The air inside your Metro Detroit home is probably not as clean as the air outside — and in a region where residents spend most of the year indoors with windows closed, that matters more than most homeowners realize. Indoor air quality problems are rarely dramatic. They show up as persistent allergy symptoms, inexplicable headaches, worsening asthma, or a musty smell that comes and goes. Understanding where the problems come from and what your HVAC system can actually do about them is the first step.

Why Indoor Air Quality Is Worse Than Most People Expect

The EPA's guide to indoor air quality notes that Americans spend roughly 90% of their time indoors, and that concentrations of some pollutants are typically 2 to 5 times higher indoors than outdoors. In a well-insulated Michigan home — which is what energy efficiency codes have been pushing toward for decades — the building holds heat well, but it also traps whatever is in the air. Combustion byproducts from a gas furnace or range, off-gassing from carpets and furniture, mold spores from a wet basement, and whatever comes in on shoes or through gaps in the building envelope all accumulate in a space that doesn't flush itself the way an open window would.

In Macomb County and the broader Metro Detroit area, the seasonal pattern matters. Winters are long, buildings are sealed tight, and combustion appliances run for months. Summers bring high humidity, mold growth risk, and pollen loads that work their way inside. Spring and fall are transitional, but they're also when condensation builds up in ductwork as temperature differentials spike. Each season has its own IAQ challenges, and an HVAC system that isn't maintained appropriately for each of them will compound the problem rather than solve it.

What Your HVAC System Is Actually Filtering

The standard one-inch air filter that most HVAC systems use is designed to protect the equipment — not to clean the air. Its job is to keep dust and large particles off the blower motor and heat exchanger. It does that reasonably well. What it doesn't do is capture fine particulate matter, most mold spores, pet dander smaller than 10 microns, or volatile organic compounds (VOCs) like formaldehyde or benzene off-gassing from building materials.

Upgrading to a higher-MERV filter addresses some of this. MERV 11–13 filters capture a significantly broader range of particles, including fine dust, mold spores, and pet dander, without the airflow restriction that true HEPA-rated filters cause when installed in systems not designed for them. The trade-off is that higher-MERV filters load faster and need more frequent changes — typically every 60 to 90 days rather than the standard 90-day guidance for lower-rated filters. A filter that hasn't been changed is worse than no filter; a clogged filter restricts airflow, reduces system efficiency, and can cause the heat exchanger to overheat.

The Carbon Monoxide and Combustion Gas Risk

In Michigan homes with gas furnaces, water heaters, or ranges, combustion byproduct management is the IAQ issue with the highest stakes. Carbon monoxide is colorless and odorless; the only reliable protection is a working CO detector and an annual furnace inspection that includes a heat exchanger check. A cracked heat exchanger — a common failure in furnaces past the 15-year mark — can allow combustion gases to enter the home's air supply without any visible warning sign.

Proper combustion air and exhaust venting are also seasonal concerns. Ice damming on exhaust flue terminations is a real failure mode in Michigan winters. A furnace or water heater that has lost its exhaust path will either lock out on a safety fault or — worse — backdraft combustion gases into the living space. A pre-season inspection that checks venting terminations is not optional maintenance for Michigan homeowners; it is a safety baseline.

Humidity: The Often-Missed IAQ Factor

Michigan's climate creates two distinct humidity challenges. Winters are cold and dry, and central heating removes moisture from the air — which increases static electricity, dries out respiratory passages, and creates conditions where viruses spread more easily. Summers are humid, which promotes mold growth in basements, crawlspaces, and ductwork, and makes the home feel warmer at any given temperature.

A whole-home humidifier mounted on the furnace addresses the winter dryness problem efficiently and consistently. The target is 35 to 45% relative humidity during heating season. A standalone dehumidifier, or a dehumidifier integrated with the HVAC system, handles summer humidity in problem areas. In homes with persistent basement moisture, addressing the source — drainage, grading, foundation sealing — is the only durable solution; a dehumidifier running continuously is managing a symptom, not a cause.

UV Air Purification and Whole-Home Filtration

For households with allergy or asthma sufferers, or where pet dander is a persistent problem, upgrading beyond a standard filter is worth the investment. UV light systems installed in the air handler kill mold, bacteria, and certain viruses that pass through the filter. Electronic air cleaners using ionization or electrostatic precipitation capture fine particles that mechanical filters miss. Neither technology replaces regular filter changes and duct cleaning — they complement them.

Duct cleaning is a topic with a lot of marketing noise around it, but there are legitimate use cases: a home that has had HVAC work done with debris left in the ducts, a home with documented mold growth in the ductwork, or a home after a renovation that generated significant dust. In those cases, professional duct cleaning removes the contamination source rather than just filtering what flows through it. For a well-maintained system with no history of problems, routine cleaning is less critical — but inspection of accessible ductwork every few years is reasonable.

Getting an IAQ Assessment

RC Heating & Cooling provides indoor air quality assessments and equipment recommendations for Shelby Township, Sterling Heights, Macomb County, and Metro Detroit. Whether the starting point is a persistent odor, a family member with worsening allergy symptoms, or simply wanting to understand what your current system is and isn't doing, we will give you a straight assessment and practical options — not a upsell list.

To schedule an IAQ assessment or HVAC inspection, contact us at rcheatcool.com/contact-us or call (586) 991-5990.

FAQ

How do I know if my home has an indoor air quality problem?

Common indicators include: persistent allergy or asthma symptoms that are worse indoors than outdoors, a musty or stale odor that doesn't resolve with normal cleaning, visible mold in bathrooms or the basement, or household members who feel better when they leave the house for extended periods. A CO detector that alarms or malfunctions is an immediate safety issue that warrants a furnace inspection. RC Heating & Cooling can assess your HVAC system and identify IAQ contributors during a service visit.

What MERV rating should my air filter be?

For most Metro Detroit homes with standard HVAC systems, MERV 8 to 11 is a good balance between filtration quality and airflow. MERV 13 provides better fine-particle filtration but requires more frequent changes and may restrict airflow on systems not designed for it. Check your system's manufacturer documentation or ask your HVAC contractor before going above MERV 11 — a filter that's too restrictive for your system reduces efficiency and can cause the blower motor to work harder than it should.

Does duct cleaning improve air quality?

It depends on what's in the ducts. If there's documented mold, accumulated construction debris, or significant biological contamination, professional cleaning removes the source. In a well-maintained system with no history of problems, the IAQ benefit of routine cleaning is more limited. A technician who inspects accessible ductwork can tell you whether cleaning would make a meaningful difference in your specific case.

Does a UV air purifier actually work?

UV systems installed in the air handler are effective at inactivating mold spores, bacteria, and some viruses that circulate through the HVAC system. They work best in combination with a quality filter, not as a replacement. The UV lamps lose efficacy over time and should be replaced annually. For households with immune-compromised members, mold sensitivity, or pets, the combination of a MERV 11+ filter and a UV system provides meaningful IAQ improvement over a standard filter alone.

How often should I change my furnace filter in Metro Detroit?

For a standard one-inch filter rated MERV 5 to 8, every 30 to 60 days during heating and cooling seasons is the right interval for most Macomb County homes with pets or multiple occupants. For a four-inch media filter rated MERV 11, every six months is a reasonable baseline, with a visual check at three months. A filter that looks heavily loaded before the scheduled interval should be changed early. When in doubt, change it — a clean filter costs a few dollars; the HVAC repair from a clogged one costs considerably more.