It’s hard to give a specific time period to change the filter because there are a lot of factors that affect the life of the furnace filter.  Some of the factors include how much crud gets in it when filtering the air, the filter type, and if you run the fan often on circulate or if you have air conditioning.

clogged residential filter-resized-600

How much crud messes up the filter depends on these main factors:

  1. Homes near construction or that have little grass covering the dirt surrounding the home and adjoining properties all affect the timing on the filtration. The debris from construction and dirt travels into the home via breezes and on the feet of people entering the home.
  2. Speaking of people… The amount of people in the home and the frequency of entering and exiting the home can affect the job that the filter does.  The household members’ habits also affect the filter load – things such as smoking can adversely affect the filter’s effectiveness. If you keep your windows and doors closed also helps reduce the particulate that enters the home.
  3. Pets with hair in the home.  Even if the pet is not a shedding pet the hair can attract pollen and dirt and it can then be transported into the home on the pet.
  4. Hobbies can affect the filtration too, cutting fabric and use of a lot of stuffing such as quiting, anything that has fumes or debris affects filtration.
  5. The filter type also affects the frequency that the filter needs changing.  A higher end filter such as a merv 10, merv 16 rated filter costs more, but lasts longer too.  It has an accordian filter design in the cardboard case and it is much thicker than the 1 or even 2 inch pleated or hepa filters.  These thicker filters are ususally for persons with allergies or when the need to have hospital grade filtration is needed (some of our customers use the higher filtration filters because they have to dust less often).  Merv 10 and merv 16 usually last between 6-12 months depending on the usage and the other factors.
  6. Circulating the air in the furnace’s fan mode or using the air conditioning helps filter the air for people with allergies because the air passes through the filter.  This means that the expectation of the filter’s life will be shortened as a direct result of the additional use.


The amount of time that the filter is being used will differ depending on conditions what all filter changes have in common is that a filter should be replaced before it reaches the point where it creates a significant restriction to airflow.  Airflow restriction makes the furnace work harder which shortens equipment life and creates higher energy bills because the equipment has to work so hard to get the desired effect. That’s important but even more important perhaps is that this restriction may cause a combustion issue – or combustion (fire) safety issue when the furnace is choked off.

The standard filters in mist furnaces have a manufacturer suggestion to change them every 3 months (thicker filters can last 6-12 months).  Check the Health House program (from the American Lung Association) they suggest to inspect the filters monthly.
The best advice is to buy a quality filter and change it per manufacturer suggestion and perhaps sooner when upon inspection it appears dirty.

If you need help with temperature, contact Cold Craft, Inc.

408.374.7292 or [email protected]

By Published On: September 25, 2014

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