Filter Comparison Chart

There is a best time of year to change your filters

Since air conditioners need more airflow than furnaces, you may want to consider possibly using a different filter during the summer months with higher airflow, than in the winter.  This is especially important if your climate gets hot enough that your air conditioner runs continuously for days at a time.  In Toronto, Ontario this happens frequently in the summer.  Since airflow is more crucial in the summer, it is important to know which months your air-conditioner runs at full speed.  There is an easy way to figure this out.  By using this tool, you can find our your local climate’s “Cooling Degree Days” or CDD.  This is basically the measure of cooling your climate requires for proper indoor comfort levels.    All you have to do is input your location (for an example lets use Toronto, On), and look at the “Base Year” column under “CDD” (2006 as an example).  You will notice that the reading is zero in months where the air conditioner is not used such as Jan, Feb, Nov, Dec.  You can change from Fahrenheit to Celsius if you wish.  I will.    In the example, Toronto requires 120 degree days for June,  240  for July and 195 for August.  There is cooling in other months but it is not a significant amount 50 or less.   I am approximating the number, but if you have to cool your house more than 4 degrees Celsius per day, you should have high airflow.  4 degrees x 30 days= 120 CDD.  I think that is a good number for  your cut off  point.  For Toronto, I only need three months of high airflow which coincides with the lifetime of one disposable furnace filter.  So that means on June 1 and Sept 1, the filters should be replaced.  If you climate is different and cool for more or less than three months, you may want to adjust your times slightly.