Video:How to Fix a Gas Furnace: Mismatching Furnace and Thermostat

Transcript:How to Fix a Gas Furnace: Mismatching Furnace and Thermostat

Hi, my name is Erick Noack. I'm an HVAC technician for ABC Plumbing, Heating, Cooling, and Electric. And we're here for About.com. Today we're going to talk about some of the issues that can come up with mismatching a thermostat and a furnace or a heating and air conditioning system.

Three Types of Thermostats

This is a communicating thermostat that works specifically with this system. There are many other types of thermostats that will work in some cases but not in others. It's important that you have the correct thermostat matching your system. So there's three basic types of thermostats. There's a millivolt thermostat, a line voltage thermostat, and a low voltage thermostat. Line voltage thermostats are typically used in commercial applications in a warehouse or a large space with a hanging heater. Millivolt thermostats are typically used in a non-powered situation like a pool heater or a jacuzzi heater possibly. Low voltage thermostats are the most commonly used thermostat used in a residential application.

Have Professional Match Thermostat and Gas Furnace

They have to be matched to the system based on the type of furnace that's used and the capacity and capability of that furnace. The best way to make sure you're going to have a thermostat that matches your system is to get it from an HVAC professional. Short of that, taking the old thermostat off and bringing it to the store with you is a great way to make sure you're going to get the correct piece.

Checking Thermostat Type

When you're attempting to identify the type of thermostat you've got, one way to find out what it is is to remove the thermostat and check out the wiring in the back. In this case, it's got very small, low voltage wires, so we know this is a low voltage thermostat. If you're going to remove this thermostat and take it to the home store for a match, you want to make sure you know where those wires went so you can get them in the right place on the new one. Attempting to install a mismatched thermostat on your system can cause damage to the furnace, could cause erratic operation or cause no operation at all. It's very important that the thermostat match the system properly.

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