If you’ve ever stood in the filter aisle staring at MERV numbers and a wall of 1″, 2″, 4″ filters, you’re not alone.

• “Higher MERV = better, right?”
• “Will this choke my system?”
• “Do I really need the super expensive allergy filter?”

Your air filter choice affects:

• Comfort
• System health & lifespan
• Indoor air quality
• Energy bills

This guide from Galaxy Heating & Air Conditioning breaks down MERV ratings, filter thickness, and practical Bay Area-specific recommendations so you’re not just guessing.

📍 Serving Contra Costa, Alameda & San Francisco counties

📞 Not sure what filter your system should use? Call or text (925) 578-3293.

What Your HVAC Filter Actually Does (And Doesn’t Do)

Your HVAC filter has two main jobs:

1. Protect the equipment
   • Keep dust, hair, and debris off the blower, coil, and heat exchanger
   • Prevent airflow problems and breakdowns
2. Improve indoor air quality (to a point)
   • Capture dust, pollen, dander, etc.
   • Help reduce stuff floating around (but it’s not a full air purification system)

What it doesn’t do by itself:

• Solve serious mold problems
• Replace a dedicated air cleaner for heavy allergies or smoke
• Make up for bad ventilation or duct leaks

But a properly chosen filter, changed regularly, is one of the easiest, cheapest ways to protect your HVAC and make your Bay Area home more comfortable to breathe in.

MERV Ratings Explained (Without the Jargon Headache)

MERV = Minimum Efficiency Reporting Value

It’s a scale (typically 1–16 for residential) that tells you how well a filter captures particles of different sizes.

Rough MERV Range Guide

MERV 1–4

• Captures: big stuff (lint, large dust)
• Often the cheapest “fiberglass” style
• Protects the equipment a little, does almost nothing for air quality
• We rarely recommend these in Bay Area homes

MERV 5–8

• Captures: dust, lint, some pollen, pet hair
• A solid “basic” filter range for many homes
• Gentle on airflow in most systems
• Good starting point if you don’t have major allergy/asthma concerns

MERV 9–12

• Captures: smaller particles (finer dust, more pollen, some smoke/soot-sized particles)
• Better for homes with allergies or pets
• Can be great if your system and ductwork can handle the added resistance

MERV 13–16

• Captures: even finer particles (more smoke, bacteria-sized particles, etc.)
• Often used in higher-end residential and light commercial systems
• Great for filtration, but can seriously restrict airflow if the system isn’t designed for it

Higher MERV = more capture, but also more resistance to airflow.

That’s why “just buy the highest MERV possible” isn’t always the best idea.

1″ vs 2″ vs 4″ Filters – What’s the Difference?

Beyond MERV, filter thickness really matters.

1-Inch Filters

Most common in existing homes

• Slide into a small slot at the return grille or furnace
• Widely available at hardware stores

Pros:

• Cheap and easy to find
• Easy to change

Cons:

• Less surface area = higher pressure drop at higher MERV ratings
• Need to be changed more often (every 1–3 months typically)
• High-MERV 1″ filters can choke airflow on older or borderline systems

2-Inch Filters

Sometimes used in slightly deeper filter racks

• More surface area than 1″, but still relatively compact

Pros:

• A bit more filter area, so they can flow better than a 1″ at the same MERV
• Can sometimes be used to improve filtration without killing airflow if the rack allows it

Cons:

• Not every system has space for 2″
• Availability is more limited than 1″
• Still generally changed every 2–3 months

4–5″ “Media” Filters

Often referred to as media filters or cabinet filters, these sit in a dedicated housing near the furnace or air handler.

Pros:

• Much more surface area = lower resistance for the same MERV
• Great way to get MERV 11–13 level filtration without suffocating the system
• Typically changed 1–2 times per year (depending on home conditions)
• Fantastic for Bay Area homes with allergies, pets, or wildfire smoke concerns

Cons:

• Usually requires installing a filter cabinet (modification to your system)
• Higher upfront cost, though long-term it often balances out
• Not something you can just “grab and jam into a 1″ slot”

If you want better air quality and healthy HVAC airflow, a properly sized 4–5″ media filter is often the sweet spot.

Bay Area Realities: Smoke, Pollen & Microclimates

Living here, your filter isn’t just dealing with “normal dust.”

• Wildfire smoke season (even if the fires aren’t right next door)
• Pollen from trees and grasses, especially in spring
• Coastal vs inland humidity and dust differences
• Older homes that can be a bit drafty

That means your filter choice may need to balance:

• Allergy relief
• Smoke & fine particle capture (when outdoor air gets nasty)
• Not over-restricting airflow in systems that already have marginal ductwork

Practical Filter Recommendations for Bay Area Homes

These are general guidelines — your exact system, ducts, and health needs matter. But here’s a starting point.

1. “Typical” Bay Area Home, Standard 1″ Filter Slot

You:

• Have a reasonably modern system
• Don’t have severe allergies or asthma
• Mostly care about protecting the equipment and keeping dust under control

We often recommend:

• MERV 7–8, 1″ filter
• Change every 1–2 months (more often with pets or lots of dust)

This gives solid protection without a big airflow penalty for most systems.

2. Homes with Allergies, Pets, or Mild Sensitivity

You:

• Care more about air quality
• Have someone with mild/moderate allergies or respiratory sensitivities
• Have a system that’s not already struggling with airflow

If staying with 1″:

• MERV 9–11, 1″ filter
• Check monthly, change every 1–2 months

But on older or borderline systems, a high-MERV 1″ filter can be a bit much. That’s where a media filter upgrade really shines.

3. Best Balance of Air Quality & System Health (4–5″ Media Filter)

You:

• Want noticeably cleaner air
• Have asthma/allergies or really care about dust and fine particles
• Are tired of changing filters constantly
• Plan to stay in the home and want a long-term solution

We often recommend:

• Installing a 4–5″ media filter cabinet
• Using a MERV 11–13 media filter
• Changing it about once or twice a year (depending on usage/pets/smoke)

This is one of the most popular upgrades we do for Bay Area homeowners who want better filtration without sacrificing airflow and system life.

4. Concerned About Wildfire Smoke

During heavy smoke events, many people want the highest filtration possible.

Options we often talk about:

• MERV 11–13 media filter as your main system filter
• Running the fan in “On” or “Circulate” mode during smoke events to continuously filter indoor air (if your system and ducts can handle it)
• Adding portable HEPA air cleaners in bedrooms or high-use areas for an extra layer of fine-particle filtration

We generally don’t recommend jamming a MERV 16, 1″ filter into a system that wasn’t designed for it — that can cause more harm than good.

How Often Should You Change Your Filter?

General rules of thumb (for Bay Area, year-round usage):

• 1″ filters (any MERV):
  • Check monthly
  • Change every 1–3 months (more often with pets, smoking, construction, or smoke events)
• 2″ filters:
  • Check monthly
  • Change about every 2–3 months
• 4–5″ media filters:
  • Check every 3–6 months
  • Change about once or twice per year

If you notice:

• The filter is visibly dirty or gray
• Airflow from vents feels weaker
• More dust than usual around the home

…it’s probably time.

Common Filter Mistakes We See (A Lot)

1. “I Bought the Thickest, Highest MERV 1″ Filter I Could Find”

Great for advertising. Not always great for your system.

High-MERV, high-resistance 1″ filters can:

• Restrict airflow
• Cause the system to overheat or ice up
• Shorten equipment life
• Increase noise and energy usage

If your ducts are undersized (very common), this can be a real problem. Better path: media filter upgrade or a more modest MERV at 1″.

2. Filters Put in Backwards

Most filters have an arrow showing airflow direction.

• The arrow should point toward the blower/furnace, i.e., into the system.
• Backwards filters can restrict airflow and let more dust bypass the media.

3. Wrong Size or Gaps Around the Filter

If the filter doesn’t fit tightly:

• Air takes the path of least resistance and flows around it
• Dust and debris get into the system anyway
• You’re basically paying for a filter that’s not filtering

Always match the size printed on the frame, and if the rack is odd-sized, we can sometimes modify it or provide the correct-size solution.

4. “I Only Change It Once or Twice a Year… on a 1″ Filter”

If you’re running a thin 1″ filter and only changing it 1–2 times a year, your system is almost definitely:

• Running with restricted airflow
• Working harder (higher bills)
• Getting dirtier internally than it should

Either set reminders to change 1″ filters more often, or talk to us about upgrading to a media filter that’s actually designed to last longer.

FAQ – Air Filters for Bay Area Homes

Q: What MERV filter should I get if I have pets?

A: Often MERV 8–11 is a good range, depending on your system. If you have a media cabinet, MERV 11–13 media filters do a great job capturing pet hair and dander without killing airflow.

Q: Is MERV 13 too high for my system?

A: It depends how it’s installed. MERV 13 in a 4–5″ media filter is usually fine on a well-designed system. MERV 13 in a 1″ filter can be too restrictive for many older or marginal setups. We can measure your static pressure and tell you what your system can safely handle.

Q: Will a better filter fix my dust problem?

A: It helps, but it’s not the whole story. Dust also comes from:

• Leaky ducts
• Infiltration from outside
• Carpets, textiles, and general household activity

A good filter is part of the solution, but sometimes sealing ducts and improving ventilation or housekeeping habits matters too.

Q: Can I just buy filters online and swap them myself?

A: Absolutely — as long as the size and MERV are appropriate and you replace them on schedule. If you’re not sure what’s best for your system, we can take a look and make specific recommendations.

Q: How do I know if I can upgrade to a 4–5″ media filter?

A: We look at:

• The space around your furnace/air handler
• Existing duct connections and filter rack
• System and duct capacity

In many Bay Area homes, we can add a media cabinet with some sheet metal work and small duct adjustments.

Want a Filter Setup That Actually Matches Your Bay Area Home?

If you’re in Contra Costa, Alameda, or San Francisco counties and not sure which filter is right for your system (or you’re tired of guessing at the store):

Galaxy Heating & Air Conditioning can:

• Inspect your system, ducts, and current filter setup
• Measure airflow and static pressure so we know what your system can handle
• Recommend MERV rating and filter thickness that fit your goals (basic protection, allergy help, wildfire season, etc.)
• Install 4–5″ media cabinets or upgraded filtration where it makes sense
• Set you up with maintenance reminders so filters actually get changed on time

📞 Call or text (925) 578-3293

💬 Or contact us through our website to schedule a filter + system check

We’ll help you move from “random filter roulette” to a setup that keeps your air cleaner, your system happier, and your Bay Area home more comfortable year-round