when you put in the whole house system, this doesn't address the
stack effect, this is a fresh air exchange system.
this allows you to continue to tighten the house, with fresh air
being provided by whsystem.
do local contractors recommend foam sealing attic with foam at
the roofline? comparing this cost to air sealing top plates etc
& adding insulation on attic floor would be where I'd start if this
install is an option for your climate.
this is a starting point for discussion, not a solution.
more info will be needed as we learn what you know
and what your house requires. as every house is different
there isn't a fixed answer, for every house.
best of luck.