Longmont summers are no joke. Between the mid-90s heat waves and the unpredictability of Colorado weather swinging from spring snowstorm to full summer heat in the span of two weeks, having a solid AC system installed by someone who knows what they are doing is less of a luxury and more of a practical necessity. The good news is that Longmont has a genuinely strong field of HVAC contractors, ranging from family operations that have been in the community for over 40 years to nimble smaller companies with fast response times and competitive pricing. The nine below represent the range well.
1. Welzig Heating, Air, Plumbing and Electric
Best for: Homeowners who want a well-credentialed, long-established company with manufacturer-level expertise and a full service catalog that extends beyond just HVAC
Welzig Heating, Air, Plumbing and Electric is a family-owned and operated business that has been serving the Longmont and Greater Boulder area since 1994. Thirty-plus years in a competitive market is the kind of track record that tends to filter out the corners that get cut. As a Bryant Factory Authorized Dealer, Welzig consistently performs to strenuous standards of technical competence, business ethics, and customer approval, with NATE-certified, factory-trained technicians equipped with leading-edge tools and a full inventory of genuine manufacturer replacement parts. The company has won Bryant’s Circle of Champions award three consecutive years, a distinction that only two percent of all Bryant dealers ever achieve.
Their service offering extends to high-velocity HVAC systems for historic or architecturally complex homes where conventional ductwork installation is not practical. For homeowners dealing with older homes, tight spaces, or complex installation scenarios, that specialized capability is genuinely useful.
They operate 24 hours a day, seven days a week, and their technicians carry a full inventory of parts so the majority of issues get resolved on the first visit rather than requiring a return trip for parts.
2. Stone Heating and Air
Best for: Homeowners and business owners who want a locally rooted Longmont company with NATE certification, A+ BBB standing, and a philosophy built around not overselling
Stone Heating and Air is a locally owned HVAC company in Longmont, Colorado, operating since 2008 and fully licensed, insured, EPA and NATE certified, servicing all brands without charging overtime. Owner John Stone has built the company around a straightforward value proposition that shows up consistently in how they describe their work: assess based on actual needs, not what generates the most revenue. At Stone, they work with clients to find the source of concerns and develop solutions based on individual needs and budget, without trying to oversell expensive products and services that are not necessary.
Stone Heating and Air is certified by the North American Technicians Excellence, works with top-name brands such as York and Rheem, and has achieved an A+ rating with the BBB. Their service area covers Longmont, Loveland, Boulder, Estes Park, and Fort Collins, and they handle both residential and commercial AC installation, repair, and maintenance. For homeowners who have felt talked into more than they needed by a previous HVAC contractor, Stone’s approach tends to feel noticeably different.
3. Circulating Air
Best for: Longmont and Boulder County homeowners who prioritize transparent pricing and a track record of honesty built over nearly three decades
Circulating Air has over 25 years of experience in the HVAC industry, with certified technicians committed to providing top-quality residential air conditioning services to homes in Longmont and surrounding communities. What stands out in their customer reviews more than anything else is repeated mentions of honest, non-inflated pricing. One reviewer noted they were great to work with and did not inflate pricing the way competing bids had, and that the crew was in and out within a day. Reviews across nearly two decades of customer relationships describe Bob and his team in terms you do not often see in the trades: honest, prompt, respectful of the home, and consistent. They work with Trane systems and cover Longmont, Boulder, Firestone, Berthoud, and Loveland.
4. Highland Heating and Air
Best for: Residential and commercial customers who want NATE-certified technicians with deep combined experience and the ability to handle both small home repairs and large commercial HVAC projects
Highland Heating and Air’s leadership team has more than 100 years of combined HVAC experience and has repaired and installed thousands of residential air conditioning units and commercial HVAC systems in Longmont and surrounding areas since 2007. The owner is NATE-certified, ICC Master Mechanical certified, and a Rinnai-certified professional, which is an unusually strong credential set for a local operation. They hold an A+ rating with the BBB.
Their commercial HVAC capability sets them apart from most of the competition in this market. Their commercial client list includes a wide range of business types, and they handle every kind of HVAC project from new and retrofit installations to mechanical room or rooftop units, tenant finishes, retail, high-tech, and industrial environments. For property managers or business owners who want a single contractor relationship that can serve both a residential property and a commercial space, Highland’s dual-market experience is worth knowing about before a project gets scoped.
5. SAC Mechanical
Best for: Customers who want a multi-decade institutional track record, A+ BBB standing, and broad brand compatibility including Lennox
Since 1982, SAC Mechanical has been a pillar in the Longmont community, delivering premium HVAC services focused on customer satisfaction and community trust, starting as Sam Ainsworth and Company and evolving over four decades into the operation it is today. As a NATE-certified company with an A+ rating with the Denver/Boulder Better Business Bureau and active membership in the Air Conditioning Contractors of America, they partner with leading brands like Lennox, AprilAire, Navien, and Honeywell.
Customer reviews describe technicians who take the time to explain findings, show the failed part, and offer transparent options rather than defaulting to the most expensive fix. One reviewer specifically highlighted a technician who serviced a furnace air intake issue at no charge while on an AC installation call. That culture of thoroughness and honesty does not appear overnight. It is the kind of thing that 40-plus years of operating in the same community either builds or destroys, and SAC has clearly built it.
6. Colorado’s Finest Heating and Air Conditioning
Best for: Homeowners who want fast turnaround, flexible financing, and a contractor who explains the reasoning behind every recommendation
Colorado’s Finest Heating and Air Conditioning has been installing and repairing HVAC systems in Longmont for over 15 years as a family-owned business, employing EPA-approved and NATE-certified technicians with a satisfaction guarantee on all work, flexible financing, and free estimates. One homeowner called on a Monday morning and had a brand new furnace and AC installed by Wednesday at noon. Owner Jordan has built a reputation for educating customers throughout the process rather than simply presenting a bill at the end, and customers consistently describe him as giving the reasoning behind his recommendations, helping with projects that range from single-family home AC installs to emergency Sunday calls during December cold snaps.
7. Tri County Heating and Cooling
Best for: Homeowners who are tired of commission-driven upselling and want a company whose only incentive is to give honest, right-sized advice
Unlike many larger AC and furnace repair companies in Colorado that pay technicians on commission, Tri County Heating and Cooling’s business is solely focused on creating HVAC customers for life, making their only incentive to provide honest, reliable, and fast service. When a technician is not being paid more to recommend a replacement over a repair, the advice they give tends to be significantly more trustworthy. Their service area covers Longmont, Berthoud, Niwot, Frederick, Firestone, Loveland, and Greeley.
Customers consistently highlight specific technicians by name and describe repeat visits across both home and business properties spanning many years. That level of personal loyalty is not something you build through slick marketing. It is what happens when people feel like they were treated fairly every single time.
8. DNI Heating and Air
Best for: Customers who need a family-owned operation with 24/7 emergency availability, flexible financing, and combined HVAC and plumbing experience
DNI Heating and Air serves Mead, Longmont, and Northern Colorado with over 28 years of expertise in HVAC, plumbing, and refrigeration services, operating 24/7 emergency service and offering competitive pricing and flexible financing as a family-owned business built on dedication and integrity. One reviewer praised the team after a new HVAC system and furnace installation, describing technicians who were prompt, friendly, courteous, knowledgeable, and careful even when the installation turned out to be more complicated than expected. Another highlighted that Nick never tried to sell them and instead made recommendations, gave options, and explained the reasoning, which is exactly what you want when you know nothing about HVAC systems and are making a significant investment.
9. Cool Ducts Heating and Cooling
Best for: Homeowners who want a locally owned Longmont contractor with EPA and NATE certification, personal owner accountability, and competitive pricing
Cool Ducts Heating and Cooling is EPA and NATE-certified, a proud member of the American Pipe Fittings Association, and provides residential and commercial customers with all-inclusive HVAC services including furnace installation, furnace repair, boiler repair, AC repair, ductless air conditioning, and smart home services. Customer reviews call out technicians by name for being helpful, efficient, and clear in their explanations, and the pricing consistently outperforms competing bids according to multiple reviewers. Cool Ducts serves all of Northern Colorado and is available 24/7.
Every one of these companies will answer the phone, show up, and install a system. What separates them is the kind of relationship they are trying to build with the customer, whether that is a one-time installation handled with precision, a decades-long service relationship with a family-run operation, or a company built specifically to cut out the commission-driven pressure tactics that make HVAC shopping feel more stressful than it has to be. Knowing what you value before you call will make the choice a lot cleaner.
