Latest / Cool Talk with Hartzell's | Your HVAC Questions, Answered! / Why Your Furnace Is Blowing Cold Air

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Why Your Furnace Is Blowing Cold Air · Cool Talk with Hartzell's | Your HVAC Questions, Answered!

• 0:00
  SPEAKER_01: Imagine you're standing in front of your van, you know, you're freezing, and you hear the furnace kick on, but it's just blowing out this freezing cold air.
• 0:07
  SPEAKER_00: Oh yeah.
• 0:08
  SPEAKER_00: That is literally the worst feeling in the middle of winter.
• 0:10
  SPEAKER_01: Right.
• 0:10
  SPEAKER_01: Your house is actively getting colder while the system is running.
• 0:14
  SPEAKER_01: So welcome to today's deep dive.
• 0:16
  SPEAKER_01: We are going to decode this exact problem because um cold air from a heat vent isn't the diagnosis, right?
• 0:24
  SPEAKER_01: It's really just a symptom.
• 0:25
  SPEAKER_00: Exactly.
• 0:26
  SPEAKER_00: It's a symptom.
• 0:26
  SPEAKER_00: And we are going to walk you through the exact troubleshooting steps today.
• 0:30
  SPEAKER_00: We'll start from a literal one-minute fix you can do yourself all the way up to complex system lockouts.
• 0:36
  SPEAKER_01: And our source material guiding today's deep dive comes directly from Dave Hartzell.
• 0:41
  SPEAKER_01: He runs Harsel's Heat and Air in Kingfisher, Oklahoma.
• 0:43
  SPEAKER_00: Yeah, and he is a Nate certified master HVAC technician, which is huge.
• 0:48
  SPEAKER_01: It really is.
• 0:49
  SPEAKER_01: And he brings exactly 47 years in the trade.
• 0:52
  SPEAKER_01: So, you know, we are talking about 47 years of seeing this specific issue in the field.
• 0:57
  SPEAKER_01: So let's just lay out the narrative here.
• 0:58
  SPEAKER_01: We'll progress logically from simple user errors up to, well, crucial safety shutoffs.
• 1:04
  SPEAKER_00: I like that approach.
• 1:05
  SPEAKER_00: It just makes sense.
• 1:06
  SPEAKER_01: So let's start with the easiest one the one-minute fix.
• 1:09
  SPEAKER_01: What is the absolute first thing you should check?
• 1:11
  SPEAKER_00: Okay.
• 1:11
  SPEAKER_00: The very first thing is your thermostat fan setting.
• 1:14
  SPEAKER_00: You need to see if it's set to on or auto.
• 1:17
  SPEAKER_01: Okay.
• 1:18
  SPEAKER_01: Because if the fan switch is set to on, the blower is just running continuously, right?
• 1:23
  SPEAKER_01: Even when the furnace isn't actively heating.
• 1:26
  SPEAKER_00: Right, exactly.
• 1:26
  SPEAKER_00: So it just pushes room temperature air or even cool air through your vents.
• 1:31
  SPEAKER_00: It makes it feel like the whole furnace is completely broken.
• 1:33
  SPEAKER_01: Aaron Powell When really you just need to switch it to auto.
• 1:36
  SPEAKER_00: Yeah, switching it to auto ensures that the blower only runs when warm air is actually ready to be moved.
• 1:41
  SPEAKER_01: Aaron Powell I mean I have to push back a little here because it seems almost too simple.
• 1:46
  SPEAKER_01: Like having such a scary problem have such an easy fix.
• 1:50
  SPEAKER_01: Running the fan on on in winter is basically just running a ceiling fan in the dead of winter, right?
• 1:56
  SPEAKER_00: That is a perfect analogy.
• 1:57
  SPEAKER_00: It just aggressively circulates cold air and gives you a wind chill effect in your own living room.
• 2:03
  SPEAKER_01: Okay, so that's the one-minute fix.
• 2:04
  SPEAKER_01: But let's say the fan is already set to auto.
• 2:07
  SPEAKER_01: Why might you still feel cold air when it first turns on?
• 2:11
  SPEAKER_00: Well, this comes down to the virtue of patience.
• 2:14
  SPEAKER_00: Furnaces, uh, they do not produce hot air instantaneously.
• 2:18
  SPEAKER_01: Like starting a car engine on a freezing morning, you can't just blast the heater the second you turn the key.
• 2:23
  SPEAKER_00: Exactly like that.
• 2:24
  SPEAKER_00: The engine block itself hasn't warmed up yet.
• 2:27
  SPEAKER_00: In a furnace, there's a whole sequence.
• 2:29
  SPEAKER_00: First, the burner's light, then the heat exchanger warms up, and only then does the blower fan turn on.
• 2:35
  SPEAKER_01: Uh, so if you are hovering right over the vent the second it kicks on, the initial push of air is naturally going to be cool.
• 2:41
  SPEAKER_00: Yeah, it's just ambient air in the ducts being pushed out.
• 2:44
  SPEAKER_00: You literally just need to give it a few minutes to see if it warms up.
• 2:47
  SPEAKER_01: Okay, so you've checked the settings and you've waited several minutes, but it's still blowing cold.
• 2:51
  SPEAKER_01: Now we move from normal operation to um a physical obstruction.
• 2:57
  SPEAKER_01: The air filter.
• 2:58
  SPEAKER_00: Yes, the clogged filter.
• 3:00
  SPEAKER_00: This introduces a fascinating mechanical paradox.
• 3:03
  SPEAKER_00: A dirty filter can cause the furnace to blow cold air because of a safety mechanism called the high limit switch.
• 3:10
  SPEAKER_01: So if a filter is choked with dust, the airflow basically just stops.
• 3:14
  SPEAKER_00: It stops dead.
• 3:15
  SPEAKER_00: And then the heat builds up dangerously inside the unit because it has nowhere to go.
• 3:19
  SPEAKER_01: Wait, so the furnace is actually getting too hot, and its reaction to being too hot is to blast you with cold air.
• 3:25
  SPEAKER_00: I know, it sounds backwards, but it's a brilliant safety feature to prevent severe overheating.
• 3:30
  SPEAKER_00: The high limit switch just completely shuts off the gas burners.
• 3:34
  SPEAKER_01: But the fan keeps running.
• 3:36
  SPEAKER_00: Yes, the fan keeps running to cool the internal system down, so that's why you get cold air at the vents.
• 3:42
  SPEAKER_00: The system will actually keep trying, overheating, and shutting down in this infinite loop.
• 3:48
  SPEAKER_01: So it's essentially suffocating on its own heat.
• 3:50
  SPEAKER_00: Precisely.
• 3:51
  SPEAKER_00: So you must take out the filter, and if you can't see light through it, change it immediately.
• 3:56
  SPEAKER_01: Got it.
• 3:56
  SPEAKER_01: So you've checked the settings, you waited, and you changed the filter.
• 4:00
  SPEAKER_01: This is the crucial pivot point in the deep dive, I think, where DIY ends and professional mechanics begin.
• 4:06
  SPEAKER_00: Definitely.
• 4:07
  SPEAKER_00: This is the hands-off zone.
• 4:08
  SPEAKER_00: Because now we have to talk about the ignition sequence and the sensors.
• 4:11
  SPEAKER_01: Right, because the furnace relies on a very precise sequence to burn gas safely.
• 4:17
  SPEAKER_01: And if that sequence fails, the system just locks out.
• 4:20
  SPEAKER_00: Exactly.
• 4:21
  SPEAKER_00: Whether you have an older standing pilot light or a modern electronic igniter, uh, you know, the ones that spark or glow, there is a component called the flame sensor.
• 4:31
  SPEAKER_01: Aaron Powell The Flame Sorry.
• 4:32
  SPEAKER_00: Yeah.
• 4:32
  SPEAKER_00: It's this small part that confirms a fire is actually lit.
• 4:36
  SPEAKER_00: If the igniter fails, or if a dirty flame sensor can't verify the flame, the furnace immediately shuts the gas off.
• 4:43
  SPEAKER_01: Aaron Ross Powell Just to prevent a massive buildup of unburned gas in your house.
• 4:46
  SPEAKER_00: Aaron Powell Right.
• 4:47
  SPEAKER_00: But again, the blower might keep pushing cold air to purge the cabinet.
• 4:51
  SPEAKER_01: So the flame sensor is basically the furnace's eyes.
• 4:54
  SPEAKER_01: Like if it's blinded by dirt, it just assumes there's no fire and cuts the gas.
• 4:58
  SPEAKER_00: That is exactly what it does.
• 4:59
  SPEAKER_00: And while you can safely look to see if the burners are lighting, cleaning those sensors, or, you know, adjusting gas valves, that is strictly for trained technicians.
• 5:07
  SPEAKER_01: Yeah, absolutely.
• 5:08
  SPEAKER_01: And speaking of gas, since we are dealing with controlled explosions in your house, we really need to talk about when to completely walk away.
• 5:16
  SPEAKER_00: Oh, for sure.
• 5:16
  SPEAKER_00: Absolute safety protocols.
• 5:18
  SPEAKER_00: If you ever smell that rotten egg odor of gas, all troubleshooting stops instantly.
• 5:23
  SPEAKER_01: Period.
• 5:24
  SPEAKER_01: Do not poke around, do not flip switches.
• 5:26
  SPEAKER_00: Right.
• 5:26
  SPEAKER_00: You evacuate the house and call 911 or the gas company from a safe distance outside.
• 5:31
  SPEAKER_01: But there's a silent danger too, right?
• 5:32
  SPEAKER_01: The heat exchanger.
• 5:33
  SPEAKER_00: Yes.
• 5:34
  SPEAKER_00: The heat exchanger is a metal barrier that separates the clean, breathable air in your home from the toxic combustion exhaust.
• 5:42
  SPEAKER_01: Which normally goes safely out the flue.
• 5:44
  SPEAKER_00: Right.
• 5:44
  SPEAKER_00: But if this metal cracks, carbon monoxide can enter your home.
• 5:48
  SPEAKER_00: The fan blowing over a crack actually pushes air into the fire, disrupts the flame, and the safety switches shut the gas off.
• 5:55
  SPEAKER_00: And again, you get cold air.
• 5:57
  SPEAKER_01: It's basically a breach in the quarantine zone between toxic exhaust and clean breathing air.
• 6:02
  SPEAKER_01: This is why trained evaluations are just non-negotiable.
• 6:04
  SPEAKER_00: You literally cannot diagnose that safely on your own.
• 6:07
  SPEAKER_01: Wow.
• 6:07
  SPEAKER_01: Okay, so while older furnaces have their risks, modern high efficiency units have a really unique uh water-based quirk that can cause this exact same cold air symptom.
• 6:18
  SPEAKER_00: This one throws people off all the time.
• 6:20
  SPEAKER_00: High efficiency furnaces create condensation that can actually clog and shut down the entire system.
• 6:27
  SPEAKER_01: Wait, a furnace makes water?
• 6:28
  SPEAKER_01: I mean, I thought it just made fire and heat.
• 6:30
  SPEAKER_00: I know, it's wild physics.
• 6:31
  SPEAKER_00: But these furnaces extract so much heat from the burning gaff that the exhaust actually hits a dew point.
• 6:37
  SPEAKER_00: It condenses into liquid water.
• 6:39
  SPEAKER_01: Oh wow.
• 6:40
  SPEAKER_00: Yeah, and this water has to drain away through a small tube.
• 6:44
  SPEAKER_00: If that drain line clogs with algae or debris, the water backs up.
• 6:48
  SPEAKER_00: A safety switch detects the backup and locks the furnace out.
• 6:52
  SPEAKER_01: So it shuts off the burners, but the fan keeps blowing cold air.
• 6:56
  SPEAKER_00: Exactly.
• 6:57
  SPEAKER_00: You might even see water pooling on the floor around the unit, but clearing that condensate lockout is absolutely a professional service call.
• 7:04
  SPEAKER_01: Right.
• 7:04
  SPEAKER_01: You're mixing water and electrical sensors.
• 7:06
  SPEAKER_01: Best to leave that alone.
• 7:08
  SPEAKER_01: So let's summarize the game plan for you.
• 7:10
  SPEAKER_01: First, set your fan to auto.
• 7:12
  SPEAKER_01: Second, wait a few minutes for the startup sequence.
• 7:14
  SPEAKER_01: Third, check for a clogged filter.
• 7:16
  SPEAKER_00: And you can check the breaker once and simply watch to see if the burner's light.
• 7:20
  SPEAKER_01: But if you still have cold air after that, or if you ever smell gas, you are out of your depth.
• 7:26
  SPEAKER_01: And I want to leave you with a final perspective shift here.
• 7:28
  SPEAKER_00: It's an important one.
• 7:29
  SPEAKER_01: Yeah.
• 7:30
  SPEAKER_01: When you are shivering in your home, it feels like your furnace is failing you.
• 7:35
  SPEAKER_01: But in reality, whether it's a high limit switch, a flame sensor, or a condensate lockout, that cold air is often proof that your furnace is highly intelligent.
• 7:45
  SPEAKER_00: Yes.
• 7:45
  SPEAKER_00: It is actively choosing to shut down to protect your home from fire, gas leaks, or carbon monoxide.
• 7:51
  SPEAKER_01: Exactly.
• 7:52
  SPEAKER_01: It's not breaking, it's protecting you.
• 7:54
  SPEAKER_00: That is the perfect way to look at it.
• 7:56
  SPEAKER_01: So if your house is still cold after the easy checks, don't tough it out.
• 7:59
  SPEAKER_01: Contact Dave Hartzell at Hartcell's Heat and Air.
• 8:02
  SPEAKER_01: They're located at 602 South Main in Kingfisher, Oklahoma.
• 8:06
  SPEAKER_00: They are a family run business, Nate certified, with exactly 47 years in the trade.
• 8:10
  SPEAKER_01: And they boast 4.8 stars with over 300 Google reviews, which is just incredible.
• 8:15
  SPEAKER_01: You can call them at 405 375 4822 or book online at heartcellsheetair.com.
• 8:22
  SPEAKER_01: Thanks for joining our deep dive today and stay warm out there.