Description

Thick, pleated filters have increased surface area and typically do not load up with particulates as quickly as standard filter media. Depending on the homeowner, it may be prudent to select this filter media type if a longer service life and decreased maintenance requirements are desired. If the furnace cabinet is installed in a location that does not provide adequate room for filter replacement, the homeowner is unlikely to replace the filter when its service life is exceeded. These factors can lead to a higher pressure drops at the filter and consequently increased loading on the furnace blower fan leading to: increased electricity consumption, reduced air flow, lower efficiency, and shorter equipment life.

Challenges

FILTER CABINET SEALING: The impact of poorly sealed filter cabinets on high-efficiency gas furnace
performance is not well understood within industry. Unlike older standard and mid-efficiency furnaces, keeping the heat exchangers clean from particulates is very important for heat transfer efficiency, quiet operation, reduced service issues, and equipment longevity. In the heat exchangers of high-efficiency furnaces the air is traveling though very tight or small openings resulting in a much a lower tolerance for particulates and other obstructions.

FILTER REPLACEMENT: Inexpensive or even higher quality 1" filters are commonly used as a result of space and cost considerations. While the pressure drop readings for virgin 1" filters are quite good, their performance can drop quite quickly if they are not replaced on a regular basis. Due to significantly less surface area, 1" filters tend to load up quickly leading to higher stresses on the furnace if they are not replaced on a regular basis.

FURNACE BLOWER MOTORS: High-efficiency furnaces typically incorporate very efficient furnace blower motors that may have difficulty providing the required air flow if the furnace filter loads
up prematurely. In order to compensate, some variable speed ECM motors may ramp up (speed up) in order to produce the desired air flow required for adequate temperature rise across the heat exchanger: this can result in noisy operation, higher electricity consumption, and increased service calls due to built in high temperature lock out and / or potential degradation to the heat exchanger due to over heating.

SPACE CONSIDERATIONS: Larger filters typically require a larger furnace footprint; however, space is often limited in furnace replacement scenarios. Commonly, the original furnace was installed in in an unfinished basements that has since been renovated and the furnace is now framed away in a very tight mechanical room: this constrains easy access to filter cabinet to make the necessary modifications.

Solutions

• Thicker, pleated filters have longer service lives and can reduce furnace maintenance requirements. When there are obstructions near the furnace cabinet, it is important to come up with a serviceable filter solution in order to protect and maintain the furnace.
• Space is rarely an issue in down-flow or horizontal flow furnace orientations. In up-flow furnace positions, there are a variety of options when limited installation space is available:
  • The most common solution is to build a lift kit (sheet metal / ductwork) and install the filter at the furnace base.
  • A second option is to locate the filter elsewhere in the return air drop ductwork.
  • A third option is to move the domestic hot water tank or to move a wall (where possible) in order to accommodate the filter.