Hot Topics: Picking the Right Thermostat
Doityourself.com's Forum features conversations between more than 250,000 experts and novices in over 120 categories, so each week we highlight a conversation that might help with your next project. This transcript has been lightly edited.
Original Post: Picking the Right Thermostat
TJMas - Member
I just moved into a new house and am looking at getting a smart thermostat. I grew up in a house with just oil heating and AC's in the rooms so a swap was easy, but now I have a CA system as well as oil. I just want to make sure I buy the right thermostat and know if I need to run a C cable. Here's what the guts of the older one look like.
PJmax - Group Moderator
Welcome to the forums.
You have two systems controlled by that thermostat. Two distinct cables.
Cable 1: The heat is on red (Rh) and white (W).
Cable 2: The AC is on red (Rc), green (G) and white (W).
You absolutely need a C connection and it comes from the AC air handler.
Check and see if there are any cut off wires in the AC cable.
TJMas - Thread Starter
Thanks for clearing that up for me. As far as wires around the AC unit I couldn't find anything that looked cut or out of place. It seems everything is hooked up right.
PJmax - Group Moderator
You have two options:
1) Run a new cable down to the stat. (recommended)
2) Lose control of the blower at the thermostat and use the fan wire as the C wire.
With this method there is no more "FAN ON" mode.
TJMas - Thread Starter
Sounds good, sorry if the info I was giving wasn't nearly helpful enough. By oil heating I mean that I have furnace and baseboard heating. And the cooling is a Goodman A24-00. You wouldn't happen to have a link to a wiring diagram so I can put that C wire in properly?
Houston204 - Forum Topic Moderator
C is the big light gray wire under your thumb in the picture that you posted.
The AC condenser connects to stat Y and air handler C so you will end up with two wires connected to the air handler C.
PJmax - Group Moderator
You have a boiler and baseboard heat—a furnace is hot air. A boiler is hot water.
Grady - Forum Topic Moderator
You have just one thermostat for heat? No others in other parts of the house?
TJMas - Thread Starter
It's a ranch so there's just the one.
PJmax - Group Moderator
So have we helped you make a decision? Any more questions?
The Ecobee 3 is a good choice. Honeywell T6 is another.
TJMas - Thread Starter
Yeah you guys have been a great help thanks a ton. I was looking at the Ecobee 3 before I took to the forums so I'll go with that and hopefully not blow up the house in the process.
