What size wiring do you use for a thermostat? I need to move one from an exterior wall to an interior one. Also, any tips on fishing wires through insulation? Bringing it up the wall and over suspended ceiling and down another wall.

18 gauge is a norm for t-stat wire.

Pulling it through is made much easier by using "fish tape" or even a coathanger.

Here are some articles about using fish tape:
http://www.google.com/search?num=100...re&btnG=Search

OOPS!! Since I made the post below I have been to Home Depot and looked at their thermostat wire. Their sign said 18 gage thermostat wire. Couldn't see the wire itself. Still think I have seen smaller wire used.


Go to a place that sells wire. Pick out some thermostat wire that has as many wires as you need and seems to follow the color code of your thermostat. If your thermostat has the additional BK and OR terminals, don't buy the red, white, yellow, green, and blue stuff. The low voltage wiring for HVAC systems run on very little power. I think the older stuff looked like 20 gage, but you may find the newer stuff labeled 26 gage.

Usually there is a 24 volt AC transformer in the furnace with the secondary winding connected to a red wire running to the thermostat and a blue wire, common, to the gas valve, A/C relay, and fan relay. From the thermostat there will be white wire to the gas valve, yellow to the A/C, and green to the fan. If your furnace uses these colors, and the thermostat uses different ones, you will need to study the directions for it to relate the terminals to the function. Color makes no difference as long as the right wire connects to the right terminal.

Looking back at your question, on fishing the wire. If you have access below the floor, I would abandon the old wiring, well maybe pull it out. In an exterior wall, you are fighting the insulation, a pain, plus the chance of messing it up. If you can, start new from the furnace. Run the wire down under the floor, across the under side to the underside of the wall cavity you intend to locate the thermostat. Drill a 1/2'' or bigger hole through the floor and plate above. Cut a hole in the wall the thermostat will cover leaving enough wall to mount the thermostat. You then should be able to push a wire up to the hole in the wall, and have room to snag it with something.