- Altitude, along with other factors, can affect how often you should change your furnace filter.
- MERV rating for a furnace filter stands for Minimum Efficiency Reporting Value.
- A thicker furnace filter is not necessarily better.
How often to change a furnace filter depends on many variables. It is not just about how often your furnace or HVAC is in use, but also outside weather conditions, the altitude, the amount of dust inside and out, whether you have pets, and more can all come into play. The experienced technicians at The Weather Changers can help you determine which air filter is best for your HVAC system and how often you should change your furnace filter.
The General Rule vs. The Colorado Reality
A common general rule for how often to change a house air filter is every 30-90 days, depending on where you live, the outdoor weather, indoor living conditions, pets, the type of air filter used, and more. Anyone who lives in Colorado likely knows that the state is 3,300 feet above sea level and higher. In fact, Colorado’s median elevation is 6,800 feet, although Denver, known as the mile-high city, sits at 5,280 feet above sea level.
Why does altitude matter when it comes to how often you should change your furnace filter? High altitude often brings dust and other debris into the air. Seasonal winds blow dust and debris around, causing furnace filters to clog faster and requiring more frequent changes. For many, that may be as often as every month or two.
Choosing the Right Filter: MERV Ratings & Thickness
MERV stands for Minimum Efficiency Reporting Value. It measures how effectively a filter traps airborne particles ranging from dust mites to microscopic pollutants. Choosing the right rating and filter type balances clean indoor air quality with healthy airflow.
The higher the MERV rating, the thicker or denser the air filter, and that may restrict airflow. It can take a toll on your HVAC system by making it work harder. To allow proper airflow, at The Weather Changers, we recommend a MERV rating of between 8 and 13 as a good standard for a Colorado home.
Homes with family members who have allergies or pets may lean toward a MERV rating of 11-13, while homes with no allergy issues may lean between 8-10.
Is Higher MERV Always Better?
Not necessarily. While a higher MERV rating traps finer particles, a filter that is too dense restricts airflow through your furnace or AC unit. Restricted airflow forces your blower motor to work extra hard, increasing energy bills, accelerating wear and tear, and potentially causing the system to short cycle or overheat. For most residential homes in Denver, a MERV rating between 8 and 13 strikes the optimal balance between high indoor air quality and proper airflow.
How Filter Type and Depth Affect Performance
Filter lifespans vary widely based on construction:
- Standard Thin Filters: Collect surface dust quickly across a smaller surface area and need frequent replacement.
- Thicker Deep-Pleated Filters: Provide significantly more surface area to trap pollutants, allowing them to last longer without restricting airflow as drastically.
Note: Always check your system’s specifications before changing filter depth. Forcing a thicker filter into a cabinet designed for thin filters blocks airflow and can cause costly mechanical damage.
Signs It’s Time for an Immediate Filter Change
If you aren’t sure when you last replaced your air filter, pull it out and inspect it under light. Look for these warning signs that mean it needs an immediate swap:
- Visible Dust Buildup: Dark gray dust layer coating the pleated material or gathering around return vents.
- Longer Run Times: Your furnace or AC runs continuously without reaching the set thermostat temperature.
- Rising Energy Costs: Unexplained spikes in monthly utility bills caused by a blower motor struggling against dust buildup.
- Musty or Dusty Odors: Burning dust or stale smells emitting from your supply vents when the heat turns on.
- System Overheating: Your furnace shuts down unexpectedly due to safety limit switches tripping from low airflow.
How Air Filters Tie into Preventative Maintenance
Replacing your filter regularly is one of the simplest DIY tasks you can perform to lower energy bills, protect indoor air quality, and extend the lifespan of your furnace and air conditioner (typically estimated around 10 to 15 years with proper care).
While filter changes are an essential home routine, your heating and cooling equipment also requires professional servicing twice a year—in the spring for AC and in the fall for heating. Routine tune-ups allow certified technicians to clean internal components, verify electrical connections, inspect heat exchangers, and catch minor issues before they turn into major breakdowns.
Whether you need guidance on selecting the right filter style, want to upgrade your home’s air filtration, or are ready to schedule seasonal preventative maintenance in the Denver metro area, contact The Weather Changers today.
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