Leadership Teams

Nate Nelson leads the construction team at Comfort Systems USA Southwest, exemplifying our core values. Nate says, “Our core value of Be Respectful is important in any work environment, with both our company team members and our customers. You’ve got to give it to receive it.” As a well-respected leader himself, he is driven to continuous improvement and the highest standard of performance across the organization.

Nate has been in the construction industry for almost 24 years and 18 of those have been spent with CSUSASW. He also had the opportunity to expand his knowledge of the General Contractor side of the business, where he spent over five years. He brings his skills in project management, purchasing, estimating, and operations to his current executive leadership role. Nate began his career in Shipping & Receiving (Shop) and is grateful for the opportunities he has been given to progress and grow within Comfort Systems USA Southwest.

Nate’s family is his greatest motivation in all aspects of his life. He enjoys spending time with them hiking, going on family vacations, or just hanging out.  He also enjoys traveling with his wife when they have the chance.

Scott Sawyer manages the financial actions for Comfort Systems USA Southwest with his high regard for integrity. His personal driver is to “do what is right and do it with commitment” and he leads the finance team with that philosophy.

Scott has 24 years of accounting and finance experience including 16 years in construction. He joined the Comfort Systems USA Southwest team in 2011. He believes that you don’t have to attend a big, well-known university to have a great career—hard work and dedication create opportunities.

Scott holds a BA in Business, is a Certified Public Accountant (CPA) and is also a member of AICPA, ASCPA, and CFMA. He enjoys investing and is a big AZ Cardinals and KC Chiefs fan.

“The choices we make dictate the lives we lead.” William Shakespeare

This simple statement establishes the framework by which Tim Plaster makes decisions every day. As Executive VP of Building Services, Tim leads the department in establishing goals, communicating those goals and inspiring the team into action. Tim says, “Setting goals are one of the most important functions of success, and I’m a firm believer that without goals and the drive to achieve them you will always fall short. Company goals also require teamwork, so the communication of our goals must be clear to the entire team and that team has to be inspired to make it all happen.”

Tim’s 42 years of industry experience includes obtaining an AAS Degree in Design, New Mexico Qualifying Party certificate, multiple licenses, and certifications in Safety, Piping, Plumbing and HVAC. Throughout his career he has attained numerous promotions, successful projects and led winning teams that have grown profitable businesses; yet he considers his most important accomplishment as having the ability to mentor and help others find success and growth in our industry and in life.

In Tim’s spare time, he enjoys traveling with his wife Josephine, photography, and restoring and off-roading Jeeps.

As Executive Vice President of Construction at Comfort Systems USA Southwest, Cory Yeager oversees Arizona construction operations, sales and estimating. With a career spanning more than 25 years, Cory brings a well-rounded perspective and a strong focus on relationships, teamwork and successful project delivery.

Cory began his career in sheet metal in 1999 and has since gained hands-on experience across nearly every side of the business. Throughout his career, he has worked in the shop and field and held roles in project management, BIM, business development, preconstruction, sales, and estimating. This broad background gives Cory a practical understanding of how decisions made during preconstruction carry through to the field and ultimately impact a project’s success.

Cory also spent eight years working for a general contractor before returning to the subcontractor side of the industry. That experience gave him a valuable perspective on what owners and general contractors need from their trade partners and continues to influence his approach today. He places a strong emphasis on communication, long-term relationships, and bringing the right people and opportunities together.

Outside of work, Cory enjoys spending time with his wife, Sarah, their two children and two grandchildren. When he’s not working or with family, there’s a good chance you’ll find him on the golf course—one of his favorite ways to spend his free time.

Fred Zais joined Comfort Systems USA Southwest in August 2026 as Vice President of Construction Sales & Estimating, bringing decades of experience in mechanical construction, estimating, preconstruction and leadership.

A fourth-generation plumber and pipefitter, Fred was born and raised in Baltimore, Maryland where he began his career through the ABC Apprenticeship Program for Plumbing and Pipefitting. Starting as an apprentice, he worked his way into field leadership and has held multiple industry licenses and certifications, including Master Plumber, Master Gasfitter, Backflow Prevention Technician, Medical Gas Installer & Brazer, and Journeyman HVAC/R.

After relocating to Arizona in 1999, Fred continued his career in the field before transitioning into estimating and preconstruction. Throughout his career, he has held progressively senior roles including Senior Mechanical Estimator, MEP Preconstruction Manager, Director of MEP Services, Director of Preconstruction and Vice President of Estimating. His experience on both the general contractor and mechanical subcontractor sides of the industry provides him with a unique perspective on projects from early planning and budgeting through construction.

At Comfort Systems USA Southwest, Fred leads the Construction Sales & Estimating team, overseeing estimating, preconstruction and sales efforts while supporting client relationships and business development. His extensive industry experience allows him to provide clients with current market insight, reliable budgeting and a practical understanding of constructability and project costs.

Fred is passionate about building strong relationships, mentoring his team and sharing the knowledge he has gained throughout his career. He believes in developing people while maintaining the accuracy, responsiveness and trust that are essential to successful projects and long-term client partnerships.

Outside of work, Fred lives in Mesa with his wife, Jennifer. Together they have five children, one grandson and three dogs.

“Through hard work and dedication, I will overcome any challenge the day will throw at me.” This is Mike Smith’s defining principle—one that has served him well throughout his life and 21-year career in the construction industry.

Since joining Comfort Systems USA Southwest in 2000, Mike completed four years of formal education at Gateway Community College, a NCCER Pipefitting apprenticeship and various training certifications. He worked his way up to journeyman and then foreman, general foreman and piping superintendent. He moved into project management and was then tasked to manage the manufacturing shop before he was promoted to Director of Preconstruction.

Currently, as Associate VP of Construction, Mike is responsible for overseeing and managing the coordination between the VDC team, Manufacturing Shop, and Field Operations. He lives life with the belief that you should treat others as you would want to be treated and you should work hard every day, so you feel you have earned everything you have gained. Mike says, “No matter how hard your body wants to quit, you push through it every day.” Without singling out a particular event, he views his greatest career accomplishment as the opportunity to be a part of such a great organization that is on its way to being the best mechanical contractor in the southwest.

Mike enjoys ranching with his wife–his best friend of 27 years. He has two children; a daughter, 25, and a son, 23.  He loves to spend as much time as possible in the great outdoors, off-roading, camping and exploring Arizona.

Leading the service team for Comfort Systems USA Southwest is Jimmy Bennett. Jimmy can be described as a dedicated leader that leads by example; maintains a high level of standards and safety and refuses to tolerate mediocrity or poor performance. He promotes building strong partnerships with all employees and customers. Jimmy practices the ‘3 C’s’ of leadership: Consideration, Caring, and Courtesy, and believes you should be polite to everyone but let no one take advantage of you. He values all employees and empowers them to use their skills and talents to live out the company mission to success.

Jimmy joined the Comfort Systems USA Southwest team in 2013 to lead the service division. He has 28 years of experience in HVACR, from service technician to operations director. He completed a 5-year HVACR degree through Emily Griffith Technical College in Denver Colorado and has earned many different industry-related Certificates throughout the years. Jimmy is responsible for overseeing the Building Services Department for all HVACR Service, Preventive Maintenance, Operations, and financials for the business.

Jimmy likes hunting and fishing, and also enjoys watching both the Denver Broncos and Arizona Cardinals football games. He has a lovely wife, Kimberly, of 24 years, and two grown children, Emilie and Grant. Jimmy and Kimberly also spend time traveling and watching Emilie play collegiate soccer for Northern Arizona University.

Gary Niver, P.E. LEEP AP, leads the engineering team and virtual construction efforts at Comfort Systems USA Southwest with his underlying philosophy (quoted by Harvey MacKay) that, hard work often leads to success–no work seldom does. 

Gary has over 40 years of engineering experience in the design, manufacturing and construction of mechanical HVAC and plumbing systems for commercial, institutional and mission critical facilities.  Twenty-five+ years into his career, Gary went back to school and passed the Fundamentals of Engineering and Professional Engineer tests without a formal engineering degree. He is now a Registered Professional Engineer in the state of Arizona and is a LEED Accredited Professional.

Gary says, “I have been blessed to have worked in a field that I truly enjoy and very fortunate to have been mentored by engineers who were open to new ideas of construction. It is my desire to share that same creative passion to our team here.  I have also been blessed to have been married to my high school sweetheart for 41 years. We have two daughters and six grandkids. We enjoy RV-ing and old cars.”

Randy Sparaco leads the Building Services Operations team with Quality at the forefront. He believes that leading a successful team requires a high level of quality in everything they do. The importance of completing even the smallest task with attention to detail is never dismissed.

Randy has over 23 years in the industry and has attained many relevant certifications, including OSHA 10-Hour, EPA Refrigerant Certification – Universal, and Fred Pryor Management Training Certificate. He received his degree in HVAC Refrigeration Technology and has attended multiple management training courses to hone his skills and become a valuable leader for Comfort Systems USA SW.

Randy is grateful for the opportunity to be a part of the successful Building Services team. He deems the highlight of his career as having been chosen to fill the role of Director of Operations. Outside of his career, he enjoys spending quality time camping with his family and jumps at the chance to spend time outdoors whenever he can.

Mario Ruiz began his career in the construction industry in 2004, working as an apprentice with Comfort Systems USA Southwest. Throughout the past 17 years, Mario has gained valuable skills, including vacuum testing, tube bending and stainless welding and much more. He has achieved certifications in Orbital welding, PUDF fusion welding, and is OSHA 10-hr trained. 

As a Superintendent in the company’s Building Services division, Mario leads with the philosophy of leading by example in the style of a servant leader. Mario says, “I serve my team members by helping in any way I can—simply by getting my hands dirty.  I know the trade well and get involved in everything from material take off’s, scheduling deliveries, purchasing material, helping with paperwork, and pre-loading trailers with material and equipment. This all rolls over into developing my team to perform at a higher level.”

Mario’s career highlight was having the opportunity to assist in the establishment of a fabrication area for the Service department in Chandler. This opened up doors for the Building Services division to head its own fabrication for projects, provided a home-base for field foremen to work, and allowed storage of materials for up-coming projects. 

When Mario is not serving the team at Comfort Systems USA Southwest, he enjoys spending time with family and traveling with friends.

“Work smarter, not harder.” Words from Plumbing Superintendent Darren Rand. He adds, “I believe in saying what I mean and doing what I say.  It is important to me to be honest and reliable…” Darren displays this viewpoint as he leads teams through successful implementation of construction projects. Along the way, he enjoys coaching and serving as a mentor to help develop top field leadership, while finding ways to work more efficiently in everything they do.

Darren brings 34 years of experience in the industry. Among his accomplishments, he built a field operations unit in the Mid-Atlantic regions from the ground-up. This included all mechanical trade disciplines, fabrication facility, transportation, superintendent/ foreman training program and safety program. Darren has multiple certifications, including Master PLM, Master Gas Fitter, Master HVAC in 3 States, Steam & Hot Water Supervisory Cert, Refrigeration Supervisory Cert, and Backflow Cert.

Outside of his career, Darren loves spending time with his wife and family. He likes to stretch his musical muscles by playing guitar and piano, and also enjoys golfing.