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Fall Specials!

Service diagnostic call special of $80 (normally $120) from now till December 31, 2023.

Cannot be combined with other offers

Need filters, humidifier pads or humidifier canisters for your upcoming maintenance visit? – CLICK HERE

Don’t Panic, Call Mannix!

Mannix Heating & Cooling is a family owned and operated HVAC company serving Gaithersburg, MD, Chantilly, VA and their surrounding areas since 2010, and serving St. Petersburg, FL and the surrounding areas since 2024.

Ask us about how to qualify for a $2,000 tax credit for a heat pump – LEARN MORE

HVAC Specials- Click Here!

We’ll Be Here When You Need Us

Chantilly, VA

(703) 777-9211

Gaithersburg, MD

(301) 260-6000

St. Petersburg, FL

(727) 999-7002

HVAC Services you can rely on.


No matter what type of heating system you rely on, whether at the beginning or toward the end of it’s service life, the key to safe, efficient, and reliable performance is regular, professional maintenance.

Heating service


Anything less than perfect performance from your cooling system is unacceptable. Even minor issues impact your everyday life, causing discomfort, aggravation, and higher running costs.

AC Service

Air Quality

Integrity of indoor air quality impacts your health, how well you sleep, efficiency of HVAC components, productivity, and furnishings. Mannix Heating & Cooling will find the right solution for you.

Air quality

Your Local HVAC Repair Service Montgomery Village, Gaithersburg, Rockville and Olney, MD as well as Chantilly, Centreville, and Dulles, VAAC Repair, Heating Repair, HVAC Service, Air Conditioning Installation & Furnace Service

Mannix Heating & Cooling meets higher standards of quality.  For heating, cooling and electrical needs in Gaithersburg, MD, Chantilly, VA and their surrounding areas and the surrounding areas, we offer home and business owners a comprehensive range of services, including installation, upgrades, seasonal maintenance, and prompt repair. We have earned distinction as a Carrier Factory Authorized Dealer, maintaining rigid criteria for customer satisfaction, technical expertise, and ethical business practices.

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Top Quality HVAC, Electrical, and Water Heating Services across Montgomery Village, Gaithersburg, Rockville and Olney, MD as well as Chantilly, Centreville, and Dulles, VA

At Mannix Heating & Cooling, we handle residential and commercial projects, achieving ideal comfort within your indoor space.  By putting greater access and tighter control at your fingertips, we give you the power to tailor your environment to your exact preferences. Combining dedicated professionalism with exceptional products, Mannix Heating & Cooling delivers results that fulfill your ongoing satisfaction.

Call Mannix Heating & Cooling to ensure your home comfort with expert heating and cooling system repairs, installations, and maintenance!

Mannix Heating & Cooling services all major manufacturers and models of heating and cooling equipment, as well as standby generators.  We recommend and install Carrier HVAC systems and Honeywell backup generators, offering home and business owners premier solutions that meet our exacting demands for value.  By specializing in the most technologically advanced options on the market, we satisfy even difficult challenges with solutions that stand up to time and weather, day in and day out, year after year.  At Mannix Heating & Cooling we implement products and strategies that exceed expectations, improve your indoor environment, and make life that much better.  Throughout Montgomery Village, Gaithersburg, Rockville and Olney, MD as well as Chantilly, Centreville, and Dulles, VA, the team from Mannix Heating & Cooling is known as … Just Honest, Fair, Good People.

Owner, Jerry Mannix

The Proud Recipient of Federated Insurance’s ACCA Super S.T.A.R. Award!

Air Conditioning Installation, Air Conditioner Service, AC Service, Air Conditioner Repair & AC Repair Saint Petersburg, FL, Chantilly, VA, Gaithersburg, MD, Clearwater, FL, Dulles, VA & Rockville, MD

HVAC Company Saint Petersburg, FL | HVAC Installation Chantilly, VA | AC Contractor Gaithersburg, MD

AC CompanyHVAC ContractorAC ContractorHVAC Company ∴ Clearwater, FL ∴ Largo, FL ∴ Potomac, MD

Mannix Rewards

Receive a $100 Mannix Heating & Cooling Visa® Prepaid Card

Customer Referral Program

Customer Reviews

Shondra J ones

They were lifesavers!!! My furnace went out and after three days of dealing with the home warranty company and the unscrupulous vendor they sent to my home, I called Mannix. The service technician was friendly, efficient but most of all honest. He found the problem after twenty minutes, saving me thousands in unnecessary replacement costs. It is refreshing to know that honest people still exist.

Lynne Wilson

I contacted Mannix from a referral of a friend who has benefitted from the excellent service this company provides. I found out a couple I know in Vienna had their heat pump stop working a few months ago and needed to be replaced. I called up the Mannix office later in the day on Monday 11/30/20 and provided information needed. I had a proposal in my email the next morning 12-01-20. This will enable me to discuss with my friends how they wish to proceed with fair financing options available too. This is EXCELLENT customer service and I would like Mr. Mannix to know that Sarah is an amazing professional face for his company. I plan to become a customer of theirs by signing up for the annual maintenance plan which is very reasonable priced. Sincerely, Lynne Wilson

Philip Slingerland

Been a happy Mannix customer for a few years now, but recently had them replace our aging HVAC system. The whole process was very painless, from Eric helping us decide which system was right for our home, to the efficient and professional installation by Billy and Matt. I am very pleased with the new system and very impressed with the level of service, communication, and detailed information I received from everyone involved. Highly recommend!


Before dealing with Mannix I used two very well-known and “reputable” HVAC companies who did nothing but rip us off over the years. I was frustrated and found Mannix Heating & Cooling about 10 years ago. They installed a new HVAC system in my old home, and installed a water heater and various other items in my new home. They also have been doing yearly maintenance for years. Their employees are the most honest, reliable, and knowledgeable individuals in this industry. We recently had an issue with our HVAC system and they came out within a few hours on an emergency call. The technician was prompt, kind, professional, and very fair. He figured out what was wrong with our system quickly and remedied it immediately. Do not hesitate to call them if you need anything–you won’t regret it!

Wendy Collins

Mannix has always been professional from service calls to repairs and replacements. The technicians are always polite and knowledgeable. They consistently exceed our expectations.

Gary Hendricks

Mannix proved very responsive in fixing my A/C system. The tech, Erick, was very professional by taking the time showing and explaining to me the system problem prior to taking action replacing the coil. Ashleigh, customer service, was excellent in addressing and following through on concerns in order to achieve total customer satisfaction.

M. Reyzer

My 24-year-old heat pump finally decided to stop working. I sent a request for a replacement estimate late one night through the Mannix website and received a phone call early the very next morning to set up an appointment. Eric Holzworth stopped by my house the next day to go over my options. He was wonderful and so easy to work with and answered every question I had. He definitely listened to me and my concerns did not push me into purchasing a high-end system which I didn’t need. The technicians arrived at 8am and were finished with the entire installation by 1pm. They were very courteous and left my house in pristine condition. I HIGHLY recommend Mannix! They always returned my calls and emails right away, and Eric made sure I received all of my equipment on time–even with Carrier factory delays/limited supplies due to COVID. So glad I chose Mannix. I love my brand new Carrier system and my cold house during these hot and humid days.


We were in desperate need of a fix on our AC system during the July heatwave. The issue arose on a Saturday. Mannix came to the rescue in short order, fixed it, and at a reasonable price.

Silvio G was the technician, and he was GREAT.

We would definitely use Mannix again!

Patricia Ryan

I have been using Mannix for years. They have replaced my HVAC system and I have them do maintenance twice a year. The past couple of visits have been done by Ramiro. He is professional, polite, knowledgeable, and very helpful in assisting me with tips on the best ways to operate my system. Today, he installed a water safety device and taught me exactly how it works and how to reset it. I’m so impressed with him! I will continue with Mannix for years to come as I find them to be very reputable and reliable. Thank you!

Rachel Craft

I’ve been using Mannix for years and have never been disappointed. They’ve replaced my HVAC, hot water heater and installed a humidifier on my furnace. Whenever I need them, they can get me on the schedule in a timely manner. All the personnel are great and I trust Jerry and his team with their recommendations and the work they do. Would highly recommend.

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