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ELECTRIC RADIANT GUIDELINES
SECTION 100. - Electric Radiant Panel Systems
Electric Radiant Panel Systems incorporate components including cables, mats, flat elements, mesh, insulated foil, thin film products and modular prefabricated panels. Systems are available for installations within the ceiling or floor assembly, on walls or under the floor.
All components must conform to relevant domestic and international standards, and installation must conform to National and local electrical and building codes. Examples of certifications include conformance to: ANSI/UL STD 1693, CAN/CSA C22.2 NO 217, National Electrical Code (NEC), including Article 424 (space heating) and Article 426 (deicing and snow-melting).
SECTION 101. - General Design
In advance of the design process, consult the manufacturer’s design and installation instructions for products under consideration, the National Electrical Code, local building and electrical codes, and other relevant references such as RPA publications, and the ASHRAE handbooks.
101.1 Insulation
Insulation should be installed in accordance with the product manufacturer’s recommendations, but must meet applicable building code requirements.
101.1.1 Slab insulation, slab in contact with soil.
When the floor is heated, slab edge perimeter insulation should be installed to
a minimum of R-0.125 per 1oF (.56oC). Design difference between Outdoor and Indoor Design Temperatures to a minimum depth equal to that of the local frost line. Alternatively, a minimum of R-10 rigid board insulation should be installed beneath heated concrete slabs on grade, for a distance of four feet horizontally inward or vertically downward from the slab perimeter .Where local sub soil and ground water conditions warrant, full coverage may be necessary.
101.1.2 Suspended floor construction, conditioned spaces.
Insulation between a heated floor and a heated space should be a minimum of R-5 for hard surface floors and R-11 for carpeted floors, unless the downward heat contribution is desired and supported by the manufacturers design criteria.
101.1.3 Suspended floor construction, unconditioned spaces.
If the space below the heated floor is unheated, the minimum R-values
between the floor and the unheated space should be R-13 for hard surface
floors and R-19 for carpeted floors respectively. When any cable is attached to the underside of a floor, there should be a minimum air space of two inches between the underside of the floor and the insulation. With self-regulating elements there should be no air gap between the underside of the floor, the elements and the insulation.
101.1.4 Heated walls, when applicable.
If a wall is heated between conditioned spaces wall insulation should be
considered as required to maintain control functions. If a wall is heated between a conditioned and unconditioned space, the wall should be insulated to a minimum of R-13.
101.1.5 Heated ceilings, conditioned and unconditioned spaces.
When a ceiling is heated, a minimum R-11 insulation should be placed above the heated ceiling. If the space above the heated ceiling is unheated, the minimum R-value should be R-30.
101.1.6 Codes
a. Where local codes specify insulation R-values greater than those specified by the RPA Guidelines or manufacturers specifications, the local codes are governing.
b. Fixed electric radiant panels shall be installed in accordance with the National Electrical Code, Canadian Code, or governing relevant jurisdictional codes.
101.2 Heat Load
101.2.1 Heat Loss Calculations.
a. Room by Room
A heat loss calculation should be done for each room or separate space within the structure. Rooms joined without a dividing wall may be calculated as a single space.
b. Methods
Heat loss or heat gain calculations will be accomplished using one of the following methods or equivalent; ASHRAE, IBR Guide, Manual J, Manual N or manufacturer’s design criteria.
c. Apply design judgment
Conventional convection heat loss calculation methodology and assumptions can develop a heat loss that is up to 20% or more above the heat loss that the radiant system will experience.
Simulation or design programs such as BLAST or BCAP incorporate mean radiant temperature into their heat balance, resulting in accurate heat loss for radiant systems.
d. Supplemental heating
For systems used for supplemental heating, the heat capacity is determined by defining the heating deficit or special requirement.
e. Floor warming
For systems used for floor warming, no heat loss calculations are required.
101.2.2 Space Heating Required Design Information
The following design information should be included with each design of radiant floors, walls or ceilings:
1. Room identification and zone information.
2. Room by room heat loss (kWh).
3. Panel area (sq.ft.)
4. Panel output (W/sq.ft.)
5. Assumed floor assembly and covering of approximate panel R-value.
6. Average panel temperature at design.
7. Panel surface temperature at design load.
8. Desired room temperature.
9. Outside temperature.
10. Supplementary heat if required.
101.2.3 Floor Warming Design Information
The following design information should be included with each design of floor warming.
1. Room identification and zone information.
2. Panel area (sq.ft.)
3. Panel output (W/sq.ft.)
101.3 Surface Temperatures
Proper design and control of panel temperatures is essential to safety, occupant thermal comfort, and thermal space conditioning.
Panel surface temperatures are defined by many factors including: the manufacturers’ performance ratings, contiguous building materials, insulation, panel coverings, certifications, listings, codes, controls, and heat loss.
101.4 Controls
All systems must have the ability to be switched on and off.
101.4.1 Floor warming.
All constant wattage radiant panels should have a control device and ground fault interrupter. Not all self-regulating radiant panels require control devices.
101.4.2 Space heating.
All constant wattage radiant panels should have a control device which maintains the space at design conditions. Some self-regulating radiant panels naturally control the design condition.
101.5 Power Supply
Power supply shall be compatible with design criteria of specific electric radiant panel.
a. Line voltage – 100 to 277 VAC
b. Low voltage – up to 50 VAC or VDC
101.6 Heat output
Radiant Panel Systems are categorized by their heat output.
a. Constant wattage
b. Self-regulating - Positive Temperature Coefficient (PTC)
SECTION 102 - Testing Procedures
102.1 Resistance Testing
All electric elements should be tested prior to installation, in accordance with manufacturer's instructions, to assure that the product matches the specifications and design. The ohmmeter is used to measure resistance for confirmation. Field panel construction must include resistance check at each step, prior, during, and after the installation. Panels must also be tested for continuity to be sure that there is no current leakage. Record the readings at the electrical circuit source to facilitate future safety and performance analysis.
102.2 Insulation Test
For insulation resistance use a megohm or equivalent device in accordance with the manufacturer's instructions.
102.3 System Validations
The installer should operate and verify that the system is operating properly as designed.
SECTION 103 - Surface Temperatures
Panel design, building material, and listing certification requirements are examples of factors that govern radiant panel temperature limits. Within these temperature maximums, the actual design temperatures are determined by meeting the objective of providing occupant thermal comfort.
ANSI/ASHRAE Standard 55-1992-R provides information about comfort levels and floor temperature with 75oF (24oC) as optimal for occupant thermal comfort in the built environment and suggests that radiant asymmetry not exceed 9oF (5oC) in relation to room air temperature.
The maximum ambient-adjusted temperature at each sensing location shall not exceed the limits specified in the UL 1693 Standard, Table 19.1 (maximum temperatures of heating products).
103.1 Floor Surface Temperatures
Floor surface temperatures should not exceed 85oF (29oC) in areas where prolonged foot contact is expected except were specified by the manufacturer, or unless flooring materials dictate a lower temperature.
103.2 Wall Panel Surface Temperatures
Wall panel surface temperatures (the surface that can be touched) for panels installed less than 6 feet above the floor, are a maximum of 150oF (65oC). Local codes must be consulted for the exact maximum temperatures permitted in a particular jurisdiction for a particular panel or installation.
103.3 Ceiling Panel Surface Temperatures
Ceiling panel surface temperatures are unique to each panel and installation design layout.
SECTION 104 - Floor Covering
104.1 Carpet and Carpet Cushion
Refer to system and flooring manufacturer's instruction regarding criteria and installation of carpet and carpet cushion for electric radiant products.
Note: Some electric radiant panel systems are not intended for use with carpet and carpet cushion.
104.2 Wood Flooring
a. Finish floor surface temperature should not exceed 85oF (29oC) when either solid or laminated hardwood flooring is used as a panel covering. Where a manufacturer’s suggested maximum surface temperature is lower than 85oF (29oC) the lowest temperature limit should be observed.
b. The wood covering should be acclimated to the dry space for a minimum of five days before installation and tested for moisture content in accordance with the wood manufacturer’s recommendations, when applied over panel heating systems.
c. When a concrete or gypsum slab subfloor is used, the slab should be cured or dried and tested for moisture content to meet the requirements of the wood floor manufacturer before the wood is applied.
d. Laminated and floating wood floors are the preferred method over radiant panel heating.
e. Solid wood floors can be successfully installed when due consideration is given to local climate, species of wood, dimension of flooring, moisture content of flooring as well as moisture content of the structure and substrata.
104.3 Tile and Natural Stone
Ceramic tile installed over suspended radiant floor panels should have a crack isolation membrane placed between the tile and the thermal mass, or as indicated by tile industry guidelines.
Note: Some electric radiant panel systems do not require crack isolation membrane.
104.4. Resilient Goods
Floor surface temperatures should not exceed 85oF (29oC) unless manufacturers recommendations allow for or require a different temperature.
SECTION 105 - Thermal Mass
105.1 Definition
Any cementitious or similar material used to embed cable for the purpose of distributing heat.
105.2 General
Use of thermal mass depends on the type of electric radiant panel element to be installed. Consult manufacturer's instructions for type and amount of thermal mass required for the system used.
a. Structural slabs
Reinforced concrete slabs should be a minimum of 4” in depth with appropriate steel reinforcement, vapor barrier, and insulation per RPA Guidelines.
Note: Some electric radiant panel systems should not be placed in direct contact with any conductive material, i.e. metal mesh.
b. Suspended floors
Subfloor and structure should be suitable as defined by the underlayment manufacturer and structural engineering practice, and be approved for use with radiant heating at required mass temperature.
c. Product should be inspected for physical damage and tested for continuity.
d. Care should be exercised during placement and finishing to avoid damage to the product and when using sharp tools and implements.
e. Circuits should be protected with planks and/or plywood where subjected to wheelbarrow traffic.
f. In the event of damage to the product during a pour, the process should halt and the product repaired.
g. Adequate heat and ventilation should be provided to insure proper curing conditions for the material.
h. No finish materials may be placed on the thermal mass until dry.
SECTION 106 - Ceiling Panels
106.1 Prefabricated Electric Panels
Prefabricated ceiling panels are generally encapsulated or framed in metal or glass, and are mounted on the surface or flush with the ceiling, or placed in a suspended grid-ceiling.
106.2 Thin Film Electric Panels
Thin film ceiling panels are laminated conductive coatings, printed circuits, or etched elements that are installed so that the heating surface is positioned between the ceiling joists and resting in direct contact for heat conduction to the ceiling gypsum board.
106.3 Electric Cable Panels
Cable heating mats can be installed between joists in contact with the ceiling and insulated above, or can be attached flush with the ceiling and covered with plaster.
SECTION 107 - Wall Panels
Concealed or embedded electric radiant panels are generally prohibited by domestic national and local electrical building codes for safety, due to the potential for electrical current contact from nails driven for hanging pictures or from building alterations.
Consult manufactures instructions and electrical and building codes to assure that panels used for surface mounted wall or baseboard heating conform with regard to surface temperature requirements.
SECTION 108 - Heated Floors
Refer to system manufacturer's installation instructions for methods of fastening the panels to the concrete or subfloor.
108.1 Electric Constant Wattage Heating Cables
A separate resistance element to generate heat usually supplied on spools and laid out by the installer.
108.2 Electric Constant Wattage Heating Mats
Cables affixed to a medium with uniform spacing providing a fixed output of watts per linear foot.
108.3 Self-regulating Heating Elements
These elements use conductive plastic to continually adjust their power output in response to changes in the ambient temperature. This means that when the ambient temperature rises, the electrical resistance increases and the consumption of electricity decreases. They come in cables or flat elements.
108.3 Metal Strips or Mesh
These products come in different forms and type of metal.
SECTION 110 – Low-voltage Radiant Panel Systems
Low-voltage radiant panel systems are normally connected to a safety-isolating transformer. Some systems can be powered AC or DC and can also be run by solar or wind-power source. They may not all have to be equipped with a ground fault interrupter.
SECTION 120 – Cable / Mat Where Applicable
120.1 Structural and Non Structural Floor
Thermal mass - element spacing should not exceed 12" unless specified through appropriate manufacturer design criteria. The element should be fastened to provide a minimum of 1/8" deep covering during the pour and should not touch or cross over itself unless manufacturer design criteria permits.
120.2 Wood Joist Spacing
A minimum 2” (50 mm) air gap between the product and the underside of the floor joist cavities should be insulated per manufacturer’s specifications.
120.3 Earth Thermal Storage
The element should be placed in a thermal storage medium. The element should be spaced and located according to manufacturer's recommendations.
SECTION 130 - PTC Cable / Element Where Applicable
130.1 Structural And Non Structural Floor
Element spacing depends on the heating needs and type of floor covering used. Follow appropriate manufacturer design criteria for minimum coverage.
130.2 Wood Joist Spacing – Flat PTC Element Only
The panels have to be placed snug against the medium to be heated, with no air gap. The underside of the floor joist cavities should be insulated per manufacturer's specifications.