| Business | Phone |
| Advanced Service Air Cond 115 Water St, Frederick 21701 | (301) 371-8807 |
| Air Mechanical Systems 520 E South St # A, Frederick 21701 | (301) 694-5340 |
| American Air Cond & Heating 5716 Buckeystown Pike, Frederick 21704 | (301) 662-5692 |
| Antietam Heating Air Cond Co Po Box 3279, Frederick 21705 | (301) 663-3456 |
| B & B Air Cond & Heating Svc 183 E South St, Frederick 21701 | (301) 662-0611 |
| Carrier Mid-Atlantic 4615 Wedgewood Blvd, Frederick 21703 | (301) 228-2688 |
| Chiller Technology Systems Inc 1572 Tilco Dr, Frederick 21704 | (301) 698-1431 |
| Conditioned Air Systems Inc 5010 Bob White Ct, Frederick 21703 | (301) 829-7950 |
| Frederick Air Inc 3 King Ave, Frederick 21701 | (301) 663-0300 |
| Frederick Heating & Air Cond 5754 Stoney Creek Dr, Frederick 21703 | (301) 698-5704 |
| General Heating Engineering Co 4640 Wedgewood Blvd # 103, Frederick 21703 | (410) 880-6222 |
| Griffith Energy Svc 200 E South St, Frederick 21701 | (301) 663-3111 |
| Harris Heating & Cooling 7818 Edgewood Church Rd # A, Frederick 21702 | (301) 473-8126 |
| M T Remsburg Heating & Air Frederick 21701 | (301) 698-6168 |
| Mid Atlantic Hvac Inc 5702 Industry Ln, Frederick 21704 | (301) 631-2021 |
| Modern Comfort Systems Inc 100 Airport Dr E, Frederick 21701 | (301) 662-8177 |
| Richard W Myers Frederick 21701 | (301) 662-1818 |
| One Hour Air Cond & Heating Frederick 21701 | (301) 695-1500 |
| Precision Heating & Cooling Frederick 21701 | (301) 898-8290 |
| Priority Service 7731 Mckaig Rd, Frederick 21701 | (301) 898-5966 |
| Proficient Air Heating & Ac Frederick 21701 | (301) 662-5070 |
| S & J Heating & Air Cond 4520 Mack Ave, Frederick 21703 | (301) 748-7951 |
| Sam Poole Heating & Cooling 1560 Tilco Dr # F, Frederick 21704 | (301) 428-0781 |
| W A Tolbard Refrigeration 1782 N Market St, Frederick 21701 | (301) 662-2515 |
| W M Brown Inc 4101 Harvard Pl # B, Frederick 21703 | (301) 874-1840 |
| W M Brown Inc 8118 Claiborne Dr, Frederick 21702 | (301) 694-8848 |
| Wyant Heating & Air Inc 1573 Tilco Dr, Frederick 21704 | (301) 620-1770 |
| Young Electric 6930 Fish Hatchery Rd, Frederick 21702 | (301) 898-0728 |