The Ironside Journal.

Industry-grade context on filtration, indoor air quality, and the science behind every Ironside spec.

News

Ironside vs FilterBuy vs Nordic Pure vs Discount Filters: An Honest Comparison
All four sell US-made pleated filters. The difference is how you pay for freight — and whether a subscription actually saves you money. Read more...
Winter Furnace Filter Guide: Why Filters Clog Faster in the Cold
Quick answer: Filters clog faster in winter because the house is closed up, the same dusty, dry air recirculates, and the furnace runs long cycles that pull more air through the media. Plan to check your winter furnace filter every month and change a 1-inch filter every 30 to 60 days. A clogged filter strains the blower and drives up your heating bill. Winter is the season a furnace filter earns its keep, and the season it loads up the fastest. You seal the windows, crank the heat, and the... Read more...
Wildfire Season HVAC Prep: Protecting Indoor Air When Smoke Rolls In
Quick answer: To prepare your HVAC for wildfire season, set the system to recirculate indoor air instead of pulling in fresh outdoor air, seal up the house so smoke can't leak in, and get the right filter installed before smoke arrives. Then stock spare filters ahead of time and be ready to swap them more often once the air turns. This is the setup piece, not the filter-shopping piece. If you want the breakdown of which rating catches what and how smoke behaves, our air filter for wildfire smoke guide... Read more...
Why Is My Air Filter Black? Soot, Mold, and What to Do
Quick answer: A black air filter is usually soot from candles, a fireplace, or cooking, and in most cases it means the filter is doing its job. The exception is black mold, which shows up as patchy spots and a musty smell instead of an even gray-black coating. Soot means replace the filter and cut the source. Mold means replace the filter and find the moisture problem feeding it. You pull the filter expecting the usual gray fuzz and instead it looks like it spent a month in a chimney.... Read more...
Humidity, Mold & Your Air Filter: A Summer Guide
Quick answer: For humidity and mold, a MERV 13 filter traps the airborne mold spores your damp summer air stirs up, and an activated-carbon layer helps knock down the musty smell. Choose a filter with moisture-resistant media so it holds up in humid conditions, and change a damp or clogged filter promptly. Just know a filter traps spores in the air, it doesn't remove humidity like a dehumidifier does. Summer humidity is more than an uncomfortable, sticky feeling. Damp air is what mold needs to grow, and once mold takes... Read more...
Spring Allergy Season: Best MERV Rating for Pollen
Quick answer: The best air filter for spring pollen is a MERV 13 for fine tree and grass pollen, or a MERV 11 for milder symptoms. MERV 13 traps the smallest pollen particles and is the highest rating most home systems can run. During pollen season, change it more often, because a filter loaded with pollen clogs faster than usual. When trees and grasses start throwing pollen every spring, your furnace filter turns into your first line of defense indoors. Every time your HVAC runs, it pulls household air through... Read more...
Ragweed & Fall Allergies: The Right Filter for Late-Summer Hay Fever
Quick answer: The best air filter for ragweed allergies is a MERV 13. Ragweed pollen is fine enough to slip past weaker filters, and MERV 13 is built to trap it. It's the highest rating most home systems can run. During ragweed season, swap it more often, and expect extra dust when the heat first kicks on in fall. Ragweed is the reason so many people who breezed through spring get flattened in late summer. A single plant throws out huge amounts of fine pollen, and it peaks from August... Read more...
The New Year HVAC Filter Reset: Your Annual 10-Minute Checklist
Quick answer: Once a year — January is as good a time as any — run a 10-minute filter reset: confirm your exact size, check you're on the right MERV, set a season-by-season change schedule, and stock the year's filters in one go. This checklist is the hub; each step links to the full how-to if you want the detail. Most HVAC filter advice is scattered across a dozen questions: what size, what rating, how often, what changes by season. This is the once-a-year version that ties them together. Think... Read more...
How Often to Change Your Air Filter by Season
Quick answer: How often you change your air filter shifts with the season. Change a 1-inch filter every 30 to 45 days in summer and winter, when the AC or furnace runs hardest, and check it monthly in spring and fall when pollen and dust climb. The heavier your system runs and the dirtier the outdoor air, the faster the filter loads. There's no single answer to how often you should change your air filter, because the honest answer changes four times a year. Your HVAC works hardest in the... Read more...
Fall Furnace Prep: The Filter Change You Can't Skip
Quick answer: Before you fire up the heat this fall, swap in a fresh furnace filter. Over the summer, dust settles on your coils and burners, and the first heat cycle burns it off, which is that "hot dust" smell. A clean filter, confirmed for size and airflow direction, keeps that dust from loading up a tired old filter and choking your system on day one of heating season. Fall is the season most homeowners skip the easy stuff. You switch the thermostat from cool to heat, the vents rumble... Read more...
How a Dirty Air Filter Raises Your Energy Bill
Quick answer: Yes, a dirty air filter raises your energy bill. A clogged filter forces your blower to work harder and run longer to move the same air, and the Department of Energy estimates that replacing a dirty filter can cut HVAC energy consumption by up to 5 to 15 percent. Since heating and cooling is usually the biggest line on your electric bill, a $10 to $20 filter is one of the cheapest energy upgrades in the house. Most people think of an air filter as an air-quality product.... Read more...
Can a Dirty Air Filter Cause AC Not to Cool? Yes — Here's Why
Quick answer: Yes. A clogged air filter is one of the most common reasons an AC stops cooling. The dirty filter chokes airflow, the evaporator coil gets too cold and ices over, and the system ends up blowing weak, warmish air while running constantly. Before you call anyone, pull the filter and look at it. If it's gray and packed with dust, a $15 filter swap may fix what looks like a $500 repair. It's mid-July, the thermostat says 78 and climbing, and the AC has been running for hours.... Read more...
Best Air Filter for Summer: Heat, Humidity & Your AC
Quick answer: The best air filter for summer is a MERV 13 for most homes, changed more often than usual because your AC runs almost nonstop. Heat, humidity, pollen, and dust load a filter faster in summer, so a 1-inch filter that lasts 90 days in spring may need swapping every 30 to 45 days once the AC is running hard. Summer works your HVAC system harder than any other season. When the AC runs, it pulls household air through your filter every single cycle, and in July that cycle... Read more...
Air Filters in Rentals: Who's Responsible, Landlord or Tenant?
Quick answer: It depends on the lease. The most common arrangement is that the landlord supplies a fresh filter at move-in and the tenant replaces filters during the tenancy, with the landlord covering them again at turnover. But norms vary by state and by lease, so the only answer that counts is the one written into your rental agreement. If the lease is silent, put it in writing before it becomes a $5,000 HVAC problem. Air filters are one of the smallest line items in a rental property and one... Read more...
The Best Air Filter for Cooking Smells (Hint: It Needs Carbon)
Quick answer: A standard pleated filter won't remove cooking smells, because odors are gas molecules thousands of times smaller than anything a particle filter can catch. What works is an activated carbon filter, which adsorbs odor molecules onto a bed of porous carbon as air circulates through your HVAC system. Pair it with an outside-venting range hood and last night's fried fish stops being this morning's problem. Everyone knows the morning-after hit: yesterday's bacon, Tuesday's curry, the garlic that has apparently moved in permanently. So people go looking for an... Read more...
Washable vs Disposable Air Filters: An Honest Comparison
Quick answer: Washable filters save money over years but typically perform at only a MERV 4 to 8 equivalent, must dry completely after every wash to avoid mold, and lose effectiveness over repeated cleaning cycles. Disposable pleated filters offer higher MERV ratings, consistent performance out of the box, and zero maintenance. If anyone in your home has allergies, or you deal with smoke or fine dust, pleated disposable is the stronger choice. The washable vs disposable air filter question usually starts with money: why keep buying filters when you could... Read more...
Northeast Wildfire Smoke Update (July 18): The Air Is Clearing
Quick answer: The worst has passed. After New York City's air quality index topped 230 — "Very Unhealthy," its highest reading in three years — on Thursday night, a weak front and weekend rain have pushed the Canadian wildfire smoke back to the south. NYC readings fell into the Moderate range on Friday and Saturday (dropping near an AQI of 68 at one point), and thunderstorms moving through today are scrubbing more of the fine particles from the air. It is not fully over: roughly 850 fires are still burning... Read more...
What an AQI of 171 Actually Means for Your Body (and How to Protect the Air Inside)
Quick answer: An AQI of 171 sits in the "Unhealthy" band (151–200), driven almost entirely by PM2.5 — the fine particles in wildfire smoke. At that level, everyone can feel effects and sensitive groups are at real risk: eye and throat irritation, coughing, headaches, shortness of breath, and aggravated asthma or heart conditions. The particles are small enough to reach deep into your lungs and cross into your bloodstream. You can't change the outdoor number, but you can dramatically lower what you actually breathe by cleaning your indoor air. With... Read more...
Canadian Wildfire Smoke Blankets the Northeast: Air Quality Tracker (July 2026)
Quick answer: Smoke from Canadian wildfires — roughly 850 fires burning nationwide, more than 180 of them in Ontario — has streamed into the U.S. Midwest and Northeast, pushing air quality into the Unhealthy range for around 100 million people. New York City climbed into the Unhealthy zone (AQI in the 170s–180s) this week, and parts of upstate New York hit "Very Unhealthy." Forecasters expect brief relief, another surge into the weekend, and real clearing once showers and thunderstorms move through. Until then, the single best thing you can do... Read more...
MERV 16 Air Filters, Explained: Do You Need Hospital-Grade Filtration?
MERV 16 Air Filters, Explained: Do You Need Hospital-Grade Filtration?
Quick answer: MERV 16 is the highest rating on the MERV scale — it captures 95% or more of fine particles down to 0.3 microns, the territory of smoke, bacteria,... Read more...
The Best Air Filter for Apartments and Condos
The Best Air Filter for Apartments and Condos
Quick answer: The best air filter for most apartments is a MERV 8 to 11 pleated filter in a compact size — 14x20x1, 16x20x1, 20x20x1 and 16x25x1 are the usual... Read more...
Is It Cheaper to Buy Air Filters in Bulk? (Yes — Here's the Math)
Is It Cheaper to Buy Air Filters in Bulk? (Yes — Here's the Math)
Quick answer: Yes — buying air filters in bulk is cheaper, and the savings come mostly from shipping. Freight on a box of filters barely changes whether it holds one... Read more...
How to Build a Corsi-Rosenthal Box (DIY Air Purifier Guide)
How to Build a Corsi-Rosenthal Box (DIY Air Purifier Guide)
Quick answer: A Corsi-Rosenthal box is a DIY air purifier made from a 20-inch box fan, four or five MERV 13 furnace filters, and tape. It costs a fraction of... Read more...
The Complete Air Filter Buying Guide
The Complete Air Filter Buying Guide
Quick answer: To buy the right air filter, you need three things: the correct size (printed on your old filter, like 16x25x1), the right MERV rating for what you want... Read more...
The Best Air Filter for Pet Owners
The Best Air Filter for Pet Owners
Quick answer: The best air filter for pets is a MERV 11 pleated filter. It traps pet dander, fur, and the dust that fur drags around, without choking your furnace... Read more...
The Best Air Filter for Allergies
The Best Air Filter for Allergies
Quick answer: The best air filter for allergies is a MERV 11 for mild symptoms and pet dander, or a MERV 13 for strong allergies and fine pollen. MERV 13... Read more...
The Best Air Filter for Asthma
The Best Air Filter for Asthma
Quick answer: The best air filter for asthma is a MERV 13 pleated filter. MERV 13 captures smoke, bacteria, and fine microscopic particles, including many of the triggers that set... Read more...
Nominal vs Actual Filter Size, Explained
Nominal vs Actual Filter Size, Explained
Quick answer: The nominal filter size is the rounded-up name printed on the filter, like 20x25x1. The actual size is the real measured size, which is about half an inch... Read more...
How Often Should You Change Your Furnace Filter?
How Often Should You Change Your Furnace Filter?
Quick answer: Change a 1-inch furnace filter every 30 to 90 days, a 2-inch filter about every 3 months, and a 4-to-5-inch filter every 6 to 12 months. Pets, allergies,... Read more...
MERV Ratings Explained: Which Filter Does Your Home Actually Need?
MERV Ratings Explained: Which Filter Does Your Home Actually Need?
MERV 8, 11, 13 — the numbers are everywhere but nobody explains what they actually mean. Here's a no-nonsense guide to choosing the right air filter rating for your home. Read more...
The Fiberglass Filter Scam: What Your Hardware Store Filter Actually Does
The Fiberglass Filter Scam: What Your Hardware Store Filter Actually Does
Those cheap blue fiberglass filters at Home Depot were never designed to protect you. They protect your HVAC equipment. Here's the difference between an equipment shield and actual air filtration. Read more...
How to Measure Your Air Filter
How to Measure Your Air Filter
Quick answer: To measure an air filter, pull out the old one and read the size printed on the side (like 16x25x1). If there's no print, measure the length, width,... Read more...
7 Signs You Need to Change Your Air Filter
7 Signs You Need to Change Your Air Filter
Quick answer: The clearest signs to change your air filter are weak airflow from vents, more dust around the house, higher energy bills, a filter that looks gray, and a... Read more...
Do Air Filters Help with Wildfire Smoke?
Do Air Filters Help with Wildfire Smoke?
Quick answer: Yes. The right air filter for wildfire smoke helps a lot. Run a MERV 13 pleated filter to catch the fine smoke particles, and add an activated-carbon layer... Read more...
Which Way Does an Air Filter Go? (Arrow Direction)
Which Way Does an Air Filter Go? (Arrow Direction)
Quick answer: Which way does an air filter go? The arrow printed on the cardboard frame must point in the direction the air flows, which is toward the furnace or... Read more...
What Is a Carbon Air Filter (and Do You Need One)?
What Is a Carbon Air Filter (and Do You Need One)?
Quick answer: A carbon air filter is a pleated filter with a layer of activated carbon that absorbs odors and VOCs (gases), like cooking smells, smoke, pet odor, and chemical... Read more...
MERV vs MPR vs FPR Ratings, Explained
MERV vs MPR vs FPR Ratings, Explained
Quick answer: MERV vs MPR vs FPR are three rating systems for the same thing: how well a filter catches particles. MERV is the universal industry standard (1–16). MPR is... Read more...
Why Your Vacuum Isn't Enough: The Hidden Pet Dander Epidemic
Why Your Vacuum Isn't Enough: The Hidden Pet Dander Epidemic
Your vacuum catches the fur you can see. But microscopic pet dander circulates through your HVAC system for hours. Here's why upgrading to a MERV 11 filter is the only... Read more...
MERV 8 vs 11 vs 13: Which Filter Should You Buy?
MERV 8 vs 11 vs 13: Which Filter Should You Buy?
Quick answer: Buy MERV 8 if you have no pets or allergies, MERV 11 if you have pets or mild allergies, and MERV 13 if anyone has asthma or you... Read more...
How Air Filters Improve Indoor Air Quality
How Air Filters Improve Indoor Air Quality
Quick answer: Your furnace filter is the single biggest lever you have on air filter indoor air quality. Every cubic foot of air your system moves passes through that filter,... Read more...
Air Filter Subscriptions vs Buying in Bulk: Which Saves More?
Air Filter Subscriptions vs Buying in Bulk: Which Saves More?
Quick answer: Skip the subscription. A 5–10% auto-delivery discount is smaller than the freight you pay across repeated small shipments. Buying in bulk wins: Ironside ships 1, 2 or 3... Read more...
How to Find Your Air Filter Size
How to Find Your Air Filter Size
Quick answer: The fastest way to find your air filter size is to pull out your current filter and read the size printed on the cardboard edge, like 16x25x1. If... Read more...
Does a High-MERV Filter Restrict Airflow?
Does a High-MERV Filter Restrict Airflow?
Quick answer: A high-MERV filter restricts airflow a little when it's brand new, but for most homes the drop is small and safe. The bigger risk is leaving any filter... Read more...
What MERV Rating Do I Need? A Simple Guide
What MERV Rating Do I Need? A Simple Guide
Quick answer: Most homes need a MERV 8 filter for basic dust and pollen, a MERV 11 if you have pets or mild allergies, or a MERV 13 if you... Read more...
Furnace and HVAC closet with a 1-inch filter slot
1-Inch vs 4-Inch vs 5-Inch Air Filters
Quick answer: A 1-inch filter is cheaper but needs changing every 30 to 90 days. A 4-inch or 5-inch filter costs more per filter but lasts 6 to 12 months,... Read more...
That Dirty Filter Is Costing You $400 a Year
That Dirty Filter Is Costing You $400 a Year
A clogged air filter increases your HVAC energy consumption by up to 15%. Over a year, that's $360+ wasted — and that's before the $1,200 blower motor replacement. Here's the... Read more...
Indoor Air Quality After Wildfires: What Every Homeowner Needs to Know
Indoor Air Quality After Wildfires: What Every Homeowner Needs to Know
Wildfire smoke doesn't stay outside. PM2.5 particles infiltrate your home through every crack and vent. Here's how your HVAC filter is your first line of defense — and why most... Read more...
Pleated vs Fiberglass Air Filters
Pleated vs Fiberglass Air Filters
Quick answer: In the pleated vs fiberglass filter matchup, pleated wins for clean air. A fiberglass filter only protects the furnace from big debris and catches almost nothing fine. A... Read more...
How to Choose the Exact MERV Rating for Your Home Environment
How to Choose the Exact MERV Rating for Your Home Environment
Filters don't just come in one size. Stop guessing what your HVAC system needs. We break down our entire industrial-grade catalog into three distinct series (Baseline, Advanced, and Extreme) so... Read more...