Map the building
Start with an honest inventory: how each room gets used, what's changed about the envelope over the years, where the comfort complaints are, and what electrical and fuel service is already available.
Measure before selecting
Heat-loss and heat-gain numbers, airflow and static-pressure readings, and water-temperature data (where there's hydronic heat) separate a true capacity shortfall from a distribution problem.
Plan both seasons
A plan built only around January or only around August misses half the job—cold-weather performance, summer humidity, shoulder-season behavior, and backup heat need to be considered together.
Compare scopes, not boxes
Line up every quote against the same checklist: load basis, distribution scope, electrical work, permits, and how commissioning gets documented—not just the total price.