How to Prevent Mold and Mildew in Your HVAC System

By GOGO Heating

on February 10, 2026

Every time your heating or cooling kicks on, it’s more than just comfort swirling through your home or business. The air you breathe is directly shaped by what’s hiding inside your HVAC system. Mold and mildew can creep in quietly, but the effect on your air—and your health—can be loud.

You deserve to breathe easy. At GOGO Heating, we’ve seen firsthand how quickly small HVAC issues can turn into big mold problems. Here’s how you can protect your space, your air, and everyone inside.

Why Mold Grows in HVAC Systems 🦠

HVAC systems are the lungs of your building. But just like real lungs, they need to stay dry and clean to work well. Mold loves moisture. It thrives in dark, damp spaces—like inside ducts, air handlers, or around old filters.

When condensation builds up from temperature swings, or leaks go unnoticed, it’s like setting out a welcome mat for spores. Even a little standing water in a drip pan or near a coil can be enough. Add in dust and organic debris, and you’ve got a buffet for mold and mildew.

Moisture: High humidity, condensation, or leaks create a perfect breeding ground.
Dust & Debris: Organic material clings to filters, ducts, and coils, feeding mold.
Poor Airflow: Stagnant air means lingering moisture and trapped spores.

The U.S. Environmental Protection Agency (EPA) warns that unchecked mold growth can damage building materials and lead to major indoor air quality problems.

Signs of Mold and Mildew

Mold isn’t always visible. Sometimes it’s silent, hiding deep inside your HVAC system. But there are warning signs:

Musty Odors: If your air smells earthy or damp, especially when the system runs, suspect mold.
Visible Growth: Black, green, or white patches near vents, on filters, or around coils.
Health Symptoms: Increase in allergies, coughing, or headaches, especially when indoors.
Condensation: Water droplets or dampness around ducts or near air handlers.

If you notice any of these, don’t ignore them. Mold can spread quickly and impact everyone’s health.

Prevention Tips for Homeowners and Businesses

Stopping mold before it starts is the best defense. Here’s how to keep your HVAC system healthy:

Control Moisture

Fix Leaks Fast: Even small drips can lead to big problems. Check pipes, drip pans, and around HVAC units regularly.
Insulate Ductwork: Prevents condensation, especially in attics or crawl spaces.
Maintain Proper Humidity: Aim for 30%–50% indoor humidity. Use dehumidifiers if needed.

Keep Air Moving

Change Filters Regularly: Dirty filters trap moisture and dust. Schedule filter changes every 1–3 months, or more if you have pets or allergies. Learn more about our filter services
Don’t Block Vents: Furniture or boxes can limit airflow and create cold spots where moisture collects.
Use Whole-House Fans: These help circulate air and reduce dampness.

Clean and Maintain

Schedule Annual HVAC Maintenance: Regular inspections catch issues before they become headaches. See our HVAC maintenance options
Clean Ducts When Needed: Especially after remodeling, water damage, or if mold is suspected. Duct cleaning services can make a real difference.
Upgrade to Smart Thermostats: Some can help you monitor humidity and air quality. If you're searching for "Thermostats near you," look for models with built-in sensors.

Mind the Details

Seal Duct Leaks: This keeps moist air from sneaking into your system.
Check Drain Pans: Make sure water drains freely. Standing water is a magnet for mold.
Use UV Lights or Air Scrubbers: These can help reduce airborne mold spores inside your system.

Professional Mold Remediation

Sometimes, even your best efforts aren’t enough. If you spot mold inside your HVAC system, it’s time to call in the pros. Mold inside ducts or on coils isn’t a DIY job—the wrong approach can spread spores or damage your system.

Here’s what a professional service, like GOGO Heating, does:

Thorough Inspection: Using moisture meters and cameras to find hidden trouble spots.
Containment: Preventing spores from spreading to clean areas.
Safe Cleaning: Using EPA-registered products and methods that meet OSHA safety guidelines.
Component Replacement: Swapping out heavily contaminated filters or insulation.
Verification: Testing air quality after cleaning to ensure the job is done right.

For severe or widespread mold, remediation is often required by building codes and insurance policies. The Centers for Disease Control and Prevention (CDC) recommends professional help for HVAC-related mold to protect occupants and ensure complete removal.

Maintaining Clean Ducts and Equipment

A little prevention goes a long way. Think of regular duct cleaning and filter changes like brushing your teeth—not glamorous, but essential for health.

Schedule Duct Cleaning: Every 3–5 years, or sooner if you notice dust, mold, or after renovations.
Upgrade to HEPA or High-MERV Filters: These trap finer particles and spores.
Keep Outdoor Units Clear: Leaves, grass, and debris can block drainage and harbor moisture.
Replace Filters Often: Mark your calendar or set reminders—consistency is key.

If your business relies on clean indoor air for staff or customers, consider periodic Indoor Air Quality (IAQ) testing to catch problems early. Indoor Air Quality help in Keene, New Hampshire

FAQs

How dangerous is mold in an HVAC system?

Mold can trigger allergies, asthma, and respiratory issues, especially in children, the elderly, or anyone with compromised immune systems. The EPA notes that even non-toxic molds can worsen indoor air quality.

How often should I check for mold?

Inspect your system every season, and after major weather events, leaks, or renovations. Any time you notice odors or symptoms, act quickly.

Can I use bleach to clean mold from my HVAC?

Don’t! Bleach isn’t recommended for HVAC components. It can damage metal parts and leave harmful residues. Professional cleaning uses products approved for HVAC use.

What’s the best filter for preventing mold?

Look for HEPA or filters rated MERV 13 or higher. Change them regularly, and check your system’s compatibility.

Local and Seasonal Considerations

In the Northeast, spring thaw and summer humidity can really test your HVAC system. Watch for condensation on ductwork after cold snaps or heavy rain. Businesses with commercial kitchens or humid processes should be extra vigilant—grease and moisture can both fuel mold growth.

Winter can be tricky, too. Ice dams or blocked vents sometimes cause hidden leaks. Check regularly, especially in older buildings or those with radiant heating systems.

The Bottom Line

Mold and mildew don’t have to take over your HVAC. With a few smart habits and some help from GOGO Heating, you can keep your air fresh, your system efficient, and your people healthy.

Call GOGO Heating now — or reach us anytime at 844-467-0847 .