Residential heating & air conditioning contractor in Merrimack, NH
GSMS is proud to serve the residents of Merrimack, NH, with top-quality heating and air conditioning services. As a family-owned business with over three decades of experience, we are dedicated to providing reliable, efficient, and professional HVAC solutions tailored to your home’s specific needs.
GSMS is proud to be your Merrimack Lennox Premier Dealer!
Whether it's an emergency repair, a total replacement, or routine maintenance, we have you covered. Call 603-424-8258 today!
Air conditioner repair & replacement
- AC Repair: We handle cooling problems big and small with speed and attention to detail. Our technicians are trained to troubleshoot and fix refrigerant leaks, thermostat issues, electrical failures, compressor problems, and more.
- AC Replacement and New Installation: Time for a cooling upgrade? We offer high-quality systems from Lennox and other leading manufacturers to improve efficiency, enhance comfort, and reduce homeowners' carbon footprint.
Furnace repair & replacement
- Furnace Repair: Dealing with a broken furnace? GSMS technicians work efficiently to track down even the smallest of problems and repair them in no time. Common furnace issues we repair include pilot light problems, thermostat malfunctions, ignition system failures, and blower motor problems.
- Furnace Replacement and New Installation: Upgrading your furnace takes your home's winter warmth to the next level. Our energy-efficient systems provide consistent heating, reduced maintenance, and enhanced safety.
Boiler repair & replacement
- Boiler Repair: Common boiler problems with pressure, thermostats, pilot lights, and leaks, can be a homeowner's nightmare. GSMS technicians work quickly to repair your boiler and get your home warm again in no time.
- Boiler Replacement and New Installation: Whether you are considering switching to a boiler system or it's time to replace your existing system, GSMS is here to help you increase efficiency and reliability with advanced units.
Mini-split heat pumps
GSMS provides comprehensive services for mini-split heat pumps, including installation, maintenance, and repair. We specialize in Mitsubishi ductless units, known for their reliability and efficiency. Whether you’re looking to install a new system or need service for your existing mini-split heat pump, our technicians are here to ensure optimal performance and comfort in your home.
Ductwork cleaning & installation
- Duct Cleaning: Regular duct cleaning helps improve air quality, increase HVAC efficiency, extend system lifespan, and eliminate odors. We use an advanced Roto Brush system to reach every corner of the ductwork and keep your home clean and comfortable.
- Duct Installation: Proper ductwork installation is crucial for airflow, efficiency, comfort, and durability. Choosing GSMS to install your ductwork gives you peace of mind that your new air ducts are safe and secure.
Merrimack plumbing services
GSMS is proud to provide comprehensive plumbing services to homeowners in Merrimack, NH. Our experienced and professional team is dedicated to delivering reliable and efficient plumbing solutions tailored to your specific needs.
Quick plumbing repairs, complete installations, and preventative maintenance are what we do best. Call 603-424-8258 today!
Water heater plumbers
- Repair: Our skilled technicians can quickly diagnose and repair common water heater issues, including inconsistent temperature, leaks, and strange noises.
- Replacement: When it’s time to replace your old water heater, we offer professional installation of both traditional tank models and modern tankless systems.
- Maintenance: Regular maintenance is essential to keep your water heater running efficiently. Our comprehensive maintenance services include inspections, cleaning, and tune-ups.
- Tankless Water Heaters: Upgrade to a tankless water heater for endless hot water, improved energy efficiency, and space savings. We provide expert installation and maintenance for these advanced systems.
Kitchen plumber services
- Faucets: From repairing leaks to installing new faucets, we ensure your kitchen faucets are functioning perfectly.
- Sinks: We handle all sink-related services, including installation, repair, and replacement, to keep your kitchen fully operational.
- Garbage Disposals: Our team can install and repair garbage disposals, ensuring efficient waste management in your kitchen.
- Dishwashers: We provide installation and repair services for dishwashers, making sure they are properly connected and running smoothly.
- Water Lines: Whether you need new water lines installed or existing ones repaired, GSMS ensures a reliable water supply for your kitchen appliances.
Bathroom plumber services
- Toilets: From fixing leaks and unclogging blockages to installing new toilets, we provide comprehensive toilet services.
- Showers and Tubs: We offer repair, replacement, and installation services for showers and bathtubs to keep your bathroom comfortable and functional.
- Sinks and Vanity Plumbing: Our team can install and repair bathroom sinks and vanity plumbing, ensuring everything operates seamlessly.
- Pipe Repairs and Replacements: Whether it’s a minor leak or a major pipe replacement, GSMS provides expert pipe repair and replacement services to prevent water damage and maintain optimal plumbing performance.
Why choose GSMS in Merrimack?
- Proven Track Record: With a long-standing presence in Merrimack, NH, GSMS has earned the trust of countless homeowners. Our dedication to excellence and reliability has made us a preferred choice for HVAC and plumbing services in the community. We are proud of our reputation and continually strive to uphold the high standards that have set us apart.
- Local Expertise and Dedication: GSMS has been serving the Merrimack, NH community for over three decades, building a reputation for excellence and reliability. As a family-owned business, we are deeply committed to our local community and understand the unique needs of Merrimack homeowners. Our local expertise allows us to provide tailored solutions that keep your home comfortable and efficient year-round.
- Comprehensive Range of Services: From HVAC to plumbing, GSMS offers a full spectrum of services to meet all your home comfort needs. Our skilled technicians are trained in the latest technologies and techniques, ensuring top-quality service for every job. Whether you need a quick repair, a new installation, or regular maintenance, we have the expertise to get the job done right.
Become a GSMS Home Club member today
Join the GSMS Home Club and enjoy exclusive benefits designed to keep your home’s HVAC and plumbing systems in top condition. Membership perks include:
- Priority Service
- No Diagnostic Fees
- 10% Off Repairs
- Home ID and Smart Monitoring
- Monthly Credits Towards Major Purchases
- Regular Maintenance
- Labor Warranty Upgrades
Call today for great service in Merrimack.
Trust the experts at GSMS to provide reliable, efficient, and top-quality services tailored to your needs. Whether you need a quick repair, a new installation, or regular maintenance, our dedicated team is here to ensure your Merrimack home remains comfortable and functional year-round.
Call 603-424-8258 today or fill out our online contact form to book an appointment!
Recent Jobs and Reviews in Merrimack, NH
Customers say: The reviews exhibit a positive sentiment, with a majority of customers expressing satisfaction with the services provided by GSMS. The recurring themes include praise for the quality of work, professionalism, responsiveness, and excellent customer service. Customers also appreciate the technicians' expertise, friendliness, and the overall positive experience they had with GSMS. Negative reviews are minimal and focus on specific issues or misunderstandings, which were promptly addressed by GSMS. Overall, the reviews suggest that GSMS is a reliable and trustworthy company that delivers high-quality services to its customers.
Our Local Reviews by City
- Amherst, NH (5)
- Atkinson, NH (1)
- Auburn, NH (1)
- Barrington, NH (13)
- Bedford, NH (18)
- Candia, NH (2)
- Chester, NH (1)
- Concord, NH (5)
- Deerfield, NH (1)
- Derry, NH (2)
- Dover, NH (1)
- Durham, NH (1)
- Epping, NH (1)
- Gilford, NH (1)
- Gilmanton, NH (1)
- Goffstown, NH (4)
- Greenland, NH (1)
- Henniker, NH (3)
- Hillsborough, NH (1)
- Hollis, NH (11)
- Hooksett, NH (9)
- Hudson, NH (5)
- Lee, NH (1)
- Litchfield, NH (1)
- Londonderry, NH (11)
- Manchester, NH (35)
- Merrimack, NH (23)
- Milford, NH (5)
- Moultonborough, NH (1)
- Nashua, NH (28)
- New Boston, NH (3)
- Newbury, NH (1)
- Northfield, NH (1)
- Northwood, NH (1)
- Pembroke, NH (1)
- Raymond, NH (1)
- Rochester, NH (2)
- Salem, NH (3)
- Sandown, NH (2)
- Stratham, NH (2)
- Tilton, NH (1)
- Weare, NH (5)
- Windham, NH (6)
Job Locations and Reviews
Five Stars

Replaced bath rm faucet
Couldn’t have asked for a better installation of dishwasher/toilets. Mark was very personable and professional. Arrived on time and finished on time. Excellent experience

Install toilets and diswasher

Install amtrol diatrol

AC preventive maintenance today. I flushed the condensate drain with cleaner and ensured it was not clogged. Please see mainteance form for more detailed results. I found a hole in the heat exchanger, I shut the gas off. The furnace is not to be operated until the heat exchnager is replaced.
Very professional in all respects.

Installation of a three-zone mini-split system to provide the home with conditioned air and supplemental heating. The outdoor unit will be placed on the back side of the home as discussed. First Floor: One indoor unit will be installed on the first floor, positioned above the fireplace. While we will aim to center the unit over the mantle, refrigerant lines will exit the home on the left side to avoid the chimney. Second Floor: Two indoor units will provide coverage for the second floor. One unit will be installed in the master bedroom. Refrigerant lines for this unit will run into the attic and then to the outdoor unit on the other side of the home. The condensate line will drain onto the garage roof and into the gutter system. The second unit will be installed in the guest bedroom. Refrigerant lines for this unit will also run into the attic to maintain a clean exterior aesthetic and avoid running lines over the chimney. The condensate line will drain down the exterior of the hom
I have been working with GSMS for close to 8 or 9 years now. Had them replace my entire HVAC system and on demand hot water heater installed. Today just had my annual service for my HVAC unit done. They really do great work and all their technicians are very skilled and knowledgeable. I highly recommend them for anybody for your HVAC and plumbing needs!

AC mainteance went great today. Please see form for details! Thank you

GSMS Homeclub maintenance. Everything went great! Please see the attached form for detailed results. Thank you!

Homeclub AC maintenance today. Everything looks great! Please see the attached maintenance form for detailed maintenance results. I took down info about the banging caused when the irrigation turns on. I will let the office know and they will talk to Mark about it. Thank you!

REPLACE OUTSIDE FAUCET AND RELOCATE SHUT OFF VALVE

A three-zone system will be installed to provide cooling and supplemental heating to the master bedroom, Emma's current bedroom, and the future basement bedroom. The outdoor unit will be placed on the gable end where currently raised garden beds are located. They will be relocated by the homeowner.

Pm on a/c unit washed condensing unit check charge and controls.Check indoor filter ok

Everything went great with your AC maintenance. There are no necessary repairs that were found. I also installed the outside hot and cold hose bib! Thank you!

AC maintenance on garage system and home system. The maintenance went great! I only had to replace the capacitor on the furnace in the garage.

Maintenance on Laars Mascot II boiler. Everything went great. New ignitor, cleaned flame rod, remove burner, clean burners, clean heat exchanger, remove condensation trap and thoroughly clean. Check combustion results. I had to adjust high and low fire to get the required 9% CO2. Thank you!

Replace variable speed motor.
Great overall service, always has done a great job for me!

Install lav sink

Check dishwasher for leak
Mark and his entire team do a wonderful job. Show up on time and treat your home with respect. Recommend them without reservations.

Replaced kitchen basket strainer

I started off with cleaning the indoor coil with Dawn soap and water. I brushed and flushed the condensate trap with cleaner. I checked electrical connections and everything looked good. I went outside and I washed the outdoor units coil with water and coil cleaner. I checked the capacitor and that was in spec. Electrical connection looked good as well. The client replaces there own filters. Lastly, I ran the unit in heating mode and the pressures looked good.
Outstanding service

Comuster has to order new sink
Granite State Mechanical Services has been serving our home for 30 years. They show up on time, complete the work and treat your home with respect. I recommend them to all our neighbors.

Started off with washing the outdoor units coil with coil cleaner and water. I checked all electrical connections and everything looked good. Next, I replaced the air filter that the client supplied. The client already turned off the humidifier. I checked some wiring connections, everything looked good. I washed the indoor evaporator coil with soap and water. I brushed and flushed the trap in the condensate pump with cleaner. Lastly, I ran the system and everything looked great.

I started off with washing the outdoor units coil with water and coil cleaner. I found a dead mouse inside of the unit, but it didn’t chew any wires. All the electrical connections and the capacitor were all good. Next I went inside and I replaced the air filter on the air handler. The client supplies her own filters. I washed the indoor coil with Dawn soap. I flushed the trap as well. I checked the capacitor and electrical connections and everything looked great. Lastly I ran the system and tested the operating pressures and everything was running good.
Excellent service
We count ourselves lucky for customers like you and look forward to working with you again in the future!

Plumbing installations. I replaced a dishwasher shut off and installed plumbing for a new sink.

I had the client operste the heat to put a load on the home. I then turned on the AC and manipulated outdoor unit pressures by restricting condenser air flow. The pressures were close to what the manufacturer requires. The subcooling is off but it is 50 degrees and wet outside so I cannot go off on this reading. The Delta T inside was well within manufacturer specifications when referencing the dry and wet bulb return air temperatures. I would like to come back when it is at least 70-75 degrees outside in order to complete the system commissioning. Thank you!

Replace toilet shut off valve
Great service as always. Turned out grandchildren tired off the emergency gas shutoff when they were playing some game
Thank you for taking the time to leave such a positive review! We're glad to hear you had a great experience with us.
Your GSMS team set the standard in your business area for integrity, honesty, performance and quality. They are courteous and we trust them being in our home.
High recommend. Called GSMS because of a leak. Jack arrive and within minutes diagnosed the problem - and fixed it. Thank you
Always a great experience!
Very polite technicians. Worked diligently all day. Cleaned up everything before leaving.
GSMS is a great trustworthy company to work with. All the staff members and service technicians are always great and very professional!
Excellent service
Mark as always did a great job
We are so grateful for your kind words.
Very professional and courteous. Arrived at the time when he said he would and took the time to what might be causing my leaking issue
Thank you for the wonderful review and for taking the time to share your feedback.
a pleasure to work with
We thank you for sharing your positive experience. It made our day.
Mark and the team always do a great job solving our issues in a timely manner!
Thank you so much for taking the time to leave us this amazing review!
Being new to our house, it was nice to get a rundown on how all of the heating systems work. It didn’t hurt that our technician grew up in this house! Both of the guys were really nice and they seemed to do a very thorough job. They answered all our questions.
We count ourselves lucky for customers like you and look forward to working with you again in the future!
Great job as always
Excellent , professional service