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How do I replace a Tekmar TN4 thermostat with Ecobee3


I have a Tekmar 422, 440 and two 355 setup controlling about 10 zones in our house all with communication TN4 thermostats. I'd like to replace one of the TN4 thermostats with an Ecobee3 for a variety of reasons, but I think I was told years ago that only TN4 thermostats will work with this setup for some reason (the right wires exist, with the extra communicating wire I'd just not connect to the Ecobee).

Is there any way basically to replace the some or all of the thermostats in this type of setup and if so do I need any more equipment or potentially to rewire some things.

Thank for any help - happy to provide more information if I've left something out.


  • EastmanEastman Posts: 927Member
    What are the variety of reasons?
  • BumblezillaBumblezilla Posts: 4Member
    We had an AC unit installed in our attic for the summer months that requires a new thermostat, so going to get the ecobee for that one anyways. I also want to explore the homekit integration with this thermostat and how it does controlling the radiant zone in that same room as compared to the tekmar (plus a few other reasons around user interface etc etc etc).
  • IronmanIronman Posts: 5,091Member
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • BumblezillaBumblezilla Posts: 4Member
    I'd have to get some Tekmar gateways and other home integration stuff however to match the homekit setup that we already have.

    Anyway to get the ecobee to work with the tekmar though?
  • EastmanEastman Posts: 927Member
    edited January 2017
    When thermostats like the ecobee and nest are marketed as being "smart", it's in the sense that they have a great user interface that ties into other consumer computing platforms like iOS and the internet in general. That's nice, but the value of those capabilities are often greatly exagerated.

    For example, all of that extra fluff doesn't actually translate into a more sophisticated interface with heating equipment. From the boilers perspective, these devices are still only dumb thermostats that provide simple on/off control.

    However, unlike common thermstats, the Tekmar system that you have provides additional information over it's tN4 network that solves a variety of system level heat management problems.
    The 422 universal reset module uses the tN4 thermostats to collect indoor temperature readings and occupant temperature set points. This indoor feedback is used in conjunction with the current outdoor temperature to adjust boiler water target temperatures and cycle lengths. Most people would consider this additional level of control as being rather unique in North America. (In Europe, there is an indoor feedback standard called "OpenTherm" that is gaining ground rapidly.)

    The Tekmar system also provides for zone start synchronization. Zoned systems allow for increased occupant control over local areas of the heating system, and that's great, but zoning also has a downside. Dividing up the heating system into separate areas that individually call for heat can wreak havoc on boilers. Zoning can cause many additional short boiler heating cycles that are inefficient and lead to premature equipment failure. Zoned systems should really have some form of management to coordinate the heating calls. With a Tekmar system, each zone synchronizes its call for heat with each other. (They synchronize the start of each heating cycle but vary the end.) In this way, unnecessary boiler cycles are mininmized.

    Even if it were possible, there is nothing that you could replace your current tN4 thermostat with that could provide better control. If you need additional features to support an AC system, or you would like additional radiant control accesories, there are other tN4 thermostat models that posses the necessary capabilities.

    If a problem exists with the radiant system for the zones in question, there may be a configuration issue --please describe your concerns.

    If you still want a "smart" thermostat for the AC, just use it for only the AC.

  • BumblezillaBumblezilla Posts: 4Member
    Thank you for the information about the sophistication of the system. I think it truly is amazing all the optimization that occurs. Unfortunately Tekmar does not produce a thermostat that provides the remote capabilities within the HomeKit framework or the API programming interfaces that I plan to take advantage of (my shift work makes changing thermostat schedules tedious).

    I've looked into the 483, and 482 gateways, but they aren't what I am looking for. I'm also not looking to replace all the thermostats on the system, so I suspect I'll still be able to maintain some of the internal temperature feedback and optimizations you mentioned.

    With that in mind, I get the impression from your post that there is no easy way to make this work with my existing equipment - is that accurate?

    Thanks again for the insight!
  • Jamie HallJamie Hall Posts: 10,548Member


    With that in mind, I get the impression from your post that there is no easy way to make this work with my existing equipment - is that accurate?...

    Close enough. Keep in mind that "smart" thermostats -- Nest, Ecobee, etc. -- are, from the standpoint of the heating system, really stupid. From the standpoint of IoT, they're pretty classy. But they are still, from the standpoint of heat, either on or off. Unlike the very sophisticated controls like your Tekmar.


    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • IronmanIronman Posts: 5,091Member
    You'll save more energy, and have a longer lasting boiler by using the Tekmar, than you will by trying to monkey with a wifi stat. Hydronic heat is not designed for setback. You're not saving anything unless the setback period is for days, not hours.

    I've used Tekmar for years and one thing that I can assure you of is that you and I are not more energy savvy than they are.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
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