How radiant heat works, importance of radiant angle (C) Daniel Friedman

Radiant Heat: Usage Guide, Strategies
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When to make use of radiant heat in buildings
Radiant heat use strategies
How radiant heat works in buildings
What are the pros and cons of radiant heating?
Operating cost comparisons for types of radiant heating
Floor gaps caused by under-floor radiant heat systems?
Odor complaints associated with some radiant heat tubing materials?
Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices
Electric radiant heat & thin film heaters for use below types of finish flooring
Questions & Answers about radiant heat flooring choices, design, installation, + diagnosis, and repair of problems

This article discusses the basics of radiant heat for auxiliary heating or basic heating in buildings, including strategies for using radiant heat. The article also compares the costs of types of heating system use and we describe hydronic (hot water) radiant heat and electric radiant heat systems. We describe typical installations of both hydronic tubing and electric radiant heat, including thin film electric radiant heat panels below several types of finish flooring.

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Radiant Heat Use in buildings: when, why, how to use radiant heating

Sketch at page top and accompanying text are reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. The sketch explains that the radiant heat effect of a hot surface depends on the angle that the surface forms with the subject. Large surfaces facing and close to the subject provide the most radiant heat.

See these articles on radiant heated floors

FLOOR, WOOD RADIANT HEAT - guide to installing wood floors over radiant heat systems
RADIANT HEAT - usage guide, Radiant Heat: how it works and when to use it - strategies for using radiant heat - this article is provided just below.
RADIANT HEAT TEMPERATURES - at the boiler, in tubing, under floors, floor surface, thermostat & control settings
RADIANT SLAB FLOORING CHOICES - wood vs ceramic tile over a radiant heated floor
RADIANT SLAB TUBING & FLUID CHOICES - tubing and fluid choices for radiant heating
RADIANT HEAT Floor Mistakes to Avoid - proper and improper radiant tubing depth in slabs & slab insulation needs - what can go very wrong when the building contractor substitutes brawn for brains
SLAB INSULATION, PASSIVE SOLAR - slab insulation & vapor barrier placement in heated floor slabs
WOOD FLOOR DAMAGE - from radiant tubing run too hot.

Also see Thin Film Radiant Heating Systems for Ceilings & Floors for examples of how electric radiant heat may be installed beneath several types of finish flooring.

"Radiant Heating, how it works, when to use it" - links to the original article in PDF form immediately below are followed by an expanded/updated online version of this article.

Radiant Heat Use [PDF] - Radiant Heat: how it works and when to use it.

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Radiant Heat Use - part 2 [PDF]
Radiant Heat Use - part 3 [PDF]

The table (left) included in this radiant heat article provides a typical fuel cost comparison for space heating.

The basics of Radiant Heating Systems

This article explains how radiant heating systems work, it describes the comfort of radiant heating systems, and it provides strategies for using radiant heat in buildings effectively. The author, Steven Bliss, explains how to use radiant heat most comfortably, citing the ability to heat large areas to relatively low temperatures (rather than providing concentrated heat source), the evenness of radiant heat, and the importance of mass inside the structure to help keep temperatures even and comfortable through the thermostat cycling on and off where radiant heating systems are installed.

The author describes relatively low-cost in-floor radiant heating systems using hot water as well as electric heating elements. In-drywall radiant heat products are also explained and described for ceiling use.

Advantages of radiant heating systems

The radiant heating system is unobtrusive - in fact not visible in the occupied space, saving floor space as well
Radiant heating systems are quiet and clean and require little or no maintenance (depending on the heating source: an oil fired heating boiler supplying a radiant heated building will still require annual maintenance).
Radiant heating systems save energy compared with comparable convective heating systems where the same fuel is being used to produce btu's of heat. Savings accrue from lower air temperatures as well as the omission of duct or pipe heat losses in the system.
Heating savings from radiant heat systems depend largely on the amount of thermostat set-back that the occupants find comfortable. Occupants of a radiant-heated building often are equally comfortable (compared with other heating methods) setting back the thermostat 5 degF - about a 20 to 25% savings on heating fuel expense.
Radiant heat "feels special" or "like being heated by the sun" - (an opinion difficult to verify objectively).

Our photo (above) shows a radiant-heated concrete slab under construction in Two Harbors, MN in 2007.

Disadvantages of electric radiant heat systems

Electricity can be the most expensive way to provide heat in some areas of the country. Check with your local utility company as special rates may be available for homes using electric heat.

One of the many foul-ups of the contractor whose radiant heat system was described at RADIANT HEAT Floor Mistakes to Avoid was that he failed to install a separate electric meter to provide service to the building where the electric radiant heat system was installed (although the meter was included in the job specs ignored by the contractor), precluding the owners' ability to take advantage of lower electrical utility rates.

Our photograph (left) shows a really nice looking electric boiler used for the radiant heat system discussed at RADIANT HEAT Floor Mistakes to Avoid - unfortunately although the boiler remains installed, the radiant floor heating system is not usable.
Extra ceiling or under-slab insulation will be needed for ceiling-mounted radiant heating systems. The worst foul-up of the contractor whose radiant heat system was described at RADIANT HEAT Floor Mistakes to Avoid was that he buried the in-floor radiant tubing so deep in the floor slab that more heat was transmitted through the under-slab insulation than reached the occupied space - rendering the heating system not usable.

Don't make this mistake. See SLAB INSULATION, PASSIVE SOLAR for under-slab and slab perimeter insulation specifications.

Floor Damage, Gaps, & Odor Complaints with Radiant Heat Installed under Wood Floors

We (DJF) have investigated a number of complaints of gaps opening between the boards of finished wood flooring and complaints of odors emitted from some types of tubing used in radiant floor heating systems.

Diagnosing gaps in finished wood flooring can be tricky, since these may appear with or without under-floor radiant heating systems installed, especially if the flooring is installed too quickly, without having adjusted its moisture level to that of the building. Installing wood flooring that is at too high a moisture level risks shrinkage and floor gaps as the building dries out.

In some cases that we investigated, flooring gaps appeared after an installer or owner pushed the radiant floor heating system to a temperature higher than recommended by the equipment and tubing manufacturers.

The temperature push was made in an attempt to "cook out" odors emitted from the radiant floor tubing when the heating system was first fired up.

Typical Cost of Radiant Heating Systems

Heating system costs are divided into installation or "first" costs, regular maintenance costs, and operating costs. Our photograph (left) shows two Therma-Ray electric radiant heat panels being installed in the ceiling of a 1960's home in Poughkeepsie, New York.

These panels were replacing previously damaged ceiling components. Be careful about cutting holes in drywall ceilings where electric radiant heating panels have been installed.

The installation cost for most radiant heating systems is between electric baseboard and conventional air or hydronic (hot water) heating systems.
Electrical radiant heating systems, if that's how your radiant heating system works, requires the least maintenance - practically none.
The fuel costs, if your radiant heat system uses electricity, will be higher than oil or gas in most areas of the country.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Thin Film Radiant Heating Systems for Ceilings & Floors - types, where to buy

An alternative to hydronic, tubing-based radiant heating systems that were discussed above, at Typical Cost of Radiant Heating Systems we cited electrical radiant heating systems including panels used in ceilings or floors. [See our photo above for an older version of electric heat in gypsum ceiling panels.]

These electric radiant floor heating systems use comparatively thin flexible heating film panels (IHS-CPF) that are wired to a dedicated electrical circut and of course controlled by a room thermostat. Some radiant heat panel sources include:

Calorique (West Wareham, MA 800 922-9276), produces thin film radiant heating panel systems used for interior building heating (ceilings or floors), snow melting, de-icing, drum and tank heaitng, agricultural uses, pet heating systems, and consumer end products.
CarbonicHeat (866-786-1806) radiant heating floor panels, .45mm thick, claim to be the thinnest radiant heating panels currently available. CarbonicHeat radiant heating panels are intended for use under ceramic tile. Radiant heat floor system products are also available for use under Saltillo tile and natural stone flooring as well as below nail-down (or staple-down) wood flooring and engineered wood flooring products.
ComfortTile adhesive-backed fiberglass mesh mats for radiant floor heating [manufacturer and distributor contact information needed - CONTACT us], used under ceramic tile or stone flooring.
FloorHeat (Lansing MI, 888-265-5455) provides electric radiant heating mats ideal for small floor areas, 12-inch wide electric heating elements for under framed floors, as well as supporting plastic grid modules, heating plates, and PEX tubing for hydronic radiant heating system s. Systems are intended for use under carpeting, hardwood, laminate floors, or parquet flooring. FloorHeat produces low-voltage radiant heating panels that might fit certain low-voltage alternative energy-designed homes. These panels can also be used in roofing applications and can tolerate being penetrated by roofing nails.
IdealHeat - see WarmRibbon flexible heating film ribbons and panels described below. [manufacturer and distributor contact information needed - CONTACT us],
In-Slab radiant heat electric cable used in concrete slabs. [manufacturer and distributor contact information needed - CONTACT us],
Nuheat electric radiant heat systems ( Richmond BC, Canada, 800-778-WARM (9276) ) for use under tile, stone, and laminate flooring, Nuheat Industries provides a cable system that permits custom layouts of heating elements as well as both standard and custom heating mats.
ThermalMat elecric radiant heat panels used under hardwoods, laminates, and engineered wood flooring; [manufacturer and distributor contact information needed - CONTACT us],
Warm Ribbon Flexible Heating Film panels [manufacturer and distributor contact information needed - CONTACT us], very thin panels, used under a variety of finish floor products. WarmRibbon products include a crystalline ribbon heater that can be used both indoors and outdoors and is intended for carpeted or parquet-flooring finish floors.

Note on Avoiding or Insulating Heat Sources rather than Producing Heat:

Too many of the electric radiant heat flooring searches we made turned up advertising pages where writers collected sources a bit hastily. We include the content below to help readers sort out the products they want (radiant heat flooring materials) from other stuff.

HeatShield panels, (Valley Center, CA 800-750-3978 ) produces heat insulating panels - in case you need to shield from heat rather than to direct heat into a building area. Heatshield Radiant Heat Mats (Amazon.com) are sold in an adhesive-backed form used, for example, in the automotive industry.

Examples of Thin Film Radiant Heat Flooring Installations for Different Flooring Materials

The Calorique company provides radiant floor heating systems in several designs including specifically for use below laminate flooring, carpeting, vinyl tile, linoleum, and ceramic tile floors. Calorique's system uses individual thin film panels connected to a 30-A electrical circuit to provide heat below these types of floor mateirals. Calorique describes these radiant heat floor installation examples:

Radiant Heat below glued carpet, wood, vinyl, or linoleum floors in dry surroundings

Finished floor surface: carpeting, wood, vinyl or linoleum (sheet flooring) with adhesive
Self leveling flooring cement or latex compound at least 1/4"thick
Thin film heating mats, electrical, wired per the manufacturer's instructions
Floor surface: concrete slab or wood

Radiant Floor heat below floating type wood, laminate, or parquet flooring in dry surroundings

Wood, laminate, or parquet finish flooring without use of an adhesive (typically mechanical clips or fasteners)
Thin film heating mats, electrical, wired per the manufacturer's instructions
Soft insulation material (see the manufacturer's specifications)
Floor surface: concrete slab or wood

Radiant Floor heat below ceramic tiles in dry surroundings

Ceramic tile finished floor surface
Thin-set / grout / tile adhesive or mastic
Thin film heating mats, electrical, wired per the manufacturer's instructions
Hard insulating material (see the manufacturer's specifications)
Floor surface: concrete slab or wood

Radiant Floor heat under tiles in wet surroundings

Ceramic tile finished floor surface
Thin-set / grout / tile adhesive or mastic
Grounding net - recommended in wet surroundings, a grounding net (for safety) is installed directly above the heating mat
Thin film heating mats, electrical, wired per the manufacturer's instructions
Hard insulating material (see the manufacturer's specifications)
Floor surface: concrete slab or woo

- Thanks to reader Jim O'Dowd for suggesting this resource.

CONTACT us to suggest other types or suppliers of radiant heating systems and equipment. InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information for the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website. We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions for our web articles.

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FLOOR, WOOD RADIANT HEAT - guide to installing wood floors over radiant heat systems
RADIANT HEAT - usage guide, strategies for using radiant heat
RADIANT HEAT TEMPERATURES - at the boiler, in tubing, under floors, floor surface, thermostat & control settings
RADIANT SLAB FLOORING CHOICES - wood vs ceramic tile over a radiant heated floor
RADIANT SLAB TUBING & FLUID CHOICES - tubing and fluid choices for radiant heating
RADIANT HEAT Floor Mistakes to Avoid - proper and improper radiant tubing depth in slabs & slab insulation needs - what can go very wrong when the building contractor substitutes brawn for brains
SLAB INSULATION, PASSIVE SOLAR - slab insulation & vapor barrier placement in heated floor slabs
WOOD FLOOR DAMAGE - from radiant tubing run too hot

  FLOOR, LAMINATE PLASTIC
  FLOOR, RESILIENT VINYL or CORK
  FLOOR, WOOD ENGINEERED & LAMINATED
  FLOOR, WOOD SOLID STRIP, PLANK
  FLOOR, WOOD ENGINEERED, LAMINATE, INSTALL
  FLOOR, WOOD FINISHES
  FLOOR, WOOD INSTALLATION GUIDE
  FLOOR, WOOD MOISTURE
  FLOOR, WOOD RADIANT HEAT

Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years. ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education. Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com.
Excerpts with updates and annotations expanding the original Best Practices Guide text can be found in the online review and book summary at BEST CONSTRUCTION PRACTICES GUIDE and also at DECK & PORCH CONSTRUCTION, at INDOOR AIR QUALITY IMPROVEMENT GUIDE, and in other articles found at InspectAPedia.com such as HOUSEWRAP AIR & VAPOR BARRIERS, SOUND CONTROL in buildings, and other topics.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Calorique Radiant Heating Floor & Ceiling Systems, Calorique LLC, 2380 Cranberry Highway, West Wareham, MA 02576 USA, Tel: 800 922-9276, produces thin film radiant heating panel systems used for interior building heating (ceilings or floors), snow melting, de-icing, drum and tank heaitng, agricultural uses, pet heating systems, and consumer end products. The company provides radiant floor heating systems in several designs including specifically for use below laminate flooring, carpeting, and tile floors. - Thanks to reader Jim O'Dowd for suggesting this resource.
FloorHeat 3130 Sovereign Drive, Lansing, MI 48911, 888-265-5455, Email: info@FloorHeatCompany.com) radiant floor heating panels,
Heatshield Panels, 27354 Valley Center Road, Valley Center, California 92082 USA, 800-750-3978
Nuheat Industries 3105 - 6900 Graybar Road, Richmond, BC Canada V6W 0A5, electric radiant heat systems for use under tile, stone, and laminate flooring, 800-778-WARM (9276) Email: info@nuheat.com
ASHRAE 25 Heating, Refrigeration, and Air Conditioning engineering standards
ASHRAE 90.1-2004 User's Manual, instructions for the design of commercial and high-end residential buildings "to ensure their compliance with ANSI/ASHRAE/HESNA Standard 90.1-2004 including the application of principles of effective energy conserving design..."
CarbonicHeat radiant heat flooring products, 866.786.1806 sales@carbonicheat.com, [no mailing address]
Passive Solar Design Handbook Volume I, the Passive Solar Handbook Introduction to Passive Solar Concepts, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v1.pdf
Passive Solar Design Handbook Volume II, the Passive Solar Handbook Comprehensive Planning Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v2.pdf [This is a large PDF file that can take a while to load]
Passive Solar Handbook Volume III, the Passive Solar Handbook Programming Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v3.pdf
The Passive Solar Design and Construction Handbook, Steven Winter Associates (Author), Michael J. Crosbie (Editor), Wiley & Sons, ISBN 978-047118382 or 0471183083 is available at Amazon.com and via the The Passive Solar Design and Construction Handbook, Steven Winter Associates (Author), Michael J. Crosbie (Editor), Wiley & Sons, ISBN 978-047118382 or 0471183083 is available at Amazon.com and via the InspectAPedia Bookstore
"Passive Solar Home Design", U.S. Department of Energy, describes using a home's windows, walls, and floors to collect and store solar energy for winter heating and also rejecting solar heat in warm weather.
"Solar Water Heaters", U.S. Department of Energy article on solar domestic water heaters to generate domestic hot water in buildings, explains how solar water heaters work. Solar heat for swimming pools is also discussed.
"Heat Exchangers for Solar Water Heating Systems", U.S. DOE describes the types of solar water heater heat exchange methods between the sun and the building's hot water supply
"Heat-Transfer Fluids for Solar Water Heating Systems", U.S. DOE, describes the types of fluids selected to transfer heat between the solar collector and the hot water in storage tanks in a building. These include air, water, water with glycol antifreeze mixtures (needed when using solar hot water systems in freezing climates), hydrocarbon oils, and refrigerants or silicones for heat transfer.
"Solar Water Heating System Maintenance and Repair", U.S. DOE
"Solar Water Heating System Freeze Protection", U.S. DOE,using antifreeze mixture in solar water heaters (or other freeze-resistant heat transfer fluids), as well as piping to permit draining the solar collector and piping system.
"Scaling and Corrosion in Solar Water Heating Systems", U.S. DOE
www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=12850 is the base U.S. DOE website for these articles
"Active Solar Heating Systems", U.S. Department of Energy, including
"Radiant Heating Systems" U.S. DOE
"Absorption Heat Pumps & Coolers", U.S. DOE
"Solar Air Heating" U.S. DOE also referred to as "Ventilation Preheating" in which solar systems use air for absorbing and transferring solar energy or heat to a building
"Solar Liquid Heating" U.S. DOE, systems using liquid (typically water) in flat plate solar collectors to collect solar energy in the form of heat for transfer into a building for space heating or hot water heating. The term "solar liquid" is used for accuracy, rather than "solar water" because the water may contain an antifreeze or other chemicals.

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Radiant Heat Use in buildings: when, why, how to use radiant heating

See these articles on radiant heated floors

The basics of Radiant Heating Systems

Advantages of radiant heating systems

Disadvantages of electric radiant heat systems

Floor Damage, Gaps, & Odor Complaints with Radiant Heat Installed under Wood Floors

Typical Cost of Radiant Heating Systems

Thin Film Radiant Heating Systems for Ceilings & Floors - types, where to buy

Note on Avoiding or Insulating Heat Sources rather than Producing Heat:

Examples of Thin Film Radiant Heat Flooring Installations for Different Flooring Materials

Radiant Heat below glued carpet, wood, vinyl, or linoleum floors in dry surroundings

Radiant Floor heat below floating type wood, laminate, or parquet flooring in dry surroundings

Radiant Floor heat below ceramic tiles in dry surroundings

Radiant Floor heat under tiles in wet surroundings

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair