Question: I have a relatively new high-efficiency furnace with a filter that I clean regularly, but it does not seem to get very dirty. It has a large metal box with plates and thin wires and another very thin metal screen that I remove and clean often. Neither of these seems to get very dusty, perhaps because I have a clean house and have no pets. I have been getting my furnace serviced and cleaned every year but I wonder if that is necessary? Should I be servicing the furnace yearly if it doesn’t need it? I would also like to know if I am cleaning my filter properly. Can you provide me with some advice on this?
— Anne Kozlowski
Answer: Determining whether to service your furnace annually will depend on the type, age and condition as much as anything else. I will give my opinion on this important maintenance issue and hopefully help you with your furnace filter management.
It is always important to determine and properly identify components of home systems before proceeding with any scheduled maintenance.
What it appears that you have is not a simple furnace filter, but an electronic air cleaner. That device is much larger than your typical one-inch thick filter and works by sending an electric charge through the filter which removes harmful products from the air. This is often accompanied by a "snapping" noise when the dust particles hit the energized filter. The thin metal filter is simply a pre-filter to prevent larger dust particles from plating out on the elements and reducing their effectiveness.
Electronic air cleaners such as yours were quite popular a couple of decades ago, before disposable pleated filters became more common.
They can be highly effective, but have a couple of drawbacks. One of these issues is that electronic air cleaners can produce a small amount of ozone from the "zapping", but that should be a minor concern if it is not damaged.
The major drawback is that they do require regular manual cleaning, which can be a little tricky. To properly maintain one of these filters, the pre-filters should be removed and cleaned every one to two months. This can be done by handwashing with mild soap in a large sink or laundry tub, or placing the filters carefully in the dishwasher. These are normally comprised of an aluminium frame with a mesh made from the same non-corrosive material, so they should last for years without damage or rust. Once washed and dried, these can simply be slid back into the narrow slot and the cleaner re-energized after replacing the cover.
The larger filter elements can be much more tricky to clean.
Prior to any maintenance, it is imperative that the power switch be shut off and the test button, if present, be pushed in before disassembling the unit. If the power is left on, you can get a significant shock by touching the energized elements. The reason for using the test button is to help release any static electricity built up, which sometimes can give you quite a start if present after you remove the access cover. After carefully removing the element or elements, they should be placed in a laundry sink or bathtub with mild soapy water and washed with a soft brush or toothbrush. Care must be taken not to damage the very delicate thin wires between the plates, as this can negatively affect the function of the unit. Once cleaned of dust and dirt, the elements should be left to air dry completely before reinstallation. Once dry, the elements should be carefully slid back into place, the cover replaced and the power switched back on. You may not see a light on the switch, or hear the crackling noises, until the furnace blower comes on during a normal cycle.
It is my guess that your electronic air cleaner is turned off and you are simply washing the dust and debris from the pre-filters, as you would with a standard cleanable static filter. That is why you are seeing little to no dirt on the elements. While this may provide you with reasonable filtration, it is not the way the system is intended to be used. I would recommend turning the switch on, if you wish to use the electronic cleaner, or remove the elements altogether.
I would recommend getting your HVAC technician to check the unit, during your annual servicing, before turning it on to make sure it is safe and functioning properly. If it is damaged, or you simply don’t want to use it anymore, ask the technician to modify the ducts to accept a standard one- inch thick filter. Then, you can simply purchase several disposable pleated filters and change them every couple of months for easier filtration.
As far as regular servicing, I normally recommend to my clients that newer high-efficiency furnaces should be serviced annually once they are more than a decade old. Typical servicing should include cleaning the blower and cabinet, adjusting the burners, and inspection for any damaged or improperly functioning components. When the furnace is newer, servicing every two to three years should be sufficient, unless there is a visible or audible problem. If you see water stains or dripping anywhere on or around the furnace then call a HVAC contractor.
Cleaning your electronic air cleaner, or static cleanable filter, requires proper knowledge of operation and how to remove it. Servicing your high-efficiency furnace annually is a good idea, but may only be necessary once it reaches its second decade of operation. As with most home systems, regular cleaning and maintenance will extend the life and provide more efficient and proper operation.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian
Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.
trainedeye@iname.com
