100% Done Right. 100% On-Time. Guaranteed! Horizon Services, Inc., is the regions largest and most well respected plumbing, heating and air conditioning company, with nearly 600 employees serving tens of thousands of homeowners throughout Delaware, Southeastern Pennsylvania, Southern New Jersey and Northeastern Maryland. After a quarter of a century in business, Horizons Services, Inc., remains fully committed to setting the industry standard for customer service, installation and focusing on things that are important to busy homeowners.