Heat rarely disappears through one dramatic failure. More often it leaves through a collection of smaller compromises: leaky frames, underperforming attic transitions, uneven sealing and airflow patterns that quietly drag comfort away.
Comfort is the better metric
Efficiency language can get abstract. Comfort tells the truth faster. If one room is always drafty or the system runs too hard at dusk, the home is telling you where the weakness is.
Windows, attic edges and access points
These areas do not always look damaged, but they are frequent culprits. The problem is often not one element alone, but a transition between materials.
A calm house usually means the envelope is doing its job quietly.
Systems should not compensate forever
If heating or cooling has to work overtime to smooth out basic envelope problems, wear and energy use both rise.