two stats to one unit.

[trintch9]

I am seeking help on adding a second t-stat to a single stage furnace and A/C without adding zone dampers. Its an older system occupants wants the second stat to operate the system from upstairs.

[OldSchoolMech]

Get them a wireless one that they can carry around with them or one that can be operated from a smartphone.

[kdean1]

Connecting two thermostats to the same system will work but it is fraught with problems.

Instead consider something designed for just what you're trying to do. The Honeywell Prestige can be outfitted with the Portable Comfort Control. That is a portable device that communicates with the thermostat and can be set as the active control instead of the thermostat.
http://www.forwardthinking.honeywell...c_feature.html

Or there's the Wireless Focus Pro
http://www.forwardthinking.honeywell.com/products/wireless/focus_pro/focus_pro_feature.html

[gravity]

very simple. add a 6 prong relay in the furnace.

if you live in MD i make relay fail in heat.

y goes to coil and one of the NO contacts
w goes on the NC set of contacts

[kdean1]

very simple. add a 6 prong relay in the furnace.

if you live in MD i make relay fail in heat.

y goes to coil and one of the NO contacts
w goes on the NC set of contacts

I understand the diagram but I don't understand how this applies to two thermostats.

[gravity]

this way they don't fight each other.

EX; 1 is on heat, the other on cool.

preferably i like to use the lower level stat to run heat and the top level to run cool. i dont hook up G to the heating stat.

If you want both stats to run both heat and cool you would need to wire a isolation relay for G so it doesn't back-feed thru the other stat and turn on AC.

Hope this helps.

[kdean1]

I think I see what you're saying. The diagram doesn't show input from both stats. I run into this sort of wiring mish-mash a lot and it takes a long time to decipher what is is supposed to do and determine if it is doing it properly. If a wiring diagram is not provided at the unit the poor guy who services it next will be lost.
I would still choose a Honeywell stat and the PCC as this is precisely what they're made for.

[HVACTECHND]

Ive done them the way Gravity is speaking off it will work, but leave a wiring diagram for the next pour soul!http://www.grainger.com/Grainger/RIB...ed-Relay-5LE35

[mgenius33]

Isn't the Y connection to the contacts redundant if you're not connecting G?

[pacnw]

use the Prestige with the portable remote, it will be easier in the log run.

I have it, use it and enjoy it.

[BaldLoonie]

The Honeywell remote makes the most sense. Or buy a cheap zone panel, skip the dampers.