Uploaded August 2026 | Updated September 2026, 3 weeks ago
When a 20-ton AC unit needs replacing but the attic access is only 30x30 inches — and the building is a historic church where you legally can't touch the roof or walls — the manual answer runs out of options fast. Roman Baugh walks through the retrofit he engineered for exactly that scenario: four or five-ton VRV/VRF indoor units stacked and manifolded together into a single cube-shaped air handling system, all sharing one thermostat and one set of supply and return ductwork.
This isn't a manufacturer-approved configuration, and Roman is upfront about that. But two years in, the system is holding steady — no fan motor failures, stable space temperatures, and a noticeable drop in energy bills compared to the old straight-cool, electric-resistance setup it replaced. He breaks down the engineering behind it: how the stacked units share ductwork without cross-talk under normal operation, the plan for handling backfeed if one unit ever fails (block-off strategy, similar to fan wall arrays), the MERV 15 filtration and CO2 demand control built into the design, and why static pressure and undersized 30-year-old ductwork are the next things on the punch list to improve.
Topics covered:
Why the church's tiny attic access ruled out a standard 20-ton replacement
How four 5-ton VRV/VRF units were stacked into a cube configuration on shared ductwork
Running multiple indoor units off one common thermostat
MERV 15 filtration, CO2 demand control, and a humidity-based outside air damper
What happens if one unit in the cube fails — and how backfeed is handled
Two years of real-world performance data: energy savings, motor life, and static pressure
Roman's take on when it's okay to build outside the manufacturer's playbook
If you've ever stared down a retrofit where every "normal" option was physically or legally off the table, this one's worth watching. Roman's not telling you to go improvise on your next job — he's showing what it looks like to understand the science well enough to take responsibility for a creative solution and make it work for the client.
Read all the tech tips, take the quizzes, and find our handy calculators at hvacrschool.com or the HVAC School Mobile App on the Google Play Store (hvacrschool.com/play-store) or App Store (hvacrschool.com/app-store).
When a 20-ton AC unit needs replacing but the attic access is only 30x30 inches — and the building is a historic church where you legally can't touch the roof or walls — the manual answer runs out of options fast. Roman Baugh walks through the retrofit he engineered for exactly that scenario: four or five-ton VRV/VRF indoor units stacked and manifolded together into a single cube-shaped air handling system, all sharing one thermostat and one set of supply and return ductwork.
This isn't a manufacturer-approved configuration, and Roman is upfront about that. But two years in, the system is holding steady — no fan motor failures, stable space temperatures, and a noticeable drop in energy bills compared to the old straight-cool, electric-resistance setup it replaced. He breaks down the engineering behind it: how the stacked units share ductwork without cross-talk under normal operation, the plan for handling backfeed if one unit ever fails (block-off strategy, similar to fan wall arrays), the MERV 15 filtration and CO2 demand control built into the design, and why static pressure and undersized 30-year-old ductwork are the next things on the punch list to improve.
Topics covered:
Why the church's tiny attic access ruled out a standard 20-ton replacement
How four 5-ton VRV/VRF units were stacked into a cube configuration on shared ductwork
Running multiple indoor units off one common thermostat
MERV 15 filtration, CO2 demand control, and a humidity-based outside air damper
What happens if one unit in the cube fails — and how backfeed is handled
Two years of real-world performance data: energy savings, motor life, and static pressure
Roman's take on when it's okay to build outside the manufacturer's playbook
If you've ever stared down a retrofit where every "normal" option was physically or legally off the table, this one's worth watching. Roman's not telling you to go improvise on your next job — he's showing what it looks like to understand the science well enough to take responsibility for a creative solution and make it work for the client.
Read all the tech tips, take the quizzes, and find our handy calculators at hvacrschool.com or the HVAC School Mobile App on the Google Play Store (hvacrschool.com/play-store) or App Store (hvacrschool.com/app-store).
