interested in a 7-day programmable thermostat.  I wanted something that could automatically turn the temperature down at night and while everyone is out during the day.  With the old thermostat, it was too easy to forget to turn the temperature down.

Do You Need a Wi-Fi Thermostat?

 I looked at Nest and some other expensive thermostats that allow you to control your heating and cooling system using a cell phone through your home's wireless network.  This seemed like more than I needed, and thermostats with wi-fi capability cost $200 or more.  It may be handy sometimes to adjust the temperature while you are away from home, but I think a good 7-day programmable thermostat would cover almost everything I want to do.

I found some good programmable thermostats in the $80 price range from Honeywell and White-Rodgers.  The Honeywell model I selected is a 7-day programmable thermostat with a full touchscreen.  There are no buttons or levers on the thermostat at all.  It has an easy menu system to program it, and a nice backlight when you touch it.


How To Install A Programmable Thermostat

Finding and buying a replacement thermostat was the easy part.  Next, I had to install the thermostat.  The first step was to carefully remove the old thermostat.  I say carefully for several reasons.  First, the old thermostat was really old and brittle.  I wanted to remove it carefully in case I needed to put it back- for example if the replacement thermostat turned out not to be compatible with the furnace and central air.  Second, the old thermostat contains a mercury switch.  It has a drop of mercury inside- kind of fun to look at, but I wouldn't want the capsule to break and spill the mercury.  Mercury is a toxic substance and can cause neurological damage.

My old Lennox thermostat had 3 layers:
  1. A cover with plastic windows to see the temperature setting
  2. A layer with the mercury switch and a thermometer coil with bi-metalic strips.  The movement of the coil causes the mercury switch to tip and makes or breaks the circuit to turn the furnace off or on.
  3. The layer with a circuit card and wire connections to the furnace
Outer Cover of Old Thermostat
Image Source: Dr. Penny Pincher

Thermometer Coil and Mercury Switch in Old Thermostat
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Circuit Card and Wire Connections in Old Thermostat
Image Source: Dr. Penny Pincher


I turned off the power to my furnace using the circuit breaker before working on the thermostat.  I turned the fan on so I could make sure I turned off the right breaker to the furnace.  When the fan turned off, I knew I had the right one.  Some furnaces have a light switch on the side that can be used to turn off power instead of the circuit breaker.

Turn Off Power to Your Furnace Before Replacing the Thermostat
Image Source: Dr. Penny Pincher

Now it was time to remove the old thermostat.  I had to carefully remove the first two layers to reveal the bottom layer which was attached to the wall with screws to mount it to a metal junction box.  The pictures above show the layers that I had in my old thermostat.  I separated the first two layers by snapping them apart carefully.  Since the mercury switch contains mercury, I'll need to find a place to safely dispose of it.  I don't want to let mercury get into the water supply.

With the circuit card exposed, I could find the wires to connect the furnace to the new thermostat.  Before removing any wires from the old thermostat, label the wires carefully.  My Honeywell replacement thermostat included stickers to label the wires.  The circuit card in the old thermostat had each of the 4 wires labeled: RC, Y, W, G.  I removed the screws holding the wires down and applied the labels.  I also took pictures before disconnecting anything.

Next, I removed the last layer of the old thermostat from the wall.  My unit had two screws holding it on the wall.  I straightened out the wires so I could easily remove the last part of the old thermostat.

Now it was time to install the new thermostat.  The directions were pretty clear.  The most important thing is to carefully label the wires and attach them to the proper place on the new thermostat.  The wires are connected using a terminal block with screws to connect the wires and hold them in place.  You'll need a small screwdriver to tighten these down.

Honeywell Programmable Thermostat Wire Connection and Mounting Plate
Image Source: Dr. Penny Pincher

Depending on how your old thermostat was mounted, you may need to install a couple drywall anchors to mount the new thermostat to the wall.  In my case, I got lucky.  The hole spacing worked fine to attach the new thermostat to the existing junction box.  That was easy!

After connecting the wires to the new thermostat, and double-checking that the wires are connected to the right spots, you get to install the front of the thermostat on the mounting plate.  Install the batteries, and then snap the front onto the mounting plate.

Honeywell Thermostat, Battery Installation
Image Source: Dr. Penny Pincher


This Thermostat Has a Nice Touchscreen with Backlight
Image Source: Dr. Penny Pincher

Here's more info about my programmable thermostat:
Honeywell RTH7600D Touchscreen 7-Day Programmable Thermostat

Saving Money with a Programmable Thermostat

This unit worked right out of the box.  The touchscreen and menus are easy to use.  I adjusted the pre-programmed temperature settings a bit by lowering the warmest temperature from 70 down to 68.  I am starting with 62 at night and during weekdays when everyone is usually away from home.  I am sure we will make further adjustments to the temperature and also the time of day when the temperature program adjusts the temperature.  I think this thermostat will pay for itself within a few months, and it keeps the indoor temperature more comfortable.  Replacing your thermostat a good project to consider if you have an older thermostat.


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