Rheia At Work

Rheia is a  proprietary “home run” design approach that ensures predictable airflows to create a balanced environment throughout the home. 

As a small diameter duct system, Rheia can be located entirely in the thermal envelope of the home, routing the ductwork through conventional 2 x 4 walls, I-joists, and open web trusses.

Rheia impacts the cost of a home in several significant ways.

20-30% of the output from a furnace or air conditioner is lost in attic installations. Equipment and ductwork located in the conditioned space of the home makes energy efficiency sense, lowering costs from equipment size reduction and installation labor savings.

The Rheia approach also results in fewer conflicts with the work of other trades, positively impacting plumbing and electrical installation.

1-Story

Typically a slab-on-grade foundation is constructed with the air handler and ductwork located in the attic, or the air handler in a mechanical closet and the ductwork in the attic.

  • Rheia installations require the air handler to be located in a mechanical closet inside the home, or in the garage (with appropriate insulation and air sealing on exterior walls).
  • A central location for the mechanical room keeps duct runs shorter which reduces cost and optimizes performance. The home is conditioned through sidewall micro-diffusers.
  • Upflow air handler to a Rheia manifold located in the mechanical closet.
  • Duct routing options are:
    Ducts in the conditioned space by locating them in inverted trusses that are air sealed and insulated.
    Ducts run in thickened walls that can accommodate the 3” or 4” duct.
    Ducts in dropped ceilings and soffits are discreetly located in hallways, closets, and bathrooms.
  • A central return with either insulated jump ducts or pass-through grilles works well for this system layout.
Routing One Story D1 1
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casestudyCentral closet with up flow air handler and manifold

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Thickened wall to enable ducts to be run horizontally in a wall

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Inverted truss soffit to enable ducts to be run without the need for dropped ceilings

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 6” dropped ceilings are used in low-impact areas

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5 Air sealed and insulated soffits for duct runs 5 of 5

2-Story

A slab-on-grade or basement foundation home is typically constructed with the air handler located in either a
first or second floor closet for slab-on-grade foundations, or in the conditioned basement under the home. Ductwork is typically located in bulkheads and chases for first-floor distribution and in the attic for second-floor distribution.

  • Rheia installations require the air handler to be located in a mechanical closet inside the home on the first or second floor, or in athe basement.
  • A central location for the mechanical room will keep duct runs shorter which reduces cost and optimizes performance.
  • Downflow air handler and Rheia manifold if located on the second floor.
  • Rheia ducts are located in the home’s conditioned space in floor cavities and in interior walls.
  • The lower floor is conditioned through ceiling diffusers, the second floor is conditioned through sidewall diffusers.
  • Insulated ducts and air-sealed chases may be needed for rooms above a garage.
  • A central return with with either insulated jump ducts or pass-through grilles works well for this system layout.
Routing Two Story
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First floor mechanical closet with up flow air handler and manifold

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Alternative down flow air handler with manifold in the floor cavity

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Precut I-joist routing for larger duct bundles

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Ducts run in joist bays to ceiling diffuser locations

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Ceiling diffusers for most ground floor rooms

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High sidewall ducts for upper floor air distribution

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3-Story

Townhome construction is typically built with a slab-on-grade foundation a living space and garage on the ground floor, and the air handler located in a mechanical closet. Ductwork is typically located in bulkheads and chases for first-floor distribution and in the attic for second-floor distribution.

  • Rheia installations require the air handler to be located in a mechanical closet inside the home, typically on the ground floor to optimize floor space usage.
  • Up-flow air handler and Rheia manifold.
  • Ductwork is routed through a vertical chase to the first and second floors.
  • Rheia ducts are located in the home’s conditioned space in floor cavities and in interior walls.
  • Lower floors are conditioned through a combination of ceiling and sidewall diffusers. The upper floor is conditioned through sidewall diffusers.
  • A central return with either insulated jump ducts or pass-through grilles works well for this system layout.
Routing Townhouse
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Lower floor mechanical closet with up flow air handler and manifold

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Vertical chase to route ducts to floors above

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Open web trusses for easier direct duct routing

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Ceiling diffusers for most ground floor and middle floor rooms

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High sidewall ducts for upper floor air distribution

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Static Pressure Control

The Rheia system utilizes a supply manifold, ducts, fittings, and diffusers that work as a system engineered to operate under static pressure limits required by the equipment manufacturers — which means a change in equipment design and operation is not necessary. A half to a one-ton reduction in cooling capacity when moving from an attic installation is typical.

In a conventional duct system, the pressure loss from fittings can be up to 90% of the total duct length loss. In a RHEIA system, the fittings and duct routing account for only about 40% of the loss. 

A RHEIA system supplies the required airflow to each room in the home. A typical Rheia air distribution duct run delivers 35-45 CFM of air. Duct runs are added to a room until the required airflow is met. This airflow can be met with a supply duct pressure drop of 0.3-0.4 in wc, and a total external pressure of 0.7-0.8 in wc.

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Central Return Simplicity

A common misconception is that multiple points of return air somehow mitigate temperature imbalances and that central returns cause rooms to be starved of supply air. In fact, the opposite is true. Using a central return system improves static pressure management while reducing costs, resulting in a better performing HVAC system.

As a more compact layout, central returns result in a lower static pressure drop on the return side, reducing the number of supply ducts needed. The supply system must distribute the air proportionally to the heating and cooling load, not the other way around.

Jump ducts and pass-through ducts ensure correct return static pressure when sized correctly. Central returns are easily integrated into the home’s conditioned space, reducing required equipment capacity and airflow.

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Easy Balancing

Rheia ducts terminate in supply boots, each equipped with a finely-adjustable damper to set each duct run airflow to the design requirements during the system balancing process. The Rheia Verify app guides the technician step-by-step through the balancing process — in about 30 minutes for a typical house — resulting in minimal room-to-room and floor-to-floor temperature differences.

Reducing temperature differences around a home is an essential contributor to feeling comfortable. The Rheia Verify app is an innovative solution that transformed a time-consuming and inaccurate process into a simple and quick operation.

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Managing Room Airflows

The Rheia Design process enables an accurate prediction of the required airflow for a room, as determined by the Manual J calculations, while simultaneously managing static pressure limitations. Rheia’s use of multiple micro-diffusers in each room mixes the conditioned air more effectively than the fewer register layouts seen in conventional designs. This approach is better at mixing the conditioned air entering a room, helping to minimize the common problem of hot or cold spots.

The positioning of the diffusers placed high on the wall or ceiling, combined with their aerodynamic design, efficiently throws air across the room, further contributing to better air mixing.

These features improve how comfortable each room feels and how consistent the temperatures are from room to room.