Does My Thermostat Need To Be Level To Be Accurate?

level thermostat

Thermostats that contain mercury bulbs need to be level to be accurate. Modern day thermostats are either snap action or digital and they should be level only for aesthetic reasons, they just look better when square and plumb with the world.

Kind of like your outdoor unit being level. They just look better.

By the way, that’s my Honeywell 8000 Pro with WiFi. in the image above. I love these thermostats. They can be either programmable or non-programmable. The setup is a walk through. Put in the batteries, set the time and date, and start answering questions.

We had the same stat in a vacation rental we owned. Just pulled up the app on my phone and adjust the temperature for the incoming renters.

A mercury bulb thermostat is simple to identify. Simply remove the front cover and if your’s contains mercury bulbs they will be right out in front and they look just like this:

An old mercury stat could contain just one bulb or many more. Each bulb is part of an electrical circuit that turns on or off a stage or just a part of a heating and/or cooling system.

Because the mercury just floats around inside the thermostat there has to be a point of reference to determine the accuracy of the thermostat. That point of reference is being level.

A thermostat that contains mercury can still be inaccurate if it is level. These thermostats have an internal component called an anticipator. Anticipators control the cycle rate of your equipment.

When an anticipator in on the wrong setting it can cause your furnace to either short cycle or run too long and before it shuts off and wait too long before it comes on again.

You end up being uncomfortable either way. If you suspect this is a problem, I wrote an entire article on how to adjust the heat anticipator. Read it and come back.

The square or rectangular thermostats are easy to make nice and level. But how do you make a round thermostat level?

Most round stats were produced by Honeywell. “The Round” I think they called it mostly. These thermostats contained mercury switches in the early days. So how do you level a round thermostat?

It had a sub-base with a flat spot to set the level. So a small screw driver removes the main control from the subbase and gives you access to the leveling portion of the base. It’s on the top, can’t miss it.

The mounting screws have pivots or elongated holes. Don’t remove the screw unless you need to remount the stat with new anchors. Just loosen them and make an adjustment.

Snap action thermostats like the one to the right are simply a switch that has a slight snap when it opens and closes. These snap action thermostats don’t care if they are level.

Snap Action Thermostat Does Not Have To Be Level But It Looks Better Level

They can hang loose on the wall for all they care. Just set the torpedo level across the top of the stat while tightening the screws with the bubble of the level centered. Most of these thermostat controls are easy to make level with a simple torpedo level.

Don’t be deceived by this bulb in the image below. It doesn’t contain mercury. It’s a snap action stat. That U shaped bar that goes over the top and down has a magnet to the right of the bulb. The magnet is moved by the handle with the orange mark. When the magnet gets close to the bulb it pulls a switch closed and the heat comes on.

Snap Action Thermostat

The bulb is to keep the contacts clean. You wouldn’t believe the dust that can accumulate on the inside of a thermostat. That dust can play havoc with low voltage contacts and even be a problem with accuracy.

The bimetals inside this type of stat is sensitive to the temperature in the room and when covered in dust and whatever they can become less sensitive.

What To Do If Your Mercury Bulb Thermostat Won’t Stay Level

So many thermostats are mounted to the sheet rock and not sufficiently secured to a stud or plate behind the sheet rock. Sheet rock will only hold for a short while if at all.

If there is no backing behind the wall board, then you will have to use molly’s or drywall anchors. If you are unaccustomed to using drywall anchors then find an old piece of sheet rock or something to learn on before destroying the wall behind the thermostat.

Once the wall is weakened sufficiently behind the stat it will make it very difficult to mount it to the wall. My favorite wall anchors are VIGRUE Plastic Self Drilling Drywall Anchors. Just a phillips screw driver and they self tap into sheet rock. Makes a solid mount for more than just thermostats.

So that your thermostat mounts flush and tight to the wall it’s important to have the anchor inserted into the wall completely flush to the wall. If you leave the slightest amount of anchor sticking out from the wall your thermostat will wobble.

Is Mercury In A Thermostat Dangerous?

Definitely is a hazardous material. We used to play with it as kids. Polish pennies and roll it around on the table. Maybe it will reduce my total years, who knows.

From the video above you can see that the mercury is contained in a glass bulb. As long as that bulb is not broken, there is no threat to human health. You would have to smash the thermostat in order create a problem.

Each bulb holds a minimum amount of around 2.8 grams of mercury. The Thermostat Recycling Corporation (TRC) says that the amount of mercury sold in thermostats in the year 2007 was 3.9 tons.

Several states now have recycle programs to recover the mercury and keep it out of the streams and other places that mercury harms. In my state it’s illegal for contractors to sell and install thermostats bearing mercury.

Oregon state law (Oregon Revised Statutes 455.355, implemented by Oregon Administrative Rules 918-440-0500-510) makes it illegal for contractors to install thermostats containing mercury in homes or commercial establishments.

That’s a lot of mercury to recoup at the rate of 2.8 grams at a time by recycling thermostats that contain mercury.

Does My Digital Thermostat Need To Be Level?

You could mount it upside down if you stand on your head a lot. Digital or programmable thermostats don’t care if they level or hanging on a nail. But you and I know we like things looking like we care.

And we don’t want to be a contortionist when we go to see what the settings are. With everything level and straight I sleep better a night. Kind of an obsessive compulsive thing. But I do go to sleep so it can’t be too much obsessiveness.


We live in a day of conveniences. Everything seems to be running our lives instead of us running the day. Little things like thermostats can either be a help or a hindrance to a peaceful experience.

Taking the time to make things right and fitment to our personalities will only make the day go smoother. Nothing is more satisfying than a completed job that is done right.

If you’re not happy with your thermostat being crooked, then straighten it. If you’re not happy with the stat itself then replace it and make it level.

Chad Peterson

Chad Peterson is a veteran of the HVAC industry since 1977. "I like to explain heating and air conditioning problems in a way the average home owner can understand. "

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