With all this heat we get the question a lot of people wondering if they have to change their furnace filter even in the summer when their furnace if off. But the answer is possibly yes depending on what type of system you have.
Throughout summer you usually have your furnace off and your air conditioner on. Some homes have combined systems (central air), which means the furnaces blower circulates the air for the heat and cooling and all the air is cleaned through the same filter. So even though you only have your air conditioner on you still need to change your furnaces filter in the recommended time frame.
So in short the answer to this question is probably yes. But it's always a good idea to keep a clean filter in your furnace even if you have it turned off and don't think it's in use.