The Ironside Journal.

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

News

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: Worth It? (The Simpler Way to Never Run Out)
Air Filter Subscriptions: Worth It? (The Simpler Way to Never Run Out)
Quick answer: Air filter subscriptions promise convenience, but for most homes they are not worth it. You can get the same never-run-out result cheaper and with zero commitment by buying... 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...