Air Filter Options
There are several air filter options to homeowners depending on their air quality needs and depending on their particular HVAC system
For specific questions about air filter options within the greater Omaha metropolitan area, give us a call today at Accurate Heating & Cooling. Call us at 402-238-2425. We can offer guidance on which air filter MERV ratings are better for your particular system as well as offer options to improve the air filtration in your home or business. Keep us in mind for all of your HVAC needs weather service or replacement equipment.
The most basic type of air filtering for a residential HVAC system is with a standard air filter that is installed in or near the furnace. This is also the case for a roof top unit on a commercial building. The air filters are installed inside the roof top unit. Different furnace designs have the air filter located in different positions.
It is good practice to check the condition of the air filter monthly. Replace the air filter if it is starting to have some dust or debris accumulation on the air filter. We recommend the use of a low MERV rated filter for most applications. The air filter will protect the HVAC system from pulling in debris that could impact the operation of the blower motor or that could restrict air flow across the furnace heat exchanger or the air conditioner’s evaporator coil.
MERV Rating of Air Filters
MERV stands for Minimum Efficiency Reporting Value and is a measuring scale used to rate how effective an air filter is at filtering material from the air. We recommend the use of a low MERV air filter for the overall performance of the home or building HVAC system. Some home HVAC systems do not perform well with the greater restriction created by a high MERV rated air filter. For more information on MERV ratings refer to this blog. Additional information on MERV ratings can be found on the National Air Filter Association website. Click here for a link to the NAFA website.
Simple MERV 2 Fiberglass Air Filters
In most applications, a MERV 2 air filter will provide adequate air filtration to keep the HVAC system operating optimally. A simple fiberglass MERV 2 air filter is shown below. This filter will provide a standard level of air filtration for a home. There are, however, additional air filter options available.
The above photo is of a MERV 2 fiberglass filter with a cardboard frame. This particular size is 20x25x1. This filter is a standard 1” wide filter.
The MERV 2 rating is shown on the sticker for the box that these filters came in for the above photo.
Pull out the air filter every month or so and look at how dirty the filter is. Replace the air filter if there are some debris deposits on the filter.
We get occasional service calls a where a dirty air filter has rendered a furnace or air conditioner inoperable. When the dirty air filter is replaced then the unit will usually operate normally.
MERV 7 Pleated Air Filters
There are higher MERV rated air filters that will filter out additional allergens from the air. Folks with pets or folks with allergies may prefer to use higher MERV rated air filters such as the pleated MERV 7 air filter shown below. This MERV 7 air filter will provide improved air filtration for a homeowner.
Pleated air filters have folds to the filter media and have an accordion look to them. The pleating allows a larger surface area of filter media to be placed within the air filter dimensions.
Air Filters Too Restrictive Causing Furnace or Air Conditioner to Fail
There have been cases where a homeowner has used MERV 2 rated filters in the past with no issues but has tried one of the higher MERV rated filters in their home only to discover that the furnace or air conditioner does not operate correctly with the higher resistance to air flow that accompanies the higher MERV rated filter. This is even when the homeowner frequently changes the higher MERV rated air filter so that it is very clean.
In these cases, a low MERV rated filter, like a MERV 2, must be used. The issue in this case is with the static pressure of the duct work in the home. When this situation occurs, it is often in an older home with duct work that just wasn’t built for optimum static pressure. There are usually no easy fixes to improve the static pressure of a home’s ventilation system, but sometimes there are. Sometimes the issue is that there is not enough return air volume and we can sometimes add additional return air grills to improve static pressure in a system. Individual systems must be evaluated on a case by case basis.
Insert Air Filter into Furnace Based On Air Flow Direction
Standard furnace air filters are one inch thick. There is an arrow printed on most air filters such that when the air filter is inserted into the furnace, the arrow points toward the furnace. For air filters that are installed inside the furnace (as opposed to being installed in the return air duct attached to the furnace), the arrow will point towards the blower motor. It is a helpful practice anytime that an air filter is replaces, to write the date that the air filter was replaced on the air filter. Many newer thermostats also have a timer setting that will remind the homeowner when a filter change is due. This feature is based on a timer, however, and usually not based on a measurement of filter differential pressure.
The standard air filters used in roof top units for commercial buildings are usually 2 inches thick, however, many commercial building owners elect to use the typical 1” thick residential style filter in their roof top unit. This decision is usually based on convenience (as in easier to obtain a 1” filter) or a decision to use a lower cost filter.
The photo above is of a 2 inch pleated air filter used in roof top units. The filter dimensions are 16x20x2.
Video Describing Air Flow Restrictions
The video below adds to the discussion about how various air filters can restrict air flow through the HVAC system. The refers to the differential pressure across the air filter, which is another way of saying that the air filter restricts air flow.
Better Indoor Air Quality from Installing 4″ or 5″ Air Filter
If it is desired to filter out more contaminants than a standard one inch air filter, there are boxes that can be installed in the duct work that will house a 4” or 5” pleated air filter. Upgrading to a 4” or 5” air filter is usually a convenient option to do at the time that a furnace is replaced as the installers will have better access to the existing duct work. In some cases, it is fairly convenient to retrofit an existing system with a 4” or 5” filter box, but sometimes there just isn’t enough room within the existing duct work to fit this filter box. While the larger 4″ or 5″ air filters provide enhanced air filtration over the standard 1″ air filter, there are still other air filter options available to the homeowner with specific indoor air quality needs.
The above photo is of a pleated 5” air filter that fits into a metal filter box that is specially installed into the return air ducting to house this filter. Some designs have a metal drawer below the furnace that houses the 5” air filter.
The 4” or 5” air filter does a good job at filtering particulates and allergens from the air. While these wider air filters do create additional resistance in the duct work, for most installations, the HVAC system can handle the slightly higher resistance with no adverse consequences to the HVAC system. In some installations, the existing static pressure within the duct work will not allow the use of these more restrictive air filters.
Air Filter Options that are Too Restrictive
We have seen a furnace shut down or an air conditioner freeze up or shut down due to the larger restriction that these 4” or 5” air filters create. We have also seen brand new MERV 7 pleated air filters shut down a furnace or freeze up an air conditioner just by the slightly higher resistance that the MERV 7 air filter creates. In these cases, the use of the MERV 2 fiberglass air filter may be necessary for the system to operate normally. On rare occasions, the use of a 4” or 5” air filter is even too restrictive for a furnace or air conditioner and a standard 1” MERV 2 rated air filter must be used for the system to operate.
Better Indoor Air Quality from Installing an Electrostatic Air Filter
A better option for improved indoor air quality is the electrostatic air filter such as the Trane CleanEffects air filter. This filter unit will remove up to 99,98% of allergens from the home ventilation system.
The Trane CleanEffects Electrostatic air filter is installed between the return air ventilation duct and the furnace.
Recommended Electrostatic Air Filter Cleaning Schedule
A recommended cleaning schedule would be to clean the pre-filter every 2 months and clean the collection cells every 6 months. The filed charger should be cleaned only by a qualified service technician annually. The unit has timers that can be set to indicate when cleaning is required. For a homeowner with additional indoor air quality needs, there is still an additional option for even more enhanced air filter options.
Air Scrubber Offers Best Air Quality
A Best option for improved indoor air quality is a 5” pleated air filter (discussed earlier in this article) with an Air Scrubber Plus by Activtek Environmental.
The Air Scrubber Plus connects to the home ventilation system and treats the air being circulated as it passes through the ducts and out into the indoor environment. The Air Scrubber Plus neutralizes odors and reduces contaminants inside the duct as it is carried through the system and into the living spaces. The Air Scrubber Plus utilizes germicidal UV light that produces peroxides and hydroxyls in the air stream which eliminate various microbes including odors, mold, bacteria, viruses, VOCs, and other contaminants. People who have installed the Air Scrubber Plus report their house has a fresh clean smell much like being in a clinical area of a facility. There are non-ozone models available for people who do not like the ozone produced from the Air Scrubber Plus.
Real World Application of Air Scrubber
Our Service and Install Manager Kelly has several large dogs at home and the Air Scrubber Plus does a great job at removing pet related odors from the air at his home. We have a portable design of the Air Scrubber Plus that a homeowner or business can borrow to try out. Kelly can speak with you about all of the various air filter options available and which option would be best for you.
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For information on older mercury switch thermostats that may be in your home, refer to this blog.
If the equipment in question is a roof top unit instead of a residential furnace, it is good practice to ensure that any low voltage transformer high side is wired for the correct line voltage. It is common for the low voltage transformer that is shipped with the roof top unit to have options for either 230v or 208v primary voltage. Based on results of a voltage test using your voltage meter, ensure that the correct primary side terminals are connected.
Before hot surface ignitors were common on newer furnaces, the direct spark ignitor was used. The direct spark igniter allowed the natural gas furnace to move away from a standing pilot system. In a standing pilot furnace, the pilot flame was always lit which meant that a small amount of natural gas was used to keep this pilot flame burning and this small amount of natural gas that was always burning lowered the efficiency of the furnace. The direct spark ignition system involved a high voltage ignition system and the high voltage wire could interfere with nearby electronic equipment in newer furnaces with circuit boards that were used to control the operation of the furnace. Modern natural gas furnaces are all equipped with a hit surface ignitor that glows bright orange hot to ignite the burner flame. For more information on the older direct spark ignition system (link under development) follow this link.
And More Information
Are you challenged to decode the Trane furnace model numbers on your residential furnace? The Trane Furnace Model Number Descriptions blog may be of help in decoding these complicated model numbers. To understand Armstrong Furnace Model Number Descriptions better, refer to this blog.
For some tips on troubleshooting a failed low voltage transformer in a residential furnace or commercial building roof top unit, refer to the Troubleshooting Failed Low Voltage Transformer blog.
For tips on troubleshooting a furnace or roof top unit gas valve, refer to this blog.
As a trusted Omaha furnace repair and a/c repair contractor, call Accurate Heating & Cooling for all your Omaha furnace service, Omaha air conditioner service, Omaha commercial roof top unit service, Omaha mini split service, Omaha geothermal unit service, and Omaha home comfort needs. We also professionally install HVAC equipment. We are licensed, bonded, insured, and experienced. Call us today at 402-238-2425.
When it is time to replace your older furnace or air conditioner, let us install one of our flagship Trane air conditioners and furnaces that will provide many years of reliable performance. We also offer a second line of HVAC products from Armstrong. For more information on the benefits of upgrading to a new Armstrong air conditioner, refer to this blog.