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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 345 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

Londonderry, NH - Completed the whole house plumbing inspection. All the drains and fixtures looked good. Completed the tankless water heater maintenance. I ran cleaner through it for 35 minutes. After I flushed 10 gallons of water through it. I cleaned both water inlet screens. I cleaned the air filter screen. I checked incoming gas pressure and that was according to manufacturer specifications. Lastly I ran the unit and everything was running great. The whole house humidifier hasn't been maintenance before. It should be done every year. I will send over an estimate for the maintenance. The first floor bathroom toilet is clogged. I tried unclogging it with a plunger and that didn't work so we will have to come back and snake it.
Qwentin G.
Qwentin G. Checked in
Completed the whole house plumbing inspection. All the drains and fixtures looked good. Completed the tankless water heater maintenance. I ran cleaner through it for 35 minutes. After I flushed 10 gallons of water through it. I cleaned both water inlet screens. I cleaned the air filter screen. I checked incoming gas pressure and that was according to manufacturer specifications. Lastly I ran the unit and everything was running great. The whole house humidifier hasn't been maintenance before. It should be done every year. I will send over an estimate for the maintenance. The first floor bathroom toilet is clogged. I tried unclogging it with a plunger and that didn't work so we will have to come back and snake it.
Londonderry, NH 03053
Windham, NH - Completed the plumbing inspection today. I checked all the fixtures and drains and everything looked great. I labeled a few emergency shut offs. I completed the rinnai water heater maintenance today as well. I started off with running cleaner through it for about 40 minutes. After I flushed 10 gallons of water out. I cleaned the water inlet screen. I cleaned the air filter screen as well. I checked incoming gas pressure and that was according to manufacturer specifications. I cleaned the electrode and flame sensors. Lastly I ran the hot water and it was working great.
Qwentin G.
Qwentin G. Checked in
Completed the plumbing inspection today. I checked all the fixtures and drains and everything looked great. I labeled a few emergency shut offs. I completed the rinnai water heater maintenance today as well. I started off with running cleaner through it for about 40 minutes. After I flushed 10 gallons of water out. I cleaned the water inlet screen. I cleaned the air filter screen as well. I checked incoming gas pressure and that was according to manufacturer specifications. I cleaned the electrode and flame sensors. Lastly I ran the hot water and it was working great.
Windham, NH 03087
Replace taco zone valve body & head. Oil boiler maintenance. Oil water heater maintenance. Replace thermostat in upstairs bedroom. Thank you!
Replace taco zone valve body & head. Oil boiler maintenance. Oil water heater maintenance. Replace thermostat in upstairs bedroom. Thank you!
Jack D.
Jack D. Checked in
Replace taco zone valve body & head. Oil boiler maintenance. Oil water heater maintenance. Replace thermostat in upstairs bedroom. Thank you!
Belmont, NH 03220
Qwentin G.
Qwentin G. Checked in
Found that the blower motor was faulty. I replaced the blower motor as well as a new capacitor for the blower motor. I tested operation and adjusted the fan speed to medium speed. I performed a temperature split and it was 45°. Everything was working good. I would recommend doing a maintenance on it, I will send over an estimate for that.
Pelham, NH 03076
Review
Always amazing service, every team member at GSMS has always been great and performed exceptionally great service.
Scott - Merrimack, NH 03054
Merrimack, NH - Completed the rinnai water heater maintenance today. I started off with running cleaner through it for 40 minutes. After that I flushed 10 gallons of water through it. I cleaned the water filter inlet screen. I pulled the electrode and flame sensors. They were dirty so I cleaned them. I vacuumed inside of the unit and I vacuumed the filter screen. I checked incoming gas pressure and that was according to manufacturer's specifications. Lastly we ran the unit and everything was working great.
Qwentin G.
Qwentin G. Checked in
Completed the rinnai water heater maintenance today. I started off with running cleaner through it for 40 minutes. After that I flushed 10 gallons of water through it. I cleaned the water filter inlet screen. I pulled the electrode and flame sensors. They were dirty so I cleaned them. I vacuumed inside of the unit and I vacuumed the filter screen. I checked incoming gas pressure and that was according to manufacturer's specifications. Lastly we ran the unit and everything was working great.
Merrimack, NH 03054
Completed the house plumbing inspection. Checked all the fixtures and drains and everything looked good. I labeled the water main shut off, hot water heater shut off, and gas shut off's . I found that the furnace was leaking from the inducer coupler due to the hose clamp not being tight.  As I was doing the water heater maintenance I found that the vent wasn't connected correctly and it wasn't even tight. I also noticed that the inducer gasket had been tampered with at some point and all that was there was clear silicone. The client wanted to go through with replacing the water heater due to the age and the fixes on the old one. When we come back to do the water heater maintenance have someone check out her master bedroom sink plunger.
Completed the house plumbing inspection. Checked all the fixtures and drains and everything looked good. I labeled the water main shut off, hot water heater shut off, and gas shut off's . I found that the furnace was leaking from the inducer coupler due to the hose clamp not being tight.  As I was doing the water heater maintenance I found that the vent wasn't connected correctly and it wasn't even tight. I also noticed that the inducer gasket had been tampered with at some point and all that was there was clear silicone. The client wanted to go through with replacing the water heater due to the age and the fixes on the old one. When we come back to do the water heater maintenance have someone check out her master bedroom sink plunger.
Qwentin G.
Qwentin G. Checked in
Completed the house plumbing inspection. Checked all the fixtures and drains and everything looked good. I labeled the water main shut off, hot water heater shut off, and gas shut off's . I found that the furnace was leaking from the inducer coupler due to the hose clamp not being tight. As I was doing the water heater maintenance I found that the vent wasn't connected correctly and it wasn't even tight. I also noticed that the inducer gasket had been tampered with at some point and all that was there was clear silicone. The client wanted to go through with replacing the water heater due to the age and the fixes on the old one. When we come back to do the water heater maintenance have someone check out her master bedroom sink plunger.
Manchester, NH 03109
Jack D.
Jack D. Checked in
Kitchen sink drain not draining. With the sample bit on my snake I pulled back grease and small food solids. I got the drain freed and treated it with lye. I reccomend putting lye down the drain once a month since that sink gets clogged often. It has a very long horizontal run in the basement. Thank you!
Windham, NH 03087
Jack D.
Jack D. Checked in
Assessment and potential restoration of disconnected baseboard heating zone. Step 1 (Diagnostic): We will isolate the disconnected piping section and perform a pneumatic (air) pressure test to identify potential bursts or leaks without risking water damage to the crawlspace. Step 2 (Conditional Repair): If the system holds pressure: We will proceed with reconnecting the loop to the main heating system to restore heat to the area. This will be tied into the main kitchen zone, as discussed. If the system fails pressure: The loop will remain capped/disconnected to prevent flooding, and we will advise on alternative heating options. Only the diagnostic rate will be invoiced.
Newmarket, NH 03857
Qwentin G.
Qwentin G. Checked in
Completed the plumbing inspection. The fixtures and drain lines all looked good. I added a couple emergency shut off tags. I completed the rinnai water heater maintenance. I flushed cleaner through it for 40 minutes. After that I flushed about 10 gallons of water through it. I cleaned the water inlet screen. I vacuumed out the inside of the unit and I vacuumed the air filter. The client was interested in whole house humidification so I will write up an estimate for steam and for a bypass humidifier. The client also noticed that in the summertime the upstairs floor would get very humid.
Stratham, NH 03885
Qwentin G.
Qwentin G. Checked in
Completed the plumbing inspection today. All the drains and fixtures looked good. I labeled the main water shut off, the hot water heater shut off and the oil tank shut off. I entered in his equipment to his profile. The water heater is two and a half months old so the maintenance will be done next winter.
Stratham, NH 03885
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
Excellent service
Paul - Nashua, NH 03062
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