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Tekmar TN4 Questions

Given the following scenario:

Tekmar 274

(2) oil-fired boilers stage/rotate

(2) zones of cast-iron radiators

(2) zones of low-mass radiant (heat transfer plates under wood subfloor)

Indirect DHW using the tekmar sensor

Each zone has a separate circulator.  The two radiant zones operate at different temperatures, and are mixed by a tekmar 3-way mixing valves (manual, no motors).

Each zone has a switching relay (old honeywell 89A equivalent).  A call from a thermostat closes the relay.  The relay then applies power to the boiler demand terminals on the 274.

The idea was to let the zones fly on the ODR.  However, radiant has a different reset curve than the CI rads.  Not the end of the world.

I was curious if adding 541 thermostats (or another TN4 thermostat) for the radiant zones would be advantageous?

If I am understanding correctly, I could set the 274 to use the CI reset curve.  When the CI zones call for heat, the boiler demand terminals are closed and the CI reset curve is used.

If the radiant zones call for heat, the TN4 thermostat would communicate over the TN4 bus and the low-mass radiant reset curve would be used.

Am I understanding correctly?  Any suggestions?


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,132

    I don't think you have it correctly.  the 274 only does one temp on reset.  I think, but I need a few minutes to look it up, you need to add a mixing control, like the 360, and switch to a motorized mixing valve, to get a different temp, that uses the odr, for your radiant (assuming both radiant zones need the same temperature, then you would need 2, or a zone manager).

    I also dont think you'll benefit by changing to a tekmar communicating thermostat, because it's only communicating with your honeywell relays, not the tekmar.  You would have to make all controls tekmar (zone control modules) to get the full benefit of communicating thermostats.

    Hopefully Rob NRT, will pick up on the post and give you a more definate answer.
  • Tim P._3
    Tim P._3 Member Posts: 50
    Thanks Steve

    The whole TN4 thing has me confused.

    The 274 has a TN4 bus you can connect thermostats to.

    As you stated, the 541 would activate the relay (terms 3&5 of the stat).  No mixing.

    The manual says the 541 allows you to select the "Heat 1 Terminal":

    This thermostat supports Outdoor Reset characterized

    heating curves when used in hydronic heating systems. By

    setting the correct terminal unit setting, the thermostat can

    improve the operation of the heating system. Each stage

    of heat has its own terminal unit setting.

    I am thinking that the stat communicates with the 274 over TN4 to read the outdoor temp and set the curve appropriately for the type of "terminal unit".

    Beyond that, without motorized mixers, it would fly on the ODR.  It would not be adjusting the mix temp, but I think it would be using a different boiler max/min/design setting., allowing the temp to fall below 140 degrees if it is radiant calling for heat (whereas if a radiant zone calls for heat now the boiler will maintain a min of 140 and a target of 160)

    Mix temp would be indirectly effected by the reduced boiler temps.  Of course, on a call for heat in a CI zone, the mix temp would rise.

    It's not a perfect solution, but wondering if the stats are a worthwhile investment that leave the door open to go to a full motorized mixing solution... or is it an all-or-nothing proposition.

    Thanks again!
  • Zman
    Zman Member Posts: 7,447

    I think a quick call to Tekmar would clear this up.

    Basically the tekmar thermostats need to tie into a tekmar zone manager. The zone manager would then connect to the bus on your controller. TN4 is capable of doing what you want, you have to buy a whole bunch of hardware to make it happen.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Tim P._3
    Tim P._3 Member Posts: 50
    Thanks zman

    Yeah I need to make the call.  Just like to get some real-world answers, but I guess this is kind of a strange application.

    Trying to avoid the "whole lot of other equipment"!

    I thought one of the Tekmar reps frequented this forum.. but I guess that's going back a few years.  Best to place the call.
  • The Wire Nut
    The Wire Nut Member Posts: 416
    tN4 and you...

    The 274 will regulate a zones water temperature based on feedback from a tn4 t-stat. It does that by regulating the time that the particular zone is "on". The 274 provides the highest water temperature required by all of the thermostats. The t-stats will fire your pumps using the existing relays.

    On the radiant floor zones it might also pay to put floor sensors on those t-stats. especially since they are wood floors. The 541 will allow you to have one external sensor...

    I think it would work for you. Just remember, there are A LOT of settings that interact on most tekmar systems. Understand what they do and you'll be on top of the game...

    Hope that helps...

    Alex (The Wire Nut)
    "Let me control you"

    Lost in SOHO NYC and Balmy Whites Valley PA
  • Tim P._3
    Tim P._3 Member Posts: 50
    Thanks stonehouse

    Thanks for the info.  Armed with these responses I think I can communicate intelligently with Tekmar on the phone.

    I did see that slab sensor option, I think you are right about it being a good option.

    I'll report back after I speak with Tekmar.
This discussion has been closed.