So a few weeks back, we decided to try a small project which could both keep us more comfortable and save us some $$ on our electric bill: Adding a digital thermostat.
After talking to some folks at Lowes and calling Honeywell directly, we decided on the Honeywell RTH7500. This timer is a slight bit of overkill, but it was recommended for our system, which is an AC and a heat pump. It has 7 separate days of programming available, so you are able to have different settings for the times of day and days of the week, which I’ll explain a bit later.
All we needed for this was a philips head screw driver, a small flat head and possibly a phone, to call Honeywell 
Turn off the breaker to the AC/Heat before beginning
After cutting the power, we had to take off the old system. Our old thermostat was likely from when the house was built, 1995 and was made by DelAir.. and ancient by the picture below. We had to remove by prying off the old faceplate and then unhooking the wires. When doing this, Honeywell includes small stickers which have letters on them that should correspond to where the cables are plugging in on the old system. Just stick these onto the wires prior to removing the old thermostat from the wall. Removing it from the wall is mainly a few screws but being careful of the mercury in the old thermostat (if that’s how old it is!). Keep in mind, that has to be recycled properly.
Once this is off, you need to place the new backplate on the wall, then snake all the cables through the middle, trying not to lose the stickers to avoid confusion later. Once the cables are through you start securing cables as shown below to the corresponding letter on the sticker and the wire terminals. Make sure to use the letters on the outside part of the faceplate if you have a heat pump and the inside letters if you have a conventional system, but regardless, the cables are inserted from the inside portion of the terminals and tighten with the small screwdriver.
All of my cables were very plug and play, except I had a couple cables which were labeled “W2″ and “W3″ which did not have homes. I read through the instructions many times, but could not find where to put these. I ended up calling Honeywell at 1-877-271-8620, but their website also has plenty of valuable information.
Once they informed me where to put these cables, they also confirmed the programming instructions to use when it comes online.
I put the faceplate on the unit, turned the power to the unit back on and put in the programming instructions and I was almost in business, just need to program it.
The instructions for setting the time/date and simply setting setting the temperature was quite easy. When actually programming it though, I had to realize that you can hit the “schedule” button and then select multiple days of the week to make them the same (like weekdays), or just schedule one day at a time, which is tedious. On each section, you need to set the “Wake” setting time and temperature for cooling or heating and then do the same for Leaving the house, coming home and going to sleep. Once these are set, it will work as expected and heat or cool as needed! Its also very easy to set it temporarily cooler or hotter by clicking the button up and down and then an option appears on the screen to have it “Hold” and it stays that way until you have it use the schedule again.
Hopefully this leads to less forgetting to set the AC up when we leave work and a more accurate temperature reading and lower electric bills!
