Work out what actually fits your room, before you buy.
Dehumidifiers, air purifiers, humidifiers and filters are sized, not chosen. Size My Air works out what fits your room from published specifications and standards - square footage, dampness, CADR, MERV, filter dimensions - and explains the reasoning so it still holds when a product goes out of stock.
Latest
Which Dehumidifier Features Matter If Nobody Is Down There?
In an occupied room you notice when a dehumidifier stops. In a basement, a power blip in March can mean you find out in June.
Sep 2, 2026 · 4 min read
Dehumidifier or Air Purifier for a Damp Basement?
Buy the purifier first and you will be filtering the symptom while the cause carries on producing it.
Sep 2, 2026 · 4 min read
Dehumidifier Dimensions: Will It Actually Fit Where You Want It?
Capacity is the number everyone shops on. Width is the number that determines whether the box you ordered can stand where you meant to put it.
Sep 2, 2026 · 3 min read
How Often Should You Change a MERV 13 Furnace Filter?
The interval on the box is a default, not a measurement. The filter itself will tell you more, if you know what you are looking at.
Sep 2, 2026 · 3 min read
What a "4,500 Sq Ft" Dehumidifier Coverage Claim Actually Means
A coverage claim is a marketing figure attached to a machine whose only regulated number is pints per day. The gap between the two is worth understanding before you buy.
Sep 2, 2026 · 4 min read
MPR vs MERV: Which Furnace Filter Number Should You Trust?
A furnace filter can carry two ratings, and only one of them lets you compare it with the filter next to it on the shelf.
Sep 2, 2026 · 3 min read
Do Air Purifiers Remove Odors? Why HEPA Is the Wrong Spec
Every performance number on an air purifier box describes particles. Odors are not particles, which is why a well-reviewed purifier can leave a room smelling exactly as it did.
Sep 2, 2026 · 4 min read
Why an Air Purifier's "1,881 Sq Ft" Might Really Mean 392
Coverage claims on air purifiers are quoted at wildly different air-change rates, and the rate is usually left off the box. When it is printed, the arithmetic is startling.
Sep 2, 2026 · 4 min read
Pet Dander: Air Purifier or a Better Furnace Filter?
These are usually presented as alternatives. They are not — they cover different rooms at different times, and which one helps depends on where your animal actually sleeps.
Sep 2, 2026 · 4 min read
How Often Do You Have to Empty a Dehumidifier Bucket?
Tank capacity and daily extraction are two different numbers, and dividing one by the other is unkind to every portable dehumidifier on the market.
Sep 2, 2026 · 5 min read
12x24x1 Furnace Filters: What to Know About the Odd Size
Less common sizes carry a hidden cost: fewer options at the rating you want, and a greater chance of a substitution that does not fit.
Sep 2, 2026 · 3 min read
What Size Air Purifier Does a Bedroom Actually Need?
Bedrooms are small, closed and occupied in long stretches, which makes them straightforward to size correctly.
Sep 2, 2026 · 4 min read
Basement Dehumidifier: Gravity Drain vs Built-In Pump
Gravity drains rely on a floor drain below the outlet; pump models push water uphill through a hose to a sink or window. The right choice depends on your basement's drainage, not on which feature sounds more convenient.
Sep 2, 2026 · 5 min read
MERV 13 vs MERV 11 for a 1-Inch Furnace Filter
MERV 13 filters more, but a one-inch filter has almost no room to do it without choking airflow. Here's how to decide between MERV 13 and MERV 11 for a standard one-inch slot.
Sep 2, 2026 · 4 min read
Whole-House Dehumidifier vs. Portable Unit for a Basement: How to Choose
A ducted whole-house dehumidifier and a portable unit solve basement moisture differently. The right choice depends on how the basement connects to the rest of the house, how damp it actually is, and whether you want the fix to run itself.
Sep 2, 2026 · 4 min read
How Many Air Purifiers Do You Need for an Open Floor Plan?
An open floor plan is one continuous volume of air, not a sum of rooms with a door between them. Sizing for it means totaling the square footage and matching a clean air delivery rate to it - not trusting a single manufacturer's headline coverage number.
Sep 2, 2026 · 5 min read
Air Purifier for a Musty Basement: What Actually Removes the Smell and the Spores
A musty basement smell is almost always a moisture problem first and an air-quality problem second. Here's how to size a dehumidifier and an air purifier so they actually fix it, not just mask it.
Sep 2, 2026 · 4 min read
What MERV Rating Can Your Furnace Handle?
Your furnace has a filter slot size and a blower, not an opinion on filtration. Here's how to figure out the highest MERV your system will take without straining it.
Sep 2, 2026 · 3 min read
MERV 13 Filter Causing Weak Airflow and AC Freezing Up: What to Do
A MERV 13 filter restricts airflow more than a MERV 8 or 11. On an older or undersized blower, that restriction can starve the coil and freeze it. Here's how to fix it without giving up filtration.
Sep 2, 2026 · 4 min read
Nominal vs. Actual Furnace Filter Size: What 16x25x1 Really Means
A 16x25x1 filter is never actually 16 by 25 by 1 inches. Here's why the gap exists, how big it usually is, and how to check your slot before you order.
Sep 2, 2026 · 5 min read
Air Purifier CADR for a 400 sq ft Room with 10-Foot Ceilings
A 400 sq ft room with 10-foot ceilings has more air to clean than the square footage alone suggests. Here's how to work out the CADR you actually need, and why ceiling height changes the math.
Sep 2, 2026 · 3 min read
Will a 50 Pint Dehumidifier Work in a 55°F Basement?
A 50-pint dehumidifier can work in a 55°F basement, but only if it has automatic defrost - and even then, the pint rating alone won't tell you if it's sized correctly for the room.
Sep 2, 2026 · 2 min read
70-Pint or 50-Pint Dehumidifier? What the DOE Rating Change Actually Means
The old 70-pint dehumidifiers and today's 50-pint models aren't rated the same way, so comparing the numbers directly is misleading. Here's what changed and how to size a dehumidifier now.
Sep 2, 2026 · 4 min read
Crawl Space Dehumidifier Sizing: Encapsulated vs. Vented
Vented and encapsulated crawl spaces carry different moisture loads, so the same square footage needs different dehumidifier capacity. Here's how to size each one and which units fit the low-clearance, unheated conditions crawl spaces create.
Sep 2, 2026 · 5 min read
What size dehumidifier do I need for a basement?
Three 50-pint dehumidifiers advertise 4,500, 4,500 and 5,000 square feet. Identical capacity, three different claims. Here is what to size from instead.
Sep 2, 2026 · 7 min read