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Why we Like Gasketed Air Filters & Dirt in HVAC Systems and Effectiveness of Washable Air Filters InspectAPedia®  -     Benefits of gasketed air filters on HVAC systems Significance of dirt and debris in the return air plenum or ducts Washable air filters for HVAC systems Air conditioning / heating system filter product sources and recommendations

Here we discuss and explain leaky air filters and the value of gasketed air filters, followed by comments on the effectiveness of washable air filters. This website answers almost any question you might ask about air filters for heating or air conditioning systems. We explain how an air conditioning service technician will diagnose certain common air conditioning system failures or defects. In these articles we are referring to filters installed on central air conditioning or central heating systems that move air through air handlers and duct systems. Standalone "air cleaners" are generally ineffective in buildings.

We include photographs to assist readers in recognizing cooling system defects. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. Readers should also see our INDOOR AIR QUALITY IMPROVEMENT GUIDE article series. The page top photograph is of a low-MERV HVAC filter in an air handler.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

The Benefits of Gasketed Air Filters on HVAC Systems

A gasketed heating or air conditioning system air filter improves the filter effectiveness. The benefits of a high efficiency air filter material when used in an air handler and duct system are not fully realized if air bypasses the filter around its installation frame due to poor fit or poor installation. [The filter shown here is not a high quality gasket-type air filter.] That's why some manufacturers emphasize the value of air-sealing gaskets on their products. Simple observations made in the field will make for agreement with the manufacturers that filter bypass is an issue at some heating or air conditioning installations. When changing an air filter at a return air inlet or at an air handler, when the old filter has been removed, take a look inside the return duct at the return register, or inside the return plenum at the air handler, to see just how much debris is passing the filter. [The photograph above shows how a badly-fit HVAC air filter can not only leak bypass air into the blower compartment but also it can collapse right into the blower fan - this is a potential fire hazard!]

Implications of dust and debris in the return air plenum

On an old heating or air conditioning system where filters have been ineffective, not properly installed, leaky, or not maintained and changed on schedule, we often find quite a bit of debris entering the air handler and duct system. This is in fact so common that most HVAC installers and technicians consider dirty ducts to be "normal". And they're quite correct: typical house dust that has collected inside of a duct system is not normally a toxic substance. But 1) a high level of dust and debris inside of an air handler or duct system indicates that system filtration has not been effective, 2) the dust level indicates that the system has been delivering dust and debris to the occupants providing poorly-filtered air, and 3) there is an increased risk of mold in the duct or air handler system if moisture enters the system from a leak or from air conditioning condensate mishandling.

How Good are Washable air filters for heating and air conditioning systems

Washable re-usable air filters are very appealing from a cost viewpoint. I would look for data to indicate whether or not the washable filter runs at a lower MERV or filtering efficiency. In our cascaded filter proposal (discussed at this website) we included and continued to use a washable filter that came with the equipment since it was not reducing the airflow CFM, but we preceded it with other filters for different purposes. The photograph shows a typical washable metal air filter. Other types of washable air filters are available as well. A metallic air filter (shown) is not very efficient (effective) at trapping airborne particles when it is clean, though efficiency improves as it gets dirty. Other pleated, fabric or paper air filters that are also washable are more efficient at trapping airborne debris.

Be sure to read Particle Sizes & IAQ for a description of the sizes and behaviors of some of the common particles that are an indoor air quality concern.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

AIR CONDITIONING & HEAT PUMP SYSTEMS
AGE of AIR CONDITIONERS & HEAT PUMPS
AIR CONDITIONER BTU CHART
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR CONDITIONER NOT WORKING
AIR FILTERS for HVAC SYSTEMS
  Air Filter Location
  Dirty Air Filter Problems
  Missing Air Filters
 OPTIMUM INDOOR AIR FILTERS
  Air Filter Efficiency
  Optimum Air Filter Design / Location
  How to Cascade Air Filters
 CONTINUOUS BLOWER FAN OPERATION
 AIR FILTER EFFECTIVENESS
  MERV, HEPA Definitions
  MERV Air Filter Ratings
  How Air Filters Work
  Particle Sizes & IAQ
  Gasketed air filters
  Debris in Return Air Plenum
  Washable air filters
 FIBERGLASS & AIR FILTERS
  Air Filters Shed Fibers?
  Fiberglass & Test Lab Accuracy
  Variations in Fiber Size
 SOURCES FOR AIR FILTERS
  OTHER AIR CLEANERS
AIR HANDLER UNIT
  DIRTY A/C BLOWERS
    Leaks, Rodents In Air Handlers
    Mold Growth in Air Handlers
  DAMAGED COOLING COIL
  DIRTY COOLING COIL
  DIRTY COIL CLEANING PROCEDURES
  FROST BUILD-UP
  BLOWER LEAKS, RUST & MOLD
  ADDING A/C: RETROFIT SIZING
ANIMAL ALLERGENS / PET DANDER
ASBESTOS in BUILDINGS
BACKUP HEAT for HEAT PUMPS
BLOWER DOORS & AIR INFILTRATION
BOOKSTORE - Air Conditioning "How To" Books
CLEANING & Legionella BACTERIA
COMPRESSOR CONDENSER
CONDENSATE HANDLING
CONTROLS & SWITCHES
COOL OFF HEAT Thermostat Switch
COOLING CAPACITY, RATED
COOLING COIL or EVAPORATOR COIL
DATA TAGS on AIR CONDITIONERS
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
DEFINITION of Heating & Cooling Terms
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DUCT SYSTEMS
DUCTS - Asbestos
DUCT SYSTEM DEFECTS
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCTS, Asbestos Transite Pipe
DUST FROM HVAC?
ENERGY SAVINGS in BUILDINGS
EVAPORATIVE COOLING SYSTEMS
FAN AUTO ON Thermostat Switch
HEAT LOSS (or GAIN) in BUILDINGS
INDOOR AIR QUALITY & HOUSE TIGHTNESS
INDOOR AIR QUALITY IMPROVEMENT GUIDE
INSPECTION LIMITATIONS
LOST COOLING CAPACITY
MOTOR OVERLOAD RESET SWITCH
OPERATING COST
OPERATING DEFECTS
OPERATING TEMPERATURES
REPAIR GUIDE for AIR CONDITIONERS
REPAIR & DIAGNOSTIC FAQs for A/C
REFRIGERANTS
SEER RATINGS & OTHER DEFINITIONS
SYSTEM OPERATION
SWAMP COOLERS
THERMOSTATS
THERMOSTATIC EXPANSION VALVES
CRITICAL DEFECTS on A/C SYSTEMS
FURNACES WARM AIR HEATING SYSTEMS
INDOOR AIR QUALITY IMPROVEMENT GUIDE

• Thanks to Mark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects" section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and home inspection educator.
• Thanks to Jon Bolton, an ASHI, FABI, and otherwise certified Florida home inspector who provided photos of failing Goodman gray flex duct in a hot attic.
• Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
• US EPA article on air filter efficiency: epa.gov/iaq/pubs/airclean.html 04/11/2009
• Wikipedia provided background information about the definition of HEPA and airborne particle interception.

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