Radiant Cooling Systems


The most effective way to optimize thermal comfort and energy use. 

Typically designed in conjunction with radiant heating, radiant cooling works by circulating cooled water through the same network of pipes where warm water circulates during winter. The cooled surfaces evenly absorb heat energy to create perfect comfort using little energy.

Suited to Many Climate Regions
Early on, radiant cooling was best suited for arid regions, however, advances in system design and control capabilities have led to successful installations in various climate zones.

How it Works

Radiant cooling works best in a tightly sealed building that integrates radiant with a downsized forced-air system to meet the building’s fresh air requirements. 

A hydronic radiant system takes advantage of the superior heat transfer properties of water to very efficiently absorb heat energy, while air-based cooling efficiently removes excess humidity. By shifting some of the cooling load to the radiant system, air handling equipment and ductwork can be significantly downsized.

Achieving Optimal Radiant Cooling Output
A radiant cooling system is designed similarly to a radiant heating system, with minor adjustments in pipe diameter and pipe spacing. The capacity of a radiant cooling system depends on factors such as insulation, pipe spacing, floor construction and indoor air temperatures. Under optimal design conditions, capacities of a floor system up to 16 Btu/h∙ft² can be achieved,3 with more typical capacities in the 8 to 12 Btu/h∙ft² range. Ceiling systems can achieve nearly double this output.

The main difference between radiant cooling and radiant heating system design is a heightened awareness of humidity control. Careful control of humidity and water temperature is essential to reduce the risk of condensation. By using an integrated design team approach including architects, engineers and contractors from the early phases of a project’s design, many buildings have realized superior energy performance with REHAU radiant heating and cooling systems.

Increasing Capacity With Bidirectional Conditioning
In REHAU radiant cooling systems, RAUPEX pipe is typically integrated into an insulated floor slab, providing unidirectional conditioning to a single adjacent space. For interior levels where bidirectional conditioning of spaces above and below is desired, the layer of insulation can be omitted. Often referred to as thermally activated slabs (TAS) or thermally activated building systems (TABS), this emerging design option increases the capacity of the radiant system. In addition, “charging up” the thermal mass can take advantage of off-peak electrical rates.


This diagram of a typical commercial radiant cooling system illustrates two installation configurations: A TAS method (Thermally Activated Slab) in the upper floor and a standard in-slab construction with an insulation barrier in the lower floor. Supply lines from the energy source are colored blue; return lines are colored red.

1. RAUPEX® pipe
2. PRO-BALANCE® manifold
3. Room thermostat / humidity sensor
4. System controller
5. Surface sensor
6. Outdoor air sensor
7. Main control
8. Valves
9. Temperature sensor
10. Circulator pump
11. Mixing valve
12. Energy supply (e.g., geothermal heat pump)

The capacity of a radiant cooling system depends on factors such as insulation, pipe spacing, floor construction and floor covering. Under optimal design conditions, capacities of up to 16 Btu/h ft² can be achievedwith more typical capacities in the 8 to 12 Btu/h ft² range.

In radiant cooling systems, RAUPEX® pipe is either integrated into a floor structure with insulation to condition the space above or without insulation to condition the space above and below.

Design Factors
Designing and installing a radiant cooling system can be straight forward, especially when integrating with a radiant heating system. A focus on controlling humidity levels and water temperatures is essential to reduce the risk of condensation associated with radiant cooling.

Radiant cooling works best in a tightly sealed building, so you will typically need supplemental ventilation, either to meet the building’s fresh air requirements or to meet peak cooling loads. 

*Olesen, Bjarne. Radiant Floor Cooling Systems, ASHRAE Journal, September 2008.


Just as ground temperatures keep the walls of your basement slightly cooler and therefore absorb heat from the rooms, a radiant system embedded in your building structure can have a similar effect, providing even, comfortable cooling to your space.

Increases Thermal Comfort
The human body feels at its best when it can regulate at least 45% of its heat emission via radiation. Radiant cooling provides a comfortable environment by optimizing the surface temperature of the occupants’ surroundings and efficiently absorbing unwanted heat from the space.

Improves Energy Efficiency
By surrounding you with cooled surfaces, radiant cooling allows you to feel comfortably cool with your thermostat set a few degrees higher. This can significantly reduce energy consumption. For the ultimate in efficiency, couple radiant cooling with geothermal. The moderate water temperatures required by a radiant cooling system are precisely the temperature ranges in which a geothermal heat pump operates most efficiently.

Improves Air Quality
A radiant cooling system can greatly improve air quality, making it ideal for hospitals, nursing homes or any facility in which air quality is critical. Also, radiant cooling can handle the entire cooling load or be used to cover the base loads in traditional cooling applications. 

Reduces Life Cycle Costs
A hybrid radiant-forced air cooling system may cost a little more upfront, but its superior energy efficiency will result in a short payback period and lower operating costs. In more arid climates where air handling equipment can be downsized dramatically, a hybrid design can actually reduce initial investment costs. You can also expect lower maintenance costs with a hybrid system.


REHAU Radiant Heating: San Diego Central Courthouse

San Diego Courthouse (San Diego, CA)

Approximately 112,000 ft (34,138 m) of 5/8 in. RAUPEX pipe runs through this 704,000 ft2 (65,400 m2) courthouse, carrying temperature-controlled fluid. Chilled and hot water are mixed to appropriate temperature, depending on the operation (cooling or heating) of the radiant floors and zones. 

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Radiant Heating Sheridan College

Sheridan College Davis Campus (Brampton, Ontario)

The energy performance of this new facility, which opened in fall 2017, exceeds the LEED Gold standard at 100 kilowatt hours per square meter per year (32.2 kBtu/ft2 /yr). The building uses REHAU radiant in-floor heating and cooling technology, which designers say was the obvious solution for tackling the challenge of maintaining comfortable temperatures in a structure with very high ceilings.

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REHAU UBC Student Centre Project

University of British Columbia (UBC) Student Centre (Vancouver, BC)

This LEED® Gold certified building, designed in part by engineering students themselves, incorporates reused materials, passive solar heating and a ventilation system combined with radiant that harnesses a “stack effect’’ to move air through the building naturally. It incorporates a REHAU Radiant Heating System featuring RAUPEX® crosslinked polyethylene PEXa pipe installed in floors throughout the building to provide precise heat to 20 separate zones.

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University of Chicago Student Residence (Chicago, IL)

Campus North Residential Commons is a 400,000 ft2 (37,161 m2) energy-efficient structure designed with modern student life in mind. The housing complex bridges the academic community with the surrounding neighborhood of Hyde Park. Common areas are heated via a traditional forced-air system, while the living quarters use REHAU in-slab hydronic radiant heating and cooling. The radiant system was chosen early in the project for the dorm rooms in order to improve energy efficiency and enhance comfort for the students. 

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JSF High School (Toronto, Ontario)

The École secondaire Jeunes sans frontiers (JSF) is dedicated to fostering an enriched, student-focused learning experience for its students. This includes providing a comfortable, healthy and sustainably designed learning environment. Installed throughout the entire 90,000 ft2 (8,463 m2) facility, the REHAU radiant heating and cooling system consists of 104,700 ft (31,913 m) of RAUPEX® 5/8-in. O2 Barrier pipe and 42 PRO-BALANCE® manifolds pre-piped with three-way valves into all recessed manifold distribution cabinets.

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Sweetwater Spectrum (Sonoma, CA) 

Recognizing a need for housing support as their children with autism advanced into adulthood, a group of Northern California families combined forces to conceptualize the Sweetwater Spectrum community for adults with autism. The residential community incorporates a combined radiant heating and cooling system in its housing areas as well as in the 2,290 square foot community center.

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YWCA Toronto Elm Centre (Toronto, Ontario)

The YWCA Elm Centre is an $80 million, 302-unit affordable and supportive permanent housing complex for women and women-led families. The complex spans an entire city block and includes residential towers, a restaurant, boutique, auditorium and other commercial space, as well as the new YWCA Toronto corporate offices. The design incorporates a variety of sustainable construction elements, including an innovative thermally-activated slab radiant heating and cooling system manufactured by REHAU. 

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Pier One Warehouse (San Francisco, CA)

The REHAU radiant floor heating and cooling system installed in a historic warehouse located on Pier One, the northernmost pier on San Francisco’s Embarcadero is, according to industry experts, one of the first documented use of a radiant floor heating system also used to cool a building in North America. Funding requirements specified that no insulation be installed on the exterior walls and that the system would not obstruct the exposed beams and rafters of the building or the "clear story" at the roof peak. The radiant floor heating system met both of these conditions. 

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Milwaukee Art Museum (Milwaukee, WI)

During initial planning, the Milwaukee Art Museum’s unique design and choice of materials left the architect and builder with a major challenge – how to keep museum guests warm. Visitors would be positioned between two beautiful but innately cold elements: buffed, imported marble flooring and a cathedral-like ceiling made of glass. Determining that forced air would be problematic, they settled on a REHAU Radiant Heating and Cooling system. 

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Spring Creek Village (Alberta, Canada)

This innovative residential community gently integrates and enhances the area’s natural waterways, forestry and mountain views. In addition to incorporating the natural environment, all buildings were designed to include energy-efficient amenities and alternative energy sources. The developer chose a REHAU Radiant Heating and Cooling System for its energy efficiency, durability and ease of installation.  An estimated several million feet of RAUPEX® pipe expected to be installed by completion of the entire project. 

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Media & Tools


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Net Zero Near the River
Engineered Systems Magazine, 09.13

Being Radiant
The Construction Specifier 06.14

VAV vs Radiant: Side-by-Side Comparison
ASHRAE Journal 05.14

Radiant Design for Performance
IE3 05.14

Colorado Aviation Training Facility Uses Radiant Heating/cooling to Reach LEED®Silver
PM Engineer 03.14 

The Path to Near Net-zero is Underfoot
HPAC 02.14

REHAU Radiant Heating and Cooling Systems Deliver on Energy Efficient Goals
PM Engineer 01.14

Don't Just Go With The Flow: Creating Hydronic Radiant Equipment Schedules is the Key to Successful Radiant Projects
HPAC Magazine 02.13

YWCA Toronto Features Thermally Activated Slab, Geothermal Design
ACHR News, 11.12

Thermally Activated Slab Technology: The Next Generation
HPAC Magazine 11.12

Radiant Design Fundamentals: Start At The Beginning
Mechanical Business 01.11

Radiant Design Fundamentals: One Thing Leads to Another
Mechanical Business 03.11

Denver Zoo’s New Exhibit Utilizes Renewable Energy
Contractor 08.11

Architecture Projects of the Future (REHAU Montana ecosmart house)
REHAU Unlimited Magazine

Researching Energy Efficiency (REHAU Montana ecosmart house)
Plumbing & Mechanical 09.1