Thermostat Reads Higher than Actual Temperature, How to Fix

When a thermostat reads higher than actual temperature, your home can get too cold in the winter.  It can also become  too warm in summer.  Now At least several factors affect the thermostat temperature reading besides actual room temperature.  These include aging components drifting out of tolerance in older thermostats.  Or, an improperly positioned thermostat might read incorrectly. Also, broken electronics inside the thermostat or lopsided thermostat installation (not level), cause faulty readings.  So here, we discuss some of these problems and offer suggestions for fixing them, to address this annoying and potentially costly situation.

Why Thermostat Reads Higher than Actual Temperature and How to Fix

We offer these causes and fixes in  order of severity.  That is, the most involved or costly problems appear near the bottom of this list.  The simpler adjustments and cost-free tweaks appear near the top.

First, Verify that your Thermostat is Indeed Reading Incorrectly

To start, obtain an accurate thermometer.  Then, place it as close to the thermostat as practical.  This assures that it’s reading the same air temperature that the thermostat sees.  We use an inexpensive refrigerator thermometer for this purpose, as shown next.

However, for the absolute BEST results, get a thermometer that reads in the 70-degree range midway up its scale.  Also, be sure it’s big enough for you to easily read.  You want to be far enough away from it so that your warm breath does not impact the temperature readings.

Picture of a Honeywell smart thermostat alongside a reference thermometer. This makes it easy to compare the temperature your thermostat reads with the reading from a known-good thermometer nearby.

A Honeywell smart thermostat alongside a reference thermometer. This makes it easy to compare the temperature your thermostat reads with the reading from a known-good thermometer nearby. Thermostat Reads Higher than Actual Temperature.

Now to the causes and fixes of incorrect thermostat temperature readings.

1. Assure that Thermostat Vents are Not Blocked by Dust, Lint, Curtains, Furniture

Picture of the Honeywell RTH9580WF Internet Thermostat, being snapped onto wall plate.

Honeywell RTH9580WF Internet Thermostat, being snapped onto wall plate. Thermostat Reads Higher than Actual Temperature.

This is of big concern in modern day thermostat models, that generate some heat from the microprocessors, memory, and other computer components inside.  If the vents are blocked by dust, furniture, Etc., the thermostat can grow extra warm inside, where the temperature sensor is found.  Thus, this vent blocking can cause higher-than-normal temperature readings.

The solution is to keep your vents open.  Vacuum the thermostat once per season, or more often if your thermostat is in a dusty, “linty” location.  Or, remove the cover and gently blow out the inside with canned air.  Or, if you don’t have canned air, use a soft, fine bristled brush and GENTLY brush out the dirt.  Note however, that some thermostats have no vents on the sides. For these, take them off the wall, and dust out in back of the unit.

2. Thermostat May Need Calibrated

Picture of the Honeywell RTH9580WF thermostat, displaying its -Indoor Display Offsets- screen with a minus 1 degree temperature offset highlighted.

Honeywell RTH9580WF thermostat, displaying its -Indoor Display Offsets- screen with a minus 1 degree temperature offset highlighted. Thermostat Reads Higher than Actual Temperature.

See our post  How to Calibrate Honeywell Thermostat Temperature RTH9580WF  for details.  This explains how to assure that your thermostat is adjusted correctly for reading the right room temperature, for a typical digital smart thermostat.  A temperature offset that is too far in the negative can make the thermostat read a few degrees higher than the actual temperature in the room.

Follow the instructions in your thermostat’s manual to adjust its display offset temperature reading.

3. Thermostat Could Need Leveling

Picture of the Honeywell Smart Thermostat RTH9580WF wall plate, mounted, with wires connected.

Honeywell Smart Thermostat RTH9580WF wall plate, mounted, with wires connected. Thermostat Reads Higher than Actual Temperature.

While leveling is not as important with today’s digital thermostats, we suggest  that you ensure that your thermostat is indeed level, especially if yours is reading room temperature incorrectly.  Not only does leveling the thermostat improve its cosmetic appearance.  It also maximizes airflow through the thermostat, helping to ensure accurate temp readings.

If its manual says to level it, then by all means, make sure the thermostat is level (horizontal and plum).  Sometimes you can get away with simply loosening its mounting screws enough to re position the unit. But if that doesn’t give you enough play to properly set it level, then don’t be afraid to take the unit off the wall and make new, more level screw holes for it.

4. Thermostat Temperature Sensor is Broken

All thermostats have some form of sensing device that detects the temperature near to the thermostat.  Now in today’s t-stats, a temperature sensitive resister such as a thermistor or varistor, can start to offer different resistance values for a given temperature.  This confuses the computer inside the thermostat. This misleads it into reading a higher than actual temp.

Older thermostats also have a sensor.  But this is usually a mechanical bi-metal spring attached to a reading gauge needle.  Some of these may offer a calibration adjustment.  But others, especially if they become bent due to tampering, are best just replaced.  Many of these mercury thermostats have two sensors.  One reads the temperature for viewing.  The other tips the mercury switch on and off as the room heats and cools. In these models, a faulty spring in the visual thermometer portion of the unit can cause exaggerating readings.

In any case though, if you have one of these mechanical thermostats, we highly recommend that you buy a newer, all-electronic model.

5. Thermostat is in Drafty, Extra Warm or Cool Location

Keep all heat or cold-producing appliances well away from your thermostat.  That includes microwave ovens, stoves, sunlamps, most fans, hair dryers, radios, — ANYTHING that produces heat!

Furthermore, do not allow sunlight or lamplight to shine directly on your thermostat, as these can make it read higher than actual room temperature. Keep candles and auxiliary heaters away!

Also, do not install a thermostat on any exterior walls or near windows, doors, as the outside climate will impact the accuracy of thermostat temperature readings.  Keep it away from heated pipes and ducts as well.

Hire an HVAC technician to relocate your thermostat to an interior wall that does not get any direct heating or cooling from the furnace / AC system that it controls.  Mount it approximately five feet above the floor

6. Faulty Wiring can Cause Excess Heat in and Around the Thermostat

Picture of the Honeywell Smart Thermostat RTH9580WF wall plate, mounted, but with wires not yet connected.

Honeywell Smart Thermostat RTH9580WF, wall plate mounted, but with wires not yet connected. Thermostat Reads Higher than Actual Temperature.

In rare cases, incorrectly wired thermostat installations have been known to cause higher than expected temperature readings.  This can occur if, for some reason, the wires inside the thermostat housing become warm due to excess current; often caused by a short circuit.

Check that the thermostat is cool to slightly warm to the touch.  It should not be very hot.  If it is, then call a qualified HVAC technician immediately to check the wiring between the HVAC unit and thermostat, for correct hook up.  Excess warmth in or around the thermostat could indicate a fire hazard, which obviously, you should take care as soon as possible.

7. Thermostat May Read Correctly But Furnace Running Too Much, or AC Running Too Little

It could be that though your thermostat appears to read too high a temperature, that it’s actually reading correctly, and your room actually IS warmer than you think.

For this issue, check that your heating is not running excessively.  If so, this could mean that your thermostat is broken in a different way than simply reading the wrong temperature.  Or, if in summer, perhaps your air conditioning is not running enough to cool your place down to the set temperature on the thermostat.  In either case, call in your trusty HVAC repairman to check out the system to see what might be the matter.

Conclusion

If a thermostat reads higher than actual temperature, don’t take it lightly.  Fix it right away.  Why?  Because this issue can seriously impact how comfortable you feel in your home.  How?  It can make you feel extra cold all year round.  And, especially in the summertime, your air conditioning may run excessively, raising your energy bills.  In winter, it can cause your furnace not to run enough, causing excessive coldness in your living quarters.  So do it up right, and make sure all is well with your thermostat.  Check that it’s reading the right temperature at least once per year, keep it clean and level, and free of any blockages around its vents.

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Revision History

  • 2019-04-15: Shortened post URL and tweaked key phrase targeting.
  • 2019-02-05: First published.




How to Calibrate Honeywell Thermostat Temperature RTH9580WF

In this post, we show how to calibrate Honeywell thermostat temperature RTH9580WF.  Now why would you wish to calibrate the temp reading on a thermostat (t-stat)?  Well, perhaps your Honeywell t-stat reads warmer or cooler than the room feels.  So you’d like to bring the t-stat temp reading more inline with how it really is.

Or, maybe you put your t-stat on an extra  warm wall in your home.  If so, the rest of the house may feel too cold in winter, and too warm in summer.  Or vice versa.  That is, if you place the t-stat on a cool wall, then the reverse may happen.  The rest of the home might feel too cold in the summer, and too warm in winter.

Now the t-stat reading may simply be wrong. Or the reading is right. But the t-stat sits in an extra warm or cool place in the home. To solve these problems,  calibration of the t-stat will likely help.

Calibrating a t-stat is a simple process really. So long as the t-stat you have has a temp offset setting, setting it the right way is easy.  Honeywell does in fact, have this offset setting in its 9000 series RTH9580WF internet controlled t-stat. This is the t-stat we use in our home. So, we’ll discuss next, how to set this offset for better comfort control from this t-stat.

Note that this post applies to the other series 9000 Honeywell t-stats as well.

How to Calibrate Honeywell Thermostat Temperature RTH9580WF

The calibration process has two main steps.  First, you figure out how far off the sensed t-stat temp is from real room temperature.  Then, you set the t-stat temp offset parameter to account for that. Simple, right?  Right!

Find Honeywell Thermostat Temperature Offset

Picture of the Honeywell RTH9580WF t-stat on same wall as a typical fridge freezer thermometer, used for temperature calibration.

Calibrating Honeywell RTH9580WF t-stat temperature, using a fridge freezer thermometer, with Both on same wall.

1. Get an Accurate Thermometer

For this demo, we used a fridge-freezer thermometer as a reference, which works pretty well.  But for best results, buy a glass thermometer that reads temps in the temp range from 50 to 90 degrees.  Not only does this thermometer read more accurately, its scale is often larger.  So, it’s easier to see.

2. Place the Thermometer Near the Thermostat

Put it as close as you can.  We hung our thermometer on the same wall as the t-stat.  See the picture above.

3. Allow Temperature Readings to Stabilize

Let the thermometer hang for twenty minutes to a half hour.  This allows it to accurately read room temp.

4. Read the Thermostat and Thermometer Temperatures

In our case, the thermometer read the room at 76 degrees F. But the t-stat read it at 77 degrees F.

5. Compute the Temperature Offset

Now assume that the thermometer reads the more right of the two.  Then, the room temp reads 1 degree less on the thermometer than what the t-stat reads.  We need this figure in the next task.

Calibrating Honeywell Thermostat Temperature Offset

Many Honeywell t-stats allow setting the -1 degree temp offset we found above with the thermometer.  Here, we show how to do it on our 9000 series RTH9580WF Wi-Fi thermostat.  You start at the   Home   screen, as shown next.

Picture of the Honeywell RTH9580WF WiFi thermostat, showing its -Home- screen, with the -Menu-button highlighted.

Honeywell RTH9580WF WiFi thermostat, showing its -Home- screen, with the -Menu-button highlighted. How to calibrate Honeywell thermostat temperature RTH9580WF.

1. Tap the  MENU  button on the Honeywell Thermostat Home Screen

This brings up the t-stat’s main menu, as shown next.

We then scrolled down using the arrow buttons, to bring the  Preferences  item into view.

Picture of the Honeywell RTH9580WF t-stat, showing its -Main Menu- screen, with the -Preferences- button highlighted.

Honeywell RTH9580WF t-stat, showing its -Main Menu- screen, with the -Preferences- button highlighted.

2. Tap the   Preferences   Button

Find this button pointed at by the pink arrow in the last picture.

The  Preferences  screen then shows, as seen next.  We then scrolled down using the arrow buttons, to bring the  Advanced Preferences  item into view.

Picture of the Honeywell RTH9580WF t-stat, showing its -Preferences- screen, with the -Advanced Preferences- button highlighted.

Honeywell RTH9580WF t-stat, showing its -Preferences- screen, with the -Advanced Preferences- button highlighted. How to calibrate Honeywell thermostat temperature RTH9580WF.

3. Tap the  Advanced Preferences  Button

This shows the first in a series of advanced settings screens then; the  Scheduling Options screen, as shown next.

Picture of the Honeywell RTH9580WF thermostat, showing its -Advanced Preferences, Scheduling Options- screen.

Honeywell RTH9580WF thermostat, showing its -Advanced Preferences, Scheduling Options- screen.

4. Repeatedly Press Green  Next   Button Until you Reach the  Indoor Display Offsets   Settings Screen

See this screen shown next.

Picture of the Honeywell RTH9580WF thermostat, showing its -Indoor Display Offsets- screen, with the -Indoor Temperature Offset- buttons highlighted.

Honeywell RTH9580WF thermostat, showing its -Indoor Display Offsets- screen, with the -Indoor Temperature Offset- buttons highlighted. How to calibrate Honeywell thermostat temperature RTH9580WF.

5. Adjust Indoor Temperature Offset

Use the UP and DOWN arrow buttons to set the indoor temp offset.  So we circled these in pink, in the last picture.

Recall that we found  -1 degree F for our temp offset.  Thus we tapped the DOWN arrow once to enter -1 degree, as shown next.

Picture of the Honeywell RTH9580WF thermostat, showing its -Indoor Display Offsets- screen with a minus 1 degree temperature offset highlighted.

Honeywell RTH9580WF thermostat, showing its -Indoor Display Offsets- screen with a minus 1 degree temperature offset highlighted.

6. Press the Red   Done   Button

Your t-stat then asks whether you wish to save your settings changes, as shown next.

Picture of the Honeywell RTH9580WF thermostat, showing its -Exit Advanced Preferences- screen, prompting for -Save Changes- confirmation.

Honeywell RTH9580WF thermostat, showing its -Exit Advanced Preferences- screen, prompting for -Save Changes- confirmation. How to calibrate Honeywell thermostat temperature RTH9580WF.

7. Press the Green   Yes   Button

The   Saving Changes   screen then briefly shows, as seen next.

Picture of the Honeywell RTH9580WF thermostat, showing its -Saving Changes- screen.

Honeywell RTH9580WF thermostat, showing its -Saving Changes- screen.

After the new temp offset setting saves, you see the next screen.

Picture of the Honeywell RTH9580WF thermostat, showing its -Preferences- screen, with the -Previous Menu- button highlighted.

Honeywell RTH9580WF thermostat, showing its -Preferences- screen, with the -Previous Menu- button highlighted. How to calibrate Honeywell thermostat temperature RTH9580WF.

8. Tap the  Previous Menu   Button

Then, doing so returns you to the  Main Menu  screen, as shown next.

Picture of the Honeywell RTH9580WF thermostat, showing its -Main Menu- screen, with the -Home- button highlighted.

Honeywell RTH9580WF thermostat, showing its -Main Menu- screen, with the -Home- button highlighted.

9. Tap the   Home   Button

This completes then, the temp offset setting routine. The Home button returns you to the t-stat’s Home screen, as shown next.  Note that this screen appears as it did before we changed the temp offset.  E.g. The temp still reads 76, and so does the set temperature.  But our place now feels a little warmer (one degree warmer, in fact).  Now had we made a bigger change, such as -4 degrees, then the current t-stat temp would read lower.

But since we changed ours just -1 degree, the furnace had enough time to raise the room temp.  This made up for that one degree.  So, the current temp stayed the same in this case.

Picture of the Honeywell RTH9580WF thermostat, showing its -Home- screen, after new temperature offset applied.

Honeywell RTH9580WF thermostat, showing its -Home- screen, after new temperature offset applied. How to calibrate Honeywell thermostat temperature RTH9580WF.

10. Done!

Finally, your HVAC system will now, for negative temp offsets, keep your place a little warmer.  Further, for positive temp offsets, your home wil stay a bit cooler.

Enjoy.

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References

Revision History

  • 2019-04-11: Removed ad code and shortened post URL. Added tags.
  • 2019-01-27: Adjusted key phrase targeting, and added some tags.
  • 2017-03-15: Originally published.