I Upgraded to Dual Fuel (Again), and I am Never Going Back!
When we moved into our new home, upgrading the HVAC system was a priority. Comfort wasn’t something we were willing to compromise on, especially after experiencing the difference a heat pump made in our previous house. Much to my own chagrin, Nate Adams was right. The consistent temperatures, reduced cycling, and quiet operation made all the difference. I learned two things: heat pumps don’t suck anymore, and occasionally, even a blind squirrel can find a nut. (Not giving Nate too much credit, after all, it was me who decided to listen to him.) This time around, I really wanted to see what a retrofit might look like in a typical home that I had very little input into the initial design.
Why Dual Fuel?
Going fully electric wasn’t practical for me – changing one appliance is enough. Dual-fuel systems provide a reliable solution by combining the efficiency of a heat pump with the proven dependability of a gas furnace. Gas is affordable, and I already have multiple gas appliances in the house, including a stove, hot water tank, and dryer, so it made sense to stick with it.
The heat pump was sized to handle most of the heating load during mild weather and all the cooling load in summer. This approach allowed me to downsize the equipment and reuse the existing ductwork, which kept costs in check. The gas furnace kicks in only when needed—either during extremely cold weather or if the heat pump fails. This ensures I’m not stuck relying on expensive electric resistance backup heat for extended periods. It’s a practical and efficient setup that provides year-round comfort and peace of mind.
Right-Sizing for Efficiency and Cost Savings
Performing a heat loss and gain analysis was a crucial step to ensure the equipment was right-sized for the house. I used Conduit Tech to generate a block load in about 15 minutes. It’s an impressive tool that uses LiDAR to measure the entire house with just an iPad. The layout of the house added some complexity, with a garage below half of the first floor, a shared south wall with a neighboring condo, and various architectural features like bay window bump-outs. Despite that, the Conduit tool made quick work of the calculations and delivered reliable results.
The heat loss/gain confirmed we could significantly downsize both the heating and cooling systems. The old system required 1,250 CFM for heating and 1,000 CFM for cooling. With the new setup, both are under 800 CFM, which resulted in lower static pressures, reduced noise, and much lower blower motor energy use. Downsizing the equipment not only improved efficiency but also allowed the existing ductwork—which was previously undersized—to perform well within its capacity. This saved a significant amount of money on the upgrade.
The Upgrade: From Oversized to Efficient
The old system was a 100,000 BTU single-stage furnace paired with a 2.5-ton straight cooling air conditioner. It ran short cycles—around 5 to 7 minutes each time—which left the house uncomfortable.
For the replacement, I went with Bosch again primarily because of the people behind the equipment—specifically their reps at CKA Sales. Support is critical, no matter how much experience you have. Even with 30+ years in the industry, I knew there would be something I’d question during the install. Sure enough, when I had a question, Matt from CKA Sales was there with the answer. Having that level of reliable support made the decision easy.
On top of that, the Bosch system in my first home performed incredibly well, so I already knew I could count on their heat pumps. This time, I was looking for the same quality because I don’t plan on putting in another system after this one.
We made a significant reduction in system size, particularly on the furnace side. The old system was a 100,000 BTU furnace at 80% efficiency, delivering 80,000 BTUs of output. We replaced it with a Bosch 60,000 BTU two-stage furnace at 96% efficiency, which provides 57,600 BTUs of output—nearly a 28% reduction. The new furnace also stages down to 37,000 BTUs, representing a 54% total reduction in output compared to the original system. 37,000 BTUs almost matches the heat loss perfectly. I am betting that – unless I do a significant setback at night – I will never use the second stage. This ability to better match the actual load during milder weather ensures optimal efficiency and comfort.
On the cooling side, we replaced a 2.5-ton air conditioner with a Bosch 3-ton VRF heat pump adjusted to a 2-ton max capacity, paired with a matching 2-ton indoor coil. These adjustments allowed us to reuse the existing ductwork, saving significant costs while optimizing system performance.
It was also my first time working with a Bosch furnace, and it didn’t disappoint. The cabinet is well-built, well-insulated, and everything fits together exactly as it should. It’s clear they put a lot of thought into the design. It uses a constant torque motor, which took a little more time to set up compared to an ECM, but once dialed in, the performance was excellent. Overall, it’s a solid, dependable system that I expect to hold up for years.
Enhanced Indoor Air Quality
Upgrading the filtration was an important part of the project too. The GeneralAire Perfect Platform worked well to adapt a larger filter into the system. The filter with foam gasketing significantly improved air quality by reducing airborne particles. There was a marked improvement after 4 hours. The results were clear on my IQAir monitor—healthy CO₂ levels and consistently clean air. A well-designed filtration system like this not only improves comfort but also dramatically extends the life of the HVAC equipment by keeping it clean.
Comfort and Performance
This system was designed with comfort as the top priority. The Bosch VRF heat pump provides precise, consistent heating and cooling, while the two-stage furnace offers reliable backup in colder weather. The variable-speed compressor on the heat pump eliminates temperature swings and reduces energy use, creating a stable and comfortable environment.
Robin and I knew we needed a system that could match the comfort we had in our previous home. As much as it pains me to say it, Nate Adams was right about Mean Radiant Temperatures and the benefits of eliminating cycling. This dual-fuel system checked all the boxes for us—quiet operation, energy efficiency, and steady comfort all year long.
Technician’s Takeaway: Practical Upgrades That Work
As a former technician, I’m always looking for practical solutions that balance comfort, efficiency, and cost. This project demonstrated the value of right-sizing equipment and taking the time to perform a proper load calculation. Downsizing the system not only cut costs but also improved performance across the board.
Dual-fuel systems are a great option for homeowners who want the efficiency of a heat pump without giving up the reliability of a gas furnace. With the right tools and proper planning, these systems can deliver exceptional comfort while keeping operating costs low. If you’re considering a similar upgrade, I’d recommend investing in quality components and taking the time to get the design right. It makes all the difference.
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