by

Upgrading From an Analog Duo-Therm Thermostat to a Programmable Digital Honeywell Thermostat

Today, I finally upgraded from an analog Duo-Therm thermostat to a digital programmable Honeywell thermostat.

This mod has been a LONG time coming! I just couldn’t justify the $50 expenditure when I wasn’t in cold climates for any length of time. But just the last few months here, when it hasn’t even been really cold, I could see that the expense would be worthwhile. One of my pet peeves is to get up into a cold room. Getting up is hard enough as it is, but the added work of shivering means I prefer to stay curled up under my duvet. So I’ve been getting a late start lately.

There have been some articles about this upgrade, but none that were recent and took into account newer digital thermostat models. So I did some research about what to look for in a thermostat and then, gasp, I made the choice on my own. I needed something that would use batteries for power, be as close in options to my existing thermostat, and most importantly, would automatically lower the temperature threshold before bed and increase it in the morning. I settled on the Honeywell Pro 4000 TH4110D1007. It was $65 locally and $40 on Amazon. I ordered my winter boots at the same time, paying all of $13 for shipping and $50 out of pocket, saving about $75 total.

I was going to town this afternoon, so I promptly opened up the box when it arrived this morning to get the size of batteries I would need to operate the thermostat. To my surprise, a pair of AA Duracell batteries were included in the box. Nice touch, Honeywell!

At first glance, the wiring on the Duo-Therm and Honeywell seemed completely different. There were some corresponding letters, but both had letters the other one didn’t. I Googled for a Duo-Therm wiring diagram and couldn’t find anything that was like mine. Apparently, most have multi-coloured wiring, but mine just had red, white, and black, not very helpful.

Having, among other things, upgraded my RV converter, a little thing like a thermostat just wasn’t daunting. So I just read and reread the Honeywell manual until I figured out which wiring diagram corresponded to mine (1H/1C System), and that eliminated all the letters in their diagram that didn’t correspond to the Duo-Therm wiring scheme. As for the Duo-Therm, the one non-corresponding letter had a white wire, which I figured was power and therefore not needed.

I turned off all power to the rig before starting. Then, I disconnected and reconnected one wire at a time, a job that would have been much easier with an extra set of hands and a proper light, but which still only took about five minutes. I did it in this order, basically going counter clockwise around the Duo-Therm: RH to R, RC to RC (don’t lose the little jumper thing!), G to G, W to W, and Y to Y. I taped off the white H wire on the Duo-Therm that I assumed was power.

All that done, I was able to mount the base to the wall and snap on the controller. I turned power back on to the rig, set the thermostat to heat, and the furnace fired right up. Good start! The AC didn’t start, but I think that’s because it was 60F in the rig at the time so there was no point in troubleshooting something that might not need to be troubleshooted.

Within a couple of minutes, I noticed a problem. The fan (on the air conditioner) ran at the same time as the furnace. This was odd as the fan control had the same options (on or auto). I always leave it to on and it never runs, but I couldn’t get it to shut off. It blows cold air, so that was unacceptable! So I pried off the cover and disconnected the G wire that runs the fan. Another thing to troubleshoot at a later date. 🙂

Then, it was time to set the temperature control schedule! This was super easy and intuitive. I started by setting the current time and day and then entered the time and temperature options as prompted. How this thermostat works is on two schedules, Monday to Friday and Saturday and Sunday, where you set a wake up, daytime, evening, and nighttime temperature thresholds.

For both schedules, I said I wanted the furnace to be set at 55 at night, 70 for an hour in the morning, 65 during the day, and 70 in the evening after 6PM. I don’t even know if there is a Celsius option, but the Duo-Therm Celsius increments were so large that I got used to using the Fahrenheit scale.

The furnace has now been running for a bit and I’ve only gained a few degrees even though it is comfortable in here. As expected, the digital model is much more sensitive than was the analog. So I may discover that I can actually keep it at lower temperatures than I did the analog. It’ll take some time to work out the kinks. The big test will be tomorrow morning.

17 thoughts on “Upgrading From an Analog Duo-Therm Thermostat to a Programmable Digital Honeywell Thermostat”

  1. I made the switch last year and threw away the old thermostat – been cussing myself out ever since. I HATE digital stuff! I can see why it would be a good thing if you want to pre-heat your house before you get up. I just throw on a heavy fleece robe and switch on my little portable electric heater while my coffee is brewing. I can never program anything digital, but that is no doubt due to my age and not so great eyesight. Plus they always have way more features than I would ever dream of needing. I hope you love it though.

  2. To me, waking up to a warm house is one luxury that I feel I deserve. I don’t keep the heat on very high during the day (low enough that I have to wear numerous layers), I open windows in the summer before turning on AC, I spend months at a time without running water or being plugged into the grid, etc. So this is one upgrade that I am planning to enjoy fully!

    This one doesn’t have that many features and is super simple to operate. So far so good!

  7. It’s just part of my continuing education, Athena. 🙂 When I looked at doing this mod my last winter in the Okanagan, it was way too daunting to contemplate seriously. Today, the thought that I could have seriously screwed up my heating system when I need it badly only crossed my mind when I was done! 🙂

  8. Having set temperatures for certain hours of the day is great. We had 2 different Digital thermostats in our house and both caused the furnace to malfunction, once on Christmas Eve. Thank goodness we had a fireplace for heat as it was a cold winter that year. The second repair guy told us not to use digital. Our new furnace came with the analog/mercury switch and has been doing great for many years. I think we are the only people to have trouble with digital thermostats, we must be cursed! We do keep it at one temp (65 in winter and 78 in summer)all the time since I read that was more efficient. The theory is you are not heating or cooling everything in the house that has either gotten cold or hot when the heat or AC was lower/higher for hours. I also run a ceramic heater in the “computer room” where I am most of the day
    set at 72.

  11. Caroline, I wonder about that, too, if it’s more efficient to just leave it at one temp 24/7 or not. I have a really hard time sleeping in the winter because the furnace cycling on and off wakes me up. I can’t seem to get used to it. Lowering the temp threshold by 10 degrees means that when I’m running electric heat, unless it’s REALLY cold out, the furnace is unlikely to cycle on and I’m more likely to get some sleep. So that to me is worth a small loss of efficiency.

    Vicki, I got what you meant in the first comment and burst out laughing! MacGyver is my hero!

  12. In my new to me coachman the fan mode needs to be in auto to prevent the air conditioner fan from running. Manual states that the fan in hi or lo setting allows the air conditioner fan to run to help prevent excess humidity in the unit. Give it a try on auto and see what happens.
    Panhandler

    • Panhandler, I tried the new thermostat on both settings and the fan always runs. That’s what it’s supposed to do according to the manual. But that ain’t gonna happen as the fan blowing negates any hot air coming in!

  13. A programmable thermostat works well if you’re on a schedule: get up at six, go to work at seven, come home at six, and so on. I had these thermostats for years when I lived in houses and apartments, and I loved them. But now that I’m retired, I’m no longer on a schedule–my bedtimes and rising times are whatever happens to be convenient and comfortable.

    So rather than swap out my old mechanical thermostat for a programmable one, I made a simpler modification. I connected a second pair of wires to the terminals of the thermostat, and ran them forward, hiding them inside upper-level cabinets, to the head of my bed. There I installed a toggle switch. When I flip the switch, the furnace turns on.

    Being able to turn on the heat whenever I wake, and then lie in bed until the coach is comfortable, is a great luxury… and it doesn’t force me to get up when a program or a timer thinks I should.

  15. Pingback: Programmable Thermostats Work Both Ways | A Life By Design

Comments are closed.