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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 333 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

Today I completed a maintenance on your Viessmann oil boiler. Everything went great during the visit. I reccomend replacing the expansion tank and the mixing valve. Please see the maintenance sheet for details of todays service. Thank you!
Today I completed a maintenance on your Viessmann oil boiler. Everything went great during the visit. I reccomend replacing the expansion tank and the mixing valve. Please see the maintenance sheet for details of todays service. Thank you!
Jack D.
Jack D. Checked in
Today I completed a maintenance on your Viessmann oil boiler. Everything went great during the visit. I reccomend replacing the expansion tank and the mixing valve. Please see the maintenance sheet for details of todays service. Thank you!
Bedford, NH 03110
Qwentin G.
Qwentin G. Checked in
Replaced the Lennox carbon MERV 16 filter and UV bulb.
Merrimack, NH 03054
I completed the oil boiler maintenance today. I replaced the oil filter, the pump strainer, and the nozzle. I checked all the boiler accessories and found that the high vent has been leaking for a while. I replaced it with a new one. all other boiler accessories looked good. I ran the boiler and performed a smoke test and got zero smoke. I performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and everything was too manufacture specifications. The boiler is running great. Client mentioned that the tub drain in the bathroom hasn’t been draining properly. I removed some hair out of the drain and put a cup of Talon drain cleaner in the drain. I flushed it with hot water and the drain was working great.
I completed the oil boiler maintenance today. I replaced the oil filter, the pump strainer, and the nozzle. I checked all the boiler accessories and found that the high vent has been leaking for a while. I replaced it with a new one. all other boiler accessories looked good. I ran the boiler and performed a smoke test and got zero smoke. I performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and everything was too manufacture specifications. The boiler is running great. Client mentioned that the tub drain in the bathroom hasn’t been draining properly. I removed some hair out of the drain and put a cup of Talon drain cleaner in the drain. I flushed it with hot water and the drain was working great.
Qwentin G.
Qwentin G. Checked in
I completed the oil boiler maintenance today. I replaced the oil filter, the pump strainer, and the nozzle. I checked all the boiler accessories and found that the high vent has been leaking for a while. I replaced it with a new one. all other boiler accessories looked good. I ran the boiler and performed a smoke test and got zero smoke. I performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and everything was too manufacture specifications. The boiler is running great. Client mentioned that the tub drain in the bathroom hasn’t been draining properly. I removed some hair out of the drain and put a cup of Talon drain cleaner in the drain. I flushed it with hot water and the drain was working great.
Londonderry, NH 03053
Today I completed an oil furnace maintenance. Everything went great. I made quite a few adjustments to address the sooting issue you are experiencing. I believe the sooting was caused from an adjustment made in 2024 that looked like it was to be burning rich. Please let us know if the issue persists. Thank you.
Today I completed an oil furnace maintenance. Everything went great. I made quite a few adjustments to address the sooting issue you are experiencing. I believe the sooting was caused from an adjustment made in 2024 that looked like it was to be burning rich. Please let us know if the issue persists. Thank you.
Jack D.
Jack D. Checked in
Today I completed an oil furnace maintenance. Everything went great. I made quite a few adjustments to address the sooting issue you are experiencing. I believe the sooting was caused from an adjustment made in 2024 that looked like it was to be burning rich. Please let us know if the issue persists. Thank you.
Dover, NH 03820
Adam P.
Adam P. Checked in
Drywall
Merrimack, NH 03054
Replacement of the failed system on the second floor with a new, high-efficiency Lennox system, similar to the new system we installed at your previous home.

The new system will feature a high-efficiency variable-speed furnace and a variable-speed heat pump unit, controlled by a new S40 thermostat.

Since the existing lineset and wiring connecting the system in the attic to the outdoor unit were installed in the wall cavity and are not accessible, we will need to cut open the wall on the second floor and on the first floor to allow us to route the new refrigerant line from the attic to the basement to get to outside. We will remove and open the wall. Patching the wall and painting repairs will be the responsibility of the client.

At the outdoor unit location, we will position the new unit in the same spot. However, we would recommend re-doing the venting penetrations, as two of the existing vents currently blow exhaust directly onto the outdoor unit, which can be detrimental to perfo
Replacement of the failed system on the second floor with a new, high-efficiency Lennox system, similar to the new system we installed at your previous home.

The new system will feature a high-efficiency variable-speed furnace and a variable-speed heat pump unit, controlled by a new S40 thermostat.

Since the existing lineset and wiring connecting the system in the attic to the outdoor unit were installed in the wall cavity and are not accessible, we will need to cut open the wall on the second floor and on the first floor to allow us to route the new refrigerant line from the attic to the basement to get to outside. We will remove and open the wall. Patching the wall and painting repairs will be the responsibility of the client.

At the outdoor unit location, we will position the new unit in the same spot. However, we would recommend re-doing the venting penetrations, as two of the existing vents currently blow exhaust directly onto the outdoor unit, which can be detrimental to perfo
Adam P.
Adam P. Checked in
Replacement of the failed system on the second floor with a new, high-efficiency Lennox system, similar to the new system we installed at your previous home. The new system will feature a high-efficiency variable-speed furnace and a variable-speed heat pump unit, controlled by a new S40 thermostat. Since the existing lineset and wiring connecting the system in the attic to the outdoor unit were installed in the wall cavity and are not accessible, we will need to cut open the wall on the second floor and on the first floor to allow us to route the new refrigerant line from the attic to the basement to get to outside. We will remove and open the wall. Patching the wall and painting repairs will be the responsibility of the client. At the outdoor unit location, we will position the new unit in the same spot. However, we would recommend re-doing the venting penetrations, as two of the existing vents currently blow exhaust directly onto the outdoor unit, which can be detrimental to perfo
Bedford, NH 03110
Pm on furnace.found leak in exhaust vent and wrong size intake vent.Redid both vents.Cleaned lav stopper on second floor lav sink.
Pm on furnace.found leak in exhaust vent and wrong size intake vent.Redid both vents.Cleaned lav stopper on second floor lav sink.
Mark D.
Mark D. Checked in
Pm on furnace.found leak in exhaust vent and wrong size intake vent.Redid both vents.Cleaned lav stopper on second floor lav sink.
Merrimack, NH 03054
Jack D.
Jack D. Checked in
Replace thermostatic mixing valve. The previous one was gunked up with minerals. That part only has a one year warranty on it. I did not have that style toilet handle on my truck. We will order a replacement. I ziptied the toilet handle to the bar for now. I replaced the hair wash faucet. The new shower head did not fit to the regulator threads. I have to get an adapter fitting. We will do everything else when we come back to complete the furnace maintenance.
Manchester, NH 03103
Review
Whenever Mark is on the way, you know it’s gonna be fixed correctly. He is awesome!
Kathleen - Nashua, NH 03064
Completed the gas boiler maintenance today. I started off with checking all the electrical connections and everything looked good. I pulled the burner tubes out and I cleaned them. I vacuumed out the boiler and the boiler tube tray. I cleaned the thermocouple. Checked incoming and outgoing gas pressures and everything was according to manufacturer specifications. I performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and the boiler was running great. I noticed that the vent pipe wasn’t screwed onto the collar of the boiler so I added sheet metal screws to it. Also, the draft hood didn’t have any sheet metal screws in it so I added three. I found that both high vents are leaking water.
Completed the gas boiler maintenance today. I started off with checking all the electrical connections and everything looked good. I pulled the burner tubes out and I cleaned them. I vacuumed out the boiler and the boiler tube tray. I cleaned the thermocouple. Checked incoming and outgoing gas pressures and everything was according to manufacturer specifications. I performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and the boiler was running great. I noticed that the vent pipe wasn’t screwed onto the collar of the boiler so I added sheet metal screws to it. Also, the draft hood didn’t have any sheet metal screws in it so I added three. I found that both high vents are leaking water.
Qwentin G.
Qwentin G. Checked in
Completed the gas boiler maintenance today. I started off with checking all the electrical connections and everything looked good. I pulled the burner tubes out and I cleaned them. I vacuumed out the boiler and the boiler tube tray. I cleaned the thermocouple. Checked incoming and outgoing gas pressures and everything was according to manufacturer specifications. I performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and the boiler was running great. I noticed that the vent pipe wasn’t screwed onto the collar of the boiler so I added sheet metal screws to it. Also, the draft hood didn’t have any sheet metal screws in it so I added three. I found that both high vents are leaking water.
Manchester, NH 03104
Completed the gas boiler maintenance today. I started off with checking all the electrical connections and everything looked good. I pulled the burner tubes out and I cleaned them. I vacuumed out the boiler and the boiler tube tray. I cleaned the thermocouple. Checked incoming and outgoing gas pressures and everything was according to manufacturer specifications. I performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and the boiler was running great. I found that both high vents have been leaking water.
Completed the gas boiler maintenance today. I started off with checking all the electrical connections and everything looked good. I pulled the burner tubes out and I cleaned them. I vacuumed out the boiler and the boiler tube tray. I cleaned the thermocouple. Checked incoming and outgoing gas pressures and everything was according to manufacturer specifications. I performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and the boiler was running great. I found that both high vents have been leaking water.
Qwentin G.
Qwentin G. Checked in
Completed the gas boiler maintenance today. I started off with checking all the electrical connections and everything looked good. I pulled the burner tubes out and I cleaned them. I vacuumed out the boiler and the boiler tube tray. I cleaned the thermocouple. Checked incoming and outgoing gas pressures and everything was according to manufacturer specifications. I performed a combustion analyzer test that checks the units CO, CO2 and oxygen levels and the boiler was running great. I found that both high vents have been leaking water.
Manchester, NH 03104
Review
Mark is always very professional and clearly communicates all options. He and his team are able to accommodate us and get the job done in a timely manner. THANK YOU!
Joyce - Hudson, NH 03051
Review
Arrived on time. Work was completed timely. Cleaned up afterwards. Very pleased with the service.
Charlie - New Boston, NH 03070
Review
GSMS is a great Family owned Company to work with. I am very happy with my new Boiler heating system. Zak explained all my options and was prompt to call back with any questions I had. Adam, the lead Technician was outstanding with the installation. Gina was great coordinating the scheduling. Mark also came out for a final inspection. You can tell they take pride in their work! I would definitely recommend them.
Sandy - Nashua, NH 03060
Review
Jack was prompt and did a great job tuning our furnace.
Vincent - Nashua, NH 03064
Review
Very happy with the job done.
Barb - Merrimack, NH 03054
Review
Did annual maintenance on the furnaces so we are all set for winter!
Lori B - Nashua, NH 03060
Review
Did annual maintenance on the furnaces so we are all set for winter!
Lori B - Nashua, NH 03060
Review
Great seeing Mark again.
Bob - Nashua, NH 03062
Review
As always, your guys are on time, polite, efficient and friendly. No worries when any of your crew is here, or at the office texting. Thank you GSMS. Susan
Susan - Salem, NH 03079
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