I have 2 wires (red, blue) from an existing stat, which terminals on a RTH221B1008 do they hook to. Tkx

See RC and RH, RC is for cool, RH is for heat, you wire the red wire to the RH or red terminal ,either one will work actually but we generally switch the hot leg of power, W is the heat circuit

Hi,
On the t-stat and the furnace make sure the wires are hooked like this...

Red to R
White to W
Green to G
Yellow to Y
Blue to C

then it should work..

Thermostat Wiring and Terminal Designations

heatman101

Hi, the problem is you have bought the wrong thermostat for the unit if it is not a heat-pump. A heat pump will have W-1, W-2 for heat strips, and Y-2 is for 2nd stage cooling. G is Green for Fan, R is Red for Power, Y is Yellow for cooling, and W would be for Heat. This is all you need if you have gas heat, Orange is for a reversing valve for a heat-pump, and the blue is also for the reversing valve on a Rheem heat-pump. The stat you need will have these terminals, if you are sure its not a heat pump, which I am sure you would know. The stat you need has these terminals. RC and RH. It will have a Red jumper wire connecting the 2 terminals. This is where the Red wire connects, to either one, as they connect together. Connect G to Green, Y to Yellow, and W to white. Since you only have one control transformer, that's why the stat has RH for Red Heating, and RC for Red cooling tied together. Just hook the red coming in to either one. You need only, R, G, Y, and W, to run this unit. Look at your old stat and check the terminals. A heat-pump, uses many more conductors to operate it. O or orange for the reversing valve, blue also depending on the unit. C for common, W1 for stage one heating, W2 for stage 2 heating, Y1 for stage one cooling and Y2 for stage 2 cooling. This stat is used for a commercial unit with multible stages of heat and cooling. If you have a common wire and no batteries on the old stat, go to the indoor unit, remove the panel, and see if you have a common wire hooked up, such as the brown, black, or maybe blue. If so, you will need to hook it up at the stat if it has a C terminal. If it has batteries, just take all of the extra wires and shove them in the wall. You won't need them. Just the R, G, Y, and W, and you will be back on line. Very easy.
Please rate me. Take it back and have them sell you the right stat. Please keep me posted and I will be here if you need my help. Thank you for using Fixya.
Shastalaker7
A/C, and Heating Contractor

Red is 24v from transformer to terminal R
Green is to Terminal G for the air handler fan motor
Yellow is to Terminal Y for calling cooling to the compressor and fan outdoor unit
White is to Terminal W for calling the heat trips which are usually sequenced to keep them from all coming on at once and over drawing Amps and kick off breakers.
Orange was for outdoor reversing valve for a heatpump system
Blue or Black is usually used for common or negative continuity in the circuit such as Red wire and Blue/Black wire to power a thermostat features on digital T-stats. If not digital T-stat then no common is needed to hook-up at T-stat

if there is a jumper across Rh and Rc then leave it, if not add a jumper and hook the red wire to one of them. Hook the white wire to the W/B terminal, the yellow wire to the Y/O terminal, and the green wire to the G terminal. If the A/C does not come on with ti this way then hook the yellow to the Y1 terminal instead of the Y/O, I'm not exactly sure which one it will be but it will be one of those. The blue wire you should not need to hookup if there is no C terminal on your t-stat. Just wire nut it off and let it there. This should get you up and going!!

. your blue is probably common and if you hooked it to Y you shorted the transformer or blew the low voltage fuse. Green is fan, yellow is AC, Red is 24volt. Is it a heatpump or just ac? I think its probably a heat pump and your brown is your Reversing valve it needs to be hooked to O on the new stat. If its a heatpump your tstat must be a 2heat 1 cool stat w/ aux heat. Without knowing what terminals the wire were hooked to on the old stat you may have to look at whats hooked up at airhandler( furnace) and on A/C (heatpump) tobe able to determine what goes where on the new one.

Two wire hookup on the old thermostat tells me that it was set up for heating only. You will most likely need a modern thermostat. But in the meantime try this with the old one. The two red wires on the furnace are probably Rh & Rc. If so these can be put "together" on the R terminal on the old stat. The two W's on the new furnace are probably W1 &v W2 This is for first and second stage heat. You can put the two "together" on the W terminal on the old stat. Do not hook up the greens (blower fan wires). Do not hook up the blue wires (They would go to the Y terminal on a modern stat for airconditioning.
Who ever sold you the furnace should have offered you a new thermostat.
Good luck....

First you are using abnormal wire colors for a furnace. Second.... if you have an air conditioner hooked up to this furnace, you will need to install a jumper wire between rh & rc. I am assuming this is a natural gas furnace. Usually the red wire to R terminals. Usaully the white wire to the W terminal. Take the door off of the furnace. Find the thermostat wire connection in the furnace. What ever color wire is on the R terminal in the furnace should hook to the R terminal on the t/stat. Whatever color is on the W in the furnace goes on the W on the t/stat. Whatever color is on the G terminal in the furnace goes to G on the t/stat. And the Y in the furnace to the Y on the stat. and the G in the furnace to the G on the stat. Most applications use only the R, W, G, & Y ( always put the jumper wire between Rh & Rc)
Good Luck
Hvac Teacher

the normal wiring for stats is white=w=heat,red=r=24volts,green=g=fan,blue=c=common,yellow=y=cooling.
see what ties into your furnace board and match the terminals.

The most common wiring is: This sometimes varies as to installers preferance.
Red wire is your supply power to the T-stat. R terminal
Green wire is the blower fan. G terminal
Yellow wire is compressor contactor Y terminal
older units used a blue wire to Y
White wire is heat auxilary or black wire W terminal
Orange wire is reversing valve O terminal
Blue wire is the common C terminal
Black wire can be emergency heat E terminal
Best thing to do is replace wire for wire from t-stat to t-stat
or write down the colors to which terminal on the old t-stat and match to the new. make sure you SECURE POWER to the Air Handler, furnace and condenser before replacing any t-stat.
It is very easy to short the wires out if the power is left on and take out your A/H low voltage fuse or transformer.