
Bay City, MI HVAC Services
Full-Service Heating & Cooling Across Saginaw, Midland & Bay Counties
Living in Mid-Michigan means dealing with real weather, freezing winters, humid summers, and everything in between. At Custom Engineering, we’ve been helping families and small businesses across Bay City, Saginaw, and Midland stay comfortable in every season since 1984.
Whether your furnace won’t kick on during a January cold snap or your AC is blowing warm air in the middle of July, we’re here to help you get your system back on track. We handle everything from new HVAC installations to same-day repairs and seasonal maintenance.
As a locally owned business deeply rooted in the Bay County community, we understand how quickly temperatures can swing around here, especially with the lake breeze and unpredictable Midwestern weather. That’s why we’re available 24/7. Someone will answer your call, assess the situation, and offer guidance on what steps to take. If needed, we can schedule same-day or emergency service when available.
Need HVAC help now? Call (989) 474-2870 or contact us online for a free estimate on installation or replacement.


Why Choose Custom Engineering?
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We make HVAC services affordable with financing options offering 0% interest for 72 months.
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No matter when you need us, we're ready to help. Someone is always available to answer your call.
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Keep your system in perfect shape all year round with our programs.
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As a proud Michigan company, we deliver honest, dependable HVAC services backed by local expertise and care.

Custom Comfort for Every Season

Our Heating & Cooling Services
We provide comprehensive HVAC solutions throughout the Great Lakes Bay Region, covering everything from new installations to routine seasonal maintenance. We work with all brands and systems, and as a trusted Trane and Mitsubishi Electric dealer, we offer energy-efficient options designed to handle Michigan’s unique weather.
Custom Engineering services include:
- New HVAC system installations. We help property owners choose the right heating and cooling system for their space, whether that’s a traditional setup or something more modern like a ductless mini-split. We handle every step from planning to installation, and back our work with a 5-year labor warranty.
- Furnace and AC replacements. If your old system is costing more than it’s worth, we’ll walk you through the replacement process and explain your options in a way that’s easy to understand.
- Same-day and emergency HVAC repairs. We offer same-day service whenever possible, with 24/7 availability to discuss your HVAC issues and help determine the best course of action, so your system gets the attention it needs when you need it most.
- Preventative maintenance and seasonal tune-ups. Regular service helps your system perform better and last longer. During a tune-up, we’ll clean the components, check electrical connections, test system operation, and look for any early signs of wear. This helps prevent bigger problems later.
- Indoor air quality services. Dry air, dust buildup, and other indoor air concerns can make your home less comfortable. We offer solutions like air purifiers, humidifiers, and upgraded filtration to help improve the air you breathe every day.
- Ductwork repair and upgrades. Leaks, gaps, or aging ductwork can reduce the performance of even the best HVAC systems. We repair and modify ductwork to help airflow and system efficiency, especially in older properties around Bay City and Saginaw.

What Else Can We Help With?
- Thermostat installations and upgrades. Upgrading your thermostat can make a big difference in how your home feels and how much energy you use. We install smart thermostats and programmable models that help you better manage your comfort.
- Ductless mini-split system service. Mini-splits are a great fit for homes without central ducts or for spaces like sunrooms, garages, and additions. We service and install ductless systems, including Mitsubishi Electric models known for their reliability and efficiency.
- Fuel oil furnace repair and maintenance. In rural parts of Bay County and the Saginaw Valley, oil heat is still common. We’re one of the few HVAC companies in the area that continues to work on oil-fired systems. Whether it’s maintenance, a repair, or a conversation about switching to another energy source, we’re here to help.
Contact us today at (989) 474-2870 or online and learn more about our financing options.
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Every employee I have had the pleasure of dealing with has been top-notch. Today's visit by Tyler for annual maintenance was great. He was punctual, friendly, and professional.- Michelle G.
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Chaz went above and beyond! He fixed my main house furnace and also advised me on my ceiling-mounted furnace in my back building. Thank you for your quick response. I will use you again!- Ann K.
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Always courteous & competent. They installed a new furnace, AC, garage gas heater, and ran a gas line into our laundry room. They stayed on the job until all was completed and we were extremely satisfied.- Terrance V.
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We bought our kitchen hood system from them, which they also installed (no small task). They are dependable, efficient, and do great work. Prices are what I would expect for the job. Don't hesitate to hire them.- Marinell S.
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I always try to keep my business local, so I called Custom Engineering. They always answered my calls promptly, and the service was friendly with experienced technicians. They were prompt, courteous, and really put my fears to rest. Great job!- Debbie M.
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Chaz did an amazing job - straightforward and very helpful. Jason and Trey set up the furnace a week ago, and it runs amazingly! It's nice to stay warm again. They just repaired and replaced my bathroom exhaust fan, too. Thank you again!- Cesily W.
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He got our furnace up and running again very quickly (on a Saturday!). Very personable and professional! We will definitely be using Custom Engineering Heating & Cooling again - thank you!- Krista W.
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We went through custom engineering for replacing our furnace and air conditioner. They went above and beyond to do what is best for our home. The whole team was respectful and informative. They answered any questions we had!- Allison E.