Three jurisdictions means three content sets, not one service area page
A page that lists the whole DMV in one breath tells a homeowner in Silver Spring nothing about whether you can actually work on their house.
The District, suburban Maryland and Northern Virginia license trades, tax and permit separately. A contractor selling across the metro operates under three sets of rules at once. Specific requirements differ by jurisdiction and are worth confirming with the relevant local building department, but the marketing consequence is fixed: your content has to say which jurisdictions you cover, in plain words, near the top of the page.
Most HVAC sites here do the opposite. They write one service area block, name a dozen places, and leave the reader guessing. Search engines get an unfocused page. Buyers get an unanswered question and go back to the results.
A better structure is one substantial page per jurisdiction, each written like someone who works there wrote it. Permitting language differs. Equipment access differs. Typical housing stock differs enormously between a Fairfax County split level and a Capitol Hill rowhouse.
There is a cost to getting this wrong that has nothing to do with rankings. A firm licensed only in Virginia that ranks across the whole metro generates inquiries it cannot serve, pays for the phone time, and disappoints people who will remember the name.