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Fan operation switch setting in thermostat (C) Daniel FriedmanThermostat Internal or Hidden Switch Settings
Set Thermostat Cycle Rate Switches, Fan Switches, Emergency Backup Heat, Reset, & other switches inside of room thermostats

This article describes the purpose and setting of tiny switches found inside of some room thermostats. These little slide or toggle switches may control the heating system on-off cycle rate or burner-on time in a manner similar to the heat anticipator feature found in other room thermostats.

Here we describe various types of internal or "hidden" switches found in some wall thermostats and in a table form we summarize their proper setting.

In most cases you can safely install a new room thermostat without worrying about these switches - just leave the switch or switches in the factory-set position. But in some circumstances setting the switches correctly may involve a change .

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

How to Set the Cycle Rate or Fan Operation Switches on a Room Thermostat

Here we describe various types of internal or "hidden" switches found in some wall thermostats and in a table form we summarize their proper setting. In most cases you can safely install a new room thermostat without worrying about these switches - just leave the switch or switches in the factory-set position.

But in some circumstances setting the switches correctly may involve a change .

How to Set the Room Thermostat Cycle Rate Switches (set switch to ON or OFF)

Termostat cycle switch settings (C) Daniel Friedman Heating System Type
Switch 1
Switch
2
Steam or gravity-hot water
On
On
High efficiency forced warm air (90%+ efficiency), hot water, or heat pump system
OFF
On
Gas or oil forced warm air (this is the factory switch setting)
OFF
OFF
Electric forced warm air heat
On
OFF

...

How to Set the Room Thermostat Fan Operation Switch (slide switch to left or right)

Example: Honeywell RTH2300 / RTH221 series wall thermostats

Fan operation switch setting in thermostat (C) Daniel Friedman Heating System Type
Switch Position 


Gas or oil (this is the factory switch setting) for systems that control the fan in a call for heat)

 

LEFT
Electric heat or heat pump (for systems that allow the thermostat to control the fan on a call for heat - a fan wire is connected to the "G" terminal)
RIGHT

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How to Set the Room Thermostat Fan / Electric Switch (slide switch to F or E)

Example: Honeywell CT2700 Electronic Round Programmable Thermostat

Thermostat F or E switch (C) Daniel Friedman Heating System Type Switch Position 

 

Factory = (Gas or oil fuel) This is the factory default position and will be correct for most heating systems

 

F (left)
Electric = (Electric heat 1) Use this position if this (low voltage) thermostat is controlling electric heat such as an electric furnace or electric boiler. The E setting allows the fan (if one is used) to turn on immediately with the heating or cooling equipment in a system in which the G thermostat wiring terminal is used.
E (right)

...

How to Set the Internal Switches & Fan Control in a Honeywell CT87K Thermostat

Honeywell CT87 Thermostat cycle rate internal switch settings - Honeywell International

Honeywell CT87 Thermostat cycle rate internal switch settings - Honeywell International

Heating System Type - Internal Cycle Rate Switches
Internal Cycle Rate Switches
Switch 1 Position Switch 2 Position 

 

Steam Heat:

 

ON
ON
High Efficiency (90% or more) warm air (furnace)
OFF
ON
Gas or Oil fired warm air (furnace) [Conventional furnaces - this is the factory setting]
OFF
OFF
Electric warm air (furnace)
ON
OFF
 
Heating System Type - Internal Fan Control Switch Internal Fan Control Switch
Gas or oil fired heating systems [this is the factory setting]
F
Electric or heat pump system Note 1
E

Notes to the table above

1. This setting is for systems that allow the thermostat to control the fan in a call for heat, if a fan wire is connected to the G terminal.

2. Thanks to reader Fred Gruber for asking about switch settings in the CT87K, 6 March 2016. Fred asked:

Please just tell me which settings give the longest cycle on the CT87K.

Reply:

Fred, There is no traditional heat-anticipator adjustment as was found on some older thermostats we describe in this article series. We should simply follow Honeywell's recommendations for the CT 87K thermostat

In the CT87 owner's manual given below you'll see that the CT87N is for 24 Vac heating and cooling systems while the CT87K is for 24 Vac heating systems - that is the N model controls both heating and air conditioning.

[Thanks to InspectApedia.com Paul for correcting our mix-up on which thermostat is which, 29 Nov. 2019]

See THERMOSTAT INSTALLATION & WIRING MANUALS

3. Illustration and table above adapted from Honeywell's CT87 Owner's manual cited here: Source: Honeywell Owner's Manual, CT87N / CT87K Round Thermostat, [PDF] Honeywell International, Inc., 1985 Douglas Drive North, Golden Valley MN, 55422 or in Canada: 35 Dynamic Drive, Toronto, Ontario M1V 4Z9, Canada, Website: http://yourhome.honeywell.com retrieved 2016/03/06.

...

How to Set the Room Thermostat HVAC Type & Heat Source Switches

Example: 3M Filtrete™ 7-Day Programmable Thermostat Model 3M-22

Watch out: the Filtrete™ 3M-22 is a battery-operated thermostat. If the batteries fail the thermostat may fail to provide heating or cooling and the building may suffer accordingly.

Filtrete 3M Thermostat switch settings (C) InspectApedia HVAC Switch Selections HVAC Type
Left Switch
Heat Source
Right Switch
NORM = conventional gas, oil, electric heat
This is the factory setting (blue arrow)
NORM (left)  
HP = heat pump HP (right)  
GAS = conventional gas or oil heat or heat pump with auxiliary gas or oil heat
This is the factory setting (red arrow)
  GAS (left)
ELEC = normal electric heat or if you have a heat pump with auxiliary electric heat   ELEC (right)
 
Emergency heat switch, 3M Filtrete thermostat (C) Daniel Friedman

Emergency (Backup) Heat Switch for Heat Pumps

Example: 3M-22

Normal Emergency

An emergency backup heat control switch is provided for the 3M Filtrete™ 7-Day Programmable Thermostat Model 3M-22. This switch is located at the top right side of the thermostat beneath the removable top cover.

If you have set this thermostat for HP (heat pump - see the HVAC switch selections explained above), then an EMER or emergency function is available. This is a manual override switch.

Set this switch to OFF (right) for normal operation.

If you set this switch to ON or EMER (left) this will disable the heat pump and will mean that you are relying on your auxiliary heat or backup heat system only. This makes sense if your heat pump is in trouble or inadequate and you want to force backup-heat to be used instead.

Watch out: as purchased, in our thermostat we found this switch had been set to ON (to the left) as you can see in our photo.

OFF



(right)

EMER
=
On

(left)
Thermostat reset switch, 3M Filtrete thermostat (C) Daniel Friedman

Thermostat Reset Switch

3M-22

   

The 3M Filtrete™ thermostat also includes a hard reset button under the top cover and located to the right of the two HVAC switches discussed above.

If your thermostat is not working properly, and provided you've already checked the obvious faults such as no power, bad batteries, loose wiring, improper settings, or manual switches in the wrong position, then you might try pressing this button.

This will re-boot the 3M-22 thermostat without losing its pre-programmed settings.

An alternative and more involved hard reset of the thermostat could also be performed by removing its batteries and disconnecting its thermostat wiring.

Button

Press once to reset the thermostat

...

How to set the Swing Rate or HVAC Cycling Rate on a Programmable Thermostat

Example: 3M Filtrete™ 7-Day Programmable Thermostat Model 3M-22

3M Filtrete 3M-22 Thermostat Swing Rate Cycle Rate setting (C) Daniel Friedman Swing or Cycle Rate Setting
3M-22
Factory Range

The 3M Filtrete 3M-22 thermostat provides an optional adjustment to the HVAC cycling rate that the company calls

Swing Rate: the desired variance in temperature between the 3M-22 setting and the room temperature before the heating or cooling system will turn on. The swing rate can be varied from 0.5o to 2.0o F.

Press SWING found under the DAY icon (second button from left, top row). Press the + / - buttons to select the desired swing from 0.5o to 2.0o F. Then press the Home button (leftmost button, bottom row) to store the setting.

Watch out: unless you have bright light and good eyes the names, labels, and functions of the forest of setting buttons on this thermostat are quite difficult to read. Check to be sure you are pressing the correct button.

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.

+/-
1o F
+/-
0.5o -2.0o F

...

How to Change the Temperature Readout Calibration on a Programmable Thermostat

Example: 3M Filtrete™ 7-Day Programmable Thermostat Model 3M-22

How to calibrate the 3M-22 room thermostat (C) Daniel Friedman Thermostat temperature display calibration
Thermostat engineers showing off or gone wild
Factory Range

The 3M Filtrete 3M-22 thermostat also provides an optional adjustment to its temperature readout described as "calibration". The thermostat is factory calibrated to an accuracy of +/- 1o F but users can deliberately change the temperature display readout to be "off-calibration" by +/- 6o F.

The 3M-22 operating guide suggests you might want to do this to make the thermostat "agree" with another in the building or "agree" with the old thermostat that it is replacing - reasons that we consider ... well, frivolous.

Imagine the confusion down the road when the next user goes crazy fiddling with the thermostat because it's "off" in temperature reading.

There might be a more subtle reason that you'd deliberately change the temperature readout to an inaccurate number, following thinking similar to changing the swing cycle discussed just above.

If the temperatures for the area being controlled by this thermostat always overshoot substantially past the thermostat's set point - something that might happen if the heat is provided by heavy cast iron radiators or baseboard - you could fudge the system by telling the thermostat that the room is warmer than it is.

Similarly if a bad thermostat mounting location means it turns off the heat while the space is still too cold you might be tempted to fudge the calibration rather than moving the thermostat.

Frankly we think changing the calibration on a thermostat is usually asking for trouble and confusion. Leave the calibration where it was set by the factory.

As we explain at THERMISTORS this thermostat is capable of very good accuracy.If your building temperatures overshoot, try adjusting the swing cycle discussed just above rather than messing with the thermostat's calibration.

+/-
1o F
+/-
6o F

Notes to the table above

These examples will not necessarily fit other brands or models of room thermostats. Consult the installation and operating instructions for your individual thermostat. Contact us by email if you are unable to find instructions for your room thermostat.

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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

On 2023-02-24 by InspectApedia Editor - On typical residential furnace controls you don't and can't adjust the run time as if there were a timer or clock

@charlie,

In case you don't have your copy, please see the Owners Guide for your thermostat here

HONEYWELL CT3200 THERMOSTAT OWNERS GUIDE

Check the FAQs section towards the end of the owners guide for some possible steps to try. Specifically note:

~ Furnace cycles too often or system cycle length is too short or too long

~ Heating does not come on

If you're still having trouble, contact Honeywell support directly for assistance. Their contact info is:

CUSTOMER ASSISTANCE
www.honeywell.com/yourhome
Call Honeywell Customer Care at 1-800-468-1502.
Before you call, please have the following information available:
— Thermostat model number and serial code (located under the battery cover).
— Type of heating/cooling system (hot water, warm air, oil, gas, etc.).
— Number of wires connected to the thermostat.

On typical residential furnace controls you don't and can't adjust the run time as if there were a timer or clock.

Instead, the on and off cycling of the blower fan is controlled by the thermostat.

As long as the thermostat is calling for heat the fan will run and the burner may turn on and off depending on the temperature in the furnace itself .

So if you're not getting the heat that you want you may want to look at the air flow and start by being sure that the ducts are not crimped or disconnected and that you have a clean air filter installed.

On 2023-02-23 by charlie

I'm using the Honeywell CT3200 wall thermostat to control a gas furnace, the heat system runned for four minutes & stop wait another 22 minutes to restart again, how can I adjust the running time for about 10 minutes and retuning time ?

On 2022-09-23 by InspectApedia-911 (mod) - how do I adjust the “swing” setting on Honeywell RTH2300 wall thermostat

@Bob B,

In programming mode, Advanced function number 5 allows you to specify the type of heating system that you have such as gas or oil and hot air or hot water. Those adjustments have some effect on what you are calling the swing setting.

If you don't have the instruction manual for your thermostat you can find it at

THERMOSTAT INSTALLATION & WIRING MANUALS

where you will find free PDF download files of instructions for just about every thermostat including yours.

On 2022-09-23 by Bob B

Hi
I’m using the Honeywell RTH2300 wall thermostat to control a gas furnace. Is there a way to adjust the “swing” setting on this particular thermostat?

Thanks

On 2022-03-28 by Inspectapedia Com Moderator

@jerry slayton,

Possibly the thermostat is defective or there's a loose connection but before going further I'd like clarification.

Are you saying you turn your thermostat down to 64, turn it down to 40, or turn it "off" ?

Or are you saying you set the temperature back down to 64 from some higher number but then the thermostat never calls for heat and the house temperature drops down to 40?

On 2022-03-28 by jerry slayton

our ct87k turned off at 64 degrees when bed time.in night 40 degrees but it doesn't turn on again.?

On 2022-03-25 by Inspectapedia Com Moderator - problems with burning up the low voltage transformer

@Gary,

When I've found problems with burning up the low voltage transformer usually the issue has been tracked to

- shorted thermostat or control wires

- overloading the transformer (too many devices being supported)

- an under-sized transformer

Honeywell also warns that the CT87K is not the right replacement for every situation (If your HVAC system thermostat was using 4 or more wires you need a different model)

You probably already have it but if not the IO and Wiring manuals for your Honeywell CT87K are at

THERMOSTAT WIRING HONEYWELL

and for your White Rodgers 1311 zone valve the IO manual is listed as a PDF download at

ZONE VALVE MANUALS & WIRING

On 2022-03-24 by Gary

I replaced Honeywell mercury stat with Honeywell ct87k... Cycle rate set switch 1 off.. 2 on.. runs couple days blows 24 transformer in boiler.. when that happens zone valve runs continually. Has new white Rodgers 1311-102 valve...

On 2021-07-13 by danjoefriedman (mod) - set the thermostat switch according to your actual heating method

@Oscar,

How is your building heated?

Electric heat, or a fossil fuel like gas or oil, or by a heat pump?

You'd set the thermostat switch according to your actual heating method.

Don't worry too much about this setting: your thermostat will work in any event, but its accuracy in choosing exactly how to turn your heating system off will be improved if the switch is set correctly.

Let me know if this answers your question or post follow up questions if you like.

On 2021-07-13 by Oscar

The switch in the back of my thermostat what's recommended to leave on gas or oil or Electric or heat pump.

On 2021-04-05 by danjoefriedman (mod)

@Bob,

I'm resisting the temptation to make up an answer when I'm not sure I understand the question. Are you talking about monitoring a home against freeze Risk by keeping an eye on its temperature independent of the thermostat setting? Where are you talking about a setting on the thermostat itself in which case I'm not sure of your use of the word monitoring?

On 2021-04-05 by Bob

I need to know what setting to have my thermostat monitor on as I have a natural gas furnace

On 2021-01-18 by danjoefriedman (mod)

Debbie,

Not every thermostat has internal switches that you need to change. So we need to start with the brand and model of your specific thermostats to know what switches it includes. You shouldn't need to turn any internal switch on or off simply to have heat.

On 2021-01-17 by Debbie

how do we turn on switch to on and off

On 2020-12-06 - by (mod) -

Although it won't make a big difference I agree that if you have oil fueled heat than you would set the switch to oil.

On 2020-12-06 by Jeremy

I wonder if it was set to electric because we have forced air to and in the winter it needs to be switched?

So if i have a fuel oil forced air furnace the tab on the back should be slid over to gas /oil? We bought the house and it was set on electric

On 2020-05-26 - by (mod) -

Anon

See our extensive diagnostics for an air conditioner that won't run, beginning at

AIR CONDITIONER WON'T START

On 2020-05-25 by Anonymous

My aircondition wont turn on

On 2019-12-12 - by (mod) -

Paul

Thank you so much for important comment clarify which thermostat models provide which functions. I always start by trusting honeywell's documentation as the most accurate. I'll review our article with that in mind. Thank you for taking the time to write about this.

The Honeywell CT87N and the CT87K are often discussed together in the same Honeywell thermostat installation guide.

The current Honeywell CT87K is a heat-only thermostat - one of the simplest to install and use, typically wired with just two wires (red and white) to turn a heating system on and off.

The Honeywell CT87N thermostat can control BOTH heating and cooling.

Right on the instruction manual you will see that Honeywell says

CT87K (24 Vac heating systems) • CT87N (24 Vac heating and cooling systems) - shown below

I mis-spoke and have fixed that text. Thank you for careful reading.

On 2019-11-29 by Paul

In reply to Fred Gruber’s 6 March 2016 comment, it is stated that the Honeywell CT87N thermostat is for 24V heating systems, and that the Honeywell CT87K thermostat is for both 24VAC heating and cooling systems- that is, the K model controls both heating and air conditioning.

However, the owner’s manual seems to say that the K model is for heat only, and the N model is for both heating and cooling, which is the opposite of what was stated in your reply to Fred Gruber. Who’s correct, the manual or you? Or am I misinterpreting both you and the manual, if that’s possible?

Thanks!

On 2019-03-07 - by (mod) -

As far as I know that's the case of course I don't have any specifics about your heating system. My best advice was in the previous comment that I posted.

Certainly if you like you could experiment to see what the duration of heat on seems to be when you switch between the different modes but are using electric heat.

On 2019-03-07 by Joe

So it doesn’t matter which mode it’s on if I have electric. Is it best for it to be on electric if I have electric or does it really matter overall?

On 2019-03-06 - by (mod) -

Joe it won't be critical which way the GAS OIL switch is set as you'll get heat in either case.

The difference in those settings is an analog to the heat anticipator on some other thermostat designs, and simply tries to adjust the thermostat to account for the probable speed with which the heater will respond on a call for heat, thus avoiding "overshoot" in which the heat continues to warm the building past the point at which the thermostat is satisfied.

On 2019-03-06 by Joe

My AC/Heat unit operates on electric, but I just noticed the little switch under “fan on or auto” switch was switched in the gas position. Even though my unit is electric. Is that a problem? What’s the difference if my house runs off electric.


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