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How to Upgrade to a Smart Thermostat without Changing the Wiring | Ask This Old House

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By Quentin Peters
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Ask This Old House plumbing and heating expert Richard Trethewey replaces an old thermostat with a smart thermostat without replacing the original two wires in the wall.

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Time: 2-3 hours
Cost: $300
Skill Level: Difficult

Tools List for Upgrading a Smart Thermostat:
Drill driver [https://amzn.to/2RNofUq]
Small flathead screwdriver [https://amzn.to/36N95Cy]

Shopping List:
Smart thermostat [https://amzn.to/2tcUF0S]
Thermostat wire [https://amzn.to/31kxP4g]

Steps:
1. Start by turning off the service switch at the furnace.
2. Remove the old thermostat.
a. Pull off the front cover.
b. Unscrew the screws inside.
c. Disconnect the wires.
d. Pull off the back cover.
3. Mount the hub in a convenient location near the furnace using a drill and a few screws.
4. Disconnect the wiring from the thermostat to the furnace and run that wiring to the hub. There’s an obvious place on the hub to screw the wires in properly.
5. Run the thermostat wire from the furnace to the hub. The red wire goes to R, the white wire goes to W, and the blue wire (common wire) goes to C.
6. Mount the new thermostat back cover at the location of the old one. This might require drilling for new screws.
7. Using the old two wires, wire the new thermostat and connect it to the back cover.
8. Turn the service switch back on at the furnace.
9. Download the smart app and program it to the thermostat following the manufacturer’s instructions.

Resources:
Richard installed the InvitaTM Wifi Thermostat 564, which is manufactured by Tekmar Controls (http://www.tekmarcontrols.com/).

About Ask This Old House TV:
From the makers of This Old House, America’s first and most trusted home improvement show,Ask This Old Houseanswersthe steady stream of home improvement questions askedby viewersacross the United States.Covering topicsfrom landscaping toelectrical to HVAC and plumbingto painting and more.Ask This Old House features the expertsfrom This Old House, includinggeneral contractor Tom Silva, plumbing and heating expert Richard Trethewey, landscape contractor Jenn Nawada, master carpenter Norm Abram,and host Kevin O’Connor. Ask This Old House helps you protect and preserve your greatest investment—your home.

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Watch the full episode:
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How to Upgrade to a Smart Thermostat without Changing the Wiring | Ask This Old House
https://www.youtube.com/user/thisoldhouse/

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7-10 minutesAsk This Old HouseAsk This Old House plumbingdiyDIY Ideasheatinghome improvementHow To BuildHow To FixHow To InstallHow to Upgradeold thermostatplumbingrenovationRenovation IdeasRichard tretheway ideasRichard Tretheweyrichard trethewey this old housesmart technologysmart thermostatsmart thermostat comparisonsmart thermostat installationsmart thermostat reviewSmart thermostat without wiresthermostatThis Old House

About The Author

Quentin Peters

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Comment (0)

  7. I'm not sure what planet Richard is living on but there are a lot of Wi-Fi thermostats that don't need a common wire "C". You may need to replace the double A batteries once a year but that is about it.

  12. Everything has to be connected to the internet. Ask yourself why do they need to have these things connected, vehicles, appliances? At what pointed they decide they can do it better than you?

  13. He could have still used his two wire heat only setup and just changed his thermostat. I use a programable wifi connected Nest thermostat with just the two wire (red and white), gets the battery charging power from the 24vac on the red wire, works fine.

  18. I'd invest in changing the wires over, with newer heating technology the more wires allows for better fine tuning of the heating appliance. Most modern gas furnaces have 2 stage heating. Increased comfort and energy savings. Also allows some future proofing, if you want hybrid heating (oil or gas + heat pump) you'd need 8 wires.

  20. I have a Honeywell T5 thermostat and when it cycles on to begin heating, the power gets cut off to the thermostat; the screen goes blank for about 20 seconds until it reboots. I've checked all of my wiring but still can't figure out what is happening…any ideas?

  23. what the heck, he has a nest and now instead using a tekmar?
    what is this garbage lol

    I was hoping to see the end result with actually using the nest

  28. Avoid Wyze thermostat . i bought two. i got sucked in by my cheap Filipino neighbour. these thermostats are pure junk. fk me they got me good for $120us plus i had to pay another $40us shipping to ship from my usa Blaine Washington mailbox to Vancouver Canada. total ive lost almost $247Cad in the exchange rate. the only a 30 day warranty.

    these wyze are famous with cheap filipinos .

    Not buying that junk no more.

    stick with Nest 3rd generation and TP-Link for your wifi seitches and plugs. avoidvtheir cheap cameras and by a Amcrest, Foscam or better Hikvision . stay away from Dollarama & Dollar General chinese quality knockoff Wyze.

    anyone giving this garbage good review and promoting it , is getting this free.

  34. As far as remote sensors go, many houses have wiring for land-line phones to multiple rooms. I have not used my land lines for several years now, since every family member has a cell of their own. The existing lines could be Isolated from the telephone network and repurposed to connect remote sensors to the central interface. Locations may not be ideal but…

  40. The old thermostat uses a bimetallic temperature sensor, and the switch is still mercury filled for make and break of the circuit. The comment was that some thermostats use mercury. Line voltage thermostats do not always use mercury bulbs in older thermostats. Low voltage thermostats for many years almost always had mercury.switches.

  43. This isn’t accurate at all. I have a 1919 Bungalow and have a two wire system for my gas boiler. I have a 2nd Gen Nest thermostat and it works perfectly with my system with no addition items added. Had it now for about 4 years with no issues. Great smart thermostat!

  44. "Now you can add air conditioning, ventilation, humidity in the future" I could have run 8 conductor wire but I'm only running 6 (ok, he didn't say that)

  46. So those 2 existing wires are now purely for digital communication between the hub (near the furnace downstairs) and the new thermostat box (upstairs)? For future if we need to add cooling systems, fan wire, etc. that would be the wiring between the hub and the furnace only? I assume this is the exclusive product features for this "tekmar"?

  49. "Usually when you think of smart thermostats, you're thinking of this really sleek looking Nest"
    "Ok, great"
    "But instead we're going to install this chunky, ugly, way less user friendly one"
    "Oh"

  52. Everyone doesn't have old wiring and thermostats. For those people the thermostat companies should make it easier on people. They should make wall plates that will work with a variety of front plates

  53. I just tried to get a smart thermostat and I only got 4 wire no C wire
    So said can’t have the WiFi thermostat
    Hvac guy said u can but it will cost $1000 plus

  60. Why would you install it on the peg board instead of a more permanent location like one of those studs? You also take up space on the peg board.
    Also, too much installation was stripped off. You can easily short the wires.

  61. I have 5 wires one wire is not connected. I can put the wire to c at the thermostat. My computer board only has three slots never could find where to connect it at the furnace.

  65. This solution is about as costly as having a professional run new wiring, in my area the estimates were $350 and up.

    So I went to Home Depot and bought 50 feet of 18/5 thermostat wire for $21 and fished it through the wall myself by tying it to the existing 2 wire (R and W) that the old thermostat used. I've never done it but with a little patience it's not difficult. Every connection is labelled on both the furnace and the thermostat (I need C, R and W and didn't have a C at all). You just plug the wires accordingly. Now I have both a sleek new Honeywell smart-thermostat and future proof wiring to the furnace without all the extra or a giant bill for an HVAC guy.

  67. Where to put the base station…. Definitely not on the furnace, how about on a joist… Not there either. Oh I got it right in the middle of the pegboard where you put your tools. I also took the liberty of stripping the crap out of the screws so you can't move it after I leave.

  69. Big issue is new stats maintain within.5 degrees, which leads to constant on and off. Too much cycling! Why can’t manufacturers use heat anticipators like the old Honeywell types. I did just that and now have a 2 degree swing which has reduced my cycling in half. I’m talking Michigan weather too! I don’t notice the swing at all!!

  71. Hired a professional plumber to install, after about 2 hours said this was not compatible with my Independence boiler. But hey, I got two free holes in my wall for my trouble.

  75. Why would you put that module so high that you have to work above your head trying to keep it out of the reach of kids just saying love your channel

  77. I learned more in the comments than I did in the video. There are so many variables in this kind of installation, I quess that this shows us a basic install. Probably the biggest issue is whether you and your wife like the same temperature not so much if you can use your phone to set the stat!

  82. there's really no reason you can't have sensors that plug into an outlet and transmit back to the base station at say, 700Mhz… when its only grabbing and sending temperature and relative humidity, it doesn't need to be that complicated…. Give it another decade, and we'll have better temperature control. until then, this is a great upgrade path when you can't just pull a new line.

  83. A good practice is to snip the bare wire shorter so there's non visible once connected to the faceplate. There looked to be at least 5-10mm bare wire shown at 5.58 and these could easily connect and cause a short or even a fire when pushing the housing back into position. This is why the wire has the plastic insulation in the first place.

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