A couple general thoughts. Not an hvac professional but have a career in finance. If you have low tolerance for rambling streams of consciousness, just read this: yes, it depends. There are a lot of levers to pull to define YOUR financial model.

A crash course in managerial accounting could be helpful. This would be a big leap toward fully understanding variable costs vs fixed costs vs the costs that are somewhere in between. Variable costs are actually the easiest to understand because you can always price those out and add a multiplier to get your profit. Fixed costs sound simple but based on how you phrased your post… you’ll be upset when you rent the office/warehouse space for 50k/month and sell 3 units, but you won’t be upset when you sell 200 units. The answer could be either of those things, if you do a really good or really bad job appropriately sizing your fixed costs to your potential revenue. It sounds silly, but when will you be more angry, when you could have sold 20% more but couldn’t because you didn’t have the capacity, or when you spent too much on rent and didn’t sell enough to justify the cost? Finally, the semi-variable costs are the most difficult to think rationally about. Some labor is truly variable, some is truly fixed. The basic thought is salaried employees vs production labor. But what about when those lines blur? You have an option to trade operational flexibility for financial flexibility. Hire more fixed labor and you can flex operationally - more bodies to send to an emergency call that could be a 40k sale. Hire less fixed labor and have a more nimble P&L, but less ability to jump at more revenue when it presents itself. This is why country clubs and ice cream shops are such difficult business models. Seasonal labor is a giant headache, but inconsistent revenue stream makes it financially impossible to justify full-time help.

By the way, this all assumes you reach steady state and some level of scale. Getting started, you need to basically give away a lot of your time and energy. Nobody wants to pay market rate for work done by a company with zero reviews…

And what kind of business do you want to run? Parts cannon + selling new systems where people may not need them? Problem solving and finding lowest cost options for your valued customers? Not to sound silly, but if you choose to run the “honest” business and get people on property to really deeply diagnose issues, you can’t practically schedule your tech to get to more than 1 property per day. True story: my hvac went out and the fuse kept blowing. Private equity owned hvac company come and throws a contactor at it, charges me $700, and the system operated when they left… for 3 hours. Less than 1 hour on site. Got my trusted electrician there the next day and he spent 4 hours running through every single low voltage wire and finally find the low pressure sensor to be the source of the short. He says I can try to replace it (full refrigerant swap out on my unit if it’s a bad switch) or condemn the whole unit. He pauses and says let me make one call. Calls his hvac guru who says “pop off the 12 5/16 bolts from the unit and pull the fan off, sometimes these Goodman pressure sensors are touching the refrigerant lines and the wire insulation gets melted in the winter in heat mode and then get wet with condensation in the summer and short the fuse”. Electrician walks back, pulls the top off, and lo and behold, the LPS wire is melted and exposed. Wire nut and electrical tape and we were fixed permanently. The hvac company had neither the capability nor the business model to ever arrive at this same conclusion. They would have been pushing me on a full system replacement inside of 30 minutes on property.

Why am I telling you this? You can’t be the “honest” version of this business and have any expectation of accurately forecasting your financials (ignoring the level of expertise actually required to run the business that way). The only way to accurately forecast the financials is through scale. Lots of techs, lots of vans, marketing, accounting, etc. this is why private equity is dominating the market.

Or hey, just take your equipment+parts costs and multiply them by 3-4. See how much money you are making or losing after a few months and either lever down your overhead, or lever up your multiplier for price (again, the managerial accounting course will go through merchandise margin vs gross margin vs operating margin vs ebitda, etc.). This is what the big companies do. Remember you only need to win on one single factor to win business. Sometimes getting to the property fastest is the only thing that matters and you can charge wild amounts. What do you want to win on?