The “Closed Window Season” is Dangerous for Your Health

In Southeast Wisconsin, we keep our windows closed for nearly six months of the year to retain heat. While this saves on energy bills, it creates a “sealed loop” environment.

Here is the reality I see in the field: Every time your furnace kicks on, it pulls air from your rooms, moves it through your cold-air returns, heats it, and pushes it back out. If that air is full of pet dander, drywall dust, and chemical vapors, your family is breathing that soup over and over again.

According to the EPA, indoor air can be 2 to 5 times more polluted than outdoor air. For families in Waukesha and Milwaukee, that concentration of pollutants is often the hidden cause of winter “colds” that just won’t go away.

The 6 Biggest Pollutants We Find in Wisconsin Ducts

It’s not just “dust.” Here is what is actually circulating in your home.

1. Mold & Mildew

The Local Risk: Wisconsin summers are humid. If your basement is damp, mold spores grow in your return drops. When the furnace runs, those spores are blasted into your bedrooms.

Health Impact: Asthma attacks, throat irritation, and chronic coughing.

2. Radon Gas

The Local Risk: Waukesha and Washington Counties have some of the highest radon levels in the state. This odorless gas seeps up through foundation cracks.

Health Impact: It is the #1 cause of lung cancer among non-smokers (Source: EPA).

3. Volatile Organic Compounds (VOCs)

The Local Risk: These are invisible gases emitted from new carpets, fresh paint, or cleaning supplies. In a sealed winter home, they can’t escape.

Health Impact: Headaches, dizziness, and long-term liver damage.

4. Dust Mites & “Bio-Debris.”

The Local Risk: In my 12+ years of cleaning, I have removed pounds of dead skin cells, pet hair, and insect debris from vents. This material acts as food for dust mites.

Health Impact: A primary trigger for eczema and allergy flare-ups.

5. Construction Debris (Drywall Dust)

The Local Risk: New-construction homes in areas such as Oak Creek often have ducts filled with sawdust and drywall dust.

Health Impact: Fine particulate matter that can bypass standard filters and damage your lungs (and your furnace motor).

5 Pro-Tips to Breathe Easier (That Actually Work)

Skip the gimmicks. Here is what I tell my own family to do.

1. Upgrade Your Furnace Filter (But Be Careful)

Don’t just buy the cheapest fiberglass filter. Look for a filter with a MERV rating between 8 and 11.

• Pro Tip: Don’t go too high (MERV 13+) unless your furnace is rated for it. A filter that is too thick can clog your system and damage the blower motor.

2. Control Your Humidity

• Winter: Keep humidity around 30-40% to prevent viruses from thriving.

• Summer: Keep it under 50% to stop mold growth. Use a dehumidifier in the basement near your air intake.

3. Stop “Masking” Odors

Stop using plug-in air fresheners and scented candles. These add VOCs to the air. If your house smells musty, you need to remove the source (usually dirty ducts or mold), not cover it up with chemicals.

4. Vacuum with HEPA Filtration

Standard vacuums often just blow fine dust back into the air. Use a vacuum with a sealed HEPA filter to actually trap the allergens.

5. Get a “Source Removal” Duct Cleaning

Vacuuming your carpet is excellent, but your HVAC system is the “lungs” of your home. If the lungs are dirty, the whole body suffers.

• Our Method: We use 5,000 CFM negative air pressure and 175 PSI air whips to physically remove the debris from the metal walls of your ducts. We don’t just “dust” them; we scour them clean.

When Should You Call a Professional?

You can handle basic dusting, but you should call a certified professional if:

1. You see visible mold growth inside rigid surface ducts or on other components of your heating and cooling system.

2. You have a vermin infestation (insects or rodents) clogging the system.

3. You see a “poof” of dust release from a supply register when the blower turns on.

4. You just moved into a new home and want to remove the previous owner’s “biological footprint.”