Author: analytics@markalon.com

It may surprise you to learn that indoor air pollution is among the top five environmental health risks. That’s why we’ve been devoting a series of posts on air filtration.  If you’ve been watching and listening to our posts, you’ve heard us talk about the MERV ratings of air filters, and how to select the best air filter for your needs. As a general rule, prices are higher for filters with higher MERV ratings. But here is one instance when the buying the best, most expensive filters those with MERV ratings greater than 16 may do more harm than good.

HEPA Filters

Among the most expensive filters are HEPA filters. Higher efficiency filters with a MERV rating of 14 to 16, are sometimes misidentified as HEPA filters.  But true HEPA filters have MERV values of 17 to 20.  HEPA which stands for High-Efficiency Particulate Arrestance – is a special type of filter that, according to DOE standards, filters out 99.97% of particles down to 0.3 microns in size… that’s 10 times smaller than a MERV 16 filter!  HEPA filters are typically used in biomedical applications to filter out bacteria and viruses.

More Harm Than Good

True HEPA filters those with MERV ratings 17 and above – are normally not installed in residential HVAC systems. A typical residential air handling unit and associated ductwork cannot accommodate HEPA filters. They do not have enough fan or motor capacity to accommodate the large pressure drop across the dense HEPA filter material. If you install a HEPA filter in an HVAC system not specifically designed for it, it will make your motor work harder because it is getting too much resistance, and this will hamper your airflow, increase fan noise, and cause your system to fail earlier. Check with your HVAC manufacturer prior to upgrading filters to determine whether it is feasible to use more efficient filters.

Let’s Get Real

According to the EPA, using medium-efficiency filters, such as those with a MERV rating of 12-13, are almost as effective as true HEPA filters at removing allergens, with much lower associated system and operating costs, and quieter fan operation.  Furthermore, many air particles never go through your HVAC filter system because they are deposited in your living space on your sheets, furniture, and carpet, for example.  So, you still need to change your sheets, vacuum, and do all those house-cleaning chores regularly to maintain your indoor air quality.

Things You Can Do

Here are some other simple things you can do to improve your indoor air quality:

• Prevent mold by controlling moisture throughout your home.  That means turning on exhaust fans in bathrooms while showering, and making sure your basement and crawlspaces are dry.
• Fix any leaks in your ductwork, in the roof, around windows and doors, and around plumbing fixtures.
• Keep your home smoke-free. Do not smoke indoors, don’t burn candles and incense, and use exhaust fans while cooking.

When you go to a hardware or big box store to purchase air filters you will find a bewildering array of products. 3M, for example, offers 9 different types of filters each with different ratings and at a different price, and then each of those comes in different sizes. It can be confusing, to say the least! We’ll help you make sense of it all, so you can choose the best air filter for your needs.

Size Matters

Size is perhaps the easiest decision: get the size filter that fits the filter holder built into your HVAC system. It should fit snugly, with no air gaps around the filter. Be aware that filters come in thicknesses of 1-inch to 6- inches, with the thicker filters having greater capacity to catch dirt without increasing resistance to air flow and increasing the time between required filter changes.  However, you cannot put a thick filter (4 or 6 inches thick) into your HVAC system if it’s designed to accommodate only a 1-inch thick filter.

Rating Matters

In our previous post, we talked about the MERV ratings of filters.  MERV is an industry standard measurement of filter efficiency.  Individual manufacturers often have their own rating system as well.  3M’s rating is called MPR, which standard for Microparticle Performance Rating.  As with the MERV rating, higher MPR numbers mean a greater percentage of particles and smaller particle sizes will be captured by the filter.

Price vs Performance

How do you decide which MERV rating to get?  Generally, the higher the MERV (or MPR) rating, the more expensive the filter.  For example, the price of a MERV 13 filter is about twice the price of a MERV 8 filter of the same size. 3M offers multiple filters having a MERV 12 rating, but with different MPR ratings, and so even among filters of the same size and MERV rating, the prices can vary.  Which filter to buy depends on how much cleaning you want your filter to do. The lowest price filters at MERV 5 will remove dust, debris and lint. This is the minimum needed to maintain the health of your HVAC system’s heat exchanger and coils.  A MERV 11 filter removes smaller particles such as pollen, dust mites, mold spores, and pet dander. A MERV 12 or 13 filter can filter some bacteria, viruses, and odors.  Since the prices jump up dramatically at MERV ratings higher than 11, and the increased efficiency is only minimally incremental, using filters with more than a MERV 11 rating is probably not cost effective, unless there is some particular medical need.  In the chart, those shown in the “green zone” in the cost column represent the best value on a price vs. performance scale.

You’ve heard us preach over and over about how important it is to change your air filters on a regular basis. But there are so many to choose from these days and prices vary widely!  We’ll help you make sense of it all in this and two subsequent posts on this subject.

What’s the purpose?

The purpose of an air filter is to keep the coils and heat exchanger inside your HVAC system clean. Dirty coils and heat exchangers can make the system work harder and cause it to be replaced earlier, so keeping the filter clean helps prolong the life of your HVAC system. Since the air in your house circulates past these filters, they also affect the quality of the air you breathe. People with allergies or asthma are especially sensitive to airborne particles like pet dander, pollen, mold and dust, and the right filter will filter out these particles.

What is a MERV rating?

When it comes to air filters, the most important thing to look for – besides the correct size for your particular system – is the MERV rating. MERV stands for Minimum Efficiency Reporting Value. It is a measurement standard designed in 1987 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to rate the effectiveness of air filters. The MERV rating is a number from 0 to 20, with most residential air filters in the 4-12 range. The higher the MERV rating, the more efficient the filter is, and the greater percentage of particles it can capture. MERV is an industry standard rating, so it can be used to compare filters made by different companies.

As a general rule, prices are higher for filters with higher MERV ratings. Often HEPA filters are rated in the range of MERV 17 to 20, and are the most expensive types of filters. But here is one instance when the most expensive may not be the best!  Most residential HVAC systems may not have enough fan or motor capacity to accommodate higher efficiency filters, such as those greater than MERV 16. Always check your HVAC manufacturer’s recommendations.

Installation Affects Performance

How a filter is installed also effects its performance. If a filter is installed such that air bypasses the filter, its effectiveness will go down substantially, so make sure the filter is the right size and it’s a snug fit. Plus, most filters are directional, meaning you have to install them facing the right direction. Check for the arrow which indicates the direction of air flow, and install the filter with the arrow pointing towards the duct. Here’s another tip: If you have your HVAC system’s fan set to “auto” then the air is only going past the filter when your system kicks on. By setting it to “on” the fan will continually move air across the filter, so the air you breathe will be continually filtered.

Most Important Thing

The most important thing to remember about home air filters is to change them regularly. Even the highest-quality filter won’t work if it is clogged with particles!  Check the filter manufacturer’s guidelines, as different filters are meant to be changed at different intervals. Plus, if you’re doing remodeling, there is construction going on, or you have pets, you will need to change your filters more frequently to compensate for the extra dust and residue in the air. Mark the date of installation along the filter’s frame, so you can clearly see when it was last changed.

Whether you call them vent covers, floor registers, or air grilles, this article deals with the part of your HVAC’s ducts that you see in the various rooms of your house.  These may be located along the floor, baseboard, or wall, and vary in size depending on the size of the ductwork.  The purpose of a vent grille is to protect the ductwork from damage and tears from things falling into it such as a person’s foot or from scratching by pets or sharp objects – while at the same time allowing air to pass.

A Decorating Statement

It’s become a high-end decorating statement to have vent grilles specially coordinated with your dêcor.  Whether you shop at Home Depot or a boutique home accessories store, you’ll see vent covers in a variety of materials, colors, finishes and designs.  Materials can be brass, bronze, cast iron, metal, steel, or wood, and they can cost anywhere from $3.00 each to $100-200 each!  Regardless, they all serve the same function and there’s more to them than just the aesthetic qualities.

Air Flow Issues

First and foremost, ensure the vents are open and unblocked by drapes or furniture. Vacuuming or stepping on a floor register could inadvertently close the register, making your HVAC system not work properly, so if you’re having uneven heating or cooling, the vents/registers are the first thing to check.

When should vent covers be replaced?

Vent covers only need replacing if they become damaged (bent), corroded (rusted), or will not stay open.  Otherwise, a periodic cleaning is all they need, using a cleaner appropriate for the type of material and finish.

How often should the vent covers be cleaned?

They should be cleaned whenever they need to be, but a minimum of twice per year fall and spring is ideal.  In high traffic or dusty environments, you may want to clean them each time you replace your air filters (minimum of every 3 months).

If you are embarking on a home improvement project, such as painting a room, doing drywall repairs, or sanding/refinishing wood floors, steps must be taken to protect the ductwork from paint, sand/dust, flumes, tools, and damage.   Remove the vent registers prior to beginning work. Then, cover the duct completely with a barrier material that can be taped all around. A large plastic garbage bag also works very nicely. If there is danger of someone walking or positioning a ladder or tools near a duct that is covered in this fashion and thus falling in and damaging the duct put the vent grille back on top of the register.  If you have the high-end designer vents (brass, etc.), consider getting a couple of the cheap vent grilles to use temporarily during your home improvement project, so your “good” vent grilles won’t inadvertently be damaged.  The last thing you want is someone putting a foot through the duct or tools falling in and tearing a hole in the duct!

Why it’s so important

Tears in the ductwork or any holes require immediate attention. They will cause your HVAC system not to function properly, and your system will not cool or heat very well.  The conditioned air (the air you paid to heat and cool) will be leaking out and mixing with unconditioned air, which is then blown back through your house.  Not only is there a lot of lost energy – costing you extra money but your HVAC system will be over-worked and wear out quicker.  You may also develop a pest problem from crawling insects, rodents, or reptiles which can come through the holes in the ducts into your home. Over time, you may also develop an odor and moisture problem.  If you are experiencing any of these issues, a hole in your ductwork may be your culprit!

If you are building a new home or an addition, make sure the contractor seals all the ductwork before the drywall is installed. It is almost impossible to clean drywall dust out of ducts, so the best solution is to keep them protected from sources like this from the outset.  For more information on duct cleaning, see our earlier post.