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How can I get more filtration with my current HVAC system? It’s a tug of war!

How can I get more filtration with my current HVAC system?  It’s a tug of war!

At a staff meeting one day, one of our team members related how the HVAC company which installed the central AC system in his new home recommended using the lowest MERV filters available.  I was shocked!  Well, after thinking about it some more, I hypothesized they were waiting for his evaporator coil (the part that transfers absorbs heat from the air by transferring it to the cold refrigerant) to plug up so they could sell him a new system.  In this day and age of availability of every type, face size and thickness of filter, a good HVAC company should be able to work with your existing system to get good filtration.  Period.

If you’ve never heard of MERV, it is an acronym that stands for minimum efficiency reporting value, developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) in 1987.    The range is from 1 to 20, and designates with what efficiency the filter removes small particles between 0.3 and 10 micrometers in diameter. (check out this post for more information on MERV).   Generally you’ll want to get the highest rating possible (more filtration) for your system, without causing too much pressure drop, because in general, increasing the MERV increases pressure drop across the filter, while HVAC equipment manufacturers want you to stay with a low pressure drop of around 0.10 inches of water column (i.w.c.) across the filter.  That’s the tug of war–but why aren’t HVAC installers figuring out how to give consumers, the ones who pay for new or upgraded systems, both?  It’s like selling a delicious drink in a cup with a straw that’s too small to get it out at any satisfying rate (like a coffee stirrer).  Sure, you could take out the straw and lid and risk getting it all over yourself as you drink it.  However, even fast food chains and gas stations figured this out years ago: larger straw and cup= convenient way to drink, more satisfaction, more sales.

In this case, though, the consumer is left to bow to the advice of greedy or ignorant HVAC installers, or do research to figure it out himself.  Yes, there is a way to get both high MERV and low pressure drop!  You just need to install a larger filter.  It sounds simple, right?  Yet, because many installers are trained to recommend standard size, 1” filter frames, you’ll probably have to do the math and specify one yourself.  Don’t get scared yet!  We’re here to help with that calculation.  

Here’s a diagram of the typical HVAC system so you know what we’re talking about/aiming for:


Image source: RemoveandReplace.com

The part we’re talking about is outlined in blue.  The filter can be installed on the side of the HVAC closet door, in a ceiling or a wall.  In the diagram the air is flowing through the filter, up through the air handling unit, through the evaporator coil, and out to various room registers/grilles.  The whole system “sucks” air through that filter, and if it’s too small, it’s like sucking a Big Gulp through a coffee stirrer–the pressure drop or suction pressure is too much!  Making the “face” of the filter larger will allow the velocity of the air through the filter to drop, which makes the pressure drop go down.  

So, what is the magic size of filter that makes the pressure drop go down?  That depends on the size of your HVAC system.  This very helpful article from industry expert Allison Bailes gives the secret requirement:  

Filter Area = 2.0 square feet (or more) for each 400 cfm of air flow

Since most filters are measured in inches, we can convert that formula to:

Filter size (sq. inches) = System Air Flow(cfm) x 288/400    OR  

Filter size (sq. inches) = 0.72 x System Air Flow (cfm)

Like in any interesting math problem, this one has a formula with some knowns and some unknowns.  The unknown is the filter size, and the known is the System Air Flow.  To find the system air flow, you can do several things: 

  • Look at the HVAC air handler information specifications.  If you don’t have the system specs, go to the air handler, take a photo of the sticker with the model number on it, and search for this model’s manual online.   For example, I replaced my air handler recently with a variable-speed unit.  It will shift fan speeds according to the heating or cooling load, with maximum 1200 cfm, 640 cfm intermediate, and 400 cfm minimum.  Since the pressure drop will be maximum at the maximum air flow, I’m going with 1200 cfm.
  • Approximate the air flow using the system tonnage: cooling units are often measured in the US by “tons”.  According to HVACtrainingsolutions.net, 350 to 400 CFM per ton of cooling is required for proper air conditioning system operation. We’ll use 400 cfm to be conservative.  If you know you have a 3 ton system, then 1200 cfm is the maximum airflow.  This lines up with the specifications on my unit.  (This equivalent of 400 cfm per ton can vary because of relative humidity, dry-bulb temperatures, wet-bulb temperatures, air density, mass flow rate, and elevation; if you want to “get technical”, check out this article!)

After you determine the cfm of your system, plug it into the filter size formula above.  In my case, 1200 cfm x 0.72 = 864 square inches of filter.  Yikes!  My own filter (24”x24”) was undersized by a third, and when I measured the pressure drop at maximum fan speed (1200cfm) it was 0.25 inches water gage, which was fairly high for a clean filter. However, if I “upgraded” to a 24x36” filter that size fit my requirements exactly (864 square inches).  The problem is that I don’t have room for such a big filter.

If you find that space or filter availability for bigger filters is a problem, you can solve it in a different way: add another return with another filter.  Many homes have 2 returns, such as one upstairs and one downstairs.  In this way, you’re getting the area and the filtration you need.  Adding a second return lowers the airflow per return, and also changes the air circulation in your home.  At the minimum, high MERV and high airflow will not be a problem!  In my case, the easiest thing to do was look at the return air duct and add another grille in the only place I could: my bedroom.  I ended up adding a 20x20 return air grill there, which lowered the pressure drop to 0.09 inches water gage for a clean filter, which eased the work of the fan unit and gave me more filtration.

This is the dilemma homeowners often face: accept the “expert” opinion of their contractor, or start doing their own research and demand equipment or installations that at least safeguard the equipment they are installing!  Many installers mean well, but by not using standard equipment like manometers (pressure-sensing devices) they have no idea what the pressure drop over the filter is.  They also don’t know what pollutants like dust, human and pet dander, and microbes are allowed  into the new system by specifying low-grade MERV filters.  Their ignorance or bad advice costs homeowners BIG when the air, and consequently the system, stays dirty.  Just like we sometimes must do with our health and doctors, we hope that you take this information to your HVAC company and specify what you need to win the tug-of war and keep you and your family healthy!

What Effects Do HVAC Systems Have on House Theatres and Entertainment Areas?

What Effects Do HVAC Systems Have on House Theatres and Entertainment Areas?

Home theatres and entertainment rooms are designed for family fun and relaxation. These rooms in your house are the most important to you when it comes to socializing, relaxing, and having fun. You and your loved ones can gather in these rooms to enjoy a performance of a film, play, or musical.

The entertainment rooms are a part of the house that should be well cared for. These areas need to be cleaned regularly to keep them in top condition. Many people in the home often use them, so it is always crucial to keep them clean. HVAC systems are another option for keeping these rooms comfortable. A good HVAC system makes watching movies or listening to music more enjoyable.

What are House Theatres and Entertainment Areas?

A theatre room with state-of-the-art projection and sound equipment is specifically designed for watching films. The walls of such spaces are typically covered in movie posters and other film-related memorabilia. In addition, they provide relaxing seating options, so you can kick back and enjoy your favorite program or film.

An entertainment area, often adjacent to the living room or family room, keeps guests entertained during social gatherings such as birthdays and anniversaries. Putting in pool, arcade, or foosball tables will give people something to do while waiting for food or drinks. This will provide them with a fun activity while waiting for their dinner to be served.

What Is an HVAC System?

HVAC stands for heating, ventilation, and air conditioning. In homes, businesses, and even indoor stadiums, air conditioning and heating systems control the air temperature inside the building. HVAC systems come in a wide variety, but they all work similarly. Mechanical ventilation provides fresh outdoor air through the system.

HVAC systems often include air cleaners to prevent the spread of airborne pathogens such as bacteria, fungi, and viruses. A specialist in the field will visit your home to assess its readiness for HVAC installation. Dallas HVAC installation service is one of the experts who will find the best HVAC setup for your home. They can install a new HVAC system for your home or business and also provide the repair service. 

To ensure your new HVAC system is installed correctly, you should hire a professional with a wealth of knowledge and experience. Professional HVAC installers help clients determine which heating and cooling systems are right for them. They can help you determine which size unit suits your space and how big your ducts need to be.

How HVAC Systems Affect Home Theatres and Entertainment Areas

When you plan to install a home theatre or entertainment area, it is crucial to understand how the HVAC system will affect these areas. The most common problems that arise from inadequate HVAC systems include the following:


Most home theatre components are not made to work in extreme heat or cold and may malfunction if exposed to such conditions. If your heating and cooling system is not running correctly, the temperature inside your home could fluctuate wildly. Either of these extreme temperature conditions can destroy sensitive audio and electronic equipment.  The equipment itself produces heat, so that must be accounted for in the “load” of the system.

The quality of the sound delivered to a home theatre will be affected by the temperature of the HVAC system. When the air temperature in a room is too low, the sound quality suffers. If the temperature is too high, you'll hear crackling sounds. The optimal viewing temperature for a home theatre is between 68 and 72 degrees Fahrenheit (20 and 22 degrees Celsius).

In addition, if your home theatre or entertainment area is sized for a number of people that significantly exceeds the people living in the house, you’ll need to consider the “load” that the extra people place on the system, because they will increase the temperature, humidity and CO2 of the room(s).  Too high or low of a temperature will also make it hard to focus on the plot of the movie or TV show you're watching. With reliable HVAC installations, you should be able to keep the temperature comfortable.


Water vapor in the air is what is quantified when discussing humidity. It affects how your home theatre and entertainment areas function.

Home theatre systems are not designed to withstand the high levels of humidity found outdoors. When exposed to humidity, most indoor equipment rusts, corrodes, or otherwise breaks down. HVAC controls ventilation, heating, and air conditioning to maintain a healthy indoor climate.

A high humidity level can make it uncomfortable to spend time indoors. You may feel overheated and wet all the time. Humidity levels in your home theatre could be quite high. Extreme heat and humidity are bad for your hair and skin. When the air in your home is too dry, you may experience a chill, discomfort, and dry skin.

If you have a humidifier in your house, ensure it's set to keep humidity levels at 30-40% during winter. For most house theatres and entertainment areas, this range is ideal. In the summer, that percentage can reach fifty to sixty percent.

An HVAC system that incorporates both a humidifier and a dehumidifier is the most efficient way to control moisture in a home. No matter the season, you can maintain optimal humidity levels in your home theatres and entertainment areas with HVAC installations.


Airflow can affect how well you hear the dialogue in movies and TV shows and how you can listen to sound effects. It also affects the clarity of your surrounding system.

The lack of proper airflow is one of the biggest problems facing people who want to set up an effective home theatre system in their homes today. 

Poor airflow can lead to condensation on the walls and windows in your house theatre. This will cause mold growth and damage your furniture or other items within the space. Mold can grow inside the space and damage appliances.

Poor ventilation from the outdoors will allow CO2 levels to rise within the space, making everyone feel drowsy and irritable, the opposite of the environment you’re planning!  Without proper ventilation, microbial contaminants can also increase as people in close proximity exhale, laugh, cough or sniffle.   It’s critical to make sure that adequate ventilation is provided to keep everyone healthy!  Adding an air sanitizer device like the Whole Home Polar Ionizer or Air Angel will work to keep all the air fresh and clean in these spaces. 

HVAC systems can help maintain constant airflow throughout your home, keeping the temperature tolerable for those inside. The HVAC system uses ducts to distribute the conditioned air to different rooms in your home and especially entertainment areas. 

What Makes a Good Home Theatre and Entertainment Area?

Home theatres or entertainment rooms are more than just couches and speakers. It's a place to take a break from the stress of everyday life with your loved ones and friends. To make the area more fun and friendlier for anybody who visits, you'd probably want to improve it a little.

Ensure the room has enough seating for all those watching shows or movies. With a well-functioning heating, ventilation, and air conditioning system (HVAC), your guests can enjoy the show in comfort.

Installing an appropriate HVAC system should be a top priority. It will keep dust off your electronics, extending their life and ensuring they function properly. It will also keep your home at a temperature that will allow you to watch comfortably.  If you already have a central HVAC system, you may want to consider adding an additional unit for these entertainment areas, like a mini-split, to make sure your home theatre HVAC system maintains a consistent temperature, humidity and airflow.


Heating, ventilation, and air conditioning (HVAC) systems for a home theatre have unique design parameters that must be strictly adhered to for the best possible viewing environment for the audience. The system must be efficient and silent for the viewing experience to be satisfying. Creating a comfortable environment for watching movies or TV shows at home requires careful planning of the HVAC installations.  With all these things in mind, choose an HVAC system that keeps your home and entertainment areas safe and comfortable.

Guest post by Daniel Martin

No-Demo Renos for Air Quality

No-Demo Renos for Air Quality

As of 2024, home renovation is still very popular in the US, but there’s been some interesting developments, such as “no demo reno”.  Eliminating demolition usually means less cost and less time--two very important commodities in renovation!  I’m waiting for designers to take it a step further to challenge themselves to redesign for air quality on a budget, to be judged by air quality experts.  Of course, you can spend thousands of dollars on the latest HVAC and purification systems, but you can also make a big impact with a lot less.  That’s what I’m talking about!

Whether you live in a sealed upper-storey apartment using forced air all the time or only use natural ventilation via windows and doors, furniture placement can affect the airflow and thus the air quality in your home.  According to a 2022 study, furniture layout is a key factor that affects the direction of airflow in a building. Different furniture heights can block or trap natural air or lower the direction of the airflow, thereby producing microscale positive or negative pressure.  It evaluated a naturally-ventilated school in Thailand which was located in a city which was plagued by high PM2.5 every January and May, mostly due to agricultural burning, and wind-blown dust. Under natural ventilation conditions, the direction of PM 2.5 distribution in the classroom was the same as that of the natural air. The air velocity and PM 2.5 concentration in the classroom were correlated positively, whereas the velocity increased, with the increasing concentration of PM 2.5. Adjusting the furniture layout of the classroom, as well as the size of the openings, affected the airflow and distribution of PM 2.5 within the classroom. 

Another study evaluated the pollution level of new furniture (VOCs).  Just by rearranging the furniture in an office with a forced-air system, there was a notable difference between the best and the worst ventilation effectiveness without any changes in the ventilation.  The key learning points were to: 

1) always try to place the pollution source (new furniture) as far away from your usual breathing zone (like sitting at the desk) as possible and, 

2) try to sit in the upflow field of the airflow.

If you aren’t trying to off-gas any new furniture, here are the rules that enable your HVAC to work at its optimum (How Furniture Placement Affects Your HVAC):

  • Make sure the furniture is not blocking any registers or vents.

  • Place furniture away from walls so that adequate airflow behind the furniture can prevent formation of mildew.  This happens when there is not enough air circulation (stagnation) to prevent humidity from saturating surfaces.  For more on how you can avoid mildew with better air circulation/ventilation, check out our article here.

  • Don’t block any windows or doors when placing large pieces such as couches or dressers near them

If you do need to obstruct a vent, try to use a deflector on the register so that air flow is directed to an open area.  They come in a number of shapes and sizes, even adjustable, to match your register/grille and desired direction of airflow.

How to visualize airflow in your space

There are professional engineering programs that can help “see” airflow, but they take quite a bit of measuring and input to get a simulation.  On the simple side, you can use the following to “see” airflow, and adjusting furniture position, window openings, vent positions and fan positions and speeds to modify air currents.

  • A helium balloon that has neutral buoyancy that “hangs” in the air below the ceiling will move with air currents (you can tie or tape a small weight onto it to adjust height).

  • A bowl of warm water with a chunk of dry ice (frozen CO2) will give off fog that moves with air currents (just be careful to use thick gloves when handling!)

  • Old-fashioned soap bubbles (you can make a wand by twisting a paperclip into a loop and use dish detergent and water) blown straight up into the air will tend to move in the direction of other air currents.

  • Candle flames/smoke may also show the direction of air currents.

  • Tape streamers or tissue paper in doorways to see which direction the air flows (tinsel also works).

  • Anemometers are fun devices to play around with, but unfortunately they usually only work very close to a vent or fan; they don’t move with minimal airflows. 

Windows: Don’t forget to pull back curtains or remove them altogether if you are using natural ventilation, because blocking windows with curtains blocks airflow and light!  Curtains are usually necessary for privacy, but you might consider trying sheer or loosely-woven curtains or a decorative fabric screen placed a foot or two inside the window, for more airflow.  If you want to open windows without letting in pollen or air pollution, check out our Nanofiber PureAir Window Screens and Window Ventilation Filters.

Fans: Portable fans can set atop furniture or even be hung on the wall to increase airflow.  Take the time to clean your ceiling fans and make sure they are running in the right direction (clockwise in the heating season and counter-clockwise for the cooling season).  

Even if you’ve lived in a space for a long time and think you have tried “every possible arrangement” of furniture, the act of rearranging furniture every so often is not futile for the following reasons (Rearranging Furniture Could Help You Use Space More Effectively and Give You a Mental Boost):

  • Moving furniture will expose dirt, dust and allergens so that you can clean under it, improving indoor air quality.

  • Moving it may force you to remove or store clutter that also collects dust

  • Moving furniture could expose other air quality problems like hidden leaks or mildew, pet stains or pest infestations

Better furniture arrangement can help you to feel less stuffy and more energetic, even if the airflow changes are minute.  Just a few last tips before you get busy redesigning a room: 

  • remember to use a measuring tape first before trying to move heavy or large furniture to a new spot! 

  • Have your cleaning supplies at the ready to vacuum up dust, cobwebs, pet hair, etc..

  • Call on your friends not only to help with the moving, but also to lend ideas.  

  • If you don't have plants, consider adding a few strategic plants as natural air purifiers (and a pop of color!)

  • Plugging in a small air purifier with a fan like the  Germ Defender or Upgraded Air Angel Mobile will freshen the air and add airflow on a micro scale.

Photo by Nathan Fertig on Unsplash