Latest / Cool Talk with Hartzell's | Your HVAC Questions, Answered! / Bigger AC Units Won't Fix Your Upstairs

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Bigger AC Units Won't Fix Your Upstairs · Cool Talk with Hartzell's | Your HVAC Questions, Answered!

• 0:00
  SPEAKER_01: So if your upstairs bedroom is, you know, ten degrees hotter than your living room this summer, the absolute worst thing you can do is go out and buy a bigger air conditioner.
• 0:08
  SPEAKER_01: Right.
• 0:09
  SPEAKER_01: Yeah.
• 0:10
  SPEAKER_01: Which completely defies common sense for well most people.
• 0:13
  SPEAKER_01: Exactly.
• 0:14
  SPEAKER_01: I mean, you would think a bigger machine just solves the problem.
• 0:17
  SPEAKER_01: But let's uh let's paint the picture that you, the listener, might actually be living in right now.
• 0:22
  SPEAKER_00: Oh, I'm sure many are.
• 0:24
  SPEAKER_01: Yeah.
• 0:24
  SPEAKER_01: So it's a sweltering July evening.
• 0:26
  SPEAKER_01: You're downstairs in your two-story home, just you know, stretched out on the couch.
• 0:31
  SPEAKER_00: Nice and cool.
• 0:32
  SPEAKER_01: Right.
• 0:32
  SPEAKER_01: The ambient temperature around you is a crisp, perfectly comfortable 72 degrees.
• 0:37
  SPEAKER_01: It feels great.
• 0:39
  SPEAKER_01: But directly above you, maybe you have a teenager trying to go to sleep, and they are absolutely sweating through their sheets.
• 0:44
  SPEAKER_00: It's miserable.
• 0:45
  SPEAKER_01: Yeah.
• 0:45
  SPEAKER_01: Their bedroom is hovering at this stagnant, stuffy 81 degrees.
• 0:49
  SPEAKER_01: They've got like a box fan running on high.
• 0:52
  SPEAKER_01: The windows are cracked open in this desperate plea for a breeze.
• 0:55
  SPEAKER_01: And it's just awful.
• 0:56
  SPEAKER_00: It's one of the most frequent and frankly, um most frustrating comfort complaints homeowners deal with across the country.
• 1:05
  SPEAKER_01: And that is exactly what we're tackling in our deep dive today.
• 1:08
  SPEAKER_01: We're going to explain the hidden physics of why your two-story home suffers from this severe temperature stratification during the summer.
• 1:15
  SPEAKER_00: And more importantly, we're going to debunk that incredibly common and wildly expensive myth that a bigger AC is the silver bullet.
• 1:24
  SPEAKER_01: Right.
• 1:24
  SPEAKER_01: And to do that, we have a really grounded stack of sources today.
• 1:27
  SPEAKER_01: We are pulling from the field data of an HEAC veteran with uh 45 years of hands-on experience, Dave Hartzall.
• 1:36
  SPEAKER_00: Yeah.
• 1:36
  SPEAKER_00: And we're combining his real-world findings with Department of Energy data on attic radiant heat.
• 1:41
  SPEAKER_01: Plus, we are also looking at the underlying math from the ACCA manual D, which you know dictates how residential ductwork is actually engineered.
• 1:49
  SPEAKER_00: Right.
• 1:50
  SPEAKER_00: The actual math behind the airflow.
• 1:51
  SPEAKER_01: Exactly.
• 1:52
  SPEAKER_01: And there is a specific case study in these field notes that anchors this whole problem perfectly.
• 1:56
  SPEAKER_00: Oh, the Yukon House.
• 1:57
  SPEAKER_01: Yeah.
• 1:57
  SPEAKER_01: A home in Yukon, Oklahoma.
• 1:59
  SPEAKER_01: Now, this isn't some century-old drafty farmhouse with zero insulation.
• 2:02
  SPEAKER_01: This is a 2018 new build home.
• 2:05
  SPEAKER_00: Basically brand new.
• 2:06
  SPEAKER_01: Right.
• 2:06
  SPEAKER_01: And the homeowner has the exact 72-degree downstairs, 81 degree upstairs split we just talked about.
• 2:12
  SPEAKER_00: Yeah.
• 2:13
  SPEAKER_01: They've already had two different HVAC companies out to diagnose the system.
• 2:16
  SPEAKER_00: And I bet I know what they said.
• 2:18
  SPEAKER_01: Yep.
• 2:18
  SPEAKER_01: Both companies offer the exact same quote.
• 2:20
  SPEAKER_01: They said, your AC is struggling.
• 2:23
  SPEAKER_01: You need to buy a larger capacity unit.
• 2:25
  SPEAKER_00: Aaron Powell Which is um it's a fundamental misdiagnosis of what that house is actually battling.
• 2:29
  SPEAKER_01: Aaron Powell So let's figure out what they missed.
• 2:31
  SPEAKER_01: I mean, before we even look at the air conditioner, we need to understand the environment the second floor is actually dealing with.
• 2:37
  SPEAKER_00: Right.
• 2:38
  SPEAKER_00: Because the assumption is usually just that, well, hot air rises, so the upstairs is naturally going to be warmer.
• 2:43
  SPEAKER_01: Which is true, right.
• 2:44
  SPEAKER_00: I mean, hot air certainly rises, yeah.
• 2:46
  SPEAKER_00: And that basic rule of thermodynamics is part of the equation.
• 2:50
  SPEAKER_00: But the rising air from your downstairs living room is really just a drop in the bucket.
• 2:54
  SPEAKER_01: Okay.
• 2:54
  SPEAKER_01: So what's the real issue?
• 2:56
  SPEAKER_00: The true thermal enemy is sitting right above the second floor ceiling.
• 3:00
  SPEAKER_00: It's your attic space.
• 3:01
  SPEAKER_01: Okay, let's look at the Department of Energy data on this because it's wild.
• 3:05
  SPEAKER_01: During a central Oklahoma summer, the sun is just relentless on those roof shingles.
• 3:11
  SPEAKER_00: Oh, absolutely.
• 3:11
  SPEAKER_00: Brutal.
• 3:12
  SPEAKER_01: And that thermal energy transfers directly through the roof deck and into the enclosed attic.
• 3:18
  SPEAKER_01: The DOE data notes that these spaces, which are, you know, very often underventilated, they routinely reach 130 to 150 degrees.
• 3:27
  SPEAKER_00: Yeah, that is a staggering amount of thermal energy.
• 3:30
  SPEAKER_00: And, you know, heat naturally moves toward colder spaces.
• 3:33
  SPEAKER_01: Wants to balance out.
• 3:35
  SPEAKER_00: Right, exactly.
• 3:35
  SPEAKER_00: It doesn't just sit there politely in the attic.
• 3:38
  SPEAKER_00: That massive 150-degree heat load radiates straight down, pushing through whatever insulation you have, penetrating the drywall, and just radiating directly into the second floor rooms.
• 3:47
  SPEAKER_01: Oh man.
• 3:48
  SPEAKER_01: So if you're sleeping in that upstairs bedroom, you're essentially sandwiched.
• 3:52
  SPEAKER_00: Pretty much.
• 3:52
  SPEAKER_01: You have the ambient heat of the house rising from below and this 150-degree radiant oven pressing down on you from above.
• 3:59
  SPEAKER_01: It's like it's like being stuck inside a thermal panini press.
• 4:02
  SPEAKER_00: Yeah, a panini press.
• 4:03
  SPEAKER_00: That paints a very vivid, very uncomfortable picture.
• 4:06
  SPEAKER_01: But wait, if I'm stuck in this panini press and I have a central air conditioning system running downstairs, shouldn't that system be overwhelming the radiant heat?
• 4:15
  SPEAKER_00: You'd think so, right?
• 4:16
  SPEAKER_00: Yeah.
• 4:16
  SPEAKER_01: I mean, why does the AC seem to just give up or ignore the second floor entirely?
• 4:21
  SPEAKER_00: Aaron Powell Well, the AC isn't intentionally ignoring anything.
• 4:24
  SPEAKER_00: It's uh it's functionally blind to the second floor.
• 4:27
  SPEAKER_01: Blind to it.
• 4:28
  SPEAKER_00: Yeah.
• 4:28
  SPEAKER_00: And this comes down to two major mechanical design flaws in how the vast majority of two-story homes are built.
• 4:36
  SPEAKER_00: The first flaw is what we call the single zone problem.
• 4:39
  SPEAKER_00: Trevor Burrus, Jr.
• 4:39
  SPEAKER_01: Meaning there is only one thermostat for the entire house.
• 4:42
  SPEAKER_00: Aaron Ross Powell Exactly.
• 4:43
  SPEAKER_00: Just one.
• 4:45
  SPEAKER_00: And builders almost always place that single thermostat downstairs.
• 4:48
  SPEAKER_01: Aaron Powell Which I guess makes sense on paper, right?
• 4:51
  SPEAKER_00: Oh, sure.
• 4:51
  SPEAKER_00: The logic is that the downstairs is the primary living space where the family cooks, eats, hangs out during the day.
• 4:57
  SPEAKER_00: But that thermostat is the sole brain of your HVAC system.
• 5:02
  SPEAKER_00: Right.
• 5:02
  SPEAKER_00: It only knows the temperature of the air immediately surrounding it in that downstairs hallway.
• 5:07
  SPEAKER_01: Oh, I see.
• 5:07
  SPEAKER_01: And the hallway downstairs doesn't have a 150-degree attic directly above it.
• 5:11
  SPEAKER_00: It sure doesn't.
• 5:12
  SPEAKER_00: So the thermostat reads a very comfortable 72 degrees and it just shuts the entire cooling system down.
• 5:19
  SPEAKER_00: Wow.
• 5:19
  SPEAKER_00: Yeah.
• 5:19
  SPEAKER_00: It is completely unaware that the upstairs bedroom is baking at 81 degrees.
• 5:24
  SPEAKER_00: The system is doing exactly what it was commanded to do based on the sensible temperature downstairs.
• 5:29
  SPEAKER_01: Okay, so the brain shuts the system off prematurely, I get that.
• 5:33
  SPEAKER_01: But while the system is running, while that cold air is supposedly pumping, why doesn't the upstairs cool down at the same rate as the downstairs?
• 5:41
  SPEAKER_01: That is a great question.
• 5:43
  SPEAKER_01: Do the air currents just like get tired on the way up?
• 5:46
  SPEAKER_00: Well, effectively, yes.
• 5:47
  SPEAKER_00: And that brings us to the second mechanical flaw, which is hidden inside your walls.
• 5:51
  SPEAKER_01: Okay, what is it?
• 5:52
  SPEAKER_00: This is where the ACCA manual D data becomes critical.
• 5:56
  SPEAKER_00: Manual D is um it's the mathematical formula that HVAC engineers use to size ductwork, calculate airflow, and determine how much resistance the air will face as it moves through the house.
• 6:07
  SPEAKER_01: Because air moving through a pipe isn't a frictionless event.
• 6:10
  SPEAKER_00: Far from it.
• 6:11
  SPEAKER_00: In most standard construction, builders use a single massive trunk line to feed the whole house just to save on costs.
• 6:17
  SPEAKER_01: Right, keep it cheap.
• 6:19
  SPEAKER_00: Exactly.
• 6:20
  SPEAKER_00: Now the branch ducts that break off to feed your downstairs vents are relatively short.
• 6:25
  SPEAKER_00: The air doesn't have to travel far at all.
• 6:27
  SPEAKER_01: Makes sense.
• 6:28
  SPEAKER_00: But the branch ducts that feed the upstairs, they have to snake their way across the basement or crawl space, up a vertical wall cavity, across the second floor ceiling, and finally down into the bedroom.
• 6:41
  SPEAKER_01: So we're talking about dozens of extra feet of ductwork plus a bunch of elbows and turns.
• 6:46
  SPEAKER_00: Yeah, and every single foot of that ductwork, every single 90-degree turn creates friction.
• 6:51
  SPEAKER_00: The air is physically rubbing against the inside of the metal or corrugated flex duct.
• 6:56
  SPEAKER_01: Wow.
• 6:57
  SPEAKER_00: This is known as friction loss.
• 6:59
  SPEAKER_00: And as the air battles that friction, it loses velocity and pressure.
• 7:03
  SPEAKER_01: You know, it's like trying to drink a thick milkshake.
• 7:05
  SPEAKER_00: Okay, I like where this is going.
• 7:06
  SPEAKER_01: If you use a normal short straw, it's fairly easy.
• 7:09
  SPEAKER_01: But if you try to drink that same milkshake through one of those novelty three-foot-long curly straws, you have to pull incredibly hard because of all the extra friction and distance.
• 7:20
  SPEAKER_00: That is a brilliant way to conceptualize it.
• 7:22
  SPEAKER_00: Yes, exactly.
• 7:23
  SPEAKER_00: The HVAC blower motor only has so much power.
• 7:27
  SPEAKER_00: Right.
• 7:27
  SPEAKER_00: So because of the friction loss along those long vertical and horizontal runs, the upstairs registers actually push out significantly fewer cubic feet per minute or CFM of conditioned air than the downstairs registers do.
• 7:41
  SPEAKER_01: Yeah, so it's a double whammy.
• 7:42
  SPEAKER_01: It reminds me of trying to water a massive yard with a single sprinkler system.
• 7:47
  SPEAKER_00: Oh yeah.
• 7:48
  SPEAKER_01: Let's say you have one water sensor controlling the whole setup and you place it right next to the very first sprinkler head.
• 7:53
  SPEAKER_00: The sensor gets drenched almost immediately.
• 7:55
  SPEAKER_01: Right.
• 7:55
  SPEAKER_01: It takes five minutes, the sensor says, okay, the lawn is watered and shuts the main valve off.
• 8:00
  SPEAKER_01: Yeah.
• 8:00
  SPEAKER_01: Meanwhile, the grass on the far side of the yard, which is connected to like a hundred feet of hose, only got a tiny trickle of water because of the distance.
• 8:08
  SPEAKER_00: Yep.
• 8:09
  SPEAKER_01: Now that side of the yard is turning brown and dying, while the grass near the sensor is practically a swamp.
• 8:14
  SPEAKER_00: You've just perfectly described the mechanical reality of the modern two-story home.
• 8:18
  SPEAKER_00: The upstairs needs more cooling to fight the attic heat, but because of friction loss, it is mechanically designed to receive less air.
• 8:26
  SPEAKER_01: And because of the thermostat placement.
• 8:28
  SPEAKER_00: Exactly.
• 8:28
  SPEAKER_00: Because of the single zone thermostat downstairs, it receives that weak airflow for a shorter amount of time.
• 8:34
  SPEAKER_01: Which brings us right back to the Yukon, Oklahoma case study.
• 8:37
  SPEAKER_01: The homeowner is told by two different companies that the solution is a bigger, high capacity air conditioner.
• 8:44
  SPEAKER_00: Right.
• 8:44
  SPEAKER_01: And I'll be honest, if I know my upstairs isn't getting enough cold air, putting a bigger engine outside to push more air sounds entirely logical to me.
• 8:54
  SPEAKER_01: Why is that common sense solution actually a trap?
• 8:57
  SPEAKER_00: Well, it requires us to sort of elevate how we think about what an air conditioner actually does.
• 9:02
  SPEAKER_00: We really have to dispel this bigger is better myth.
• 9:04
  SPEAKER_01: Okay, let's do it.
• 9:05
  SPEAKER_00: When you buy a larger capacity AC, say, moving from a three-ton unit to a four-ton unit, it doesn't necessarily mean the air coming out of the vents is colder.
• 9:14
  SPEAKER_01: Wait, really?
• 9:14
  SPEAKER_00: Yeah.
• 9:15
  SPEAKER_00: It just means the system is capable of removing a larger volume of heat from the home in a shorter amount of time.
• 9:21
  SPEAKER_01: Okay, but it drops the temperature faster.
• 9:23
  SPEAKER_01: Wouldn't that help?
• 9:24
  SPEAKER_00: It actually makes the stratification much worse.
• 9:26
  SPEAKER_00: And it has to do with sensible versus latent heat.
• 9:29
  SPEAKER_01: Sounds technical.
• 9:30
  SPEAKER_01: What's the difference?
• 9:31
  SPEAKER_00: Sensible heat is what you read on a thermometer, the actual temperature of the air.
• 9:35
  SPEAKER_00: Latent heat is the thermal energy trapped in moisture, basically, the humidity in your house.
• 9:40
  SPEAKER_01: Ah, gotcha.
• 9:42
  SPEAKER_01: And anyone who has lived through a humid summer knows that 75 degrees with high humidity feels radically more oppressive than 75 degrees in dry air.
• 9:51
  SPEAKER_00: Exactly.
• 9:52
  SPEAKER_00: An air conditioner is essentially a giant dehumidifier that happens to cool the air.
• 9:56
  SPEAKER_00: Okay.
• 9:57
  SPEAKER_00: To remove that latent heat, to pull the humidity out of the air, the system has to run for a sustained period of time so the indoor coil can get freezing cold and condense that moisture.
• 10:07
  SPEAKER_01: Okay, so if we drop a massive oversized AC unit into this single zone house.
• 10:20
  SPEAKER_01: Oh, I see where this is going.
• 10:21
  SPEAKER_00: Yeah.
• 10:22
  SPEAKER_00: The thermostat reads 72 degrees in perhaps 10 minutes instead of 20, and it shuts the system down.
• 10:27
  SPEAKER_00: This is called short cycling.
• 10:29
  SPEAKER_01: Wow.
• 10:29
  SPEAKER_01: So the upstairs only got 10 minutes of that weak friction-heavy airflow before the system just completely shut off.
• 10:36
  SPEAKER_00: Exactly.
• 10:37
  SPEAKER_00: You are actually decreasing the total cooling runtime for the upstairs.
• 10:41
  SPEAKER_00: But um it gets worse.
• 10:43
  SPEAKER_01: How could it be worse?
• 10:44
  SPEAKER_00: Because the system short cycled, it never ran long enough to properly extract the latent heat.
• 10:49
  SPEAKER_00: It didn't pull the humidity out of the air.
• 10:51
  SPEAKER_01: Oh man.
• 10:51
  SPEAKER_01: So you just spent, what,$15,000 on a massive new AC, and your reward is that your upstairs gets less total airflow and your downstairs feels like a cold, clammy swamp.
• 11:03
  SPEAKER_00: It is an incredibly expensive mistake.
• 11:05
  SPEAKER_00: A larger AC is the exact enemy of what the second floor desperately needs.
• 11:09
  SPEAKER_01: Yeah, it's crazy.
• 11:10
  SPEAKER_00: You don't need a blast of cold air.
• 11:12
  SPEAKER_00: You need long, steady run times so the air has time to travel up those long ducks, combat the radiant heat from the attic, and gradually pull both the heat and the humidity out of the upstairs rooms.
• 11:22
  SPEAKER_01: That is wild.
• 11:24
  SPEAKER_01: I can imagine the heartbreak of a homeowner writing a huge check for a new unit, only to realize they made the physics of their home worse.
• 11:32
  SPEAKER_00: It happens all the time.
• 11:34
  SPEAKER_01: So let's talk real solutions.
• 11:35
  SPEAKER_01: Since buying a bigger AC is completely off the table, what can you, the listener, actually do today to fix a sweltering upstairs bedroom?
• 11:44
  SPEAKER_00: Right.
• 11:45
  SPEAKER_00: Let's get into the fixes.
• 11:46
  SPEAKER_01: I want to go through them, starting with the cheap band-aids and moving to the more surgical solutions.
• 11:50
  SPEAKER_00: Okay, let's start with manipulating the airflow you currently have.
• 11:53
  SPEAKER_00: You can do this today for free.
• 11:55
  SPEAKER_01: Nice.
• 11:55
  SPEAKER_00: Go to your downstairs registers, the vents on the floor or the ceiling, and manually close the dampers by about 30 to 40%, and then make sure every single register upstairs is a hundred percent wide open.
• 12:07
  SPEAKER_01: Okay, but I have a feeling the specific percentage matters here.
• 12:10
  SPEAKER_01: Why?
• 12:11
  SPEAKER_01: Just thirty to forty percent.
• 12:13
  SPEAKER_01: If I want to force all the air upstairs, why not just close the downstairs vents completely?
• 12:18
  SPEAKER_00: Because if you close them a hundred percent, you are choking the airflow back to the indoor unit and you will fundamentally break the refrigeration cycle.
• 12:26
  SPEAKER_01: Wait, how so?
• 12:27
  SPEAKER_00: Well, inside your indoor unit is an evaporator coil.
• 12:30
  SPEAKER_00: It's filled with refrigerant that gets incredibly cold.
• 12:33
  SPEAKER_00: It requires a constant flow of warm house air blowing over it to absorb heat.
• 12:39
  SPEAKER_00: Okay, I follow.
• 12:40
  SPEAKER_00: If you close too many vents and choke off that airflow, there isn't enough warm air to transfer heat into the refrigerant.
• 12:47
  SPEAKER_00: The coil's temperature will drop below 32 degrees, and the natural condensation on the coil will literally freeze into a solid block of ice.
• 12:55
  SPEAKER_01: Oh wow.
• 12:56
  SPEAKER_01: So you restrict the air, you freeze the system solid, and you end up with zero cooling and a hefty repair bill.
• 13:02
  SPEAKER_00: Precisely.
• 13:03
  SPEAKER_00: That's why you only close the downstairs vents 30 to 40%.
• 13:06
  SPEAKER_00: It creates just enough back pressure in the main trunk line to force slightly more air up those long vertical ducts to the second floor without starving the evaporator coil.
• 13:15
  SPEAKER_01: Okay, so that helps the duct work problem.
• 13:17
  SPEAKER_01: But what about the panini press?
• 13:19
  SPEAKER_01: How do we fight the 150-degree attic?
• 13:21
  SPEAKER_00: You have to tackle the radiant heat transfer.
• 13:23
  SPEAKER_00: First, get the heat out of the attic.
• 13:25
  SPEAKER_01: How do you do that?
• 13:26
  SPEAKER_00: Add ventilation, ridge vents, soffit vents, or solar attic fans.
• 13:31
  SPEAKER_00: Anything to allow that trapped 150-degree air to cycle out of the house.
• 13:36
  SPEAKER_00: Second, you must stop the heat from penetrating the ceiling, and that means looking at your insulation.
• 13:42
  SPEAKER_01: The sources mention the Department of Energy recommending an R49 insulation value.
• 13:47
  SPEAKER_01: What does that actually look like in an attic?
• 13:49
  SPEAKER_00: Well, the R stands for resistance to heat flow.
• 13:52
  SPEAKER_00: R49 equates to roughly 16 to 18 inches of standard fiberglass blown in insulation just sitting on your attic floor.
• 14:00
  SPEAKER_00: Okay.
• 14:00
  SPEAKER_00: Many older homes, or even newer homes built to minimum code, might only have six or eight inches up there.
• 14:06
  SPEAKER_01: That's a big difference.
• 14:07
  SPEAKER_00: Huge.
• 14:08
  SPEAKER_00: If your insulation is undersized, that radiant heat is pouring right through.
• 14:12
  SPEAKER_00: Beefing up your insulation is a highly effective, relatively low-cost way to block that thermal transfer.
• 14:17
  SPEAKER_01: So we're managing the airflow and we are putting a thicker shield between the bedroom and the attic.
• 14:22
  SPEAKER_01: The field dose also mentioned a trick with the thermostat settings involving the fan.
• 14:25
  SPEAKER_00: Yes.
• 14:26
  SPEAKER_00: This one is very specific but can be super helpful.
• 14:28
  SPEAKER_01: Lay it on us.
• 14:29
  SPEAKER_00: Normally you want your thermostat fan set to audio, which means the blower motor only turns on when the AC compressor is actively running a cooling cycle.
• 14:38
  SPEAKER_00: Right.
• 14:39
  SPEAKER_00: But during the absolute worst part of the day, that hot late afternoon window between 4 p.m.
• 14:44
  SPEAKER_00: and 8 p.m.
• 14:45
  SPEAKER_00: when the upstairs is just baking, you can switch the fan setting from auto to on.
• 14:50
  SPEAKER_01: Okay, now wait.
• 14:51
  SPEAKER_01: If turning the fan to on constantly circulates the air, mixing the hot upstairs air with the cooler downstairs air to balance things out, why wouldn't I just leave it on 24-7?
• 15:03
  SPEAKER_00: It goes right back to the psychometrics we talked about earlier, sensible versus latent heat.
• 15:06
  SPEAKER_01: Oh, the humidity?
• 15:07
  SPEAKER_00: Exactly.
• 15:08
  SPEAKER_00: Remember that your AC acts as a dehumidifier.
• 15:10
  SPEAKER_00: When it runs a cooling cycle, the cold evaporator coil pulls moisture out of the air.
• 15:15
  SPEAKER_00: Right.
• 15:15
  SPEAKER_00: When the cycle finishes and the outdoor compressor shuts off, that indoor coil is still sitting in the dark and it's soaking wet with condensation.
• 15:23
  SPEAKER_01: Oh, I see the trap.
• 15:24
  SPEAKER_00: Yeah.
• 15:25
  SPEAKER_00: If you leave your fan set to un all day, the blower continues to push unconditioned air over that soaking wet coil.
• 15:32
  SPEAKER_00: It essentially evaporates all of that moisture right back into the ductwork and pumps the humidity directly back into your living space.
• 15:40
  SPEAKER_01: Wow.
• 15:40
  SPEAKER_01: You're literally paying electricity to undo the dehumidification work your AC just did.
• 15:46
  SPEAKER_00: Yep.
• 15:46
  SPEAKER_00: And your house will feel incredibly clammy.
• 15:49
  SPEAKER_00: So the fan trick is a tactical move.
• 15:52
  SPEAKER_01: Use it strategically.
• 15:53
  SPEAKER_00: Right.
• 15:54
  SPEAKER_00: Use the onsetting strictly during that 4 p.m.
• 15:56
  SPEAKER_00: to 8 p.m.
• 15:57
  SPEAKER_00: window to help de-stratify the air when the upstairs is at its absolute worst, but always return it to auto so the system can properly dehumidify it the rest of the time.
• 16:06
  SPEAKER_01: That makes perfect sense.
• 16:07
  SPEAKER_01: Now the sources are clear that these are interim fixes.
• 16:10
  SPEAKER_01: If a homeowner does all of this, you know, they tweak the vents, upgrade to R49 insulation, use the fan trick.
• 16:16
  SPEAKER_01: What kind of real-world result does the field data actually show?
• 16:19
  SPEAKER_00: If executed properly, Dave Hartzel's data indicates you will see about a four to five degree improvement in the upstairs temperature.
• 16:24
  SPEAKER_01: Aaron Powell Which is significant.
• 16:26
  SPEAKER_01: I mean, dropping an 81 degree room down to 76 degrees is the difference between sweating and sleeping.
• 16:31
  SPEAKER_00: It really is.
• 16:32
  SPEAKER_01: But we're still not entirely closing the eight to twelve degree gap that exists in some of these homes.
• 16:38
  SPEAKER_00: We aren't.
• 16:39
  SPEAKER_00: To get the full correction to make the upstairs exactly as comfortable as the downstairs, you really have to perform the ultimate fix.
• 16:47
  SPEAKER_00: It's what the industry calls zoning.
• 16:49
  SPEAKER_01: Uh the surgical solution.
• 16:52
  SPEAKER_01: Yeah.
• 16:52
  SPEAKER_01: How does zoning fundamentally change the mechanics of the house?
• 16:56
  SPEAKER_00: Zoning is a retrofit where an HVAC professional goes into your existing ductwork and installs a series of motorized dampers.
• 17:04
  SPEAKER_01: What are those?
• 17:05
  SPEAKER_00: Think of them as mechanical gates inside the ducts that can electronically open and close to direct air.
• 17:10
  SPEAKER_00: And most importantly, they install a second thermostat upstairs.
• 17:14
  SPEAKER_01: Oh.
• 17:15
  SPEAKER_01: So you are finally giving the second floor its own brain.
• 17:18
  SPEAKER_00: Yes, exactly.
• 17:19
  SPEAKER_00: You eliminate the single zone problem entirely.
• 17:21
  SPEAKER_00: The upstairs thermostat strictly monitors the upstairs environment.
• 17:25
  SPEAKER_00: When that radiant heat pushes the upstairs to 75 degrees, the upstairs thermostat calls for cooling.
• 17:31
  SPEAKER_00: The system turns on, the motorized dampers automatically swing shut to block off the downstairs ductwork, and a hundred percent of the system's cooling capacity is forced up through those long vertical runs to the second floor.
• 17:44
  SPEAKER_01: Because it overcomes the friction loss, all the pressure suddenly routed to one place.
• 17:48
  SPEAKER_00: Yes.
• 17:49
  SPEAKER_00: It cools the upstairs until that specific zone is satisfied, independent of whatever is happening downstairs.
• 17:54
  SPEAKER_00: It fixes a structural flaw on day one.
• 17:57
  SPEAKER_01: But this is a mechanical retrofit.
• 17:58
  SPEAKER_01: I mean, what kind of investment are we looking at here?
• 18:00
  SPEAKER_00: The field data notes that retrofitting a two-zone system typically costs anywhere from$2,500 to$4,500, depending heavily on how accessible your ductwork is.
• 18:10
  SPEAKER_01: Which, to put it in perspective, is just a fraction of the$10,000 or$15,000 a homeowner might waste buying a bigger AC unit that would actually make the problem worse.
• 18:18
  SPEAKER_00: That is the crucial takeaway here.
• 18:20
  SPEAKER_00: It is about applying the correct investment to the actual mechanical flaw.
• 18:24
  SPEAKER_01: Aaron Powell And we really need to highlight where this invaluable field data comes from.
• 18:29
  SPEAKER_01: This isn't just theoretical modeling.
• 18:31
  SPEAKER_01: This is deeply practical, real-world application from Dave Hartzell of Hartzell's Heat and Air, based in Kingfisher, Oklahoma.
• 18:38
  SPEAKER_00: Yeah, he is a NAT certified master, which, for those unfamiliar, is essentially the highest board certification standard in the HVAC industry.
• 18:46
  SPEAKER_01: He's been diagnosing these exact airflow and stratification issues for 45 years.
• 18:52
  SPEAKER_01: And if you happen to be in their central Oklahoma service area and you are dealing with this exact Panini press situation we've been talking about, they actually offer free estimates on zoning retrofits to figure out if it will work for your layout.
• 19:04
  SPEAKER_00: That's fantastic.
• 19:05
  SPEAKER_01: Yeah, you can reach them at 4005-375-4822 or check out the specifics at HeartSoldsheetAir.com.
• 19:12
  SPEAKER_00: Having localized expertise that understands both the climate and the structural physics of these homes is invaluable.
• 19:17
  SPEAKER_00: Absolutely.
• 19:17
  SPEAKER_00: And if there is one thing you take away from this deep dive, let it be this.
• 19:21
  SPEAKER_00: If your upstairs is significantly hotter than your downstairs, your AC capacity is almost never the problem.
• 19:27
  SPEAKER_00: You have an air delivery and thermal boundary problem.
• 19:30
  SPEAKER_00: It is your ductwork friction, your lack of zoning, and your underinsulated attic causing the pain.
• 19:36
  SPEAKER_00: The fix must be targeted specifically to those areas.
• 19:40
  SPEAKER_01: It's all about working smarter and not just throwing a bigger, louder machine at a plowing problem.
• 19:44
  SPEAKER_00: Exactly.
• 19:45
  SPEAKER_01: And that leaves me with one final thought I want you to mull over today.
• 19:48
  SPEAKER_00: Okay.
• 19:49
  SPEAKER_01: If the standard single zone HVAC system is so fundamentally mechanically flawed for two-story homes, if it physically cannot overcome the friction loss to deliver comfort to the second floor, think about the immense amount of energy and money we are collectively wasting across this country.
• 20:07
  SPEAKER_00: Oh, it's staggering.
• 20:08
  SPEAKER_01: Think of millions of homes drastically overcooling their downstairs living spaces, cranking the thermostat down to 68 or 66 degrees, just to force a tiny bit of extra cold air upstairs so the bedrooms are barely tolerable for sleep.
• 20:22
  SPEAKER_00: Yeah, it's a massive waste.
• 20:23
  SPEAKER_01: It really makes you wonder are our modern building codes, which fully allow and endorse these single zone, single trunk designs and two story homes, actually setting us up to fail from the moment the foundation is poured?
• 20:35
  SPEAKER_00: That is a great question.
• 20:37
  SPEAKER_01: It's definitely something to think about the next time you hear that AC kick on while you're sweating upstairs in the dark.