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Our Service Area

Proudly Serving New Hampshire Homeowners

At GSMS, we are proud to serve New Hampshire with our comprehensive range of HVAC and plumbing services.

As a family-owned business with 35+ years of experience, we have built a reputation for excellence, reliability, and outstanding customer care. Our skilled technicians are dedicated to providing top-quality repairs, installations, and maintenance tailored to meet the unique needs of New Hampshire homeowners.

Explore our service area below, read reviews in your city, and see why homeowners across New Hampshire trust GSMS for their HVAC and plumbing needs.

Contact us online today or call 603-424-8258 to schedule your service and experience the GSMS difference.

Recent Jobs and Reviews

Rated 5.0 out of 5 stars based on 346 customer reviews

Customers say: The recent reviews exhibit a predominantly positive sentiment, with recurring themes of satisfaction, professionalism, and expertise. Customers express gratitude, recommend the company, and acknowledge the quality of the work performed. Positive reviews frequently mention friendly and knowledgeable technicians, timely responses, and efficient service. Negative reviews are minimal and do not represent a clear, recurring trend. Overall, the reviews suggest a positive experience with the company, with many customers expressing satisfaction with their HVAC and plumbing needs.

Job Locations and Reviews

Review
A+
Scott - Nashua, NH 03064
Adam P.
Adam P. Checked in
Intermittent problem with furnace. Checked in incoming gas pressure at 5.9 inches, manifold pressure was 3.5 inches. Check the pressure switch rollout switch. Look for loose wire connections check air filter. Check condensate tube turn furnace on and off multiple times was not able to replicate problem.
Merrimack, NH 03054
Install new venting for Lennox furance. We will need to cut an access panel in the garage ceiling to confirm the joist bay is open for us to install a new vent.

Venting exposed in the garage will be insulated with 1/2" wall insulation jacket. We will seal garage wall to interior wall penetration points with fire-rated sealant foam. 

Client understands the new venting for the furnace will suspend below the ceiling, being a few inches lower than the existing sections of drywall in the garage that are boxed in.

The client is responsible for the carpentry work for patching.
Install new venting for Lennox furance. We will need to cut an access panel in the garage ceiling to confirm the joist bay is open for us to install a new vent.

Venting exposed in the garage will be insulated with 1/2" wall insulation jacket. We will seal garage wall to interior wall penetration points with fire-rated sealant foam. 

Client understands the new venting for the furnace will suspend below the ceiling, being a few inches lower than the existing sections of drywall in the garage that are boxed in.

The client is responsible for the carpentry work for patching.
Jack D.
Jack D. Checked in
Install new venting for Lennox furance. We will need to cut an access panel in the garage ceiling to confirm the joist bay is open for us to install a new vent. Venting exposed in the garage will be insulated with 1/2" wall insulation jacket. We will seal garage wall to interior wall penetration points with fire-rated sealant foam. Client understands the new venting for the furnace will suspend below the ceiling, being a few inches lower than the existing sections of drywall in the garage that are boxed in. The client is responsible for the carpentry work for patching.
Raymond, NH 03077
Mark D.
Mark D. Checked in
<p>Conversion of the existing 5' bathtub unit with a new walk-in shower unit, complete with new shower fixtures. The client will provide the shower fixtures, while GSMS will provide the shower unit as listed below.</p><p>An estimated price is included to relocate the laundry appliances to the opposite wall of the bathroom. We will install new hot and cold water supply lines and drainage for the washing machine, with this estimate based on the ability to tap into existing plumbing. This does <strong>not</strong> include the venting for the dryer.</p><p>Additionally, we will disconnect and install a new dishwasher in the kitchen, with the dishwasher unit to be provided by the client.</p>
Nashua, NH 03064
Adam P.
Adam P. Checked in
No heat. Oil pressure no spark. Went through wires on primary checked connections. Put back together,
Merrimack, NH 03054
Completed the boiler maintenance today. I started off with checking all the wiring connections and everything looked good. I pulled out the burner tubes and I cleaned them. I cleaned out the burner box as well. I checked all the boiler accessories and they were newer, everything looked good. I checked incoming and outgoing gas pressures and everything was according to manufacturer's specifications. I had to adjust incoming gas pressure. Lastly I ran the boiler and performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and everything was running great. I labeled some emergency shut offs. I noticed that the indirect water tank is starting to leak for the bottom. The boiler and the water tank are from 2005. We will send over an estimate to replace the indirect water tank.
Completed the boiler maintenance today. I started off with checking all the wiring connections and everything looked good. I pulled out the burner tubes and I cleaned them. I cleaned out the burner box as well. I checked all the boiler accessories and they were newer, everything looked good. I checked incoming and outgoing gas pressures and everything was according to manufacturer's specifications. I had to adjust incoming gas pressure. Lastly I ran the boiler and performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and everything was running great. I labeled some emergency shut offs. I noticed that the indirect water tank is starting to leak for the bottom. The boiler and the water tank are from 2005. We will send over an estimate to replace the indirect water tank.
Qwentin G.
Qwentin G. Checked in
Completed the boiler maintenance today. I started off with checking all the wiring connections and everything looked good. I pulled out the burner tubes and I cleaned them. I cleaned out the burner box as well. I checked all the boiler accessories and they were newer, everything looked good. I checked incoming and outgoing gas pressures and everything was according to manufacturer's specifications. I had to adjust incoming gas pressure. Lastly I ran the boiler and performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and everything was running great. I labeled some emergency shut offs. I noticed that the indirect water tank is starting to leak for the bottom. The boiler and the water tank are from 2005. We will send over an estimate to replace the indirect water tank.
Epping, NH 03042
Scope of Work:
Replacement of the existing oil-fired boiler with a new, reliable Cast Iron Oil Boiler featuring an internal tankless coil for domestic hot water.

Hydronic Piping Upgrade (GSMS Standard):

Circulator Conversion: We will remove the existing system of zone valves and a single pump. The system will be repiped to feature dedicated circulator pumps for each of the two heating zones. This upgrade provides better flow, redundancy, and reliability.

Near-Boiler Piping: Installation includes our complete piping package: new isolation flanges, high-performance air eliminator, expansion tank, automatic feed valve, and backflow preventer.

Domestic Hot Water:

The new boiler will include an internal Tankless Coil to generate domestic hot water, maintaining the same style of operation as the current system.

Venting & burner:

A new high-efficiency oil burner will be set up and calibrated.

The boiler will be connected to the existing chimney flue.
Scope of Work:
Replacement of the existing oil-fired boiler with a new, reliable Cast Iron Oil Boiler featuring an internal tankless coil for domestic hot water.

Hydronic Piping Upgrade (GSMS Standard):

Circulator Conversion: We will remove the existing system of zone valves and a single pump. The system will be repiped to feature dedicated circulator pumps for each of the two heating zones. This upgrade provides better flow, redundancy, and reliability.

Near-Boiler Piping: Installation includes our complete piping package: new isolation flanges, high-performance air eliminator, expansion tank, automatic feed valve, and backflow preventer.

Domestic Hot Water:

The new boiler will include an internal Tankless Coil to generate domestic hot water, maintaining the same style of operation as the current system.

Venting & burner:

A new high-efficiency oil burner will be set up and calibrated.

The boiler will be connected to the existing chimney flue.
Adam P.
Adam P. Checked in
Scope of Work: Replacement of the existing oil-fired boiler with a new, reliable Cast Iron Oil Boiler featuring an internal tankless coil for domestic hot water. Hydronic Piping Upgrade (GSMS Standard): Circulator Conversion: We will remove the existing system of zone valves and a single pump. The system will be repiped to feature dedicated circulator pumps for each of the two heating zones. This upgrade provides better flow, redundancy, and reliability. Near-Boiler Piping: Installation includes our complete piping package: new isolation flanges, high-performance air eliminator, expansion tank, automatic feed valve, and backflow preventer. Domestic Hot Water: The new boiler will include an internal Tankless Coil to generate domestic hot water, maintaining the same style of operation as the current system. Venting & burner: A new high-efficiency oil burner will be set up and calibrated. The boiler will be connected to the existing chimney flue.
Merrimack, NH 03054
Preventative maintenance completed on your Ideal combi boiler. Everything went great. Please see the maintenance form for details of todays servicing. I was able to recreate the noise that you are experiencing. I sent a video to our manufacturer representative. We will contact you with a solution. Thank you!
Preventative maintenance completed on your Ideal combi boiler. Everything went great. Please see the maintenance form for details of todays servicing. I was able to recreate the noise that you are experiencing. I sent a video to our manufacturer representative. We will contact you with a solution. Thank you!
Jack D.
Jack D. Checked in
Preventative maintenance completed on your Ideal combi boiler. Everything went great. Please see the maintenance form for details of todays servicing. I was able to recreate the noise that you are experiencing. I sent a video to our manufacturer representative. We will contact you with a solution. Thank you!
Merrimack, NH 03054
Qwentin G.
Qwentin G. Checked in
The steam boilers automatic water feed seems to be acting up. We will order the new one today. We would also like to get access to all the apartments that the steam boiler heats. Regarding apartment #4 for not being heated I'm pretty sure that the pipes froze going to that apartment. If this problem continues to exist we will have to take a look at it further. We will be in touch with when we can come back out to replace the part.
Milford, NH 03055
Jack D.
Jack D. Checked in
Toilet repair and water test.
Londonderry, NH 03053
Completed the house plumbing inspection today. I checked all the drains and fixtures and everything looked great. I labeled a bunch of emergency shut offs and I showed the client where they were. I completed the rinnai tankless water heater maintenance. I ran cleaner for 35 minutes. After I flushed 10 gallons of water through it. I cleaned the water inlet screen and somehow wood got inside of it. I checked incoming gas pressure and that was according to manufacturer's specifications. I cleaned the electrode and flame sensors. Lastly I ran the unit and it was running great!
Completed the house plumbing inspection today. I checked all the drains and fixtures and everything looked great. I labeled a bunch of emergency shut offs and I showed the client where they were. I completed the rinnai tankless water heater maintenance. I ran cleaner for 35 minutes. After I flushed 10 gallons of water through it. I cleaned the water inlet screen and somehow wood got inside of it. I checked incoming gas pressure and that was according to manufacturer's specifications. I cleaned the electrode and flame sensors. Lastly I ran the unit and it was running great!
Qwentin G.
Qwentin G. Checked in
Completed the house plumbing inspection today. I checked all the drains and fixtures and everything looked great. I labeled a bunch of emergency shut offs and I showed the client where they were. I completed the rinnai tankless water heater maintenance. I ran cleaner for 35 minutes. After I flushed 10 gallons of water through it. I cleaned the water inlet screen and somehow wood got inside of it. I checked incoming gas pressure and that was according to manufacturer's specifications. I cleaned the electrode and flame sensors. Lastly I ran the unit and it was running great!
Hudson, NH 03051
Review
Always amazing service, every team member at GSMS has always been great and performed exceptionally great service.
Scott - Merrimack, NH 03054
Review
Excellent Service
Guimont - Londonderry, NH 03053
Review
Very nice and personable person. Explained everything to me in a way I could understand
Dave - Hooksett, NH 03106
Review
I never thought I’d meet anyone as cool nice and kind as Mark but Jack was amazing. He took on the dirty job.. No problem He was super communicative and explained everything. I’m really grateful to have Granite State Mechanical on speed dial.
Kathleen - Nashua, NH 03064
Review
Jack was once again on time, diagnosed the problem quickly and fixed it. All GSMS staff are courteous and extremely professional. I wouldn’t go with anyone else.
Ronald - Merrimack, NH 03054
Review
Excellent work
Turning - Manchester, NH 03103
Review
Great service!
Colleen - Manchester, NH 03104
Review
Working with GSMS was a fantastic experience. There was attention to detail from the estimate to the clean up at the end of the project. Especially during the planning process, Zak helped me evaluate different options, quickly readjusted as I changed my mind... without ANY pressure! Superior, prompt communication during the whole (and post) process.
Ethel - Londonderry, NH 03053
Review
No heat emergency situation handled immediately on a Sunday evening. Great service!
Paul - Amherst, NH 03031
Review
Love dealing with this company. Their techs are always prompt, efficient and courteous. We've been happy to be their customer since 2010.
Skip Sagris - Bow, NH 03304
Response from GSMS Air•Heating•Plumbing:

Thank you so much for the kind words and for being part of the GSMS family since 2010! It means the world to us to have earned your trust over the years. I’m proud of our team for continuing to deliver the kind of service that keeps clients like you coming back. We truly appreciate your loyalty and support. – Zak D., Second-Generation Owner

Review
Qwentin was on time, very friendly and professional. He was able to identify the issue, communicate it effectively, and then fix it. Highly recommend.
Phil Cutler - Bedford, NH 03110
Response from GSMS Air•Heating•Plumbing:

Thank you so much for the kind words and for trusting GSMS to take care of your home. Qwentin is a rising star on our team, and it means a lot to hear that his professionalism and communication made a strong impression. As a local, family-run business, we’re grateful for your recommendation and honored to have earned your trust. – Zak D., Second-Generation Owner

Review
Great water heater service. On time and professional l He gave me some helpful tips on other water related issues. Highly recommend GSMS.
Katherine Turner - Exeter, NH 03833
Response from GSMS Air•Heating•Plumbing:

Thank you for the great review! I’m glad to hear our Specialist was able to get your water heater squared away and offer some extra tips while he was there. We always aim to go beyond just the repair, and I really appreciate you taking the time to share your experience. Thanks for choosing GSMS — it means a lot to our family and our team. – Zak D., Second-Generation Owner

Review
David DiNardo - Bedford, NH 03110
Response from GSMS Air•Heating•Plumbing:

Thank you for the 5 stars, David! We really appreciate you choosing GSMS and supporting our family-run team. If there’s ever anything more we can do for you, don’t hesitate to reach out. – Zak D., Second-Generation Owner

Review
claire lafond - Merrimack, NH 03054
Response from GSMS Air•Heating•Plumbing:

Thank you so much for the 5 stars, Claire! We’re grateful for your support and truly appreciate you choosing GSMS. It means a lot to our family and our entire team. – Zak D., Second-Generation Owner

Review
Great work, fair prices.
Tom Grasse - Manchester, NH 03104
Response from GSMS Air•Heating•Plumbing:

We thank you for sharing your positive experience. It made our day.

Review
top notch service, always professional. would recommend to anyone needing HVAC service, repair or install.
Ben Bouchard - Nashua, NH 03062
Response from GSMS Air•Heating•Plumbing:

It was a pleasure serving you and your family. Thank you for sharing your kind words with us. It means the world to us and to our entire team!

Review
Had an issue with our heat pump. Reached out for assistance and they had someone on site that afternoon. Problem was resolved quickly. Super friendly service. The tech was exceptionally friendly and an excellent communicator. Highly recommend
Mark Cooke - Greenland, NH 03840
Response from GSMS Air•Heating•Plumbing:

It was a pleasure serving you and your family. Thank you for sharing your kind words with us. It means the world to us and to our entire team!

Review
Adam, Quin and Mark did a wonderful job installing my replacement oil boiler and oil tank. I have trusted GSM for 3 installs at my house because of their professionalism, workmanship, honesty, transparency and integrity for how they conduct their family business. Everyone who has worked at my house has always been informative, on time and respectful. I would recommend GSM to anyone who needs to have major plumbing or heating/cooling done in their home. Gina in customer service is the best at relaying information and gets back to you in a timely fashion. Zak is wonderful to work with and the entire team at GSM treats you with kindness. Thank you again for another wonderful experience because when it comes to your home it is one of the largest investments you will make in your life, and I trust GSM to be there for me in the future.
Kimberly Cichon - Newmarket, NH 03857
Response from GSMS Air•Heating•Plumbing:

We thank you for sharing your positive experience. It made our day.

Review
As usual, Jack's work is stellar.
Bob Bedrosian - Merrimack, NH 03054
Response from GSMS Air•Heating•Plumbing:

We are so glad to hear that you had a good experience.

Trusted Quality & Service