Thermostat Heat Anticipator Adjustment (A Simple Guide)


Thermostat Heat Anticipator

Whether your furnace is electric, gas or oil matters not, and you have a non-digital thermostat and with the cover off you can see a small dial inside that reads “longer cycles” you can make some simple adjustments. Turn the dial counter clockwise for longer cycles for furnace on time and clockwise for shorter cycles.

In this article I’ll teach you how you can simply adjust your heat anticipator to maximize your furnaces efficiency by two methods. One sort of flying by the seat of your pants and the other more technical using a meter to measure amperage.

A little shortcut that is not available on all furnaces is to look on the label. Some manufacturers put the setting in writing, right on the label.

A heat anticipator anticipates the room temperature before it gets uncomfortable. It is a resistor and it creates a resistance to the load of the control it’s connected to, such as a gas valve or electric furnace sequencer. The load on this resistor is measured in amps.

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Because these loads vary from furnace to furnace it requires that the thermostat have an adjustable feature that compensates for these different load and that adjustable feature is called an anticipator.

An adjustable heat anticipator located inside of thermostat.
White Rogers thermostat adjustable differential

Here are the symptoms of a maladjusted heat anticipator.

  1. You get too hot, and then you get too cold
  2. The furnace cycles on and off and you are never warm enough

If you’re experiencing symptom number one with the wild temperature swings, the anticipator is probably set at the longer cycles position of .8 amps or close to it.

If number two is your problem then the anticipator will be at a setting closer to .15 amps.

Be sure when reading the setting that you are looking at the number that the arrow is pointing towards not the end touching the small wire circled around the little round fiber board holding the thing together.

But then I just removed this thermostat and it has no arrow for the anticipator setting. You may need to study up close to understand the individual construction of the anticipator in the particular thermostat you are adjusting.

Also pay attention to the dust collected on the bi-metal toward the bottom of the image below. If your thermostat is in this condition, get a can of air or something to blow it out.

Dirt and grime can interfere with a thermostat’s operation. See the dust collected on the bi-metal in the lower left of the image below.

Which Anticipator Is Adjustable, Heat Or Cool?

Honeywell T874D1165 Two Stage Thermostat

The image above is a good representation of which anticipator is adjustable. The arrows pointing at stage 1 and 2 are the adjustable anticipators for heat.

The arrow labeled fixed cooling anticipator, although a little hard to see, is pointed directly at a small resistor tucked under the mercury bulb mounting plate.

Why Is The Anticipator Setting Important?

What should a thermostat differential be set at? The correct anticipator setting is the one that keeps your home at the temperature you set the thermostat to heat. That’s how you achieve the ideal thermostat swing.

Probably on of the most neglected and least understood settings in an installers setup of a new system. Just a guess, but I would say that nearly half of the service calls I make that have mercury bulb or snap action (non-digital) thermostats have never had a meter put to them to test the setting.

Some furnaces have the anticipator setting listed on the wiring diagram or somewhere within the furnace cabinet.

Most newer systems have upgraded to digital thermostats that are preset at the factory. Within the setup of most higher end digital stats there is a cycle rate adjustment which is essentially the same as an anticipator. Technical support for those thermostats will likely suggest that doesn’t need to be adjusted.

How Would A Thermostat React Without An Anticipator?

This is a really good question, because it will help you understand why a thermostat actually needs an anticipator.

When a thermostat has a call for heat (which simply means the switch in the thermostat closes and wants to turn on the furnace) their is a time lag. It take a minute or two for the furnace to heat up and the fan to kick on.

Then it take a bit of time for the warm air created by the furnace to heat up the duct work and actually deliver warm air into the structure or home.

While this is going on the house is still getting colder, maybe by a degree or two.

Following the above chart starting at number one your home begins to cool down and somewhere along the red line without an anticipator the thermostat says turn on some heat.

By the time the furnace starts and the ducts warm up you may feel a chill when you get to number two.

Heading up to number three it’s going to get warm and when it finally shuts off at number three and the fan keeps running to cool down the elements or heat exchanger you may start taking off some clothes.

But follow the black wavy line (sorry it’s not a pretty line, I’m working on my graph skills) the gap between on and off is much smaller meaning the temperature in the room didn’t swing as wide and you are much more comfortable with an anticipator in your thermostat.

How Should You Accurately Determine The Heat Anticipator Setting On A Room Thermostat?

Aside from moving the setting up and down until you reach a satisfactory comfort level their is a technical way to adjust the anticipator. To accurately adjust a heat anticipator on your room thermostat it requires an amp probe or am-meter as they are sometimes called.

Care needs to be taken at this point if you intend to use a jumper and a meter to measure heat anticipation.

Remove one of the wires, usually red or white. These are normally labeled “R” or “W” on the thermostat. If you jumper the R and W without removing one you run the risk of burning the small resistor wire in the anticipator.

With the thermostat wires removed, jumper the the wires leading to the furnace. Place a digital am-meter over the wire and wait for the furnace to come on completely, fan and all.

If you want to be a handyman you have to have a multi-meter. You’re a lot safer knowing how to test for electricity than ignoring the problems.

Just recently a customer called me about a breaker that kept tripping and the breaker was running very hot. I put my amp meter around the main wires to the furnace and the amp draw was well withing the limits of the breaker.

Turns out every wire in his panel was loose. A lot of heat can be created by loose wiring. Could have been a real problem if left unchecked.

If you want to be that handy person and learn to use a meter I’ve researched a few multi-meters that can do the job without breaking the bank. Check this one out on my recommended products page.

Since you’ve read this far, why not travel just a bit further and scope out a couple of my favorite heating and cooling products and tools.

Thank you for reading my article. I hope the information has led to your ability to make good decisions in either working on or discovering how to solve problems in your home HVAC equipment. These are affiliate links, so if you do decide to use any of them I do earn a commission. In all honesty they are products that I would use in my own home or the homes of my friends and family.

Fireplace remotes by Skytech Remote Control Products . My wife loves this and it probably took all of 30 minutes to install. Replace that wall switch or thermostat for your gas fireplace. Easy installation and instructions. In fact I wrote an article that covers the job pretty thoroughly I think.

Honeywell Thermostats. My favorite two Honeywell stats are the T6 Pro and the 8000 Pro series but their is a bunch to select from besides those two models. You can select WiFi that has the capability of operating your system from your smart phone no mater where you are. Honeywell tech support for homeowners is the best out there. Call them if you need at 800-468-1502 or comment below if you have questions.

Fieldpiece HS33 Expandable Manual Ranging Stick Multimeter for HVAC/R. I carry two of these in my service truck. Just like a spare tire, when I get out away from everything, it’s no time for a break down. The Fieldpiece HS33 gives me the ability to do any aspect of my trade. I can measure motor or element amps, check capacitors, and AC or DC voltages. Even different scales of OHMS for finding shorted windings or grounded conductors in motors or compressors.

Chad Peterson

Chad Peterson is near 40 year veteran of the HVAC industry. "I like to explain heating and air conditioning problems in a way the average home owner can understand. "

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