Frequently Asked Questions
You have questions and we have answers. Below is a list of frequently asked questions about Rheia air distribution systems. If we missed one, use this form to contact us and we will do our best to find the answer for you!
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Basement, Upflow, Downflow (all boxes).
Rheia makes meeting Title 24 easier, primarily through the design process of moving ducts into the conditioned space. Current approaches are either expensive or flawed. Keeping ducts in the unconditioned attic (by deeply burying them in insulation), still runs the risk that condensation will form on ducts and boots at vulnerable spots where the insulation is compromised. Adding a spray foam layer to the ductwork to prevent moisture migration is cost prohibitive and time consuming. Similarly, conditioning the attic is expensive and increases the cooling load of the home, often requiring additional cooling tonnage.
Airflow is managed by adding or removing ducts. Since all ducts are the same diameter, this is an easy process in the Rheia design software. The total amount of airflow delivered to a room is dictated by the Manual J calculations. The duct has a per linear foot pressure loss factor, as do the fittings. Once a designer has established the appropriate route from the manifold to the diffuser, a pressure estimate for that run can be determined. Meeting the required airflow in a given room requires the designer to add ducts until that pressure requirement is met.
With Rheia it’s easier. In a conventional duct system, large bulkheads and chases are required to house ducts which are unsightly, costly and use up valuable square footage. Ducts that can be routed in floor structures also use up a lot of room and create conflicts with other mechanical systems. The Rheia duct system fits compactly inside wall and floor structures. In the instances where a chase, bulkhead or drop ceiling is required, their depth is relatively small, impacting ceiling heights in architecturally unimportant areas.
Rheia has developed a proprietary process to enable cost-effective system commissioning, which includes the easy to use Rheia Verify app to set balancing dampers, measuring airflow at registers, and comparing performance to the original design. Balancing adjustments can be made to set the optimum comfort level of the home.
Yes. Rheia has a partnership with WrightSoft to provide training on using the Rheia duct design module within the Wrightsuite application.
Rheia is highly adaptable to zoning solutions. Rheia has developed a series of zoning design configurations and component recommendations that work seamlessly with Rheia. A benefit of the Rheia system is that in some home configurations that would normally be zoned, a zoned solution may not be required, saving costs while still providing the comfort needed.
Rheia registers are located high on interior walls to take full advantage of the way the air is delivered into a room. Through detailed engineering, the diffusers (aka registers) have been designed to throw air across a room and mix much more effectively than current register designs. Throwing air from interior walls (when floorpan design allows) keeps duct runs shorter and minimizes the number of diffusers.
The design process for Rheia is built into the Wrightsuite application in use by almost all HVAC designers. This is a familiar environment and follows a similar design process to conventional HVAC system designs, which have been streamlined due to the simplicity and low SKU count of the Rheia system.
A better number is how many per ton. It varies based on the floorplan, orientation and design of the home, but typically there’s about 10-12 ducts per ton of cooling load.
Simply put, yes. Rheia systems are designed to operate within equipment constraints as specified by the manufacturer.
The manifold design is an important part of the Rheia system. Rheia provides design guidelines to the HVAC design and contractor on how to properly size the manifold, assemble it correctly, and properly install into the home.
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.
Dedicated returns often result in high static pressure and are expensive to install. Central returns have been in use to great affect by production builders for many years proving to be effective and cost-efficient.
It’s up to the designer, but Rheia provides easy to implement methods to allow installers to balance a Rheia to multiple orientations.
Rheia registers should not be installed at the floor level. They are designed to throw air into a room and create a mixing environment that leads to increased comfort.
Yes. Rheia has several patents pending on the overall system and design of the system components.
The Rheia design process uses all the same principles and calculation methodology as Manual D. Like Manual D, a Rheia duct design uses friction rates, duct lengths, fitting losses, and static pressure calculations to determine the overall static pressure of the duct system. Manual D uses this information to determine duct sizes, whereas Rheia uses this information to determine the number of 3” and 4” ducts required for each room.
The manifold design is an important part of the Rheia system. Rheia provides design guidelines to the HVAC designer and contractor on how to properly size the manifold, assemble it correctly, and properly install into the home.
Rheia micro-diffusers are located high on interior walls to take full advantage of the way the air is delivered into a room. Through detailed engineering, the diffusers have been designed to throw air across a room and mix much more effectively than current register designs.
Temperature stratification (the difference in temperature from the lowest to the highest floor) is a common problem in homes. Rheia addresses the issue through the Rheia design process using a combination of small ceiling diffusers designed to throw more air down into a room, floor boots to deliver air lower in a room, and thoughtful design of diffuser locations.
Rheia works equally well with upflow or downflow equipment, based on the house floor plan and duct configuration. This gives the HVAC designer a lot of design freedom to create a solution that is both cost-effective and optimized for performance.
A thoughtful design process, components engineered to improve air mixing and airflow into a room, and the innovative Rheia Verify balancing process all contribute to improving the comfort of a Rheia home.
Rheia is a system that at its core is an engineered HVAC air distribution system. The engineered approach ensures a better performing system, that is designed to be labor-efficient, cost competitive, and energy efficient.
Yes. Rheia has a partnership with WrightSoft to provide training on using the Rheia duct design module within the WrightSoft application. You can request training here.
Yes. Connect to Rheia’s case studies section to learn more about Rheia customers in markets across the country.
Yes. Rheia provides a warranty for the Rheia system, but it mandates that the system is balanced using the Rheia Verify app.
Contact Rheia.
The Rheia system is very compact. When kitted for a typical home installation, the supply components, duct, and return ductwork, etc., can be shipped on a 4′ x ‘4’ pallet to the home. This compares to a 4′ x 12′ pallet used for a typical conventional installation. You can expect to see a significant reduction in warehouse inventory storage with Rheia.
Following standard vendor-customer business practices, Rheia will set you up with access to our ordering system which will handle the ordering of components and ductwork based on the agreed-to terms.
Rheia uses a balancing process that compares the design performance to what was actually measured in the field, and then facilitates a balancing procedure based on the actual onsite measurements. That process combined with better air distribution and mixing results in a better-balanced system that will be more comfortable.
There are several benefits: It is easier to design a system with equal sized ducts that receive the same air pressure at the manifold, making the entire system much more predictable when measuring airflow at the registers during the commissioning process.
Contact us to find out if Rheia is available in your area.
Yes. Rheia has dedicated regional field experts who can provide hands-on training at your location. Rheia also has a series of training documents and videos, and courses here [insert link]. We currently do not certify installers but are planning to release a comprehensive training program in the future.
While there are more ducts, each duct is installed with an air sealed, snap fit connection, so there is no additional air sealing needed. The small diameter ducts are lightweight, convenient to handle, and easy to route through the structure of the building. The home run design approach combined with the low SKU count, is much simpler to understand versus current multi-diameter systems, resulting in quicker installation and less errors.
Rheia meets 2022 Title 24 which allows uninsulated ducts to be run in the conditioned space of the home. Keeping ducts in the unconditioned attic (by deeply burying them in insulation), runs the risk that condensation will form on ducts and boots at vulnerable spots where the insulation is compromised. Constructing conditioned attics is expensive and labor-intensive which impacts the house cycle time.
Aside from current and pending building code changes in some markets requiring ducts to be in conditioned space, doing so simply makes sense. Attics experience significant temperature extremes in the summer and winter (hot and humid or extremely cold) affecting how effectively a duct in the attic can deliver conditioned air at the right temperature. The result is a system that has to run longer to heat or cool a room due to the significant amounts of energy loss along each insulated duct run. In addition, the risk of condensation in areas where duct insulation r-value is compromised, such as at the register boot, hanging straps, and areas where ducts are pinched or kinked also negatively impact the efficiency of the duct. Moving ducts into conditioned spaces resolves these issues.
Rheia is simpler in its design, and its easier to install. There are a number problems that can be created by flaws in HVAC systems, and Rheia strives to address any source through a combination of design engineering and product.
In a Rheia system, there are more registers for the drywall contractor to have to cut around. The process and tools they use today are the same for Rheia, using the same techniques as that used to cut around an electrical box. Once the drywaller gets a feel for the Rheia boot shapes, the process is quick and easy.
Insulated ductwork is typically used in specific locations, such as garage ceilings, where the structure of the home does not permit ducts to be run through the framing. Insulated and uninsulated ducts can be easily combined in a Rheia installation, enabling the designer to minimize costs and installation time by using insulated ducts only where needed.
Rheia has developed a boot and diffuser specifically for floor applications. In addition, in specific circumstances, wall diffusers can be used lower on a wall to help prevent temperature stratification. The HVAC designer can use these options based on the design need.
A thoughtful design process, components engineered to improve air mixing and airflow into a room, and the innovative Rheia Verify balancing process all contribute to improving the comfort of a Rheia home.
Rheia components are manufactured in high-performance engineering thermoplastics. These are the same materials used in the automotive industyry. The connector components meet UL 181C which includes a crush resistance test, a long-term heat exposure test, mold growth test, and other durability tests. In addition, the Rheia duct has been on the market for over 30 years, andis 181-listed meeting all the same performance requirements as the plastic components. The parts are made from similar materials that are used in electrical boxes and similar components in use today.
Rheia has developed an app, Rheia Verify, which the technician uses to balance each Rheia installation. Rheia Verify makes commissioning an installation quick and accurate. The Verify app uses the Rheia design to confirm the installation meets the system’s intended performance. Adjustments to individual dust airflows are then made using dampers in each duct to fine-tune the installation.
Building codes require ducts to be sealed to meet Energy Star duct leakage standards, but do not specify the application of mastic or tape. Rheia exceeds this leakage standard without the use of mastic or tape. In fact, the leakage test required by UL (part of UL 181C), with which Rheia also complies, is much more stringent than the Energy Star standard.
Rheia makes meeting Title 24 easier, primarily through the design process of moving ducts into the conditioned space. Current approaches are either expensive or flawed. Keeping ducts in the unconditioned attic (by deeply burying them in insulation), still runs the risk that condensation will form on ducts and boots at vulnerable spots where the insulation is compromised. Adding a spray foam layer to the ductwork to prevent moisture migration is cost prohibitive and time consuming. Similarly, conditioning the attic is expensive and increases the cooling load of the home, often requiring additional cooling tonnage.
Airflow requirements are managed by adding or removing ducts. Since all ducts are 3 or 4 inches in diameter, this is an easy process in the Rheia design software. The total amount of airflow delivered to a room is dictated by the Manual J calculations. The duct has a per linear foot pressure loss factor, as do the fittings. Once a designer has established the appropriate route from the manifold to the diffuser, a pressure estimate for that run can be determined. Meeting the required airflow in a given room requires the designer to add ducts until that requirement is met.
We don’t put ducts in the attic. Ducts in attics are a bad idea. Aside from pending building code changes requiring ducts to be in conditioned space, doing so simply makes more sense. Attics experience significant temperature extremes in the summer and winter (hot and humid or extremely cold) affecting how effectively a duct in the attic can deliver conditioned air at the right temperature. The result is a system that has to run longer to heat or cool a room due to the significant amounts of energy loss along the duct run. Duct insulation is not sufficient to make these losses insignificant. In addition, the risk of condensation in areas where duct insulation r-value is compromised, such as at the register boot, hanging straps and areas where ducts are pinched or kinked also negatively impact the efficiency of the duct. Moving ducts into conditioned spaces eliminate all of these issues.
Rheia is designed in accordance with all applicable industry building and energy codes. In addition, Rheia has worked with UL to develop a new standard that is designed specifically for these types of systems. Rheia is the only system on the market that meets this stringent new standard. Visit our codes section to get the details. [Insert link to Code Officials page].
Simply put, yes. Rheia systems are designed to operate within equipment constraints as specified by the manufacturer.
Airflow balancing as part of the commissioning process is an important step in any HVAC installation and is usually overlooked by installers because it is time-consuming and difficult to do with current systems, leading to unbalanced systems and comfort problems in homes. Rheia has simplified the balancing process, making it quick and easy to do, resulting in more efficiency for the HVAC technician and greater comfort for the homeowner.
Rheia is compact enough to move ductwork into the conditioned space of the home. Installing ducts in conditioned space is a significant HERS benefit of at least 2-3 points.
Dedicated returns often result in high static pressure and are expensive to install. Central returns have been in use to great affect for many years proving to be effective and cost-efficient.
Yes. Rheia has several patents pending on the overall system and design of the system components.
When considering total system installation costs (components, ductwork, framing, insulation, etc.), Rheia is cost competitive versus conventional systems. In markets that are predominantly sheet metal ductwork, significant savings are achieved through bill of material and installation labor reductions. In flex duct markets where ducts and equipment are in the attic, savings are predominantly equipment size reduction and installation labor time. In markets with high-performance energy codes, such as California and Washington, where duct work and equipment must be in the conditioned space, builders will see the added benefit that Rheia will meet code without complicated and expensive enclosure designs such as conditioned attics. Other aspects of the Rheia system such as waste reduction, reduced call backs, and cycle time reduction also positively impact the bottom line.
Aside from the savings from labor and materials; equipment size savings, cycle time reduction, lower HERS scores, fewer call backs, less job site waste, and homeowner comfort satisfaction, are other major benefits.
A Rheia system installed in the conditioned space requires a mechanical closet and options, or a combination of, strategically placed dropped ceilings and bulkheads, thickened walls, or inverted soffits. The costs to install a conventional system include building a support platform for the air handler, duct splitter boxes, an attic access hatch, running electrical, condensate, and refrigerant lines, and installing trusses able to handle the weight of the air handler. All of the aforementioned costs along with the parts and labor of the system must be considered when comparing the costs to convert to a Rheia installation.
When comparing the cost of Rheia to a conventional HVAC installation (sheet metal and/or flex duct) it should be evaluated at the system level. Depending on the market Rheia installations can be up to twice as quick quicker than current installations, reducing cycle time and labor costs. When comparing a typical contractor bid for labor and materials, Rheia is very cost-competitive.
Basement, Upflow, Downflow (all boxes).
Rheia makes meeting Title 24 easier, primarily through the design process of moving ducts into the conditioned space. Current approaches are either expensive or flawed. Keeping ducts in the unconditioned attic (by deeply burying them in insulation), still runs the risk that condensation will form on ducts and boots at vulnerable spots where the insulation is compromised. Adding a spray foam layer to the ductwork to prevent moisture migration is cost prohibitive and time consuming. Similarly, conditioning the attic is expensive and increases the cooling load of the home, often requiring additional cooling tonnage.
Airflow is managed by adding or removing ducts. Since all ducts are the same diameter, this is an easy process in the Rheia design software. The total amount of airflow delivered to a room is dictated by the Manual J calculations. The duct has a per linear foot pressure loss factor, as do the fittings. Once a designer has established the appropriate route from the manifold to the diffuser, a pressure estimate for that run can be determined. Meeting the required airflow in a given room requires the designer to add ducts until that pressure requirement is met.
With Rheia it’s easier. In a conventional duct system, large bulkheads and chases are required to house ducts which are unsightly, costly and use up valuable square footage. Ducts that can be routed in floor structures also use up a lot of room and create conflicts with other mechanical systems. The Rheia duct system fits compactly inside wall and floor structures. In the instances where a chase, bulkhead or drop ceiling is required, their depth is relatively small, impacting ceiling heights in architecturally unimportant areas.
Rheia has developed a proprietary process to enable cost-effective system commissioning, which includes the easy to use Rheia Verify app to set balancing dampers, measuring airflow at registers, and comparing performance to the original design. Balancing adjustments can be made to set the optimum comfort level of the home.
Yes. Rheia has a partnership with WrightSoft to provide training on using the Rheia duct design module within the Wrightsuite application.
Rheia is highly adaptable to zoning solutions. Rheia has developed a series of zoning design configurations and component recommendations that work seamlessly with Rheia. A benefit of the Rheia system is that in some home configurations that would normally be zoned, a zoned solution may not be required, saving costs while still providing the comfort needed.
Rheia registers are located high on interior walls to take full advantage of the way the air is delivered into a room. Through detailed engineering, the diffusers (aka registers) have been designed to throw air across a room and mix much more effectively than current register designs. Throwing air from interior walls (when floorpan design allows) keeps duct runs shorter and minimizes the number of diffusers.
The design process for Rheia is built into the Wrightsuite application in use by almost all HVAC designers. This is a familiar environment and follows a similar design process to conventional HVAC system designs, which have been streamlined due to the simplicity and low SKU count of the Rheia system.
A better number is how many per ton. It varies based on the floorplan, orientation and design of the home, but typically there’s about 10-12 ducts per ton of cooling load.
Simply put, yes. Rheia systems are designed to operate within equipment constraints as specified by the manufacturer.
The manifold design is an important part of the Rheia system. Rheia provides design guidelines to the HVAC design and contractor on how to properly size the manifold, assemble it correctly, and properly install into the home.
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.
Dedicated returns often result in high static pressure and are expensive to install. Central returns have been in use to great affect by production builders for many years proving to be effective and cost-efficient.
It’s up to the designer, but Rheia provides easy to implement methods to allow installers to balance a Rheia to multiple orientations.
Rheia registers should not be installed at the floor level. They are designed to throw air into a room and create a mixing environment that leads to increased comfort.
Yes. Rheia has several patents pending on the overall system and design of the system components.
The Rheia design process uses all the same principles and calculation methodology as Manual D. Like Manual D, a Rheia duct design uses friction rates, duct lengths, fitting losses, and static pressure calculations to determine the overall static pressure of the duct system. Manual D uses this information to determine duct sizes, whereas Rheia uses this information to determine the number of 3” and 4” ducts required for each room.
The manifold design is an important part of the Rheia system. Rheia provides design guidelines to the HVAC designer and contractor on how to properly size the manifold, assemble it correctly, and properly install into the home.
Rheia micro-diffusers are located high on interior walls to take full advantage of the way the air is delivered into a room. Through detailed engineering, the diffusers have been designed to throw air across a room and mix much more effectively than current register designs.
Temperature stratification (the difference in temperature from the lowest to the highest floor) is a common problem in homes. Rheia addresses the issue through the Rheia design process using a combination of small ceiling diffusers designed to throw more air down into a room, floor boots to deliver air lower in a room, and thoughtful design of diffuser locations.
Rheia works equally well with upflow or downflow equipment, based on the house floor plan and duct configuration. This gives the HVAC designer a lot of design freedom to create a solution that is both cost-effective and optimized for performance.
A thoughtful design process, components engineered to improve air mixing and airflow into a room, and the innovative Rheia Verify balancing process all contribute to improving the comfort of a Rheia home.
Rheia is a system that at its core is an engineered HVAC air distribution system. The engineered approach ensures a better performing system, that is designed to be labor-efficient, cost competitive, and energy efficient.
Yes. Rheia has a partnership with WrightSoft to provide training on using the Rheia duct design module within the WrightSoft application. You can request training here.
Yes. Connect to Rheia’s case studies section to learn more about Rheia customers in markets across the country.
Yes. Rheia provides a warranty for the Rheia system, but it mandates that the system is balanced using the Rheia Verify app.
Contact Rheia.
The Rheia system is very compact. When kitted for a typical home installation, the supply components, duct, and return ductwork, etc., can be shipped on a 4′ x ‘4’ pallet to the home. This compares to a 4′ x 12′ pallet used for a typical conventional installation. You can expect to see a significant reduction in warehouse inventory storage with Rheia.
Following standard vendor-customer business practices, Rheia will set you up with access to our ordering system which will handle the ordering of components and ductwork based on the agreed-to terms.
Rheia uses a balancing process that compares the design performance to what was actually measured in the field, and then facilitates a balancing procedure based on the actual onsite measurements. That process combined with better air distribution and mixing results in a better-balanced system that will be more comfortable.
There are several benefits: It is easier to design a system with equal sized ducts that receive the same air pressure at the manifold, making the entire system much more predictable when measuring airflow at the registers during the commissioning process.
Contact us to find out if Rheia is available in your area.
Yes. Rheia has dedicated regional field experts who can provide hands-on training at your location. Rheia also has a series of training documents and videos, and courses here [insert link]. We currently do not certify installers but are planning to release a comprehensive training program in the future.
While there are more ducts, each duct is installed with an air sealed, snap fit connection, so there is no additional air sealing needed. The small diameter ducts are lightweight, convenient to handle, and easy to route through the structure of the building. The home run design approach combined with the low SKU count, is much simpler to understand versus current multi-diameter systems, resulting in quicker installation and less errors.
Rheia meets 2022 Title 24 which allows uninsulated ducts to be run in the conditioned space of the home. Keeping ducts in the unconditioned attic (by deeply burying them in insulation), runs the risk that condensation will form on ducts and boots at vulnerable spots where the insulation is compromised. Constructing conditioned attics is expensive and labor-intensive which impacts the house cycle time.
Aside from current and pending building code changes in some markets requiring ducts to be in conditioned space, doing so simply makes sense. Attics experience significant temperature extremes in the summer and winter (hot and humid or extremely cold) affecting how effectively a duct in the attic can deliver conditioned air at the right temperature. The result is a system that has to run longer to heat or cool a room due to the significant amounts of energy loss along each insulated duct run. In addition, the risk of condensation in areas where duct insulation r-value is compromised, such as at the register boot, hanging straps, and areas where ducts are pinched or kinked also negatively impact the efficiency of the duct. Moving ducts into conditioned spaces resolves these issues.
Rheia is simpler in its design, and its easier to install. There are a number problems that can be created by flaws in HVAC systems, and Rheia strives to address any source through a combination of design engineering and product.
In a Rheia system, there are more registers for the drywall contractor to have to cut around. The process and tools they use today are the same for Rheia, using the same techniques as that used to cut around an electrical box. Once the drywaller gets a feel for the Rheia boot shapes, the process is quick and easy.
Insulated ductwork is typically used in specific locations, such as garage ceilings, where the structure of the home does not permit ducts to be run through the framing. Insulated and uninsulated ducts can be easily combined in a Rheia installation, enabling the designer to minimize costs and installation time by using insulated ducts only where needed.
Rheia has developed a boot and diffuser specifically for floor applications. In addition, in specific circumstances, wall diffusers can be used lower on a wall to help prevent temperature stratification. The HVAC designer can use these options based on the design need.
A thoughtful design process, components engineered to improve air mixing and airflow into a room, and the innovative Rheia Verify balancing process all contribute to improving the comfort of a Rheia home.
Rheia components are manufactured in high-performance engineering thermoplastics. These are the same materials used in the automotive industyry. The connector components meet UL 181C which includes a crush resistance test, a long-term heat exposure test, mold growth test, and other durability tests. In addition, the Rheia duct has been on the market for over 30 years, andis 181-listed meeting all the same performance requirements as the plastic components. The parts are made from similar materials that are used in electrical boxes and similar components in use today.
Rheia has developed an app, Rheia Verify, which the technician uses to balance each Rheia installation. Rheia Verify makes commissioning an installation quick and accurate. The Verify app uses the Rheia design to confirm the installation meets the system’s intended performance. Adjustments to individual dust airflows are then made using dampers in each duct to fine-tune the installation.
Building codes require ducts to be sealed to meet Energy Star duct leakage standards, but do not specify the application of mastic or tape. Rheia exceeds this leakage standard without the use of mastic or tape. In fact, the leakage test required by UL (part of UL 181C), with which Rheia also complies, is much more stringent than the Energy Star standard.
Rheia makes meeting Title 24 easier, primarily through the design process of moving ducts into the conditioned space. Current approaches are either expensive or flawed. Keeping ducts in the unconditioned attic (by deeply burying them in insulation), still runs the risk that condensation will form on ducts and boots at vulnerable spots where the insulation is compromised. Adding a spray foam layer to the ductwork to prevent moisture migration is cost prohibitive and time consuming. Similarly, conditioning the attic is expensive and increases the cooling load of the home, often requiring additional cooling tonnage.
Airflow requirements are managed by adding or removing ducts. Since all ducts are 3 or 4 inches in diameter, this is an easy process in the Rheia design software. The total amount of airflow delivered to a room is dictated by the Manual J calculations. The duct has a per linear foot pressure loss factor, as do the fittings. Once a designer has established the appropriate route from the manifold to the diffuser, a pressure estimate for that run can be determined. Meeting the required airflow in a given room requires the designer to add ducts until that requirement is met.
We don’t put ducts in the attic. Ducts in attics are a bad idea. Aside from pending building code changes requiring ducts to be in conditioned space, doing so simply makes more sense. Attics experience significant temperature extremes in the summer and winter (hot and humid or extremely cold) affecting how effectively a duct in the attic can deliver conditioned air at the right temperature. The result is a system that has to run longer to heat or cool a room due to the significant amounts of energy loss along the duct run. Duct insulation is not sufficient to make these losses insignificant. In addition, the risk of condensation in areas where duct insulation r-value is compromised, such as at the register boot, hanging straps and areas where ducts are pinched or kinked also negatively impact the efficiency of the duct. Moving ducts into conditioned spaces eliminate all of these issues.
Rheia is designed in accordance with all applicable industry building and energy codes. In addition, Rheia has worked with UL to develop a new standard that is designed specifically for these types of systems. Rheia is the only system on the market that meets this stringent new standard. Visit our codes section to get the details. [Insert link to Code Officials page].
Simply put, yes. Rheia systems are designed to operate within equipment constraints as specified by the manufacturer.
Airflow balancing as part of the commissioning process is an important step in any HVAC installation and is usually overlooked by installers because it is time-consuming and difficult to do with current systems, leading to unbalanced systems and comfort problems in homes. Rheia has simplified the balancing process, making it quick and easy to do, resulting in more efficiency for the HVAC technician and greater comfort for the homeowner.
Rheia is compact enough to move ductwork into the conditioned space of the home. Installing ducts in conditioned space is a significant HERS benefit of at least 2-3 points.
Dedicated returns often result in high static pressure and are expensive to install. Central returns have been in use to great affect for many years proving to be effective and cost-efficient.
Yes. Rheia has several patents pending on the overall system and design of the system components.
When considering total system installation costs (components, ductwork, framing, insulation, etc.), Rheia is cost competitive versus conventional systems. In markets that are predominantly sheet metal ductwork, significant savings are achieved through bill of material and installation labor reductions. In flex duct markets where ducts and equipment are in the attic, savings are predominantly equipment size reduction and installation labor time. In markets with high-performance energy codes, such as California and Washington, where duct work and equipment must be in the conditioned space, builders will see the added benefit that Rheia will meet code without complicated and expensive enclosure designs such as conditioned attics. Other aspects of the Rheia system such as waste reduction, reduced call backs, and cycle time reduction also positively impact the bottom line.
Aside from the savings from labor and materials; equipment size savings, cycle time reduction, lower HERS scores, fewer call backs, less job site waste, and homeowner comfort satisfaction, are other major benefits.
A Rheia system installed in the conditioned space requires a mechanical closet and options, or a combination of, strategically placed dropped ceilings and bulkheads, thickened walls, or inverted soffits. The costs to install a conventional system include building a support platform for the air handler, duct splitter boxes, an attic access hatch, running electrical, condensate, and refrigerant lines, and installing trusses able to handle the weight of the air handler. All of the aforementioned costs along with the parts and labor of the system must be considered when comparing the costs to convert to a Rheia installation.
When comparing the cost of Rheia to a conventional HVAC installation (sheet metal and/or flex duct) it should be evaluated at the system level. Depending on the market Rheia installations can be up to twice as quick quicker than current installations, reducing cycle time and labor costs. When comparing a typical contractor bid for labor and materials, Rheia is very cost-competitive.
In the 1950’s, as new duct technologies such as flex duct and rigid fiberglass were entering the market, the building regulations governing body needed a standard to ensure these new products could demonstrate acceptable fire performance, structural integrity, and performance when installed in residential buildings. The development of UL181 Standard for Factory-Made Air Ducts and Air Connectors addressed that need.
Today, the major code bodies now require commercial and residential factory made air ducts to comply with UL181. The standard requires air ducts to comply with range of rigorous tests prior to release into the marketplace. The tests are organized into three categories:
Fire Tests:
- Surface Burning Characteristics – Evaluates flame spread and smoke developed characteristics in accordance with UL723 (ASTM E84) – FS less than 25; SD less than 50
- Flame Penetration – Duct wall sections withstand exposure from a furnace fire for 30 minutes while supporting an 8 lb weight
- Burning – Resistance to sustained flaming and flame travel are evaluated in horizontal, 45 degree, and vertical orientations
Material Tests:
Corrosion Resistance, Mold Growth and Humidity, High and Low Temperature Tests
Integrity Tests:
Puncture, Static Load, Impact, Erosion, Pressure, Collapse, Tension, Torsion, Bending, and Leakage Tests
In 2017, during the development of Rheia, we contacted UL to clarify which industry standards in the building codes we would need to comply with. UL’s investigation revealed a lack of clarity in the codes regarding the use of plastic components as part of the duct system, and that UL181 was not fully compatible with plastic fittings. Refer to this table for detailed list of the tests required for a UL 181 and UL 181C listings. To address these issues, UL developed a new standard UL181C.
UL181C is currently not referenced in the model codes. The current status of UL 181C is that it is an Outline of Investigation. An Outline of Investigation is a document that contains the construction, performance, and marking criteria used by UL to investigate a product when the product is not covered by the scope of an existing UL Standard for Safety.
Review this article more information on UL standards and building codes:
https://code-authorities.ul.com/about/ulstds/
https://www.ul.com/news/when-its-hot-lets-be-thankful-air-ducts
About the flame spread and smoke developed index.
Ratings for flame spread and smoke development of construction materials are incorporated into the model building codes as published by the International Code Council (ICC) Building codes published by the ICC include the International Building Code (IBC), the International Residential
Code (IRC), and the International Fire Code (IFC) to name a few.
Testing to establish a flame spread index was developed in 1944 by Al Steiner of Underwriters Laboratories. It has since been referenced as UL 723, or the Surface Burning Characteristic of Building Materials test. The American Society for Testing Materials adopted the same test into its own standards, referred to as ASTM E84, the Standard Test Method for Surface Burning Characteristics of Building Materials. Both UL 723 and ASTM E84 are referenced in the building codes.
The Flame Spread Index and smoke Developed Index are based on an arbitrary scale in which asbestos-cement board has a value of 0, and red oak wood has 100:
FLAME SPREAD INDEX: A numerical reference that measures how fast and far a flame spreads during a 10-minute test.
SMOKE DEVELOPED INDEX: A measure of the concentration of smoke a material emits as it burns during a 10-minute test.
The flame spread and smoke developed index results are reported on a scale from 0 (cement board) and 100 (red oak). The flame spread index (FSI) for pipe and duct insulation used in an air plenum must be 25 or less and smoke developed index (SDI) 50 or less, commonly referred to as “25/50” rated.
Rheia’s ST-L 181-listed duct has a flame spread of 25 and a smoke developed index of 50 (25/50) which is a class A rating and the best possible rating, awarded to fire-resistant building products. UL181 requires a Class A rating for all duct. It is worth noting that the building codes allow wall and ceiling finishes to have a smoke-developed index of not greater than 450.
Rheia is an innovative supply air duct system designed to be compatible with residential grade air handling equipment. It works with any equipment manufacturer’s gas furnace, electric furnace, or heat pump air handler. Rheia is not a high static or high velocity system. The Rheia air distribution system uses many 3” or 4” ‘home runs’ from a central manifold to deliver air throughout the home. Each home run comprises flexible ducts that are UL181 listed, assembled using plastic connector components that terminate with boots with integrated airflow dampers.
Compared to a conventional duct system, a Rheia system will deliver the same amount of air to each room at similar static pressure. Rheia uses multiple smaller duct runs to each room rather than one or two larger ducts. For example, three 3” ducts can deliver about the same amount of air as one 6” or 7” duct. Home runs also have the advantage of not using wye branches, tee fittings or splitter boxes which add significant static pressure to the duct runs which deliver airflows that are very difficult to estimate.
Rheia will not change the heating and cooling equipment installed in the home. Manual J heat load calculations will still be performed, and Manual S equipment selections will still be used. Rheia systems are approved for all climate types. In cold climates, the heating equipment is responsible for maintaining minimum temperatures. In hot climates, the cooling equipment is responsible for maintaining maximum temperatures. In humid climates, the cooling and optional dehumidifying equipment is responsible for humidity control. Properly sized equipment is the key for temperature and humidity control. The duct system is responsible for distributing the air throughout the home proportionally to the heat load. Rheia does this through the design and commissioning processes.
The Rheia Design process uses the Manual J to determine how much air is required to each room. Mechanical designers use the Rheia Design process to design a system that will deliver adequate air to each room without exceeding the static pressure limits of the heating and cooling equipment. 5-position balancing dampers built into each Rheia supply boot are used to ensure the correct amount of air is being delivered to each room. Those damper positions are estimated during the design process, and fine tuned during the commissioning process called Rheia Verify.
Rheia Verify is an innovative airflow balancing process developed specifically for the Rheia air distribution system. It is a web based mobile phone app. Technicians use a flow hood to measure airflows at each supply diffuser and input those measurements into Rheia Verify. Rheia Verify compares those measurements to the Manual J room by room airflows and instructs the technician on how to adjust the balancing dampers. This process ensures each room receives airflow per the design intent.
Whether UL181C is or isn’t mentioned in the building codes is irrelevant. What matters is that the duct system complies with what is in the code. All duct installed in a residential home must be UL 181 listed. The Rheia duct is UL 181 listed. Listing File No. MH8698.
This section also lists an exception: “Exception: Ducts or portions thereof located completely inside the building thermal envelope”. The exception addresses the fact that ductwork within the thermal envelope is already protected from energy loss by virtue of being within the thermal envelope.
There is no language in the code restricting the use of plastic ducts above ground. Rheia ducts comply with all the applicable sections of M1601.1.1. See below.
The Rheia duct is a Class 1-rated UL181 listed Duct. Duct systems are not required to be UL181 listed. Only the duct is required to be listed.
The Rheia duct design process differs from a Manual D design but uses all the same principles and calculation methodology. Similar to Manual D, a Rheia duct design uses friction rates, duct lengths, fitting losses, and static pressure calculations to determine the overall static pressure of the duct system. Manual D uses this information to calculate duct sizes, while Rheia uses this information to calculate the number of 3” and 4″ Rheia ducts required for each room.
Meeting the requirements for UL94 and UL2043 is not a reason for disqualification. We selected these additional standards to help the code enforcement community assess the performance of our parts where the code lacks clarity, for example there is no specific code requirement for plastic duct fitting performance.
The code does not require the ‘duct system’ to comply with any UL test as an assembly, because there are many possible combinations of fittings and duct. It does however require the ‘duct’ (which is defined separately from ‘duct system’ in the codes) to comply with UL181.
The test to determine a component’s flame spread index is UL723 (ASTME84) (which is also a test in UL181). The purpose of the test is to determine the comparative burning characteristics of the material under test by evaluating the spread of flame over its surface and the density of the smoke developed when exposed to a test fire. This method of test for surface burning characteristics of building materials is applicable to any type of building material that, by its own structural quality or the way it is applied, can support itself in position or being supported in the test furnace to a thickness comparable to its intended use. The test specimen is required to be 24 ft in length. It is not possible to test our discrete components in this apparatus. It is therefore not possible to attain a flame rating of a component that does not comply with the test standard protocol. UL 2043 is the best standard to evaluate a small component burning characteristics. This is also why UL181C was developed by Underwriter’s Laboratory.
Upon reviewing the Rheia plastic components, they decided that the fittings that were an integral part of a duct run should comply with UL 181C (their new standard for assessing plastic duct fittings). This is to ensure that the plastic fittings have a similar flame spread and smoke development characteristics as ducts in order to minimize the spreading of a fire in a home.
Underwriters Laboratory reviewed the Rheia system and developed a new test standard for plastic fittings that replicated the tests with which a UL181 duct must comply. UL181C is a good way to assess the performance of Rheia’s plastic fittings because there is nothing in the building codes that addresses these new types of fittings.
We decided to specify the Distribution Components (the boots and take-offs) in the same material as the high-performing Connector Components to ensure all our fittings perform to the highest level possible. The thermoplastic material we use for all of these components is a V-0 rated material according to the UL94 test protocol.
There is nothing in the building codes that specify the performance requirements of our Diffusers. We specified a UV stable thermoplastic material to prevent discoloration over time.
The Rheia design methodology is available to HVAC designers as a plugin to Wrightsoft’s Right-Suite Universal software used by about 85% of the HVAC design industry.
Firestopping protocol should be followed per code. This usually required the use of firestopping material where the ducts transition between floors.
We have installed Rheia in markets across the US. The builder needs to take the same precautions to meet the code required air sealing requirements of the thermal envelope. Rheia ducts have a lower risk of condensation inside the thermal envelope as uninsulated metal ducts due to the lower emissivity of the material. As part of the approval process in California the California Energy Commission funded research into the risk of duct condensation. You can access the report here: https://title24stakeholders.com/measures/cycle-2022/analysis-of-duct-insulation-requirements-for-ducts-in-conditioned-and-indirectly-conditioned-spaces/
Rheia is approved in California, we currently have Rheia installed in pilot homes in Sacramento. The current version of Title 24 (2022) allows the installation of uninsulated ducts in the conditioned space of the home. The previous edition of Title 24 (2019) did not allow this.
Section M603.8 applied to underground ducts. Our system, which is installed above ground in the conditioned space of the home, does not need to comply with this section of the code.