Experience The Horizon Difference. On-Time Service. Up-Front Pricing. And The Job Done Right and Clean the First Time. GUARANTEED! Horizon Services is the region's 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 remains fully committed to setting the industry standard for customer service, installation, and focusing on things that are important to busy homeowners: respect for their time, their home and their property; up-front pricing, and an unconditional 100% money back guarantee.