From the perspective of saving the maximum amount of energy that is economically justifiable, the biggest ``fuel'' switching concern is from heat pumps to a combination of central air conditioners and electric resistance heating.
(the maximum amount of energy; is; economically justifiable) (the biggest ``fuel; switching; concern) (the biggest ``fuel'' switching concern; is; from heat pumps to a combination of central air conditioners and electric resistance heating)
the maximum amount of energy the biggest ``fuel the biggest ``fuel'' switching concern
is switching is
economically justifiable
concern
from heat pumps to a combination of central air conditioners and electric resistance heating