Air Cleaners:
Furnaces and central air conditioners are equipped with a panel air filter
whose main purpose is to prevent dust and dirt from entering the heating
and cooling equipment and causing it to malfunction. These filters are effective
for removing particles or particulates above 5-10 microns in size. (There
are 25,400 microns to an inch, and it takes 200 microns to reach across a
dot made by a sharp pencil!) Air cleaners remove from 90% to 99% of air-born
particles and are effective in trapping particulates as small as 0.01 microns.
An air cleaner removes most of the dust and dirt that is circulated through
the heating/cooling system. The average system circulates the air 4-5 times
per hour. Whether you choose a room-type or one that is mounted on your furnace,
air cleaners can only remove particles in the air that pass through them. Three
common types of air cleaners are:
• HEPA (High efficiency particulate air) cleaners - must remove 99.97%
of all particulates down to 0.3 microns in size, including spores, pollen,
and tobacco
smoke particles. They use a high efficiency pleated filtering media to remove
particles, and are typically available only in portable, room-size models.
• HEPA-type
cleaners - remove 99%+ of all particulates 6.0 microns or larger, including spores,
pollen,
and tobacco smoke particles. They are less
effective on very small particles. They also use high efficiency pleated
filtering media to remove particles, and are typically mounted onto the furnace.
• Electronic
air cleaners - remove 99%+ of most particulates of all sizes, including spores,
pollen,
and tobacco smoke particles. They use collection
plates and ionizing wires to attract electrically charged particles; however,
the plates and wires must be frequently cleaned to achieve a 99%+ removal
rate. Some models emit ozone - a known lung irritant.
Big Air Conditioner, Big Cooling?
When it comes to air conditioners, bigger is not necessarily better.
Choosing the properly sized air conditioner will give you the
best performance for
your cooling dollars. A common rating term for an air conditioner's
size is the "ton," and refers to its ability to remove 12,000
British Thermal Units or Btu's of heat per hour.
An oversized air conditioner
costs more to buy, uses more electricity, and does not "cycle" properly.
Frequent cycling means your air conditioner:
• Uses energy less efficiently.
• Removes
less moisture from the air (humidity), leaving you feeling less comfortable.
• Wears
out your compressor
and electrical components more quickly.
• Causes
indoor temperatures to fluctuate more.
Buy the most efficient, highest quality air conditioning unit you can afford,
and consult a professional about the sizing.
Oversized Heating Systems
Many
heating systems have a much larger heating capacity than is necessary. "Oversized" heating
systems cost more to buy initially, provide less comfort and efficiency,
and have higher maintenance and operating costs.
Some heating contractors may suggest "derating" the system by installing a smaller gas burner orifice (the small opening where gas flows to the combustion chamber) in order to save energy. The manufacturer generally does not recommend this. Excessive derating can lead to problems with flue gas, water condensation and corrosion in the heat exchanger or vent system. Unfortunately, the best solution is to replace the oversized unit with one that is properly sized for your home.
If you have decided to replace your present system with a new high efficiency
furnace or boiler, here are some things to consider:
1. Look at the AFUE rating.(Annual Fuel Utilization Efficiency) These ratings
help you to compare the efficiency of different models in a way similar to
listing gas mileage ratings on cars. They also give an estimate of the annual
cost to operate. Look for the ‘Energy Star’ label for help in selecting
more efficient models.
2. Make sure your new system is sized properly. The most common mistake a contractor makes is over-sizing. The contractor should not replace your furnace with another that is the same size without doing "Manual J" calculations. "Manual J" is published by the Air Conditioning Contractors of America (ACCA). Make sure your new furnace/boiler is sized according to Manual J or another procedure that is approved by ACCA. Just because the original furnace is a particular size does not mean the new one should be the same size. Before construction procedures for homes became more air tight, it was common to install a furnace with much larger capacity. Correct sizing involves considering how well the home is insulated, the size and condition of its windows, how many occupants there are, the local climate, and "air sealing" improvements the owners may have made.
3. Determine if the existing vent is the correct size for the new energy-efficient unit. Many older furnaces or boilers are oversized, and as a result, the original vent and flue may be too large to accommodate the new furnace or boiler. Masonry chimneys may also require a chimney liner for safety.
High efficiency furnaces
and boilers are generally more expensive, but the annual reduction in fuel
usage should
ultimately provide savings. How quickly
you reach your "payback" figure depends on the reduction in your
annual fuel costs and maintenance, and how much you spent on the unit and its
installation. Be careful when you select your contractor. The performance of
your new system will depend a great deal on his experience, skill, and knowledge.
Back