I think that it is pretty obvious that you already know the answer
to your question.

Many years ago we often gave in to the same temptation - opening
windows on cool evenings "to save some money" and "to get
some fresh air." The first problem is the fact that the cool evening
air may still have very high humidity and the next day when you
turn the AC back on, it will consume a lot of electricity removing
that moisture from your house. Often your electric bill would be
lower by leaving the windows shut on those marginally cool
evenings and you are driving up your electric bill by getting that
"free" evening cool air.

The bigger issue for allergy sufferers is the fact that it is often very
stupid to let the allergins into the house. By analogy, it generally
takes 6 months after pets have been removed from a house before
the allergins related to them are no longer bothering family members.
Obviously airbourne allergins won't take 6 months to remove, but
without a very outstanding HEPA filtering system and a furnace fan
set to run 24 hours a day, you probably don't have the windows closed
long enough to provide allergy relief before the next time the family
member opens the windows again.

If a family member insists on opening windows in the evening,
then I would pretend to be installing more expensive filters while
actually buying cheaper, marginally acceptable filters. Why waste
money humoring somebody who is ignoring reality?

I notice that you are already getting advice from somebody who
questions why you would run the AC when the temp is below 75.
Perhaps because it is your home, your comfort level & your money.

You're also getting bright advise "Just because you are filtering the
air at times does not mean you gotta turn your house into a bubble
of sorts. Live life." This is obviously from somebody who is ignorant
of the suffering that others can go through because of allergies.
And certainly this is somebody who has never had to rush a child
to the ER at 3AM due to an asthma attack. Some folks have to turn
their homes into bubble homes to "survive." Anybody who can't
understand that fact is a moron.

Off on a tangent - I hope that your family member is getting optimal
medical treatment for allergies. Flonase and Loratadine (ie, Claratin)
are cheap and extremely effective for many people. For some, they
are miracle drugs.

Good luck,
Gideon

==============

Percival P. Cassidy wrote in message ...
Does it make any sense to buy more expensive filters that are alleged to
reduce allergens when another occupant of the house (the one who suffers
from allergies) insists on turning off the AC and opening windows as
soon as the outside temperature drops below 75F?

Perce