boltonblue

During the nearby lightning strike the other night I lost a thermostat that apparently got zapped.
Being an early adopter kind-a-guy I decided to use this as an opportunity to upgrade and go smart home.
yup got me one of them newfangled wifi based thermostats.

As a was mounting the baseplate I noticed little "Caution, C terminal must be attached" label.... uh-oh

Yup see your old standard thermostat was really nothing more than a switch.
They put power in that would complete the circuit to close the relay turning on heat/AC etc.
It wouldn't take much current to close the relay and when closed, oops there goes your power.

fast forward to devices that are "smart".

They have little computers in them and even though they very efficient, they still need steady state power.
Now the programmable units would have batteries you changed out every 6 months or so.
When you add WIFI however, batteries can't cut it anymore, they just won't last long enough.
So basically the C lead is the separate power return for the computer instead of the relays.
The only problem is the older "just a switch" thermostats didn't need no stinking power return and one isn't wired in normally.
This means you've got to find the ground side of the 28V transformer and run a new wire.
I'm lucky I have extra wires i just need to find out which side is which.
Preferably without zapping my derriere into next week somewhere.

Oh and did I mention that this little transformer is in the air handler that is up in the attic.
of course it's only about 120°F up there and i only have about 4 feet of head room from the floor.


Ain't this cutting edge tech grand????

stay tuned.... I may just default back to the old battery programmable unit.

paS2K

smarthouse stuff may be best for new "smart" construction IMHO

NNY S2k

^^^
Levi

Chuck S

I put in a Honeywell "super-smart" thermostat back in January or February to keep track of the interior temperatures of the beach house we bought over the winter. Wifi and I can check/change almost everything from my iPhone or PC. Honeywell "Total Connect." 'Course you need a wifi setup in the house to use the remote function. But neither my wife nor daughter have been known to stray beyond a wifi connection anywhere in the past 5 years...

The "C" wire is necessary on mine but (as noted) was in place in the old installation or there are usually extra wires anyway do the C-wire can be easily connected at both ends.

-- Chuck

cosmomiller

If you are cold, the smart thing to do is throw a log on the fire.
Too warm? Back up or open the window.

boltonblue

Goods news, extra wires to be able to add "C" wire.
Bad news, I have 10 wires at one end, and 6 at the other.
So somewhere along the line somebody probably moved the thermostat and added a length of wire.
of course they didn't connect all of the leads.

back to the store it went. and got the older style programmable.

Chuck S

Tracing the wires is easy and I recall the Honeywell only used 4, maybe 5 wires. No more than 6. They're marked or connected to marked terminals in your old unit. I've not replaced the 25 year old battery-powered Honeywell in the main house only because I don't feel like repainting the wall where the giant unit used to sit.

-- Chuck