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Can I have two thermostats connected to the same zone on my Taco Controller? I have two Taco Controllers with a total of 9 Hot Water zones. One of my Hot Water zones is for the Entrance Hall, Living Room and Dining Room. The thermostat is in the dining room and set to 70 during the day and I’m trying to establish a minimum temperature for the Entrance Hall area.

On cold day’s the entrance hall will be 10-12 degrees colder than the Living and Dining Room. I wanted to know if I could add a second thermostat that is wired directly to same Taco zone. I would set this second Thermostat to call for heat and stop calling for heat a a temperature below 70 degrees. For example, the Entrance Hall Thermostat might call for heat at 64 Degrees and stopped calling for heat at 68 degrees. The Dining Room Thermostat would call for heat when the dining room was below 70 degrees.

I do realize that when either thermostat is calling for heat, all areas in that zone would be heated.

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  • What's your plan to keep the entrance hall thermostat setting from getting messed with? – ThreePhaseEel Dec 9 '20 at 0:42
  • Not knowing anything about your setup, but is there a way to throttle back the heating in the dining room? Some circ pumps have speed settings. What you are suggesting could seriously over-heat the dining room. EDIT: your system is not balanced. Is it hydronic under the floor? Radiators? Baseboard? Your best bet is to try to balance the system so that all zones are heated evenly. – George Anderson Dec 9 '20 at 2:35
  • You usually can put 2 controller inputs in parallel to open the valve on the zone you have that is cool. I have not worked with a taco. With hydronic systems in some cases we have to sacrifice to get what we want as the systems are fixed once bedded in the slab or a mortar bed I have put in extra zones and still run into this, always something you missed unless repeating a previously used plan and even then minor changes can affect the heat in different zones. So I would add an additional stat and see if that works. – Ed Beal Dec 9 '20 at 3:59
  • @EdBeal Ed: I almost always agree with you and learn from you, but in this case, I have to say I think the OP should try balancing his system better if possible. Almost always hydronic in-floor systems have manifolds with adjustment valves for each loop. If the OP has this, it should be possible to restrict the flow in the living, dining rooms and provide more flow to the entry. I'm just concerned that the living/dining room would over-heat if the entry tstat kept calling for heat. – George Anderson Dec 9 '20 at 14:45
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    I won't comment again, so as not be belabor the point, but this is a classic XY question. The OP proposes a solution and asks how to do it, rather than ask about the original problem. The question should have been: "My entryway is usually 10-12 degrees colder than my living/dining rooms. They are all on one hydronic zone. What's the best way to address this?" Anyway, I'll shut up about it now, but I still think trying to balance the system is best. Take care and stay safe. – George Anderson Dec 9 '20 at 17:41
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As others have commented: The answer is yes. The area will be heated until both thermostats turn off, and one area might be overheated.

A cleaner way to do this would be to buy a digital thermostat with a remote sensor (e.g. an ecobee) and have a schedule that either switches the driving input between the base and the remote sensor or averages them. You can use heat correction factors to instruct the thermostat to do something like '70 in the living room or 65 in the entryway'.

Longer term, a fan, an extra zone, an extra space heater or a new loop may be necessary to get a more balanced temperature.

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