1. [Home](/) 2. [Guides](/guides/) 3. [Furnaces and winter heating in Southwest Ohio](/guides/furnace-guide/) 4. Furnace filters: which one and how often # Furnace filters: which one and how often The furnace filter is the simplest maintenance job in the house and one of the easiest to get wrong. Here is how to choose one, how often to change it, and when a higher rating works against you. ## Key takeaways - MERV is a scale that describes how small a particle a filter can catch. Higher numbers catch smaller particles but resist airflow more. - Check your furnace's manual or ask a HVAC contractor which filter type and thickness your system is designed for. - Change the filter on a schedule that fits the filter type, with extra attention during heating season and in homes with pets. - If you want cleaner air than a basic filter gives you, consider options that do not choke the furnace. ## What MERV means MERV stands for minimum efficiency reporting value. It is a rating from 1 to 16 for residential and commercial filters, and it describes how well a filter captures particles of different sizes. A higher number means the filter catches smaller particles. In general terms: - **Low ratings** are thin fiberglass filters. They protect the furnace from large debris like lint and hair but do little for the air you breathe. - **Middle ratings** are pleated filters, which catch much more dust, pollen, and pet dander. These are a common choice for homes. - **High ratings** catch very fine particles, but the filter material is denser and air has a harder time passing through. The rating tells you what the filter catches. It does not tell you whether your furnace can handle it. ## Choosing the right filter for your furnace Start with size and type. The filter slot or cabinet is built for a specific size, and some systems use a thick media cabinet instead of a standard one-inch slot. The dimensions are printed on the edge of the existing filter. Use that size exactly, because gaps let unfiltered air bypass. Then check what the furnace is designed for. Furnace and air handler manufacturers specify limits on airflow resistance. A system designed around a basic filter may struggle with a dense one. If you are not sure, a HVAC contractor can check the system's static pressure and tell you what range is safe. For many homes, a pleated filter in the middle of the MERV range is a reasonable balance. Choose by what your system can handle and what your household needs, not by the highest number on the shelf. Filter arrows should point toward the furnace, the direction the air flows. ## How often to change it The label on the filter gives a maximum, and your home may need to beat it. A one-inch filter is commonly changed every one to three months. Thicker media filters last longer and are often changed once or twice a year, following the manufacturer's directions. Change it sooner if: - you have shedding pets; - someone in the home has allergies or asthma; - you have had construction, sanding, or remodeling work; - the home is dusty or near fields or roads; - the furnace runs often during a long cold stretch. A simple habit is to check the filter at the start of each month and hold it up to a light. If you cannot see light through it, replace it. Heating season in Southwest Ohio keeps windows closed for months, so dust and dander build up faster than in summer. Write the date on the frame so you know when it was last changed. ## Pets and allergies Pet hair clogs a filter quickly, and dander is fine enough that a basic filter does not catch much of it. A pleated filter in a middle range helps, and checking it more often matters just as much. For allergies, a better filter is one piece of the answer. Reducing dust sources, keeping ducts in good condition, and controlling humidity all help. Heating season air is often dry, and some homes use a humidifier. In this region, water can be hard, so humidifiers need regular cleaning and pad changes to work well. If filtration is a priority, ask about options designed for the job, such as a dedicated media cabinet or an air cleaner installed in the ductwork, instead of forcing a dense filter into a slot that was not made for it. See [indoor air quality](/services/indoor-air-quality/) for what is available. ## Airflow tradeoffs Every filter resists airflow a little. A dense filter, or a dirty one, resists a lot. When the furnace cannot pull enough air, the heat exchanger runs hotter than designed, the high-limit switch can shut the burners off, and the blower motor works harder. Over time this shortens the life of the furnace and can crack the heat exchanger. It also makes the same system perform worse in air conditioning season. Signs that a filter is too restrictive include short cycling, a whistling sound at the return, weak airflow at the vents, or a furnace that overheats and shuts down. If you have upgraded the filter and notice any of these, go back to a lower-resistance filter and have the system checked. Annual [maintenance](/services/maintenance/) is a good time to ask a HVAC contractor to confirm that the filter you are using suits your system. ## Frequently asked questions Can I wash and reuse a disposable furnace filter? No. Disposable filters are not designed to be washed, and a damp filter can grow mold or release trapped dust. Only filters labeled as washable should be cleaned, and they must be completely dry before you put them back. Does a higher MERV filter always make the air cleaner? It captures more fine particles, but only if enough air passes through it. If the furnace cannot move air through a dense filter, the result is worse performance and possible damage, so match the rating to what your system allows. Where is the filter located? It is usually in a slot at the furnace's blower compartment or in a return air grille in a wall, ceiling, or floor. Some homes have more than one. If you cannot find it, a HVAC contractor can show you during a visit. 3 min read. ### Want us to handle it? Fairfield-Hamilton Heating & Cooling works in Fairfield, Hamilton, Springdale, Sharonville, New Miami, Millville, Mason, Monroe. [Get a quote](/contact/)[Call (513) 540-1716](tel:+15135401716) ### More in this guide - [Furnaces and winter heating in Southwest Ohio](/guides/furnace-guide/) - [Furnace warning signs to take seriously](/guides/furnace-guide/furnace-warning-signs/) - [Repair or replace an aging furnace?](/guides/furnace-guide/repair-or-replace-furnace/) ### Related services - [Furnace Repair & Replacement](/services/furnace-repair/) - [Heat Pumps](/services/heat-pumps/) - [Tune-Ups & Maintenance Plans](/services/maintenance/) ### Service areas - [Fairfield](/areas/fairfield/) - [Hamilton](/areas/hamilton/) - [Springdale](/areas/springdale/) - [Sharonville](/areas/sharonville/) - [New Miami](/areas/new-miami/) - [Millville](/areas/millville/) - [Mason](/areas/mason/) - [Monroe](/areas/monroe/) ### Other guides - [Air conditioning through an Ohio summer](/guides/air-conditioning-guide/) - [Heat pumps, humidity and indoor air quality](/guides/heat-pumps-and-air-quality-guide/) ## Call (513) 540-1716 or send a quote request and tell us what your system is doing. [Get a quote](/contact/) [Call (513) 540-1716](tel:+15135401716) --- **Fairfield-Hamilton Heating & Cooling** · 6660 Dixie Highway, Suite 302, Fairfield, OH 45014 · (513) 540-1716 · inbound@fairfieldhamiltonhvac.com [Get a quote](/contact/) · [Services](/services/) · [Guides](/guides/) · [FAQ](/faq/)