Calendar icon February 6, 2023

Air Filter Sizes & How They Work

What is an undercut? What does nominal mean? All the answers are right here.


One of the more needlessly confusing elements of home wellness is air filter sizing. We didn't make it this way, but we are making it is as simple as possible for you right here. Let's get started.

The two types

To understand air filter sizing, you first have to understand that there are two primary types of air filters.

  • 1-inch and 2-inch air filters
  • Whole house air filters

Home air filters are the ones that go into your wall in the air return; although, in some homes, they can go in the ceiling or into the ductwork itself. Your "air return" is aptly named—it's where "air returns" to your HVAC system from inside your home. Most filters for your return are 1" thick. While 2" filters are found in some homes, it's a lot less often.

Whole house filters usually go into an air handler, which is typically situated next to your HVAC system itself. In some homes, these go directly into the ductwork too. It's worth noting that, while you usually only have one, it's possible to need more than one whole house filter for your home. Whole house filters always have a thickness of 4, 5, or 6 inches.

You may have noticed that we did not mention 3-inch filters. While 3" filters technically do exist, they're particularly rare. If you need a 3" filter, you are special.

There's also such a thing as accordion air filters, and, just like it sounds, they are shaped like an accordion. If you have one of these in your home, we sell those too, but...well, that's just weird.

Air Filter Sizes: Length and width

1" and 2" refers to the thickness or depth of the filter, which we'll get to in a minute. First, let's talk about length and width. Length and width are technically interchangeable, but for discussion purposes, a 12x20 is 12 inches long and 20 inches wide. It's a very common size that is easy to find, and it's on a short list of sizes that are common enough for air filter companies like us to keep in stock. Some other common sizes are:

If you have a 1" or 2" air filter that is not on this list, you'll likely need a custom cut, and the hardware store definitely can't help you here. We've got you covered, though. With our custom air filters, there are 66,000 possible different sizes. We know! That's a lot.

To put 66,000 in perspective, that's roughly the population density of Manhattan per sq mi. That's also approximately how many Orangutans are alive today. Take those facts to trivia.

Undercuts and roundings

A 20x20x1 air filter is actually 19-¾" x 19-¾" x ¾". This is what is known as the undercut. All 1" and 2" filters are undercut by a quarter of an inch to provide a little bit of leeway to ensure it fits into the air return without being too big. This includes custom sizes, so a 27-⅜" x 23-⅝" x 2" (which is the weirdest size we could think of) is actually 27-⅛" x 23-⅜" x 1-¾".

At, you'll see an actual size that shows the undercut when you enter a custom size. You'll want the custom size you pick to be the size of your return measurements, which allows the actual size to be a quarter-inch less.

Undercuts exist on whole house filters as well, but not in the same way they do for 1" and 2" filters. In fact, undercut is a bit of a misnomer when it comes to whole house air filters. These are actually just rounded to whole numbers in a somewhat arbitrary fashion. Allow us to explain.

Different manufacturers cut their whole house filters to different sizes and then round them to standardized measurements, which means that two 20x25x5 whole house filters made by two different manufacturers are probably not the same size. Below are some examples:

  • Honeywell has a 20x25x5 is actually 19-3/4" x 19-7/8" x 4 3/8"
  • Filtrete has a 20x25x5 is actually 19.75" x 24.4375" x 4.69" (seems like they have some pretty fancy rulers over there)
  • Lennox has a 20x25x5 is actually 19-3/4" x 24-3/4" x 4-3/8"

And that all makes total sense...?

Because of this, it's necessary for those of you that need a whole house filter to know the exact filter size you need. If you can't find that on the filter, you can provide Second Nature with the nominal size and the brand that you had previously been using, and we'll be able to find the filter you're looking for.

Nominal vs. Actual size

All filters are sized two different ways. Yep, you read that correctly. All filters have an actual size and then a nominal size. The actual size is the exact dimensions with no rounding; whereas, the nominal size is the rounded dimensions of the filter. This means that on 1" and 2" air filters, the nominal size does not include the undercut, and the actual size does include the undercut. On whole house filters, the nominal size is the rounded size, and the actual size is just the unrounded. Pretty easy stuff here.

Sizes can be reversible

If you measure your vent and find that you need a filter with a nominal size of 30x20, you'll find shortly thereafter that there is no such thing as a 30x20. There is only a 20x30, and that is what you actually need. Whether the pleats on the filter run horizontally or vertically won't impact the effectiveness of your filter, so the number of unique air filter sizes on the market can simply be cut in half by always listing the smaller measurement first instead of having a 20x30 and a 30x20 as two completely different products. If you find that you need a 15x34, grab yourself a 34x15 and just rotate it 90 degrees. It's the same thing.

And that's how air filter sizes work. It's probably a little more complicated than it needed to be, but we try to make it easy. Now you'll never be confused by things like undercuts again.

tl;dr: air filters have weird sizes. Leave the rest to us—we'll make sure the right ones get to you right when you need them.

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Property Management Pest Control Gone Wrong: Resident Horror Stories & Nightmares

In the world of property management and real estate investing, maintaining a clean and pest-free environment is central to the well-being of the residents who live in your properties. That being said, effective pest control is not only a best practice, but also a strategic move that enhances your properties’ living experience, making your life as a property manager easier and your residents happier. Pest control is crucial for several reasons: Investing in pest control saves significant potential costs by avoiding large-scale infestations and property damage, enhancing resident satisfaction with a healthier, pest-free environment, and preserving property value. This approach reduces health risks, protects against liability, and maintains a good reputation by demonstrating the property management company’s dedication to providing safe, comfortable living spaces for great tenants. Ultimately, pest control sets professional property management companies apart from DIY and amateur real estate investors by safeguarding both residents' well-being and property assets. By addressing these points, you can foster a positive living environment that benefits both you and your residents. It’s important to note that our goal is not to call out “good tenants” vs. “bad tenants.” Instead, we always aim to foster a constructive dialogue focused on addressing problems and finding solutions. By emphasizing respect and fairness, we can help create a positive environment that benefits all residents, ensuring their rights and dignity are always respected. Also note that even though we here at Second Nature prefer the term "resident" over "tenant" to foster the human element, the word "tenant" may still be used occasionally due to its long-standing legal and real estate context. "House of Horror" Stories Most property managers have encountered their share of resident horror stories – and many, not for the first time. These tales often involve unexpected and severe pest infestations, made worse by residents' behaviors. Indeed, from bedbugs and roaches (the truly bad tenants any property manager is looking to be rid of) to animal issues, the range of pest problems is vast and daunting. Our "House of Horror Stories" video provides a vivid account of these situations, including some landlord horror stories that are too distressing to include here. Maggots falling from the ceiling: A tenant reported maggots falling from the ceiling onto their bed. The pest company discovered that these maggots were larvae of beetles infesting the air ducts in the neighborhood. Pets and extensive damage: Animals in one property caused extensive damage by covering all floors with feces and chewing through doors, door frames, flooring, HVAC systems, and appliances, with clean-up costs exceeding $15,000. Flushable wipes backup: A tenant flushing baby wipes caused a major sewage backup, leading to water damage throughout multiple rooms (including the living room and master bedroom), with clean-up costs close to $5,000. Donkey in the basement: During the purchase inspection, a donkey was found tied to the deck and later moved to the basement to hide it from animal control, calling for its quick removal. Rodents damaging appliances: Rats infested a property, chewing through a new dishwasher, insulation, and electrical wires, requiring repeated pest control visits and extensive repairs. These stories from a range of contributors highlight the unpredictable and often extreme challenges property managers face in maintaining their properties and ensuring the safety and well-being of their residents. How to Control Resident Pest Issues A robust pest control program is often the property manager’s best friend. After all, infestations can be difficult to proactively defend against, given that background checks, references, and tenant screening go only so far in uncovering the pest issues that can befall even the best tenants. Regardless of the challenges residents may present, a comprehensive pest control plan can mitigate potential infestations before they escalate into true horror stories. This includes timely intervention, and educating residents about maintaining cleanliness. Providing residents with clear guidelines on waste disposal and food storage can also significantly mitigate pest problems. Additionally, offering pest control services as part of a Resident Benefits Package can encourage residents to report issues early, allowing for swift action. Planning Ahead When dealing with problematic residents, it's essential to have a clear action plan. Issuing notices to clean the property promptly (e.g., with a 7-day notice period) is a critical first step. Leveraging a notice-to-clean template can streamline the process and ensure that you comply with tenant laws and legal standards. If worst things come to worst, an eviction notice may become necessary. However, this process is governed by various rules and regulations that can differ significantly across federal and state lines. It's important to be well-versed in these laws to avoid legal pitfalls. A detailed “notice to vacate” template can be incredibly helpful for property managers looking to take care of these complex situations. Nipping Things in the Bud In conclusion, maintaining a pest-free environment is integral to property management success. On-Demand Pest Control is a service in Second Nature’s fully managed Resident Benefits Package (RBP). It offers predictable, cost-effective, and fast solutions when a pest issue arises. Instead of expensive scheduled preventive treatments, residents can request service as needed. This approach ensures fast response times, directly addressing the problem at hand and saving costs over recurring treatments Property managers simply select the best pest plan from four tiers of service levels to include in their RBP. When an issue arises, the resident reports it in the On-Demand Pest Control portal, and the pest issue will be resolved. Learn more about On-Demand Pest Control by getting in touch, or read our latest study on the impact of our RBP on the resident experience.

Calendar icon July 3, 2024

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Your Guide to Property Management Laws, Regulations, & Rules

Property management activities involve overseeing rental properties, ensuring they’re maintained, residents are managed, and finances are handled effectively. While a real estate license is not always necessary to manage rental properties, licensing requirements can vary significantly by state. Typically, states may require property managers to hold a real estate license or work under a licensed broker. Property managers should familiarize themselves with the specific regulations in their state to ensure compliance. What Are Some Important Property Management Rules and Regulations? Property management laws encompass various areas, ensuring the safety, rights, and responsibilities of both property managers and tenants. Key areas include: Anti-discriminatory laws: Fair housing laws such as the Federal Fair Housing Amendments Act (FHAA) prevent discrimination based on race, color, national origin, religion, sex, familial status, or disability. Lease paperwork: Legally binding lease agreements must include specific terms and comply with local regulations. Safety, maintenance, and repairs: Property managers must ensure properties meet habitability standards, including weatherproofing, heating, water, and electricity. Financial management: Proper handling of security deposits, monthly rent collection, and financial records is essential to comply with regulations and avoid disputes. Property management laws by state Each state has specific property management laws that property managers must adhere to. For instance, in many (but not all) jurisdictions, property managers must obtain a real estate broker license to operate. These laws are typically drafted and enforced by various regulatory bodies such as the state's Department of Real Estate or similar agencies. For instance, the California Department of Real Estate is responsible for regulating real estate activities, brokers, and salespersons, including those who work in property management, while the Texas Real Estate Commission handles these responsibilities in Texas. These agencies ensure compliance with state licensing laws and often provide resources and guidelines for property managers of both residential properties and commercial properties. Below is a table linking to the respective government sites for state-specific regulations: State State Body Alabama Alabama Real Estate Commission Alaska Alaska Real Estate Commission Arizona Arizona Department of Real Estate Arkansas Arkansas Real Estate Commission California California Department of Real Estate Colorado Colorado Division of Real Estate Connecticut Connecticut Department of Consumer Protection Delaware Delaware Real Estate Commission Florida Florida Department of Business & Professional Regulation Georgia Georgia Real Estate Commission and Appraisers Board Hawaii Department of Commerce and Consumer Affairs' Real Estate Branch Illinois Illinois Department of Financial and Professional Regulation Indiana Indiana Professional Licensing Agency Iowa Iowa Department of Inspections, Appeals, & Licensing Kansas Kansas Real Estate Commission (for commercial real estate property management only) Kentucky Kentucky Real Estate Commission Louisiana Louisiana Real Estate Commission Michigan Michigan Department of Licensing and Regulatory Affairs Minnesota Minnesota Department of Commerce Mississippi Mississippi Real Estate Commission Missouri Missouri Division of Professional Registration Montana Montana Department of Labor and Industry Nebraska Nebraska Real Estate Commission Nevada Nevada Real Estate Division New Hampshire New Hampshire Real Estate Commission New Jersey New Jersey Real Estate Commission New Mexico New Mexico Real Estate Commission New York New York State Division of Licensing Services North Carolina North Carolina Real Estate Commission North Dakota North Dakota Real Estate Commission Ohio Ohio Division of Real Estate & Professional Licensing Oklahoma Oklahoma Real Estate Commission Oregon Oregon Real Estate Agency Pennsylvania Pennsylvania Real Estate Commission Rhode Island Rhode Island Department of Business Regulation South Carolina South Carolina Real Estate Commission South Dakota South Dakota Real Estate Commission Tennessee Tennessee Real Estate Commission Texas Texas Real Estate Commission Utah Utah Division of Real Estate Virginia Virginia Department of Professional and Occupational Regulation Washington Washington State Department of Licensing West Virginia West Virginia Real Estate Commission Wisconsin Wisconsin Department of Safety and Professional Services Wyoming Wyoming Real Estate Commission Note: This list excludes resources from Idaho, Maine, Maryland, Massachusetts, and Vermont. Tenant screenings Tenant screenings are a critical step in property management, involving background checks, credit checks, income verification, employment verification, rental history, and proof of ID to assess prospective tenants. This process helps ensure that potential renters are reliable and financially responsible. It's important to obtain signed consent before running credit checks, as required by the Fair Credit Reporting Act (FCRA), to comply with legal standards and protect tenant privacy. Another important guidance is provided by the Fair Housing Act, which prohibits discrimination in housing-related activities based on race, color, national origin, religion, sex, familial status, and disability, ensuring equal access to housing for all individuals. Learn more about Tenant Screening Tips for PMs Lease agreements A lease agreement is a legally binding contract between the landlord and tenant, outlining the terms of the tenancy. Key components of rental agreements include lease terms, rent amount, security deposit regulations, and common clauses such as maintenance responsibilities and lease renewal terms. Regulations governing lease agreements can vary by state, so it's essential to ensure that leases comply with local laws. For instance, state laws often contain security deposit limits, provisions for the return of unused portions, as well as a clear accounting for any deductions. Consulting with a lawyer is crucial to ensure your agreement is legally sound and reflects your specific circumstances. We’ve shared some relevant resources below: Learn more about property management agreements, featuring a free template Learn about security deposit insurance, and its pros and cons Financial management Effective financial management in property management involves establishing clear rent collection procedures and maintaining organized financial records. This includes tracking rent payments, managing tenants’ security deposits, and adhering to landlord-tenant laws to avoid legal disputes and financial penalties. Keeping detailed records can help property managers resolve issues efficiently and ensure transparency with tenants and property owners. Solutions such as property management software can streamline financial operations, automate routine tasks, and perhaps most importantly - ensure accuracy and regulatory compliance with respect to various accounting regulations and legal requirements. Evictions Evictions are a legal process to remove a tenant from a property. Common reasons for eviction from rental units include nonpayment of rent, property damage, lease violations, and criminal activity. Property managers must follow their state's rules for eviction notices, such as unconditional quit terminations and termination for lease violations, to ensure the process is lawful and fair. State laws regarding unconditional quit terminations and terminations for violation of a lease vary widely. Unconditional quit notices typically demand that tenants move out immediately without an opportunity to remedy the violation. States like Indiana and Mississippi allow landlords to issue these notices for serious or repeated violations, with Mississippi requiring 14 days to move out. For lease violations, the notice period and the opportunity for tenants to remedy the breach also differ by state. For example, in Kentucky, tenants generally have 15 days of written notice to cure a violation, but if the same violation occurs within six months, landlords can issue a 14-day unconditional quit notice. In contrast, states like Iowa and Maine require a seven-day notice period for tenants to address lease violations before eviction proceedings can begin. In California, on the other hand, tenants must be given three days or more to cure the violation before landlords can file for eviction (source). These legal nuances emphasize the importance of PMs and tenants understanding their specific state regulations to navigate eviction processes appropriately. Property maintenance and repairs Maintaining rental properties is a legal obligation for landlords, ensuring that properties are safe, habitable, and free from hazards like lead, asbestos, and mold. This includes weatherproofing, providing adequate heating and water, and ensuring electrical systems are functional. You can find out more about these issues in our Property Maintenance Guide for PMs. Landlords must also give notice to tenants before entering the property for repairs, as required by most state laws. When in doubt, consult a legal advisor to ascertain the specific laws that apply to you in your state. Tenants have the right to a habitable living environment, and failure to meet these standards can lead to legal consequences as well as issues with occupancy rates. Indeed, when landlords fail to make required repairs, tenants have several options depending on their state's laws. Tenants may withhold rent, make the necessary repairs themselves and deduct the cost from the rent, pay a reduced rent, report the issue to local building inspectors who can order repairs, or even break the lease and move out. Additionally, tenants can sue the landlord for a partial refund of past rent or for damages caused by the substandard conditions, including discomfort and emotional distress. Get our preventative maintenance checklist for property management Learn about the importance of pest control to maintain a pest-free environment Second Nature's Guidance Staying informed about state-specific regulations, maintaining organized records, and ensuring compliance with federal laws such as the Fair Housing Amendments Act is key to successful property management. On a practical level, understanding and adhering to property management laws and regulations is crucial for property managers to ensure smooth operations, maintain property value, and foster positive tenant relationships. Learn more about property management company best practices, marketing, and more in our Second Nature Community.

Calendar icon July 3, 2024

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