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Old 12-29-2013, 01:44 PM   #1
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Controlling separate heat and AC devices from a single thermostat


I have hydronic radiator heat powered by a gas furnace situated in one mechanical room of my house and a currently being installed central AC whose air handler is situated in another mechanical room (separate locations).

I would like to control both of these units from a single thermostat with separate thermostat wires going from the thermostat to each respective unit.

1. Is this possible? Do I need a special thermostat or can any modern thermostat support this split functionality?

2. Product recommendations?

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Old 12-29-2013, 01:59 PM   #2
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Controlling separate heat and AC devices from a single thermostat


Any thermostat that has RH and a RC terminal can do this.

Personally, I would use a thermostat that has an EIM, and just have one set of wires running to the thermostat, and have the equipment wires all going to the same mech room.

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Old 12-29-2013, 02:14 PM   #3
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Controlling separate heat and AC devices from a single thermostat


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Originally Posted by beenthere View Post
Any thermostat that has RH and a RC terminal can do this.

Personally, I would use a thermostat that has an EIM, and just have one set of wires running to the thermostat, and have the equipment wires all going to the same mech room.
what are RH, RC, and EIM? can you provide any product recommendations?
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Old 12-29-2013, 02:18 PM   #4
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Controlling separate heat and AC devices from a single thermostat


OK, I get that EIM is "Equipment Interface Module". But what does it give me? There isn't a Wikipedia page
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Old 12-29-2013, 02:26 PM   #5
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Controlling separate heat and AC devices from a single thermostat


RH, Red Heat. RC, Red Cool.

IAQ, YTH9421.
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Old 12-29-2013, 02:29 PM   #6
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Controlling separate heat and AC devices from a single thermostat


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OK, I get that EIM is "Equipment Interface Module". But what does it give me? There isn't a Wikipedia page
The module is mounted at either the boiler or A/C. Which means you don't have to pull another set of wires to the thermostat. Because the EIM to thermostat connection only needs, 2, 3 or 4 wires depending on which brand thermostat your using.

Not having to fish wires to the thermostat is a time saver. Plus, no clicking upstairs from the thermostat.
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Old 12-29-2013, 03:10 PM   #7
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Controlling separate heat and AC devices from a single thermostat


Flip side is it is expensive and one more expensive thing to go wrong eventually. Any modern tstat that has a separate RC and RH can do your job. Personally I would install a separate tstat on a easy wall to get to. Out of drafts and sunlight and it is OK. You may get some dumb tech later who cannot understand what you did and screw it up with the combined system. You may not be home when that happens and your family has to deal with it or him. Separate tstat eliminates that problem.
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Old 12-29-2013, 03:18 PM   #8
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Controlling separate heat and AC devices from a single thermostat


I don't have to do any fishing (framing open). Is there still any advantage to the EIM?
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Old 12-29-2013, 03:29 PM   #9
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Controlling separate heat and AC devices from a single thermostat


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I don't have to do any fishing (framing open). Is there still any advantage to the EIM?
Silence. No clicking from the thermostat. All the little clicking relays are on the EIM.

A 5 wire thermostat bundle between the EIM and stat gives you etra wires if any of them are damaged down the road. So less chance of ever having to pull a new wire.

If you decide later that you want an outdoor temp sensor for some reason(decide to get a heat pump), don't have to pull another wire up the wall.

The IAQ(YTH9421) has been out for 7 years now, and has proven very reliable. Has a 5 year warranty on it.

It is not however, "dumb tech" proof. Not much really is though.
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Old 12-29-2013, 03:40 PM   #10
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Controlling separate heat and AC devices from a single thermostat


I couldn't tell if this is RH/RC separate (not marked on the box). Does anybody know?

Controlling separate heat and AC devices from a single thermostat-forumrunner_20131229_164005.jpg
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Old 12-29-2013, 03:42 PM   #11
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Controlling separate heat and AC devices from a single thermostat


It does.
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Old 12-29-2013, 09:10 PM   #12
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Controlling separate heat and AC devices from a single thermostat


Can one of you guys explain how the RH and RC terminals work?
Does this just allow you to put different 24vac supplies on the stat? One 24vac from the heating system and a seperate 24vac from the cooling side?

I'd just use a standard stat and use it to pull in separate relays, one for the heat and another for the cooling. That's if I ran out of programmable controllers.
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Old 12-30-2013, 09:58 AM   #13
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Controlling separate heat and AC devices from a single thermostat


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Can one of you guys explain how the RH and RC terminals work?
Does this just allow you to put different 24vac supplies on the stat? One 24vac from the heating system and a seperate 24vac from the cooling side?YES

I'd just use a standard stat and use it to pull in separate relays, one for the heat and another for the cooling. That's if I ran out of programmable controllers.
Not a good idea as any relay that goes between the tstat and furnace board can stick ON and then the heat runs wild/never shuts off. seen that happen a few times
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Old 12-30-2013, 03:00 PM   #14
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Controlling separate heat and AC devices from a single thermostat


Quote:
Originally Posted by 52Caddy View Post
Can one of you guys explain how the RH and RC terminals work?
Does this just allow you to put different 24vac supplies on the stat? One 24vac from the heating system and a seperate 24vac from the cooling side?

I'd just use a standard stat and use it to pull in separate relays, one for the heat and another for the cooling. That's if I ran out of programmable controllers.
RC during a cooling call is what energizes Y and G.

RH during a heating call is what energizes W.

No relays needed.
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Old 12-30-2013, 03:15 PM   #15
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Controlling separate heat and AC devices from a single thermostat


apparently, Nest thermostats are the sh*t: https://nest.com/thermostat/life-with-nest-thermostat/

a bit pricey but i think i will invest. i want to be able to use my smart phone to turn the system on 30 min before i get home to arrive to a comfortable house.

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