Straight talk about filter choices…
Air conditioning and heating filters are big business. There are literally hundreds of products to choose from at all price ranges. What’s a consumer to do?
Let’ take a moment to discuss the issue with common sense and a realistic set of expectations.
In setting expectations we must realize a filter in its self, will not keep a home clean. Don’t laugh. We have been in homes with $1500.00 air cleaners and the resident did not understand why there was dirt on the floor. There remains no substitute for a vacuum or a broom and a dust pan. I know, “What’s a dust pan?”
90 percent of organic contaminants (dirt, larger dust particles or hair) brought into the home are heavier than air. This means once inside the home the particulate will often fall off the carrier when disturbed. This is where the vacuum or broom comes in handy. This is the majority of dirt in the home. Other lighter than air objects are the things that get trapped in a filter or on the return or cold air intake. This describes how floor returns are nasty in most cases, low wall returns can get congested and ceiling returns seldom pick up more than a light coat of dust monthly. This also reinforces the idea that the return air or cold air return (cooling or heating climate respectively) have little to do with actual air currents or flow patterns in the home.
We need to remember we live among all sorts of organic matter. Generally what is outside our home is inside as well. Our homes breathe. Homes built on pier and beam or over basements prior to the 1960’s breathe really well in most instances. Homes were built in the 1960’s and 1970’s breathe a little less if they are slab on grade construction. Dwellings built in the 1980’s to mid 1990’s are even less drafty. Finally homes built in the 2000’s begin to be reasonably tight and quality homes built after 2005 will need ventilation added. Wherever ventilation is added, there must be a separate filter for the fresh air. The logic for a lesson in construction history is simple. If you live in a home built before 2000 adding a true HEPA filter may not be logical. If you live in a newer home with Fresh Air as an option you should use a media filter for that fresh air intake and spending money on a better filter may make sense. For those of us that own a home built prior to 2000 a relatively inexpensive media filter may be the desired alternative.
Most importantly, a particular filter may not be all they are hyped… There is a cost associated with using high-efficiency filtration and it is not just associated with the cost of the materials. There is a restriction cost of air flow known as static pressure reduction. A filter might do a great job of pulling particulate out of the air but may be extremely restrictive at the same time limiting the air flow through the media or material within the filter. We overcome this restriction cost by adding surface area or with deeper pleating within the media or by adding more filters. It is important to balance the number of filters in use. That is to say you may be better off with less filters but use a higher quality filter.
Without getting into a long discussion, the simple answer is, the smaller the holes in the filter, the less particulate will move through. Cigarette smoke is the most common occurring pollutant and one of the most difficult to get remove from the air (viruses excluded).
With all the above information in mind, to assume the air within your home is clean because a high quality filter is in place may not be a reasonable expectation.
Remember each furnace or air handler has a specific amount of air it must move depending on its size or BTU delivery. Filters are rated to flow at three measurements. These are Cubic Feet per Minute, CFM (volume), Feet Per Minute, FPM (velocity or speed) and Static Pressure, SP (pressure against flow). When the space the air flows is restricted by the size of the furnace cabinet (opening at the air intake) or the area of filter we speed up the air to make sure we deliver the proper volume. As we continue to speed up the air the Static Pressure will rise costing energy.
Filter data is specific. Never should we exceed 500 FPM in any brand filter. Most manufacturers recommend not exceeding 350 FPM on any one inch filter. Static pressure should run in the .1 to .2 range in an efficient duct system.
Getting confusing. You are not alone.
Logically the more surface area (deep pleated filters) will perform better than shallow pleated one inch filters. If any system in your home is over 3 tons, (36,000 BTU) you will need two of the most efficient filters #1 or #2 listed below. If you must use one inch filters do not exceed a MERV 7.
Filter types…
#1- The best filters are a combination of electronic and a type of media. These filters can be restrictive and do have the potential for mechanical failure, however they are the best at removing or reducing pollutants in the air. These filters remove 95% to over 99% percent of indoor pollutants.
#2- The next best filter is the deep pleated filter that are installed in a cabinet specific to the manufacturers. These filters offer great value and are near HEPA for trapping dirt, dust mold, allergens, and bacteria.
#3- The final choice in filters is a one or two-inch pleated. These filters fit in most furnace or air handlers and filter racks such as those that are placed under or on the side of the furnace or air handler. These filters can be very costly in back pressure that is placed on the blower section.
Conclusion…
Seldom will a single filter provide adequate air flow with quality filtering outside of a deep pleated filter. Any system above 3 ton (nominal) will require more than one deep pleated filter. Before you pay for an expensive filtering system please assess your homes realistic needs.
to learn more…..
Let talk about filter terms.
ASHRAE 52.5, HEPA, arrestance, efficiency and MERV.
ASHRAE 52.5: American Society of Heating, Refrigerating, and Air-Conditioning Engineers standard for testing air filtration.
HEPA: High efficiency particulate air being, using, or containing a filter usually designed to remove 99.97% of airborne particles measuring 0.3 micrometers or greater in diameter passing through it. Just about everything is picked up by these filters.
Arrestance: A measure of the ability of an air filtration device to remove a synthetic dust from the air. Under ASHRAE 52.5 a particular size synthetic dust is used to perform the above test.
Efficiency: The ability of a device to remove particulate or gaseous material from an air stream by measuring the concentration of the material upstream and downstream of the device. This is a before the filter and after the filter test comparison.
MERV: Minimum Efficiency Reporting Value or a scoring value when arrestance test is performed. Distributors have used this scale in the past to assist consumers in selecting the proper filter for use at home. Generally distributors have come up with other means to market to consumers at this time.