Hi Richard!
We work with a lot of home service (HVAC, pest control, landscaping) companies and from our experience we've found that (like Tymen mentioned) dropdowns are ok as long as you don't make them keep dropping out further and further. It also depends on the amount of services you are trying to fit in the navigation.
Majority of our clients' websites' top level navigation would have - About | Landscape Maintenance | Landscape Design/Build | Portfolio | Contact - or something about those lines. Under "Landscape Maintenance" we might include Lawn Mowing, Irrigation Services, etc., in the drop down, but instead of continuing to add to the drop down, we would only link the top priority services from the drop down and list additional services with internal links from the main Landscape Maintenance page.
On our HVAC clients we might have "Heating" listed at the top most link in the navigation that has a drop down to Furnaces and Heat Pumps, and then we would include another drop down that includes links to the Installation, Maintenance, and Repair pages for both these services. I would only recommend doing double drop downs if your navigation doesn't include many services. For instance, if you have a bunch of services listed under Heating that ALL have an additional drop down, it could negatively impact user experience.
We try to pair down the main navigation to be as simple, but helpful/effective as possible, and include links to additional (less prominent) services from other landing pages instead of trying to jam pack everything in the top level navigation.
I hope this helps you figure out how to pair down the services!