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How Wire a 3M Filtrete Thermostat

3M-22 3M-30 3M-50 Filtrete
Thermostat Wiring Connections

Thermostat wiring details & connections for the 3M Filtrete room thermostats. This article gives tables showing the proper wire connections for the 3M-22 Filtrete thermostat used to control heating or air conditioning equipment.

Room thermostat installation & wiring guide: this article series explains the basics of wiring connections at the thermostat for heating, heat pump, or air conditioning systems.

Page top photo: 3M's 3M22 Filtrete 7-Day Programmable Thermostat.

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- Daniel Friedman, Publisher/Editor/Author - See WHO ARE WE?

3M-22 Filtrete™ Room Thermostat Wiring Guide

3M-22 Thermostat wire connection terminals (C) Daniel Friedman

Complete tables of all wiring connections for the 3M-22 Filtrete Room Thermostat are given here along with PDF downloads of Filtrete thermostat wiring instructions and operating guides.

Our photo above shows all eleven possible thermostat control wire connection points on this device. (We don't like that sharp crimp in the red wire, nor should you.)

Note in our photo above that the white wire is connected to W and the red wire is connected to RH and the uninsulated jumper wire is left in place between the RH and RC terminals?

Wired as shown, this thermostat works only from its own internal battery power.

Article Contents

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How to Wire a 3M-22 Filtrete Room Thermostat For 2-wire Heating Only Systems
Thermostat
Terminal ID		 Wire Color

or ID		 Two-Wire Heat Thermostat Hookup - Comments
W
White or W White wire coming to the thermostat from the heater or from the secondary (C) terminal on the transformer, this wire connects the heat.
RH
Red
or R or RH

Red wire coming to the thermostat from transformer secondary (R) terminal. This connects the heat power.

Leave in place the jumper wire between RH and RC.
C
 C
if present		 If a third "C" wire is present this wire is used to provide power to the 3M-22 thermostat. Otherwise this thermostat is powered only by its batteries.

Notes to the table above

This wiring procedure works for 2-wire heat, oil or gas millivolt or 24VAC systems

On a call for heat (room temperature drops below the thermostat set point, the thermostat connects W - RH to turn on the heating system.

Watch out: this is a battery-operated thermostat. If the batteries fail, the thermostat may fail to provide heating or cooling and the building may suffer accordingly.

Watch out: if your smart thermostat needs a C-wire or COMMON wire and none is provided at the thermostat, you'll need to provide one.

See details at COMMON WIRE at THERMOSTATS

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How to Wire a 3M-22 Filtrete Room Thermostat For 3-Wire Heat Systems
Thermostat
Terminal ID		 Wire Color

or ID		 Comments
W
White or W W connects to heat
RH
Red
or R or RH 		RH connects to heat power
G
 
Green
or G or F (fan)		 This wire (if present) controls the fan in forced warm air systems, fan convector heaters, and similar systems that use a fan.
C
 C - Common If a "C" wire is also present this wire is used to provide power to the 3M-22 thermostat. Otherwise this thermostat is powered only by its batteries.

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How to Wire a 3M-22 Filtrete Room Thermostat For 4-Wire Heating & Air Conditioning Systems
Thermostat
Terminal ID		 Wire Color

or ID		 Comments
W
White or W W connects to heat
Y 
Yellow or Y Y connects to the cooling compressor/condenser unit
RH
Red
or R or RH 		RH connects to heat power
G
 
Green
or G or F (fan)		 This wire (if present) controls the fan in forced warm air systems, fan convector heaters, and similar systems that use a fan.
C
 C - Common If a "C" wire is also present this wire is used to provide power to the 3M-22 thermostat. Otherwise this thermostat is powered only by its batteries.

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How to Wire a 3M-22 Filtrete Room Thermostat For 4-Wire Heat Pump System
Thermostat
Terminal ID		 Wire Color

or ID		 Comments
B
O or B wire

Connect the O or B wire to terminal O - this operates the reversing or "change-over" valve that switches between heating & cooling mode.

If both O & B wires are present (as with Trane heat pumps), connect O wire to O terminal

For Trane heat pumps connect the B wire to the C terminal.

For other HVAC equipment, tape off the B wire.

Watch out: do not connect the B wire to the B terminal on this thermostat.
Y 
Yellow or Y Y connects to the cooling compressor/condenser unit
RH
Red
or R or RH 		RH connects to heat power
G
 
Green
or G or F (fan)		 This wire (if present) controls the fan in forced warm air systems, fan convector heaters, and similar systems that use a fan.
C
 C - Common If a "C" wire is also present this wire is used to provide power to the 3M-22 thermostat. Otherwise this thermostat is powered only by its batteries.

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How to Wire a 3M-22 Filtrete Room Thermostat For 5-Wire Heating & Air Conditioning Systems
Thermostat
Terminal ID		 Wire Color

or ID		 Comments
W
White or W W connects to heat
Y 
Yellow or Y Y connects to the cooling compressor/condenser unit
RC-RH Jumper
Jumper wire between these two terminals Remove this jumper wire or clip so that RC and RH are no longer connected together
RH
Red
or R or RH 		RH connects to heat power
RC
RC wire RC connects power
G
 
Green
or G or F (fan)		 This wire (if present) controls the fan in forced warm air systems, fan convector heaters, and similar systems that use a fan.
C
 C - Common

If a "C" wire is also present this wire is used to provide power to the 3M-22 thermostat.

Otherwise this thermostat is powered only by its batteries.

See COMMON WIRE at THERMOSTATS

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How to Wire a 3M-22 Filtrete Room Thermostat For 5-Wire Heat Pump with Auxiliary or Backup Heat
Thermostat
Terminal ID		 Wire Color

or ID		 Comments
B
O or B wire

Connect the O or B wire to terminal O - this operates the reversing or "change-over" valve that switches between heating & cooling mode.

If both O & B wires are present (as with Trane heat pumps), connect O wire to O terminal

For Trane heat pumps connect the B wire to the C terminal.

For other HVAC equipment, tape off the B wire.

Watch out: do not connect the B wire to the B terminal on this thermostat.
W2
W2 wire

The W2 wire controls the auxiliary heat or backup heat source.
Y 
Yellow or Y Y connects to the cooling compressor/condenser unit
RH
Red
or R or RH 		RH connects to heat power
G
 
Green
or G or F (fan)		 This wire (if present) controls the fan in forced warm air systems, fan convector heaters, and similar systems that use a fan.
C
 C - Common If a "C" wire is also present this wire is used to provide power to the 3M-22 thermostat. Otherwise this thermostat is powered only by its batteries.

Notes to the table above

Some heat pumps with auxiliary / backup heat use staged backup heat and additional controls and wires may be required. See the next table.

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How to Wire a 3M-22 Filtrete Room Thermostat For Heat Pump with Two-Stage Auxiliary or Backup Heat
Thermostat
Terminal ID		 Wire Color

or ID		 Comments
W
White or W W or W1 operates the auxiliary stage 1 backup heat
W2
W2 wire W2 operates the auxiliary stage 2 backup heat
Y 
Yellow or Y Y or Y1 operates the first stage cooling system
Y2
Y2 wire Y2 operates the second stage of 2-stage cooling systems
RH
Red
or R or RH 		RH connects to heat power
C
 C - Common If a "C" wire is also present this wire is used to provide power to the 3M-22 thermostat. Otherwise this thermostat is powered only by its batteries.

We provide thermostat wiring connections for just about every type of residential heating or cooling room thermostat as well as a description of thermostat wiring color codes & conventions.

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3-M Filtrete Thermostat Manuals - Free Downloads

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: wiring a 3M-50 thermostat

I have a Bryant gas furnace/air conditioner that is being controlled on the main level by a Honeywell Pro TH4110D Thermostat that has both the B and O wires connected.

I want to replace it with the 3M-50 thermostat.

I have read the warnings about B and O in the installation manual, but I'm still not sure what to do.

Since it is not a Trane heat pump, it would seem to say connect O to O and tape off B.

Is this correct, and why?

There is also a zone for the lower level with a separate Ultra Zone thermostat. - Denny 2022/09/09

Moderator reply:

Frankly given the amount of trouble I've read from people trying to use the thermostat you cite, I can't recommend that approach. Here are the ususal connections for your case

Rc-Rh=RcRh
Y=Y
G=G
O=O
W1=W2
X2= left off

The thermostat manuals below may be helpful as they give the manufacturer's advice but frankly the instructions for several versions of this thermostat have been a bit confusing when faced with questions like yours.

Despite the 3M name, the instructions indicate that these are an offshore product - but there is a customer support number that we give at

3M-FILTRETE THERMOSTAT MANUALS

Question: Replace a round Honeywell T87 with a Digital Honeywell Thermostat?

Hello - I am replacing a round Honeywell thermostat with a non-programmable digital Honeywell unit.

I have a hot water system with multiple zones and with no air conditioning. There are three wires at the thermostat. On the old round unit the red wire went to the R terminal, the white wire went to the w terminal and a green wire went to B terminal.

I hooked up the new stat the same way but it would not work. If I selected "fan on" instead of "fan auto" the zone would heat up but would not shut off (hot water kept flowing even if I selected a temp below room temp). Appreciate your help. - Patrick - 1/20/12

Reply:

Patrick, typically the three wire thermostat hookups would be exactly the same for the old and new thermostats.

For details of wiring a typical and simple digital Honeywell thermostat,

see Honeywell 5-2 Day Programmable Thermostat - RTH2300B1012.

For help in understanding the wiring of your old thermostat.

 

Question: Replacing a mercury thermostat with a digital unit

I am replacing an old mercury thermostat with a digital. my system is a heat pump. my neighbor gave me the digital, no instructions, no box.

I'm trying to decide if this is even a heat pump compatible thermostat. on the therm it has c, g, rc, rh (which are linked by a black wire.) w, y, b, and o. coming out of my wall is, white connected on old therm w2, yellow connected to y, green conn g, black conn e, red to r, blue to b and bro to x. any help would be great. - Kurt 6/4/12

Reply:

Kurt, as you see in the examples at For help in understanding the wiring of your old thermostat,

see Three-Wire Honeywell Wall T87-F type Thermostat wiring and

also see Generic HVAC Thermostat Control Wiring Points.

Many thermostat wiring setups are straightforward or "cookbook" but why not find the brand name on your thermostat and then you can obtain the installation instructions right from the manufacturer?

Also, Honeywell's thermostat replacement advice (and most likely that of all thermostat manufacturers) warns:

Watch out: MERCURY NOTICE: Do not put your old thermostat in the trash if it contains mercury in a sealed tube. Contact your local waste management authority for instructions regarding recycling and proper disposal.[5]


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