Thermostat Heat Anticipator FAQs

How Heat Anticipators Work FAQs

Ohm's Law explains why the heat anticipator operates as a little heater: more heat at lower resistance settings

According to the copy of Ohm's that I have,

Watts = Volts² / Ohms 

See DEFINITIONS of ELECTRICAL TERMS for definitions of watts, volts, & ohms or resistance. - Ed.

Therefore watts (and heating effect) goes up as the resistance goes down, given the same voltage. This also applies to amps (volts / ohms). This would explain what Honeywell is telling you.

Since electrical resistance is a measurement of the opposition to (resistance to) the flow of electric current, lower resistance means more current flow. (Mar 18, 2014) Tim

Reply: we agree. Lower resistance = more current = more heat at the anticipator = heat turns off sooner

Moving the heat anticipator so that the current runs through a shorter wire lowers the electrical resistance of the heat anticipator.

Lower electrical resistance (measured in Ohms) will permit more current to flow in a wire when we don't change the voltage.

Higher electrical current (measured in Amps) is expected to cause more energy to be released in the form of heat. Why?

Current flowing through a wire that acts as a resistor will convert electrical energy to heat.

More current flow = more heat.

More heat from the heat anticipator means more warming of the interior of the room thermostat, causing it to turn OFF the heating system a bit sooner.

Why the Heat Anticipator Heater Gets Hot

The comparatively large #18 copper thermostat wire that brings electrical power to the room thermostat has maybe 50 times less resistance than the short length of nichrome wire in the thermostat heat anticipator's heater.

So the 24VAC fed into the little heater warms up the nichrome wire - where it's functioning similarly to the filament in a light bulb fed by #14 copper wire in a house circuit.

When we adjust the heat anticipator to a higher Amps number we shorten the nichrome wire to lower its resistance still further, more current is pushed through it and it gets still hotter.

See ELECTRICAL RESISTANCE vs HEAT GENERATED for details about resistance of wires and why they get hot - or don't.

See HEAT ANTICIPATOR SET & TEST by AMMETER for a description of the typical amps range of a room thermostat circuit.

Heat Anticipator Adjustment FAQs

Which way to move the heat anticipator?

I think one of your pictures at your home page for this topic HEAT ANTICIPATOR OPERATION is wrong (the fourth picture, the one that is black and white with some red).

According to your article, at the lower numbers (all the way to the right), you would get a shorter burn time.

However, it says "longer burn-on" in the picture. (Dec 11, 2016) Burt s

Reply: heat anticipator adjustment position vs heat anticipator output explained here

Thanks foot the comment, Burt.

We repeat the photo here.

Honeywell put the word "longer" on the right.

We also show the current path through this device. A shorter the electrical wire path length means less resistance. Less resistance means more current flow. More current flow means more heat generated on the tiny heater in the thermostat. More heat by the heat anticipator means more warming of the thermostat's sensor. More warming of the thermostat's sensor means heat turns off sooner.

The shortest burner-on time will be when the heat anticipator puts out the most heat.

This warms up the thermostat's room temperature sensor and therefore tells the thermostat the room is up to set temperature earliest.

The longest burner-on time will be when the heat anticipator puts out the least heat, thus does not turn off heat early, thus lets the burner keep running longer.

Moving the heat anticipator position changes the length of the nichrome wire in the active circuit.

Longer Wire = More electrical resistance = less current flow = less heat generated by the heat anticipator = less pre-warming of the thermostat = longer heat on cycle.

Shorter Wire = Less electrical resistance = more current flow = more heat generated by the heat anticipator = more pre-warming of the thermostat's sensor = shorter burner on time

Now look at our second photo below, showing the current path through the heat anticipator: That little right-angle stainless steel spade below the right line is my pointer, NOT part of the heat anticipator.

Moving the arrow to the right, over towards "LONGER" and towards (.10A ) is actually going to give a longer heat on time: less current = less heat generated at the heat anticipator.

Some Honeywell thermostats included an ARROW below the word "LONGER" - note which way it pointed: it points to the LEFT towards 1.2A. It's so hard to see that I've enlarged part of the original photo - below.

I infer that if LONGER at the right end of the scale really means the heat should stay on longer at that position (the heat anticipator should generate less of its own heat and thus not pre-warm the thermostat's room temperature sensor), less current should be flowing, less heating of the heat anticipator, so heater stays on longer.

Notwithstanding confusion about the location of the word LONGER and the arrow pointing to higher numbers on the Amps scale of the heat anticipator,

at HEAT ANTICIPATOR ADJUSTMENT we quote Honeywell's instructions:

If the furnace stays on beyond the thermostat set temperature, move the anticipator down by .1 ampere.

If the furnace shuts off before the set temperature is reached, move the anticipator up by .1 ampere.

Explain the Operation of the Heat Anticipator on a Honeywell T832A Day-Night Setback Thermostat

I have a Honeywell T832A thermostat with a mechanical setback timer and I don't quite understand how it's anticipator is supposed to work. It can be set from 0.4 to 1 amp but moving the pointer seems to do nothing as the cycles are always too long.

I partially disassembled it to show how it's made and you can see that the anticipator isn't anywhere near the bi-metal coil, it's sitting about 2" above it above the mechanical timer assembly.

It's also wired in a way I don't understand.

Can anyone explained how this is supposed to work? Look at these photos. 2017/10/30 hil.racicot said:

Moderator Reply: Heat Anticipator Operation on the Honeywell T832A - numbers run opposite to newer thermostats

Hil R.

I took a look at your photos of the Honeywell T832A thermostat and have reproduced them here for other readers.

The Honeywell T832 day-night thermostat was first produced by Honeywell in 1960 continuing the sophistication of Honeywell's round thermostat series originally designed by Henry Dreyfuss and first sold in 1953.

The T832 1960's day-night setback thermostat, shown above and edited from one of your photo series, contains a wind-up timer that permitted an automatic night time temperature setback.

The Honeywell 832 number continues in use as the Honeywell TH832R1001 Vision Pro electronic, programmable touch screen thermostat that is an entirely new device.

Watch out: Honeywell, in instructions for its CT87A,B,J Round Thermostat warns [that unless your specific primary control manufacturer says otherwise]

Never adjust the heat anticipator below 0.3A

You'll see that you have set the heat anticipator adjustment pointer to the left end of the scale - that's somewhere around 0.1A of current, calling for least current in Amps [assuming this scale is expressed in Amps], least heating by the heat anticipator.

That is in violation of Honeywell's instructions that we quoted above as you've set the anticipator beloe 0.3 Amps.

On the T87 shown just above, moving the pointer from left to right moves towards the wide or greater number of windings, towards a lower number on its scale, and in the direction of LONGER.

Heat anticipator operation is explained in detail

at HEAT ANTICIPATOR OPERATION.

Please take a look at that article.

Separately at HEAT ANTICIPATOR SET & TEST by AMMETER we describe using an ammeter to confirm that a heat anticipator is working properly

In our HEAT ANTICIPATOR OPERATION article we explain that

Watch out: A heat anticipator will not work accurately unless the following conditions are met:

The heating or air conditioning system itself has been adjusted to match the electrical current of the valve or relay which the thermostat is controlling.

This is a technical problem for your heating or air conditioning service technician, not something a homeowner can address.

The thermostat is installed at a location where voltage and current (amps) fall on or within the limits of the adjustable heat anticipator

The thermostat is not installed on a power pile system (don't ask).

The heat anticipator on the thermostat should be set to match the requirement & electrical characteristics of the particular heating or air conditioning control circuit that it is switching on and off.

At HEAT ANTICIPATOR ADJUSTMENT we quote Honeywell:

If the furnace stays on beyond the thermostat set temperature, move the anticipator down by .1 ampere.

If the furnace shuts off before the set temperature is reached, move the anticipator up by .1 ampere.

Other defects can also prevent a thermostat from working properly, described

at TEMPERATURE RESPONSE of ROOM THERMOSTATS

The range of effect of a thermostat's heat anticipator is not enormous, typically just a few degrees. So if your room heat is overshooting the set temperature on the thermostat by a large amount (you should tell me that number) we need to look for a different cause.

Something as simple as accumulation of dirt, debris, dust, even a coating of nicotine and oils from decades of nearby tobacco smoke can affect how the bimetallic spring of the thermostat will respond to temperature.

It would be diagnostic if you could tell me if the behaviour of your Honeywell T832A thermostat has changed or if it has always acted as you describe. If it has changed that suggests that dirt, debris, or damage or perhaps a setting change have affected the thermostat.

Watch out: Looking at your photo of the heat anticipator circuit on the T832A in your photo, it looks to me as if there might be some corrosion on the plate behind the wound nichrome wire, and also I see a deep gouge that has been cut into the wire by the contactor of the sliding pointer.

Both of those could suggest that the anticipator has been damaged.

Heat Anticipator Dial Markings & Arrows FAQs

Honeywell class 2 lr1620 thermostat heat anticipator dial has an arrow indicating LONGER in the direction of the HIGHER numbers

I have an OLD ('70s) Honeywell class 2 lr1620 and the anticipator dial has an arrow indicating LONGER in the direction of the HIGHER numbers (like the ones you show above).

It is a completely different dial with a metal connector used to set the amps using your fingernail.

It would seem that the direction of the "LONGER" arrows in both units is not a mistake by Honeywell, as you seem to be querying.

The unit is reaching temp, shutting down (mercury switch tipping), then failing to start up again, despite the mercury switch being clearly engaged. Thought it might be the anticipator which is set on 0.4.

Any ideas? Thanks Adam. Melbourne Australia boogweig@gmail.com 17 June 2015 Adam Williams

Reply: The arrow is correct, the location of the word LONGER can be confusing.

Which scale is on the thermostat heat exchanger: Amps or Ohms? Answer: Amps - per Honeywell's own documentation.

Higher resistance, less current, less heat at the heat anticipator, heat runs longer: Amps (Current) vs Ohms (Resistance)

Higher current (amps) = more heat at the heat anticipator = heat will turn off sooner.

Adam

You are right: in sum, at higher resistances less current will flow in the heat anticipator, less heat will be generated, the heat anticipator will heat up less, so the heat will run longer before the thermostat turns it off.

But generally you can trust what the manufacturer says. If they say move the anticipator in the direction of the arrow for a LONGER ON cycle then do that.

But normally you would not adjust the heat anticipator more than +/- 0.1A past the actual Amps or current drawn by the primary controller of the heater itself.

Here are Honeywell's own recommended heat anticipator settings in their sketch below, to be used if we have no other data about the actual amps current draw of the heater's primary control devicve.

Once again, the use of the word "LONGER" and the arrow below it are confusing.

I have edited, clarified and expanded the article HEAT ANTICIPATOR OPERATION where I include your question and a nauseating long reply drawn from several electrical engineering and physics sources.

How Heat Anticipator Affects Room Temperature FAQs

What is the relationship between setting the heat anticipator higher or lower and the resulting room temperature?

if the heat anticipator sets was too low, whether the room temperature lower or higher?

I want to know that if the heat anticipator sets was too low, whether the room temperature lower or higher? - Thanks Hyuk Lim.

Reply: set the heat anticipator to a higher Amps number to turn heat off earlier (shorter ON cycle) thus to make the room a bit cooler

Typically if you set the heat anticipator to a lower number (a lower Amps number on most thermostats) you are causing the heat anticipator to heat up less, thus decreasing the "gap" or amount by which the heat anticipator anticipates the amount by which heat delivery will "coast" when the thermostat stops calling for heat.

At higher current or Amps (or in some designs lower electrical resistance) a hotter heat anticipator will cause the the thermostat to turn off the heating source sooner.

In our example photo (left) at 1.2A (the highest Amps number on the scale) the most current flows, the most t heat is generated, and the heat anticipator does its most anticipating, or it turns the heating system off sooner.

If you click to enlarge our heat anticipator photo you'll see that the settings range from 0.10 to about 2 Amps - a scale quite similar to the mini Ammeter used to fine-tune thermostat heat anticipators based on the circuit resistance (Ohms) and current flow (Amps) as we discuss above.

In order to keep the room from becoming much hotter than the thermostat set point, a heat anticipator turns off the heating boiler ahead of time or before the room temperature has actually reached the thermostat set point.

What will happen if the anticipator is set too low

What will happen if the anticipator is set too low? (Feb 16, 2015) Wadia

Reply: your heat may stay on longer than you wish and the room temperature may rise a bit above the "set" temperature on the thermostat

Wadia

If by "low" you mean setting the heat anticipator to turn off later (less current, more resistance) the heat anticipator will heat up less so the heat will stay on a bit longer.

The room may overheat a bit - that is the boiler may keep sending heat a bit longer than necessary to satisfy the thermostat.

Which Way Do I Move the Heat Anticipator Adjustment to get "more or longer heat"?

All this technical mumbo jumbo...Bottom line. WHICH way to I set the heat anticpator to get MORE longer heat? - On 2016-02-12 by joe

Reply by (mod) - move the pointer to a slightly higher number

Honeywell's instructions typically say

If the furnace shuts off before the set temperature is reached, move the anticipator up by .1 ampere.

So for "more heat" or "longer heat" try setting the heat anticipator UP to a HIGHER NUMBER on the scale by a increment of 0.1A.

Also take a quick look at the start of this article HEAT ANTICIPATOR ADJUSTMENT where we have a section titled

Which Way Do I Move the Heat Anticipator Adjustment?

Or notice the table below excerpted from Honeywell's T87F thermostat instructions. So if we want "more heat" and it's this thermostat we'd set to a lower number on the scale.

Heat Anticipator Damage or Failures

Heat anticipator repairs - not working, can I just use a toggle switch?

I've tried adjusting my heat anticipator setting to the lowest, highest, and even somewhere in the middle. No matter what I try, my wall heater comes on for only 2-3 minutes at a time and does this short cycle every 20 minutes or so.

Would it be safe to simply put a toggle switch on my wall for the Red wire and White wire to be manually controlled? 17 January 2015 ReyAlonzo91

Reply:

Rey

Rather than installing a toggle switch I'd try first to debug the problem as there may be something else that needs attention for safety or reliability of the heating system.

First disconnect the thermostat completely and connect the thermosat terminals directly at the heater control board - which should be exactly the same as the thermostat calling for heat at the wall mounted thermostat location.

If then the heater runs normally the trouble is in the thermosat, its settings, or its wiring. If the heater still short cycles then there is a problem with the heater that needs to be found and fixed.

In that case see these two articles found in the ARTICLE INDEX

HEAT WON'T TURN OFF

HEAT WON'T TURN ON

Early heat turn-off traced to bad thermocouple sensor

I just wanted to thank you for helping me solve the short cycling problem with my thermostat.

I thought it was the heat anticipator because my heat was turning off prematurely (before reaching desired temperature) and would only run for a few short minutes at a time. As it turns out, I simply needed to clean my thermocouple.

I used a steel wool sponge to sand off the dirt/grime. My wall heater works great now! (Jan 21, 2015) ReyAlonzo91

Reply:

Thanks so much, Rey. I've learned from your reply too. I know that the thermocouple is sticking out there in the air but unlike a bimetallic spring that is easily clogged with dust, I hadn't considered that a thermocouple too might become debris blocked. Nice going.

See THERMOCOUPLE REPAIR / REPLACEMENT for help in replacing a failing thermocouple. Often we just clean off the tip of the thermocouple only to find that soon it fails again because the root problem was not soot but improper placement in the flame or a failed sensor itself.

Or if you actually were referring to the thermistor used as the temperature sensor on some room thermostats -

see THERMISTORS in ROOM THERMOSTATS

Heat Anticipator vs Compensator FAQ

Should the heat anticipator on a room thermostat be called a compensator?

After reviewing the helpful information on Thermostat Anticipators, I wondered… wouldn’t a more appropriate name for the anticipator be “compensator”?

By measuring the current at the thermostat, aren’t we really compensating for any current draw thru the controller and other components like zone valves and circulators on boilers or fans on forced air furnaces and their wiring?
I worked on an older furnace with a Honeywell L8048E auquastat controller.

I installed new thermostats and of course there was no documentation for the older controller to set the anticipator(s). After finding documentation on the newer Honeywell L8148E controller, the anticipator setting is shown to be .2.

Am I wrong with such a short cycle, the thermostat stops calling for heat too soon, closing the zone valve and shutting off the circulator, which never allows the residual water from the boiler to circulate after high limit on auquastat shuts off the burner reducing efficiency? 2 Feb 2015 Chuck Stutz

Reply: why is the heat anticipator called that? Causes & Effects of heater short-cycling.

Thanks for the interesting comments, Chuck.

Indeed the topic of function and adjustment of heat anticipators in thermostats has draw lots of remarks from both homeowners and service techs who find the concept, operation, and instructions for heat anticipator adjustment a bit confounding.

You're right that the device is in a sense a compensator as you described it.

My guess is that the company chose the term "anticipator" most likely thinking that would be clear to normal people as it suggests that the thermostat is "anticipating" that the room heat is about to be reached and is turning off (stopping the call for heat) a bit in advance so as to reduce overheating of the space or "heat overshoot".

Because individual building heating system performance in heating cycle or heating temperature "overshoot" in the occupied space can vary due to a number of factors it is reasonable to change the heat anticipator if you find that heat is turning off too soon - under-shooting the thermostat setting.

If adjustment doesn't prove satisfactory I'd look for a different problem in the heating system controls.

A loose wire connection, intermittently-shorted thermostat wires, or poor thermal contact between the aquastat's sensor probe and the sensor well side can also cause odd on-off or cycling behaviour at a heating system.

I also agree very much with the principle that too-short burner on-cycles are inefficient (we don't heat up the combustion chamber enough to get complete combustion so we waste fuel and maybe with heating oil we also soot-up the system leading to operating trouble). But this sort of "too-short" on cycle depens on the fuel and burner design to define just what is "too short".

In my experience, an oil fired heating system needs to be on for 5 minutes or longer to reach fully stable operating conditions.

Finally, let's separate some control functions. It's the burner-on time that defines the efficiency worry that I mentioned, not the ultimate temperature at which the burner turns off (though there is an argument that higher water temperatures in baseboards or radiators give more efficient heat transfer to the heated space).

Control wiring and designs vary but in general, if the thermostat stops calling for heat and the boiler temperature is above the LO/DIFF settings in an aquastat (designed to keep the boiler hot for the tankless coiul) then it's ok with me for the burner to shut off immediately.

Letting it run to heat up the boiler if that boiler water is not going to circulate into the occupied space (because the room thermostat is satisfied) is unnecessary.

Of course if we are not circulating water through the boiler and the burner continues to run, because the volume of water to be heated is then small, the burner won't run much longer anyway, even if it runs up to the HI.

Where are Heat Anticipators Used? FAQs

Do heat anticipators also work for cooling systems?

I assume that it is same for cooling / heat pumps--- settings. (June 1, 2015) Jimmer

Reply: no

Jim

I don't think so. Heat anticipators "heat up" the thermostat to tell it to stop calling for heat slightly early so as to reduce the heating "overshoot".

In cooling mode we'd need a thermostat "cooler" to do the equivalent - a feature I've never found present.

Does the heat anticipator delay the turn-on time of the fan motor or blower?

I have a heating system only,which uses a heating thermostat.when the thermostat calls for heat,the burners come on and 20 seconds later the fan motor starts and results in cold air coming out of the ducts before the real heat comes out.my question to you is it the anticipator or the time delay on the fan motor or blower. (Apr 6, 2016) George Kotzias

Reply: no

No, George, the heat anticipator does not direct the start-up operation of the blower fan.

Essentially the heat anticipator shuts the heat OFF slightly before the thermostat is satisfied, anticipating that some additional heat will flow into the space, thus avoiding over-heating.

For a forced warm air system that additional heat coasting will be small or zero.

You'll see that in Honeywell's recommended heat anticipator setting of about 0.4A for traditional forced warm air heat, shown on my annotated drawing below, excerpted from Honeywell's T87 thermostat instructions.