The difference between a good HVAC sale and an average one is decided in the year before marketing, not in the negotiation. Three things move the number: converting one off customers into agreements, taking yourself out of selling and estimating, and having records a buyer can verify in a week rather than a month.
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Months one to six: the recurring base
Every maintenance agreement signed is contracted revenue with a renewal history attached, and buyers pay a different multiple for it than for replacement work. Convert what you can, record contract value and renewal rates properly, and separate that revenue clearly in your accounts so the argument makes itself when a buyer reads them.
Months six to nine: reduce the dependency
If you are the estimator and the closer, the business does not survive your departure and the buyer knows it. Train and document. A named service manager, a documented estimating method and a technician pay structure written down are all evidence that the earnings continue when you stop turning up.
Months nine to twelve: the file
Three years of clean financials, a documented add back schedule, an asset list with maintenance history, agreements and renewal data, staff records with pay rates and any restrictive covenants, and the lease. Diligence on a trades business is not exotic; it is just long, and a prepared file removes weeks from it.
Other questions people ask
What is the biggest single lever?
The share of revenue under maintenance agreements, because it changes the multiple rather than just the earnings.
Do I have to stay after the sale?
Usually for a transition, longer if the license or the customer relationships are personal to you. Both are reasons to reduce the dependency early.
Should I keep bidding on large installs before a sale?
Yes, but do not chase volume at low margin to inflate revenue. Buyers reconstruct margins by job, and a year of cheap work reduces the price rather than raising it.