Why Is My Thermostat Hissing?

So your thermostat is hissing and you aren’t sure if that’s a sign of a serious problem.

First off, if you hear a hissing noise coming from your thermostat you have a pneumatic thermostat. These types of thermostats frequently hiss. It’s normal and it’s actually part of the “communication” process between the thermostat and the AC or heating system.

But if your pneumatic thermostat is hissing constantly and won’t stop, there’s a problem that requires a professional.

Let’s take a closer look at when “hissing” is normal and when it’s not.

Pneumatic thermostats often hiss when they’re telling your AC or heating system to turn on or off.

Pneumatic thermostats use small bimetallic strips that “read” the temperature. These strips bend back and forth in response to temperature changes. As they bend, they release or restrict pressure inside small tubes filled with compressed air. And when pressure is released, the tubes “hiss”.

Those pressure changes tell your HVAC system when to switch the air or heating on/off. So, the frequent hissing noises coming from your thermostat are simply the metallic strips adjusting the air pressure inside those tubes.

If you hear a hissing noise coming from your pneumatic thermostat that doesn’t stop, that’s not normal.

Most likely, the problem is an air leak somewhere along the tubing connected to your thermostat. Over time, those tubes become brittle and can crack, releasing air constantly while your thermostat struggles to maintain the pressure levels inside that tube.

So, what should you do if your pneumatic thermostat is leaking air?

If your pneumatic thermostat won’t stop hissing, your best bet is to have a professional inspect the air-filled tubes. In some cases, a tech can repair the leak. And in other cases, they’ll need to replace the tube altogether.

However, because pneumatic thermostats are so outdated, you’re better off upgrading to amodern digital thermostat.

Digital thermostats use electrical resistance to measure the temperature in your home and are much more precise when it comes to maintaining your desired temperature.

They can also help you save money if you decide to invest in a programmable thermostat. In fact, Energy Star estimates yearly savings of $180 when you use a programmable thermostat correctly.

Whether you need to fix your pneumatic thermostat or upgrade to a more modern thermostat, George Brazil is here to help.

Just contact us today and we’ll send a professional over as soon as possible to keep you comfortable all year round.