|
Indoor air pollution is a growing concern. These air contaminates may include:
- Solids (dust, fumes, smoke)
- Liquids (mist)
- Gases (carbon monoxide, hydrocarbons)
The job of the filter is to trap some of these contaminates and other airborne particles, prevent them from passing through the system (damaging the unit), collecting on the blower, and being re circulated into the air. The average residential filter traps only the solids.
There are several types of filters available:
Disposable filters
- Adhesive filters are very common. The fibers are usually coated with an adhesive to help trap dust.
- Disposable filters come in many styles and are made from a variety of materials including, glass, cotton, and synthetics.
- Maintenance should include: Replacing the filters as they become clogged, usually a minimum of twice a year. If there are pets or plants in the house, the frequency may increase. Hold a bright light up to the filter to look for heavily loaded areas, or any holes in the filter itself.
Washable or reusable filters
- Washable, includes aluminum, synthetics (many different styles available). Stay away from frame-less filters, they are susceptible to failure, and can be sucked into the plenum, and allow dirt to bypass. Some washable filters are adhesive as well. A spray can be utilized to enhance the adhesive coating.
- Pleated or deep pocket type filters, allow for a larger filtering surface, some are reusable and others are disposable.
- Hepa filters, resemble a coffee filter material. These are very efficient for collecting particles in the air.
- Electrostatic filters use a passive charge to attract and hold the particles. Some may restrict air flow a cause a pressure drop across the coils.
Electronic Air Filters:
These filters are a very effective method of cleaning the air. As air passes to the filter it usually passes through a pre-stage filter that traps larger particles. The air then moves to the electronic filter where it passes through a highly ionized field. A series of wires puts a high positive voltage on the particles as they pass through the field. The particles are then attracted to the negative grounded plates.
Maintenance should include: Cleaning every few months. Most washable filters can be put in a dishwasher or hosed off. Check to see what the manufacturer recommends.
These filters however, are not always successful in removing odors and other gases. There are a number of specialty filters available which include:
- Carbon (removes odor and bacteria)
- Ultraviolet light (ozone producing, which kills bacteria)
Humidifiers
With a forced air heating system, the air in the house may become very dry. This can be uncomfortable to the occupants in the house, and be related to dry skin and difficulty in breathing. The relative humidity should be around 35%. Low humidity can also dry out wood-work, furniture, and other possessions in the house. Humidifiers add water vapor to the air. They can be introduced directly into the heating ductwork, or be an entirely independent system. Excessive humidity may cause mildew and molds to form. The humidity level is controlled by a humidistat.
There are several styles of humidifiers:
- Drum
- Mist
- Evaporation
- Electric
Maintenance may include: Annual service and cleaning. Hard water or well water may make frequent cleaning necessary. The nozzles and drains are susceptible to clogging, and the floats should be checked for sticking. If the reservoir is allowed to overflow, the water could back into the furnace and cause damage and corrosion. Some humidistat's, are difficult to service and may require a heating specialist. If there is a lot of corrosion on the unit, it should be serviced.
S. SHOWALTER, THE HOME INSPECTOR'S GUIDE TO TRAINING THE REAL ESTATE PROFESSIONAL, HVAC Filtration (2d ed. 1998).
|
