When an HVAC update is mandatory but it’s essential not to disturb the walls or the plaster, there is a whole-house option: mini-duct systems, offered by companies such as Unico, Space Pak, and Hi-Velocity. These cleverly conceived HVAC delivery systems consist of flexible, mini-duct tubing small enough to be routed between studs in walls and in cavities under floors and above ceilings, powered by an air handler. Tubes a mere 2" wide send high-velocity air throughout the house by aspiration, producing relatively even heat or cooling from floor to ceiling. The system creates a gentle circulation pattern and, unlike some forced-air systems, is very quiet. Mini-splits are also an excellent way to add air conditioning to a house with a functional heating system but without the large ducts required by traditional air conditioning.
Even the air handlers can fit into tight spaces, as shown by a Unico System air handler slotted in under the basement floor joists.