How a Furnace Works | Repair and Replace

How a Furnace Works | Repair and Replace

Hi, I’m Vance and welcome back to Repair and Replace. Furnace is something you never really think about until it stops working, but with a little bit of knowledge, it’s much easier to troubleshoot problems. So today we ‘re gonna learn how a gas furnace works. First we’ll cover the basics, then we’ll dive a little deeper into the sequence of operation. So you can understand what each component does. Let’s begin ! Although there are some differences, all gas furnaces work in the same basic way. Natural gas is burned to warm up the heat exchanger.

The exhaust fumes are released through the flue gas vent. The blower fan then pushes air over the heat exchanger and circulates it around your home. The furnace runs until the thermostat detects the right temperature and shuts the furnace off. Modern furnaces use a draft inducer fan to help exhaust the emissions, this force draft also increases the efficiency. Condenser furnaces use a dual heat exchanger to condense water vapor , this extracts even more heat out of the combustion. Furnaces are rated by AFUE or (Annual Fuel Utilization Efficiency). This number is a ratio of the fuel burned versus the fuel converted into heat. Older furnaces will have an efficiency rating of 70 AFEU or less, meaning that only 70 percent of the fuel is turned into usable heat. Mid efficiency furnaces are around 80 and High-efficiency condenser furnaces are generally 90 and above. Furnaces can be single stage or dual stage. Single stage furnaces run at one speed, which means it’s either full heat, or no heat. Two stage furnaces can run at full speed or a reduced speed when less heat is needed.

This allows for the furnace to run quieter and may contain a more consistent temperature. Modern furnaces have a set of safety switches that shut down the furnace, when the system is compromised. if a switch is tripped, it will cause the furnace to lockout. The furnace will attempt ignition, several times before going into a hard lockout for up to an hour. Every time a lockout happens the furnace will use flashing lights, as codes to identify the source of the shutdown These codes are unique to each model so check your furnace manual to see what each code means.

When the thermostat calls for heat, voltage is sent to the control board. Next the draft inducer fan pulls fresh air into the burner, which allows for clean and efficient combustion. When the draft motor reaches full speed the pressure switch will close, allowing for the sequence to continue. The pressure switch ensures that there is enough airflow inside the heat exchanger to safely operate the furnace. If the pressure is low, the switch will stay open and will prevent the furnace from igniting. If the pressure is good, then voltage is sent to the hot surface igniter. Some furnaces might use a spark igniter instead. After the igniter heats up the gas valve opens and the burners ignite. When the flame will continue as long as the safety switches remained closed. If the flame isn’t detected after 7 seconds the flame sensor will shut off the gas. When the burner is lit, the blower fan is too late from running to allow the heat exchanger to warm up.

This prevents the furnace from circulating cold air. The blower fan then pushes the air over the heat exchanger and circulates it around your home. The limit switch monitors the temperature of the air passing over the heat exchanger and will shut off the furnace if the system overheats. Any restriction of the airflow might cause the heat exchanger to overheat. That’s why it’s essential to replace the furnace filter every three to six months. Once the thermostat signals that the temperature of the home is normalized, the gas is shut off and combustion stops. The blower motor will continue to run for several minutes until the furnace is cooled down. Finally the unit is placed in standby until the thermostat calls for heat again. Hopefully, this has given you a better understanding of how a furnace works.

Now if your furnace is having trouble running, then watch our troubleshooting guide for a step-by-step breakdown and there’s a link to this in the description below. If you found this video useful then subscribe to our Channel. We’re constantly filming new content every week, so let us know what repairs you’d like to see next and if you need a part for that repair then visit our website. We stock thousands of hard-to-find parts, and we’ll ship it out to you the same day. Thanks for watching .

T4E – Furnace/Winter Tune Up Part 2 (Testing)

T4E – Furnace/Winter Tune Up Part 2 (Testing)

So, we will attach the power. And we could run up to the thermostat and turn the thermostat on but, we like to do it down here where we can be in control. So, this is a jumper wire. And what I’m going to do is hook it up to terminal R, which is my power. And I’m going to hook it up to terminal W. There’s W. So, we’ll put it on W. Okay. Let’s turn the gas on. Normally in a home, that would be on. The door switch is the next safety to protect you from working in here. So, we’re going to push the door switch in. These two lights should come on. There they go. The inducer motor just came on. And that is creating a positive draft up the flue. It’s going to prove to this switch that it’s running.

That signal comes down to the board; will come out of the board and go up here and turn on our hot surface igniter. And all of this is timed by the board. So, it’s what we call a sequence of operation. Now, there’s my pilot or igniter. It’s on. The next thing the board will do is open the gas valve. The flame– the gasoline in lit. We have a flame. Now the board has a timer and in thirty seconds or so, it will turn the blower motor on and blow that heat up and into the house. If I stand up here I’ll be able to feel the blower when it turns on. There it goes. It came on. The blower’s now running, pushing air up, which is pushing that hot air up into your house to heat your house. When the thermostat reaches a temperature it will shut off the furnace; which will shut off the flame. The blower motor will continue to blow till it blows all that heat up into the house and then the blower motor will cycle off.

This is what a service tech does to ensure that your furnace is working properly for the winter. One other thing he or she might do would be do a test for carbon monoxide gases. And again that would be in a video later we’ll do. This process that the furnace is going through now is what we call the sequence of operation. And a service tech always wants to make sure that that operation– that sequence is performing as it should, and that everything is safe electrically and with gas. I did this complete winter tune-up with two nut drivers and a flashlight.

It’s very easy to do. This is a very smart thing that everybody should have done to their furnace in the winter time because if anything goes wrong– the blower just shut off. If anything goes wrong there could be a potential for a fire. And we don’t want to take that chance with anybody getting hurt. There’s also a potential for carbon monoxide poisoning.

And again, we will test at another video; and all these things a service tech will test to make sure your furnace is safe for this winter. Now that it’s done that, we take the door. We put it back on. When we put the door on, it will depress that switch I was holding. And so, putting the door on is important. You want make sure you put it in at the bottom. Slide it up. Raise it up. Push in, and down. And that will secure that it’s on. And I can look in there and see that red and green light flashing so I know I’ve got power again. I take the top door. It goes in at the top. Go up. Push in at the bottom, and down. And that locks the doors on there. The furnace is all back together, and ready to go.

This is what service techs are doing this time of the year. And they call it a winter tune up. .