Replaced mercury t-stat with new honeywell programmable t-stat. want to wire fan switch so fan can be turned on only. Is this possible.

How many wires do you have?

No wire for fan at t-stat. can I run a wire from t-stat to furnace

Yes you can run a new wire, you only have 2 wires now? Make sure to turn the power off at the furnace before changing any wires.

o.k. will the furnace be marked for fan wire ?

Your still not answering my question. How many wires doe you have now? Do you have ac or just heat? The fan wire will be hooked to g at the furnace just as it is hooked to g at the stat.

2 wires now. No a/c. sorry

Thank you for your help. Auto mechanic by trade. Didn't want to burn the house down.lol

OK well I would say if you run a new wire that you pull enough wire to have 5 wires the are and w you have now, you need a g for fan, and with the new stat you need a common wire or you battries will be dying out fast. So if you are going to need 4 wires you may as well pull 5 so you can have the why for ac if so disired later.

Sounds like a plan. Have my project for the day. Thanks again.

No probem

R to r at the furnace
W to w
C to c
G to g