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You can count on Zien's team of Union tradesmen to do the job right.

Zien offers turnkey installation and service of new and retrofit Direct Digital Controls and complete Building Automation Systems.

Zien is an authorized dealer of Reliable Controls Building Automation Systems, which offers world-class, BTL-listed solutions.

We specialize in developing energy-saving programming for your commercial HVAC systems to maximize your energy dollars. 


We focus on the long-term operational performance, air quality, occupant comfort and efficiency of your building. Helping you save money on energy is just a bonus. 

Zien's Mechanical Services include designing, building and installing commercial and industrial Process Piping systems. 

Transporting and distributing liquid and gaseous materials safely across complex systems requires mission-critical mechanical solutions. At Zien, we pride ourselves in completing our Process Piping jobs within the strictest tolerances while adhering to the highest safety standards in the industry.

Our engineers and experienced Union Pipefitters work together to ensure pipe design, selection, routing, painting, labeling and insulation meet or exceed required codes.

Process Piping is serious business and Zien Mechanical is renowned for its commitment to safety and health industries Best Practices.  


Our Refrigeration Division provides installation, retrofitting, repair and maintenance of all types of commercial/industrial refrigeration equipment.


From chillers and heat recovery systems to line coolers and walk-in freezers, Zien's highly experienced team of technicians work hard to optimize your systems to extend equipment life, reduce energy costs, prevent expensive repairs and reduce the risk of equipment downtime. 


Unlike many HVAC contractors, Zien has a full-service Sheet Metal shop in-house. This allows us to expedite processes that normally slow down jobs.

With our 20-foot Plasma Cutter, 90-ton Pressbrake, and various Lock-Former stations, we can quickly fabricate metal as needed to speed your job's completion.

Our Union Tradesman are skilled in Metal Trades ranging from duct work, fume hoods, catwalks, guard rails, mezzanines, plus equipment guards and supports.

We save time and money and we pass these savings on to our customers.


Zien has been heating homes and businesses in Southern Wisconsin for almost 100 years. In 2002, we ceased servicing residences to focus our priority on commercial, industrial and institutional customers. 

We install, service and repair ALL brands of heating, cooling and refrigeration equipment including boilers, heat pumps, packaged heating and AC units, chillers and more.

Our experienced engineers and project managers handle every aspect from design and installation to commissioning and maintenance.

We help you get the most out of your HVAC system investment.

Operating since Zien's founding in 1919, our plumbing division is one of the most experienced in the field. 

We handle both installation and repair at numerous commercial, industrial and institutional sites throughout Southeastern Wisconsin and Northeastern Illinois.


Our 30 experienced plumbers are available 24 hours a day, 7 days a week to handle all your problems - regardless of size or complexity.  

Our plumber's state and union certificates enable them to not only perform standard repairs, but also provide additional special services.

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