Stop wildfire smoke with your HVAC

Smoke rolls into Kingfisher from a panhandle grass fire or a controlled burn three counties over, and your HVAC is either pulling that poison into your house or keeping it out. Depends on three settings most homeowners have never touched. This episode covers what to do at the thermostat when the air goes brown, which filter actually catches PM2.5, and the one move I see homeowners get wrong every smoke event in central Oklahoma. More episodes: https://hartzellsheatair.com/podcast/

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Transcript

Brown Skies And False Safety

SPEAKER_00 0:00

Picture waking up. You step outside to, you know, grab the paper, or maybe you're just letting the dog out, and the sky has this heavy, almost unnatural brown tint to it.

SPEAKER_01 0:09

Yeah, that eerie lighting.

SPEAKER_00 0:10

Exactly. And you smell the smoke before you even fully process what you're looking at. I mean, it could be a grass fire raging 200 miles away, or uh maybe a controlled agricultural burn three counties over. Right. But the smoke has arrived, and suddenly your own front porch smells like a campfire gone completely wrong.

SPEAKER_01 0:29

It's an incredibly visceral experience, you know. And the immediate instinct for, well, almost everyone is to just run back inside, slam the door, lock the windows, and think that you've shut the threat out.

SPEAKER_00 0:40

Yeah, you feel like you've secured the perimeter.

SPEAKER_01 0:42

Right. But the science of building dynamics tells us a very different story. That instinct is mostly uh giving you a false sense of security.

SPEAKER_00 0:49

Aaron Powell, which is exactly why we are jumping into this topic today. In this deep dive, we are exploring how to actually weaponize your home's HVAC system against wildfire and grassfire smoke. We're looking at a stack of sources that tackle this from a few different angles. We've got homeowner-focused resources from the EPA, highly technical professional guidelines from HSRE.

SPEAKER_01 1:12

That's the American Society of Heating, Refrigerating, and Air Conditioning Engineers, by the way.

SPEAKER_00 1:16

Right, thank you. And some really fascinating on-the-ground insights from HVAC professionals who dealt firsthand with the severe smoke events in Oklahoma.

SPEAKER_01 1:26

And this is just crucial to understand, honestly, regardless of your zip code, you might assume wildfire smoke is like an isolated problem for heavily forested places like California or parts of Canada.

SPEAKER_00 1:38

Sure.

SPEAKER_01 1:39

But as the 2023 Oklahoma panhandle fires proved, massive smoke plumes travel hundreds of miles. I mean, they ride the upper atmosphere and just ignore state lines entirely.

SPEAKER_00 1:50

Wow. So whether you're a homeowner trying to figure out how to prep for fire season, or you just want to understand the uh invisible mechanics of the building you live in, this deep dive is going to look at how a few simple adjustments to equipment you already own can mean the difference between breathing clean air or pulling toxic particulate matter right into your living

Why Smoke Gets Indoors

SPEAKER_00 2:07

room.

SPEAKER_01 2:07

Yeah. And to get there, we really have to start by dismantling that comforting myth we just mentioned.

SPEAKER_00 2:12

Aaron Powell The idea that a closed house is a safe house.

SPEAKER_01 2:15

Exactly. We like to think of our homes as these impenetrable fortresses, but structurally speaking, houses breathe. They have to. They're not, you know, hospital-grade, hermetically sealed environments.

SPEAKER_00 2:28

Aaron Powell Well, wait, what about new construction? Like, if someone just bought a modern, tightly built house with heavy insulation and double pane windows, aren't they relatively sealed off?

SPEAKER_01 2:37

You'd think so, but no. Even the absolute tightest modern builds leak to some degree. And when we talk about wildfire smoke, we aren't talking about big, visible chunks of falling ash.

SPEAKER_00 2:48

Right. It's not like raining soot.

SPEAKER_01 2:49

No, we are primarily talking about something called PM2.5. That stands for particulate matter that is 2.5 microns or smaller in diameter.

SPEAKER_00 2:57

Okay, 2.5 microns.

SPEAKER_01 2:58

To put that in perspective, that is roughly 30 times smaller than a single strand of human hair. Oh wow.

SPEAKER_00 3:04

That is tiny.

SPEAKER_01 3:05

At that microscopic scale, the particulate essentially behaves like a gas. It just rides the subtle pressure differentials of your house and slips effortlessly through the tiny gaps around your window frames, underneath exterior doors, straight through your attic vents.

SPEAKER_00 3:21

So basically, the smoke is getting in. That's just a physical reality we have to accept.

Switch The HVAC Fan To On

SPEAKER_01 3:26

It is. Which means your primary line of defense isn't your walls, it's the fan setting on your thermostat.

SPEAKER_00 3:32

Interesting.

SPEAKER_01 3:33

Yeah, most thermostats have a switch for the fan that toggles between auto and on. Under normal, clear sky conditions, auto is the standard recommendation. It means the blower fan only kicks on when the compressor or furnace is actively working to change the temperature.

SPEAKER_00 3:48

Okay, but during a smoke event, leaving that fan on auto seems like a terrible idea if the smoke is constantly seeping in, right?

SPEAKER_01 3:56

Oh, it is actually a trap. During a severe smoke event, you must switch that setting to on so the blower runs continuously 24 hours a day.

SPEAKER_00 4:04

Wait, constantly.

SPEAKER_01 4:06

Constantly. Imagine a cool, breezy spring morning. The temperature outside is mild, so your air conditioner might not need to kick on for three or four hours. Right, yeah. If your fan is set to auto, your system's filter is just sitting dormant in the dark. It is doing absolutely nothing while that invisible PM2.5 smoke steadily infiltrates your living space.

SPEAKER_00 4:27

Aaron Powell Okay, let's unpack this for a second because I feel like, well, if my house leaks anyway and the smoke is already finding its way inside, I think a lot of people would assume that running the HVAC fan constantly is just going to stir up the toxic air that's already in the room. Wouldn't keeping the air completely still be safer?

SPEAKER_01 4:44

I get why you'd think that. It's a very common assumption, but the physics of indoor air quality just work differently. Still air doesn't mean clean air, it just means the PM 2.5 is hanging out right at head level.

SPEAKER_00 4:54

Yikes.

SPEAKER_01 4:55

Yeah. The air and whatever is suspended in it has to be forcefully moved through a filtration medium to be clean. If the fan is off, your lungs become the default filter for the room.

SPEAKER_00 5:06

Oh, I hate that image.

SPEAKER_01 5:07

Right. But if the fan is on, the HVAC system takes over that job.

SPEAKER_00 5:12

It actually makes me think of a fish tank filter. Like if you turn off the water pump, the water in the tank just gets murky and toxic.

SPEAKER_01 5:19

Exactly.

SPEAKER_00 5:19

The filter media is completely useless unless the water is actively cycling through it.

SPEAKER_01 5:24

That analogy translates perfectly to air dynamics. Your home needs that continuous cycle to scrub the environment. But that heavy lifting brings us to a significant mechanical hurdle, and it's a massive catch-22.

MERV Ratings And The Filter Trap

SPEAKER_00 5:36

Okay, what is it?

SPEAKER_01 5:37

Standard factory filters are not built to catch microscopic smoke, but the high efficiency filters that can catch smoke run the risk of breaking your air conditioner.

SPEAKER_00 5:46

Wait, really? Which feels like a cruel irony. I mean, you are trying to save your lungs, but you end up basically suffocating your house. Let's dig into the filter itself, specifically the MRV rating. The sources mention MRV quite a bit, but what does that actually measure?

SPEAKER_01 6:01

So MRV stands for minimum efficiency reporting value. It is essentially a grading scale from one to sixteen that tells you how effectively a filter can trap tiny particles. Most people just grab whatever standard, you know, one-inch thick cardboard filter is on sale at the local hardware store. Those are typically a MERV 6 or maybe a Merg 8.

SPEAKER_00 6:20

Right, the cheap ones.

SPEAKER_01 6:21

Yeah. And they are designed to protect the HVAC equipment from big debris dog hair, pollen, and large dust bunnies.

SPEAKER_00 6:29

But against something as small as PM2.5 smoke, a MERV8 filter isn't going to do much, is it?

SPEAKER_01 6:35

Practically nothing. The microscopic smoke just sails right through the relatively wide gaps in a MERV8 filter. To catch fine smoke particles effectively, the sources and HHRE's professional guidelines are very clear. You need to upgrade to a minimum of a MERV 13 filter.

SPEAKER_00 6:52

Aaron Powell But here is where we hit that suffocation paradox you mentioned. You can't just blindly jam a MERV 13 filter into any old furnace.

SPEAKER_01 6:59

You really can't. And it comes down to aerodynamics. Higher filtration efficiency naturally creates more air resistance.

SPEAKER_00 7:05

Because it's thicker.

SPEAKER_01 7:06

Because the fibers in the filter have to be woven much tighter together to catch tinier particles. When you put a tightly woven RV-13 filter into a standard one-inch slot, it acts almost like a solid piece of cardboard blocking the airflow. Ah, got it. Older HVAC systems, especially single-stage units installed in homes built before the year 2000, were simply not engineered to handle that massive pressure drop.

SPEAKER_00 7:28

So the blower motor has to work twice as hard to pull the same amount of air through this dense wall of fabric.

SPEAKER_01 7:34

Exactly. It creates a vacuum effect. The motor strains and can literally overheat and burn out, or because the air is moving so slowly, your evaporator coil might freeze over into a block of ice because there isn't enough warm ambient air washing over it.

SPEAKER_00 7:48

Oh man, what a nightmare. So what is the workaround? If you have an older system that struggles with airflow, how do you catch the smoke without destroying your furnace?

SPEAKER_01 7:57

There are two paths

Deep Media Filters Fix Airflow

SPEAKER_01 7:58

here. The first is a compromise. You might have to step down slightly to a Mervey Levin. It won't catch quite as high a percentage of the PM 2.5, but it allows enough airflow to keep your blower motor alive.

SPEAKER_00 8:09

Okay, and the second path.

SPEAKER_01 8:10

The vastly superior solution, and the one the HVAC professionals in our sources strongly advocate for, is retrofitting your system with what's called a deep media filter housing.

SPEAKER_00 8:21

I found this part of the research fascinating, honestly, because I'm so used to those flimsy one-inch thick filters. These media filters are massive, usually four or five inches deep.

SPEAKER_01 8:31

Yeah, they're bulky.

SPEAKER_00 8:32

But how does making the filter thicker solve the airflow problem? Wouldn't that just create even more resistance?

SPEAKER_01 8:38

It's actually the opposite. Because of how they are constructed, the filter material isn't just a thick, solid block. It is pleated like an accordion.

unknown 8:47

Right.

SPEAKER_01 8:48

If you were to take a five-inch deep media filter and unfold all those deep pleats, the material would probably cover your entire living room floor. Because there is exponentially more surface area for the air to pass through, the resistance drops significantly.

SPEAKER_00 9:02

So you're basically spreading the workout over a much larger canvas.

SPEAKER_01 9:06

Precisely. You can achieve that gold standard MRV 13 filtration, capturing the microscopic smoke without choking your system's airflow. This resolves the suffocation paradox entirely.

SPEAKER_00 9:18

Brilliant.

SPEAKER_01 9:19

And as a bonus, because they have so much capacity, they last up to six months instead of needing to be changed every 30 days. Oh, okay. This is why the HVAC industry heavily relies on these deep media filters. They perfectly balance the high-level filtration required for human health with the airflow required for mechanical longevity.

SPEAKER_00 9:39

Okay, so the central system is fortified. We have the fan running continuously on, and we've upgraded to a deep media filter so we are safely trapping the PM 2.5. We've built the fortress.

SPEAKER_01 9:50

Structurally, yes. But the biggest threat to a fortress is usually an inside

Dampers Exhaust Fans And Dryers

SPEAKER_01 9:54

job.

SPEAKER_00 9:54

Wait, meaning what? Exactly.

SPEAKER_01 9:56

I mean, the appliances and habits you engage with every day are often actively working to bypass that filtration system and pull smoke right into the house.

SPEAKER_00 10:03

Oh boy. Let's talk about the saboteurs then. The sources point out that modern homes sometimes have fresh air dampers or ERVs, energy recovery ventilators.

SPEAKER_01 10:12

Right. If you live in a newer, high-efficiency home, it might be built so tightly that it actually has a mechanical damper designed to pull outdoor air inside on purpose, just to keep the indoor air from feeling stale. Okay. During a smoke event, you must go to your control panel and ensure that damper is closed, or switch the system to recirculate mode.

SPEAKER_00 10:30

That makes complete sense. Don't deliberately pump the brown sky into your living room. But the sources also highlight some really surprising culprits: bathroom exhaust fans, kitchen rain chips, and the one that completely caught me off guard, the clothes dryer.

SPEAKER_01 10:47

Yeah, that one shocks a lot of people.

SPEAKER_00 10:48

I would have immediately guessed the chimney or a drafty window, but a clothes dryer wasn't even on my radar.

SPEAKER_01 10:54

It all comes down to a physics principle called negative pressure. Your house is essentially a sealed container of air. Let's lick the dryer. When you turn it on, it takes the conditioned air inside your house, heats it up, tumbles it with your wet clothes to evaporate the moisture, and then forcefully blasts that humid air outside through the four-inch vent in your wall.

SPEAKER_00 11:15

So you are physically removing air from the container.

SPEAKER_01 11:17

Yes. And physics demands equilibrium. Nature abhors a vacuum. If your dryer pushes 100 cubic feet of air outside every minute, your house becomes negatively pressurized.

SPEAKER_00 11:27

Oh, I see where this is going.

SPEAKER_01 11:28

Yeah, to balance the equation, the house immediately sucks in 100 cubic feet of outdoor air through all those tiny thermal bypasses, window cracks, and door gaps we talked about earlier.

SPEAKER_00 11:39

So what does this mean for laundry day during a fire? It means running your clothes dryer is basically like sticking a giant straw out the window and sucking the wildfire smoke directly into your hallway.

SPEAKER_01 11:52

That is the exact mechanical reality. You are turning your entire house into a vacuum cleaner, and the dirt it's sucking up is the outdoor smoke.

SPEAKER_00 12:00

Man, that's wild.

SPEAKER_01 12:02

So the playbook here is to just skip laundry day. Do not run the bathroom exhaust fan after a shower unless absolutely necessary to prevent mold. Keep the kitchen exhaust hood off. You have to neutralize the negative pressure.

SPEAKER_00 12:14

And speaking of the kitchen, there was another category of friendly fire that really

Avoid Indoor Smoke From Cooking

SPEAKER_00 12:18

stood out. It's not just about pulling outside air in, it's about what we are creating inside.

SPEAKER_01 12:23

Right.

SPEAKER_00 12:23

The sources strongly advise against heavy cooking, bringing candles, and using aerosol air fresheners during a smoke event.

SPEAKER_01 12:30

This touches on a really interesting psychological response we have to bad smells. When a house starts smelling like a distant campfire, the immediate human instinct is to try and freshen the air.

SPEAKER_00 12:40

Right. You want it to smell nice.

SPEAKER_01 12:42

Yeah. So people light a pine-scented candle, or they spray a floral aerosol freshener to mask the odor.

SPEAKER_00 12:48

But chemically, they're just adding more particulate matter to the room.

SPEAKER_01 12:52

They are actively worsening the indoor air chemistry. Candles, aerosols, and heavy cooking like pan searing a steak or frying bacon release, tremendous amounts of fine particulate matter and volatile organic compounds, or VOCs. These aren't just smells, they are physical microscopic particles.

SPEAKER_00 13:12

So you're creating massive amounts of new indoor pollution that is now directly competing with the wildfire smoke for real estate on your HVC filter.

SPEAKER_01 13:20

Exactly. You are forcing your MVR V13 filter to work twice as hard to clean up the bacon grease and candle soot, leaving less capacity to catch the toxic PM 2.5 from the actual fire.

SPEAKER_00 13:30

That is so counterintuitive.

SPEAKER_01 13:32

During a smoke event, the absolute best thing you can do for your indoor air chemistry is to just leave it alone, no candles, no aerosols, and maybe stick to the microwave or the slow cooker for dinner.

SPEAKER_00 13:42

It's wild to think that lighting a candle to cover up the smoke is actually compounding the problem. So we've stopped making things worse. We've shut off the saboteurs. Now let's look at the ultimate optimization.

Seal Tight Run Clean Rules

SPEAKER_00 13:55

Let's dive into Ash H R E's playbook and what the HVAC pros in Oklahoma refer to as the Dave Protocol.

SPEAKER_01 14:03

Ah, the Dave Protocol. So Ash H RE boils their core professional philosophy down to four words for these severe events. Seal tight, run clean.

SPEAKER_00 14:12

Seal tight, run clean.

SPEAKER_01 14:14

Right. You seal the building envelope as best you can, and you run the cleaning equipment continuously.

SPEAKER_00 14:19

But there is always that one contrarian who says, hey, the house feels stuffy. Why not just open the windows at night and let the house air out?

SPEAKER_01 14:26

The sources address this directly because timing is everything. Opening windows can be a great strategy, but only under highly specific verified conditions.

SPEAKER_00 14:34

Like what?

SPEAKER_01 14:35

Well, the smoke source must have stopped burning, the wind must have shifted to clear the plume, and you must verify the local air quality using the EPA's airnow.gov map.

SPEAKER_00 14:45

How does that map scale work?

SPEAKER_01 14:46

It measures the concentration of PM 2.5. If the number is under 50, which puts you in the green, healthy zone, then yes, open the windows for a quick fresh air flush. But if the source is still active, opening the windows just resets your indoor air clock to zero. You completely lose all the progress your central filter just spent hours making.

SPEAKER_00 15:06

To give some context on those air now numbers, you mentioned under 50 is fine. During the worst of the 2023 panhandle fires in Oklahoma, when those agricultural burns got out of control, those numbers were hitting well over 200.

SPEAKER_01 15:19

Yeah, that's really bad.

SPEAKER_00 15:20

That is deep into the hazardous category. When the air is at 200, you do not crack a window for a nice evening breeze.

SPEAKER_01 15:26

Which brings us to the Dave protocol. Dave is one of the HVAC professionals mentioned in the sources who was fielding calls during those exact 2023 Oklahoma fires.

The Dave Protocol Layered Defense

SPEAKER_01 15:36

He provides a brilliant 80-20 rule for long-term defense based on what actually worked for his clients.

SPEAKER_00 15:41

Yeah, the 80-20 rule breaks down like this. Dave says that doing what we've just talked about, flipping the fan to on in, upgrading to a Merv13 media filter, and neutralizing the negative pressure by keeping windows and exhaust fans off handles 80% of the problem. You dramatically improved your air quality with equipment you already own. But then he brings in the final 20%. And honestly, this part surprised me. Dave, backed up by EPA research, says that final 20% is going out and buying a portable HEPA air cleaner and putting it right in your bedroom.

SPEAKER_01 16:12

It's a great strategy.

SPEAKER_00 16:14

But I had to pause when I read that. If I just paid an HVAC technician to install a highly efficient deep media filter on my central air unit, why does the EPA still want me to go to a big box store and buy a standalone machine just for where I sleep? It feels redundant.

SPEAKER_01 16:29

I get that. It might seem redundant on the surface, but it's actually a masterclass in layered defense. HEPA stands for high efficiency particulate air. These filters catch 99.97% of particles. Think about the layout of a standard home. You spend roughly a third of your life in your bedroom.

SPEAKER_00 16:44

Okay, sure.

SPEAKER_01 16:45

Your central HVAC system is doing the broad, heavy lifting for the entire square footage of the house, but it has blind spots.

SPEAKER_00 16:54

Like the corners of rooms that are furthest away from the central return vents in the hallway.

SPEAKER_01 16:58

Exactly. The EPA has conducted extensive methodology on this. They found that bedrooms often suffer from air stagnation, especially at night when doors are closed. The central system struggles to pull the air out of those closed rooms effectively.

SPEAKER_00 17:12

Oh, that makes sense.

SPEAKER_01 17:13

By adding a portable right-sized HEPA cleaner to the room where you sleep, their studies show you drop the indoor PM2.5 levels in that specific room by an additional 50 to 80 percent.

SPEAKER_00 17:25

So you use the central system as your primary shield for the whole house, and the portable HEPA acts as a uh localized high-intensity scrubber for the stagnant air you're breathing while your body is trying to rest and repair itself.

SPEAKER_01 17:38

Aaron Powell That's the exact strategy. Now the source has also touched briefly on some of the more futuristic long-term upgrades you hear marketed to homeowners, things like electronic air cleaners or UV light systems that get installed inside the ductwork.

Long Term Upgrades And Big Questions

SPEAKER_00 17:49

Right, the gadgets. Do those actually hold up against heavy smoke?

SPEAKER_01 17:52

They are heavily debated within the industry. But when you look at Aishusria's professional position, they clearly state that physical filtration, literally forcing air through a dense medium like a MERV 13 or HEPA filter, is the proven reliable move for smoke.

SPEAKER_00 18:08

Good to know.

SPEAKER_01 18:08

Anything involving electronic fields or UV should be evaluated on a very careful, case-by-case basis. The beauty of physical filters is that they don't break down mechanically or suffer electronic failure. They just get full and need to be replaced.

SPEAKER_00 18:22

Keep it simple. Rely on the physics. Yeah. So what is the ultimate takeaway playbook here? Let's summarize it so you can keep it in your back pocket for the next time the wind shifts and the sky changes color.

SPEAKER_01 18:31

Let's do it.

SPEAKER_00 18:32

Step one, switch the fan to on M, not auto. Keep the air moving continuously. Step two, filter up safely. Uh-huh. Find a way to get to M RE13. And if your older system strains, look into a deep media filter housing.

SPEAKER_01 18:46

Absolutely.

SPEAKER_00 18:47

Step three. Keep the fresh air dampers closed and keep your saboteurs, the exhaust fans, and your dryer off. Don't suck the smoke inside. Step four, check the air now map before you even think about opening a window. And finally, layer your defense by getting a portable HEPA filter for your bedroom.

SPEAKER_01 19:07

It really is an empowering set of guidelines. You don't need to feel entirely helpless when a smoke event rolls into town. And importantly, you don't need to uproot your life and move away from areas prone to grass fires or necessary agricultural burns. You just need to be much smarter about the mechanics of the equipment that is already sitting in your utility closet.

SPEAKER_00 19:26

It's an incredibly cheap practical fix for a problem that used to feel completely apocalyptic. But, you know, looking at all this research does leave me with a much larger question to ponder.

SPEAKER_01 19:36

Oh, yeah.

SPEAKER_00 19:36

Yeah. We know that climate patterns are shifting, the window for control, necessary agricultural burns is changing, and as we've seen from the data, that smoke is traveling further and more frequently than ever before.

SPEAKER_01 19:47

It's rapidly becoming a geographically universal problem, not just a regional one isolated to the coasts.

SPEAKER_00 19:53

Exactly. Which makes me wonder. In the very near future, will smoke readiness become as standard a feature in assessing the value of a home as having a good roof or a strong foundation?

SPEAKER_01 20:06

Hmm.

SPEAKER_00 20:06

Are we fundamentally shifting from viewing our homes as passive shelters that just keep the rain off our heads to actively managing them as enclosed, pressurized life support systems?

SPEAKER_01 20:16

That is a fascinating way to look at it.

SPEAKER_00 20:18

It's something to think about the next time you wake up to step outside and see a brown sky. Thanks for joining us on this deep dive. We'll catch you next time.