Heating system

A heating system which may include a bonding membrane having a water permeable lamina, an electrically conductive ink-based radiant heater, and a first adhesive adapted to adhere to both the conductive ink-based radiant heater and the bonding membrane. The heating system may be incorporated in a floor including a substrate, the heating system and a decorative floor surface. The heating system may also be in the form of a multilayer panel having a bonding membrane, an electrically conductive ink-based heater including a plurality of electrically resistive strips printed on a first polymer sheet connected by electrically conductive buses, and electrical conductors extending from the buses to at least an edge of the panel.

FIELD OF THE INVENTION

This invention relates to heaters that can be installed in buildings such as under conventional decorative flooring. Further, this invention relates to a floor heating system that can be used in wet environments, such as kitchens and bathrooms.

BACKGROUND OF THE INVENTION

The use of heating elements in flooring provides a combination of beauty and comfort. Heated floors in cool areas of a building can provide supplemental heat to the space that is evenly distributed. In homes, warmed floors in a bathroom are kind to an occupant's feet, especially on a cold winter morning.

Several techniques are known to create heated floors. In some applications, heating elements are installed under the subfloor, between floor joists. Using this technique, the heating elements warm the air space under the subfloor, the subfloor and the decorative floor, as well as any mastic, grout or underlayment that may be present. A relatively small percentage of the power used to generate heat actually comes through to the top surface of the decorative floor to be enjoyed by the room occupants. This technique also cannot be used during a remodeling project unless a homeowner is willing to replace the subfloor or ceiling, which is an expensive project.

Heating wires can be embedded in a mortar layer. A second mortar layer is applied to hold ceramic tiles in place. Wires are placed on the subfloor in a custom configuration. The mortar must be sufficiently thick to cover the wires, changing the depth of the floor. Finally, special precautions must be taken by the applicators not to scratch or nick the wires while applying the second layer of mortar. Installation of this type of system is laborious and expensive.

Woven wire mesh heaters having no busses are made whereby thin wires are woven into a mesh mat. The mat can be placed under a laminate floor or under a subfloor. However, these mats must be custom made to fit odd-sized spaces and cannot be altered at the job site. This increases the cost of the heaters and installation, and makes the process of changing the heater layout during installation significantly more difficult.

Polymer-based heaters are made using electrically resistive plastics. A conductive bus on either side of the resistance heaters completes the circuit. The result is a cuttable heating surface; however currently available products exhibit significant thickness.

Conductive ink-based heaters are made from resistive inks printed on plastic sheets. A conductive bus on either side of the resistance heaters completes the circuit. A second plastic sheet is then placed over the circuit to protect the heating elements. The result is a thin, flexible, cuttable heating surface. Conductive ink-based are known for use under laminate floors, where they lay unattached in the space between the floor boards and the subfloor or, in the case of a remodel, an old floor. The plastic sheets that protect the device provide a poor surface for adhesion of ceramic tiles.

Thus, it would be advantageous to be able to utilize a polymer-based heater under ceramic tiles if a system could be devised where there is the proper adhesion between the heater and the tile. The flooring system should be inert to water penetration for use in wet environments, such as a kitchen or bathroom. Further, the system should be cuttable in the field, allowing the exact shape of the heater to be varied as it is being installed and to minimize cost.

SUMMARY OF THE INVENTION

A heating system is provided, which, in an embodiment includes a bonding membrane having a water permeable lamina, an electrically conductive ink-based radiant heater; and a first adhesive adapted to adhere to both the conductive ink-based radiant heater and the bonding membrane. The heating system may be incorporated into a thin and flexible panel.

The bonding membrane may include a basemat and a coating. In an embodiment, the coating comprises at least 55% of a hydraulic component such as fly ash and silica fume. The fly ash may be a Class C fly ash. The coating might further be a water-soluble, film-forming polymer. The hydraulic component may be present as a crystal matrix. The water-soluble, film-forming polymer may be present as a matrix of film strands. The crystal matrix may interlock with and be distributed throughout the matrix of film strands. The coating might further be a filler such as perlite, sand, talc, mica, calcium carbonate, clay, pumice, volcanic ash, rice husk ash, diatomaceous earth, slag, metakaolin, pozzolanic materials, expanded perlite, glass microspheres, ceramic microspheres, plastic microspheres or combinations thereof. The basemat may be a meltblown lamina sandwiched between two spunbond laminae.

The conductive ink-based radiant heating element may further comprise a polyester sheet onto which resistive strips have been printed with a conductive ink. The conductive ink may be formed with at least one of carbon and silver.

In an embodiment, at least two buses are provided to supply current to or remove current from the resistive strips. In some embodiments, at least three buses are provided to supply current to or remove current from the resistive strips. The buses may be made of any material having good electrical conductivity such as copper foil strips.

In an embodiment, a conductive material may be provided between the resistive strips and the buses.

In an embodiment, a multi-functional layer is adhered to the radiant heater using a second adhesive. The multi-functional layer may be at least one of a low density foam, a polymeric sheet, a rubber sheet and combinations thereof.

In an embodiment, the invention is a floor including a substrate, a heating system and a decorative floor surface. The heating system might include a bonding membrane having a water permeable lamina, an electrically conductive ink-based radiant heater, and a first adhesive adapted to adhere to both the conductive ink-based radiant heater and the bonding membrane.

In an embodiment, the decorative floor surface may be laminate flooring or wood flooring. In another embodiment, the decorative floor surface may be ceramic tile. With ceramic tile, the floor may also include an adhesive positioned between the subfloor and the heating system and a mortar between the heating system and the ceramic tile.

In an embodiment, the substrate may be wood, cement, linoleum, ceramic tiles or combinations thereof.

In an embodiment, the bonding membrane includes a basemat and a coating. The coating may be at least 55% of a hydraulic component such as fly ash, silica fume or combinations thereof.

In an embodiment, the invention provides a heating system in the form of a multilayer panel. The panel may include a bonding membrane, an electrically conductive ink-based heater including a plurality of electrically resistive strips printed on a first polymer sheet connected by electrically conductive buses, and electrical conductors extending from the buses to at least an edge of the panel for receiving a connection to another conductor, such as a wire, or the conductors may themselves extend beyond the edge of the panel, such as in a wiring harness.

In an embodiment, the plurality of resistive strips may be arranged parallel to one another and terminate at ends spaced from a perimeter edge of said polymer sheet.

In an embodiment, two buses are provided, one at each end of said resistive strips. The buses may be copper strips that terminate at ends spaced from a perimeter edge of the polymer sheet.

In an embodiment, the first polymer sheet may be a polyester sheet. In an embodiment, the resistive strips may be a carbon-based ink.

In an embodiment, a conductive material, such as a conductive polymer, may be positioned between the resistive strips and the buses, to assure a good connection therebetween.

In an embodiment, a second polymer sheet is provided to overlie the resistive strips and buses. Further, two additional plastic sheets may be provided to encapsulate the first and second polymer sheets and the resistive strips and buses. In some embodiments, only one additional plastic sheet may be provided to overlay either the first or the second polymer sheet. In some embodiments, the plastic sheets may be water impermeable.

In an embodiment, the bonding membrane may be a basemat and a coating formed from a mixture of a hydraulic component, a polymer and water. The hydraulic component may be at least 55% fly ash. The polymer may be a water-soluble, film-forming polymer.

In an embodiment, the basemat may be a first spunbond lamina, a second spunbond lamina and a meltblown lamina between the first and second spunbond laminae.

In an embodiment, a multi-functional layer may be included in the multilayer panel that is adhered to the radiant heater using a second adhesive. The multi-functional layer of may be thermal insulation, sound suppression material, waterproofing material, electrical insulation or crack isolation material. The multi-functional layer may be one of a low density foam, a polymeric sheet, a rubber sheet or combinations thereof.

In an embodiment, the panel includes a layer of adhesive material on one outer surface.

In an embodiment, the electrical conductors include a portion of the buses that extend to the edge of the panel.

In an embodiment, an adhesive may be arranged between the bonding membrane and the polymer sheet of the conductive ink-based heater.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In an embodiment of the invention, a heating system20is provided in the form of a multilayer panel22. The panel22may be thin and flexible with each of the layers not being thicker than 1 to 200 mils. The heating system20can be used in a variety of different locations for providing heat to that location. One such location is to use the heating system20in a floor. Although the present invention is not limited to such a location, and could also be used in walls, ceilings and other locations, for purposes of providing a description of an embodiment of the invention, it will be described in such a location.

One of the layers of the panels22is a bonding membrane24(partially shown inFIG. 1). Another layer is an electrically conductive resistance heater26. A first adhesive27adapted to adhere to both the bonding membrane24and the heater26may be positioned between the bonding membrane and the heater. In an embodiment, the adhesive27could be any adhesive that is compatible with cyclic temperature, moisture and possesses suitable bond strength. Suitable adhesives include transfer tapes from 3M, such as 300LSE Transfer film, 468 MP/200 MP Adhesives transfer film and 467 MP/200 MP Adhesives transfer film. Other suitable heat cured or liquid adhesives are envisioned.

The heater26in some embodiments may be a conductive ink-based radiant heater that includes a plurality of electrically resistive ink-based strips28printed on a first polymer sheet30which may be connected by electrically conductive buses32. The use of individual strips allows the heater26to maintain a relatively high resistance since for any given ink, the wider the strip (up to the full width of the polymer sheet30) the lower the resistance. Electrical conductors33such as wires may extend from the buses32to at least a perimeter edge34of the panel22or beyond. The conductors33may also be extensions of the buses32or conductors other than wires or the buses.

The panel22may be formed with a rectangular perimeter as shown inFIG. 1, or may have other shapes as desired. If formed in a rectangular shape, it may have one of a variety of different sizes, depending on the application for the panel. For example, panels may be provided having a width of 12 inches or 18 inches, or a multiple of 12 inches or 18 inches, or panels may be provided having a width of 25 centimeters or a multiple of 25 centimeters. Also, panels22may be provided having a length of 12 inches or 18 inches, or a multiple of 12 inches or 18 inches, or panels may be provided having a length of 25 centimeters or a multiple of 25 centimeters.

Referring toFIGS. 1 and 2, a heating system, generally35, includes the conductive heater26, and the bonding membrane24. The heating system35is supported by a subfloor100(FIG. 4), such as plywood, cement, and the like. In some embodiments, the heating system is optionally supported by a previous floor102as long as the previous floor is sufficiently firm to provide a stable platform for the heater. Carpet is not recommended as a previous floor102. Examples of previous floors102that can support the heating system include tiles, such as ceramic tiles104or sheet linoleum products.

A new decorative floor106to be warmed is placed on top of the heating system35. Any flooring may be used as the decorative floor, including hard wood, sheet flooring, linoleum sheets or tiles, carpet, laminate floors, ceramic tiles104and the like. The ceramic tiles104are held in place by a mortar108under the tiles and grout110between the tiles.

The heater26is placed between the subfloor100and the new decorative floor106. In some applications, it is adhered to the subfloor with an optional adhesive112(FIG. 2).

The bonding membrane24may include a basemat36and a coating38formed from a mixture of a hydraulic component, a polymer and water.

A preferred bonding membrane24is described in U.S. Pat. No. 7,347,895, issued Mar. 23, 2008 entitled “Flexible Hydraulic Compositions,” and European Patent EP179179, and in pending U.S. Patent Application US2006/0054059 published Mar. 16, 2006 entitled “Flexible and Rollable Cementitious Membrane and Method of Manufacturing It”, all herein incorporated by reference in their entireties and for all purposes. With the use of such a flexible cementitious membrane, the heater26may be put in the form of a roll with very small diameters (˜≧1 inch). Further, such a membrane is extremely lightweight, having a weight of less than 500 pounds per thousand square feet, and down to less than 200 pounds per thousand square feet.

Any hydraulic components that include at least 55% fly ash may be useful in the coating38. Class C hydraulic fly ash, or its equivalent, is the most preferred hydraulic component. This type of fly ash is a high lime content fly ash that is obtained from the processing of certain coals. ASTM designation C-618, herein incorporated by reference, describes the characteristics of Class C fly ash (Bayou Ash Inc., Big Cajun, II, La.). When mixed with water, the fly ash sets similarly to a cement or gypsum. Use of other hydraulic components in combination with fly ash are contemplated, including cements, including high alumina cements, calcium sulfates, including calcium sulfate anhydrite, calcium sulfate hemihydrate or calcium sulfate dihydrate, other hydraulic components and combinations thereof. Mixtures of fly ashes are also contemplated for use. Silica fume (SKW Silicium Becancour, St. Laurent, Quebec, CA) is another preferred material. The total composition preferably includes from about 25% to about 92.5% by weight of the hydraulic component.

The polymer is a water-soluble, film-forming polymer, preferably a latex polymer. The polymer can be used in either liquid form or as a redispersible powder. A particularly preferred latex polymer is a methyl methacrylate copolymer of acrylic acid and butyl acetate (Forton VF 774 Polymer, EPS Inc. Marengo, Ill.). Although the polymer is added in any useful amount, it is preferably added in amounts of from about 5% to 35% on a dry solids basis.

In order to form two interlocking matrix structures, water must be present to form this composition. The total water in the composition should be considered when adding water to the system. If the latex polymer is supplied in the form of an aqueous suspension, water used to disperse the polymer should be included in the composition water. Any amount of water can be used that produces a flowable mixture. Preferably, about 5 to about 35% water by weight is used in the composition.

Any well-known additives for cements or polymer cements can be useful in any of the embodiments of the instant composition to modify it for a specific purpose of application. Fillers are added for a variety of reasons. The composition or finished product can be made even more lightweight if lightweight fillers, such as expanded perlite, other expanded materials or either glass, ceramic or plastic microspheres, are added. Microspheres reduce the weight of the overall product by encapsulating gaseous materials into tiny bubbles that are incorporated into the composition thereby reducing its density. Foaming agents used in conventional amounts are also useful for reducing the product density.

Conventional inorganic fillers and aggregates are also useful to reduce cost and decrease shrinkage cracking. Typical fillers include sand, talc, mica, calcium carbonate, calcined clays, pumice, crushed or expanded perlite, volcanic ash, rice husk ash, diatomaceous earth, slag, metakaolin, and other pozzolanic materials. Amounts of these materials should not exceed the point where properties such as strength are adversely affected. When very thin membranes or underlayments are being prepared, the use of very small fillers, such as sand or microspheres are preferred.

Colorants are optionally added to change the color of the composition or finished basemat36. Fly ash is typically gray in color, with the Class C fly ash usually lighter than Class F fly ash. Any dyes or pigments that are compatible with the composition may be used. Titanium dioxide is optionally used as a whitener. A preferred colorant is Ajack Black from Solution Dispersions, Cynthiana, Ky.

Set control additives that either accelerate or retard the setting time of the hydraulic component are contemplated for use in these compositions. The exact additives will depend on the hydraulic components being used and the degree to which the set time is being modified.

Reinforcing materials can be used to add strength to the basemat36. The additional of fibers or meshes optionally help hold the composition together. Steel fibers, plastic fibers, such as polypropylene and polyvinyl alcohols, and fiberglass are recommended, but the scope of reinforcing materials is not limited hereby.

Superplasticizer additives are known to improve the fluidity of a hydraulic slurry. They disperse the molecules in solution so that they move more easily relative to each other, thereby improving the flowability of the entire slurry. Polycarboxylates, sulfonated melamines and sulfonated naphthalenes are known as superplasticizers. Preferred superplasticizers include ADVA Cast by Grace Construction Products, Cambridge, Mass. and Dilflo GW Superplasticizer of Geo Specialty Chemicals, Cedartown, Ga. The addition of these materials allows the user to tailor the fluidity of the slurry to the particular application.

Shrinkage reducing agents help decrease plastic shrinkage cracking as the coating38dries. These generally function to modify the surface tension so that the slurry flows together as it dries. Glycols are preferred shrinkage reducing agents.

While preferred, the basemat36need not be coated and may be coated on the jobsite using traditional mortars used for setting ceramic tile.

A preferred basemat36for the floor heater system35may include at least a first spunbond lamina40. The first spunbond lamina40is optionally bonded directly to the conductive heater26. In other embodiments, an optional meltblown lamina42resists migration of liquids through the basemat36, adding to the resistance to the flow of water or other liquids across the bonding membrane24. The first spunbond lamina40is placed on the top side of the meltblown lamina42to provide high porosity on at least one surface of the bonding membrane24. Porosity of the spunbond material allows for good infiltration and absorption of the mortar108. The large fibers become incorporated into the crystal matrix of the mortar108, forming a strong bond.

Optionally, a second spunbond lamina44is present on the meltblown lamina42on the surface opposite that facing the first spunbond lamina40. In this embodiment, the meltblown lamina42is sandwiched between the first spunbond lamina40and the second spunbond lamina44. This embodiment has the advantage that it has the same surface on both sides and it does not matter which surface is applied to the conductive ink-based radiant heater26and which surface is facing the new decorative flooring106.

The laminae40,42,44are bonded to each other by any suitable means. Three-ply composites or this type are commercially available as an S-M-S laminate by Kimberly-Clark, Roswell, Ga. This product is made of polypropylene fibers. While providing a barrier to liquids, the material is still breathable, allowing water vapor to pass through it. Depending upon the end application and the performance requirements, other lamina may be more suitable for a particular application. U.S. Pat. No. 4,041,203, herein incorporated by reference, fully describes an S-M-S laminate and a method for making it.

In a commercial scale production line, the basemat36is preferably made by a process beginning with unwinding the basemat36from a spool and running it toward the mixing area. If the basemat36is permeable by the slurry, an optional release paper is useful underneath the basemat to contain overspill of the slurry. With an impermeable basemat36and proper design of the coating station, the need for the release paper can be eliminated. The basemat36is aligned with and placed on a surface to be fed to coating equipment for application of the slurry.

The coating38is prepared by mixing the polymer and the hydraulic component in water. Preferably the mixing is done in a high shear mixer. Either a continuous or a batch mixer is useful, depending on the size of the batch being prepared.

The basemat36is provided and the coating38is applied to it. Any coating apparatus is adaptable for use with the coating slurry, including rod coaters, curtain coaters, sprayers, spreaders, extrusion, pultrusion, roller coaters, knife coaters, bar coaters and the like to coat the basemat36and form a sheet. One preferred method of spreading the slurry is by utilizing a screed bar. The screed bar can be metal, plastic, rubber or any material that scrapes excess coating from the basemat36. A thin coating is obtained by keeping the screed bar in contact with the basemat36. As a head of slurry builds up in front of the screed bar, the slurry spreads and uniformly covers the face of the basemat36.

When spreading the slurry, it can be advantageous to position the screed bar over a flexible surface or no surface at all. Pressure is applied to the screed bar to build up a head and to obtain a thin coating of slurry. In testing, when pressure was applied with the basemat36positioned over a firm surface, the basemat stopped moving and started to tear. Moving the coating operation to a portion of the line where the basemat36was supported by a flexible belt allowed sufficient pressure to be applied to the mat to obtain a thin coating without bunching or tearing of the basemat. It is also possible to coat the basemat36with no surface directly under the basemat. In this case, a screed bar or other coating device is positioned over the suspended basemat36. A device for catching and recycling excess coating material is preferably positioned underneath, but not touching, the basemat36.

Thicker coatings38of slurry are obtainable by repeating the coating process multiple times. Preferably, two screed stations are present for application of two coatings38that are substantially similar. If it is desirable to have a non-directional sheet, the cementitious slurry is applicable to both sides of the basemat36.

After the slurry38has been applied to the basemat36, it is allowed to dry, set and harden. Any method of drying the slurry is useful, including, air drying at room temperature, oven or kiln drying or drying in a microwave oven. When allowed to dry at room temperature, a membrane is ready to use, package or store in a few hours. More preferably, the coated mat or coated paper is sent to an oven where it dries and sets rapidly. A slurry38thinly applied to a basemat36dries in less than 10 minutes in a 175° F. (80° C.) oven. The polymer is also curable using light, particularly light in the ultraviolet wavelength range. If the coating38is made with hot polymer, curing time is decreased, but the pot life is also decreased. Exact drying times will depend on the exact composition chosen, the thickness of the slurry and the drying temperature. When the composition is set, the release paper, if present, is removed by conventional methods.

Use of many types of heaters is contemplated for the present invention. Suitable radiant heaters are made using electrical cables either alone or positioned on a mesh or scrim. Any electrical radiant heater mat that is thin and cuttable may be used in this application. A preferred heater utilizes a conductive ink to form the heater. This technique makes a very thin heating system that does not significantly increase the height of the floor under which it is installed.

Several different types of conductive ink-based radiant heaters26are sold commercially. One type of conductive ink-based radiant heater26is printed with a carbon-based ink having a variety of resistances. Another type of conductive ink-based radiant heater26is printed with silver-containing inks having a variety of resistances. Yet another conductive ink-based radiant heater26is a circuit printed onto a polyester film.

Referring now toFIG. 3, a preferred conductive ink-based radiant heater26is similar to that marketed by Calesco Norrels (Elgin, Ill.). Heating is provided by printed ink resistive strips28on the first polymer sheet30. The resistive strips28are placed on the polymer sheet30using any known method. One technique of laying down the resistive strips28is by printing them with a carbon-based ink. The conductive ink is selected to form a resistive material when dry and to adhere to the first polymer sheet30so that it does not flake off or otherwise become detached when the conductive ink-based radiant heater26is flexed. In an embodiment, the polymer sheet30may be made of polyester.

The electrically resistive strips28of the heater26may be arranged parallel to one another and may terminate at ends46,48spaced from a perimeter edge50of the polymer sheet30. In other embodiments (seeFIG. 7), the strips28may criss-cross one another, or they may have a serpentine or other non-linear shape.

The resistive strips28are incorporated into an electrical circuit51using at least two buses32as shown inFIG. 5. One bus32is placed at or near each end46,48of the resistive strips28on the opposite side of the resistive strip from the polymer sheet30. Additional buses32, for example connecting the mid-points of the resistive strips28, may be added as desired. Use of additional buses32in this manner minimizes the area of the sheet30that does not provide heat when part of a bus32is cut away during fitting as described below. An example of a preferred bus32is a strip of copper foil or other conductive material. The copper strips of the buses32may terminate at ends52,54spaced from the perimeter edge50of the polymer sheet30. In other embodiments, one end52of the buses32may extend all the way to the edge50of the polymer sheet30to act as the conductors33as described above.

If needed, a thin conductive material56is placed between the resistive strips28and the bus32where they intersect to promote good conductivity between them. Preferably the conductive material56is a conductive polymer. Common classes of organic conductive polymers include poly(acetylene)s, poly(pyrrole)s, poly(thiophene)s, poly(aniline)s, poly(fluorene)s, poly(3-alkylthiophene)s, polytetrathiafulvalenes, polynaphthalenes, poly(p-phenylene sulfide), and poly(para-phenylene vinylene)s. In any event, it is preferred that the connection between the buses32and the strips28is made in a waterproof manner.

The buses32and the conductive material56may be bonded to a second polymer sheet58. When the conductive ink-based radiant heater26is assembled, the second polymer sheet58is arranged so that the conductive material56is adjacent to the resistive strips28on the first polymer sheet30so that the second polymer sheet will overlie the resistive strips28and the buses32. The polymer sheets30,58, when made of a waterproof material, will render the connection between the buses32and the resistive strips28waterproof.

To protect the circuit materials from being damaged or scratched during installation, in an embodiment, the polymer sheets30,58, resistive strips26, buses32and conductive material36may be covered by one or encapsulated between two additional plastic sheets60. Preferably the plastic sheets60and the polymer sheets30,56are laminated together. An example of a suitable plastic sheet60is a sheet of polyethylene film. In order to provide a measure of water impermeability to the panels22that incorporate the plastic sheets60, the plastic sheets may be water impermeable. Sealing of the buses32and the resistive strips26within the plastic sheets60also allows the conductive ink-based heater to be used in wet environments and promotes long life. A wire33attached to each of the buses32extends outside of the plastic sheets60. These wires33are used to electrically attach the finished panels22of the heating system20to each other and to a circuit62providing an electrical current, such as a house circuit.

The circuit62includes a voltage source64to provide an electrical current. The heaters26are connected to each other in parallel in the circuit such that the addition of heaters26to the circuit will not reduce the voltage drop across any of the heaters, thereby maintaining the current passing through each heater and maintaining a heat flux produced by each heater. In this manner, any number of heaters26may be added to a circuit (as permitted by the total current load permitted for the circuit) as is necessary to underlie a desired portion of the floor and to provide a desired level of heat into the room where the floor is located. Other components of the circuit62are discussed below.

The heaters26may be constructed in a manner so as to provide a predetermined heat flux by selecting an appropriate conductive ink and selecting a width, thickness and length of the strips26. Inks having different surface resistances can be selected and the width and thickness of the strips26can be chosen to produce a desired resistance, which will translate into a desired heat output for each strip. The strips26can be arranged with selected spacings there between to produce a desired heat output for the panel22. If a center bus32is utilized (as shown in phantom inFIG. 6), the width and thickness of the strips26will be adjusted to accommodate the shortened length of the strips between the buses. Also in such an arrangement, the outside buses would be connected to the same power supply connection, while the center bus would be connected to an opposite power supply connection.

Referring toFIG. 4, a heated floor, generally114, is made using the floor heating system20. The heating system20is placed between the subfloor100and the decorative flooring106. Depending on the decorative flooring106selected, it may not be necessary to use the adhesive112to bond the heating system20to the subfloor100. Where, for example, a laminate floor, such as PERGO is selected as the decorative flooring106, the floor heating system20can be placed between the subfloor100and the laminate floor106with no bonding. In this case, movement of the heater26with respect to the decorative flooring106or the subfloor100causes no harm.

However, where ceramic tile104is selected as the decorative flooring, stabilization of all materials under the tile is important. In this case, it is important that there be the adhesive112between the subfloor100and the heating system20as described above. The heating system20is also advantageous when used under ceramic tile104as the bonding membrane24is a particularly good surface for adhesion of the mortar108that holds the ceramic tile104in place.

To prepare the heated floor114, the heating system20is placed under the decorative floor106by any method known in the art. In some embodiments, sheets of the heating system20are laid out on the subfloor100or previous floor102and cut to length. The resistive strips28and the buses32in the panels24are spaced from the perimeter edge34of the panels to provide electrical insulation and isolation of those components. If the panels24need to be cut to fit a particular installation requirement, the panels are to be cut along a line (such as line69inFIG. 6) parallel to the resistive strips28, in those embodiments where the strips are spaced and parallel to each other. This will result in two exposed portions of the buses32which will need to be insulated and isolated from the cut edge of the panel, such as with insulating tape, a liquid non-conductive polymer, or other known methods of electrical insulation. If the size of the installation requires cutting of the panel24along its length (cutting though all of the resistive strips28), then it is preferred to obtain a narrower prefabricated panel, or to limit the area under the floor provided with the heater26, in order to avoid having to electrically insulate the large number of exposed ends of the cut strips. Since the panels are to be joined together in a circuit with parallel connections, extra panels can be added as needed.

The floor heating system20is then optionally bonded to the subfloor100with the adhesive112. Mechanical fasteners (not shown), such as nails or screws, are also used if desired. A thermister71is placed on the floor100,102to monitor and self-regulate the heaters26. The new decorative floor106is placed on top of the sheets30or60of the floor heating system20. In the case of ceramic tiles104, the mortar108is spread over the sheets of floor heating system20and the ceramic tiles104installed with grout110. Wires33attached to the buses32are hooked to an electrical junction66, and a ground fault circuit interrupter68to complete the circuit. Preferably the circuit includes a switch70for ease in activating and deactivating the heating system20. The wires33may be a part of a wiring harness which may be color coded for ease of installation by the floor installer.

In addition, a thermostat72is installed to monitor temperatures in the space where the floor is located. This thermostat72controls on and off conditions for the heating system20. Components for controlling floor heaters are commercially available from Honeywell Corp. (Morristown, N.J.).

An alternate embodiment of the heating system is illustrated inFIG. 8. In this embodiment, there are multiple layers as described above including a flexible cementitious coating38, a single or multi-layered base mat36, an adhesive layer27, an electric radiant heat mat26, an optional adhesive layer112and an optional release liner74. A new functional layer76is provided and adhered to the heat mat26via an adhesive layer78which may provide a single function or multiple functions.

For example, layer76may have sound suppression properties, it may comprise thermal insulation, it may comprise electrical insulation, it may provide waterproofing and it may provide enhanced crack isolation. Further, this layer76may provide more than one of the above properties by means of individual component layers or more than one of these properties might be provided in a single layer. Further the adhesive layers78and112(and release liner74) as well as the functional layer76may be combined in a single composite laminate80to be adhered to the radiant heat mat26.

As examples of possible components comprising the functional layer76, the sound suppression properties, particularly for impact noise, could be achieved with a layer of low density foam, rubber or plastic. The adhesive layers78and112securing the functional layer76to the electric radiant heat mat26and to the sub floor100(if used) could be pressure sensitive adhesive transfer tape or pressure sensitive double sided adhesive tape or even spray or liquid applied adhesives. The use of double sided adhesive tapes are preferred when enhanced crack-isolation and waterproofing performance are desired. Low density foams, which also may provide thermal insulation and/or electrical insulation, may include polyethylene foams such as 3M polyethylene foam tape 4462 or 4466, polyurethane foams such as 3M urethane foam tape 4004 or 4008, polyvinyl foams such as 3M polyvinyl foam tape 4408 or 4416, ethylene vinyl acetate foams such as International Tape Company polyethylene foam tapes 316 or 332, acrylic foams such as 3M VHB 4941 closed-cell acrylic foam tape family, and EPDM (ethylene propylene diene monomer) foams such as Permacel EE1010 closed cell EPDM foam tape. Silicone foams include Saint-Gobain 512AV.062 and 512AF.094 foam tapes. Rubber foams include 3M 500 Impact stripping tape and 510 Stencil tape. Elastomeric foams include 3M 4921 elastomeric foam tape and Avery Dennison XHA 9500 foam tape. Rubber or recycled rubber sheets can be obtained from Amorim Industrial Solutions or IRP Industrial Rubber.

The use of the adhesive layer112and the release sheet74allows the panels to be self-adhering to a desired substrate surface, in the nature of a peal and stick arrangement. This permits the installer to quickly place the panels in their desired locations without the need for mixing or applying adhesive materials and assures that the adhesives adequately cover the panels and are applied in the correct amounts.

A further embodiment of the invention is illustrated inFIG. 9which has all of the layers described with respect toFIG. 8(other than the release sheet74). In addition, this embodiment includes a rigid panel composite layer82by means of which the heating system20is provided on a building panel that can be incorporated into floors, walls, ceilings and other structural components of a building. The rigid panel composite layer82may comprise mesh reinforced cement board, fiber reinforced cement board, gypsum panels, gypsum fiber panels, plywood, oriented strand board or other types of wood-based panels, plastic panes as well as other types of rigid panel composites. The panel thicknesses may range between 0.125 to 10 inches, preferably between 0.250 to 2 inches and most preferably between 0.250 and 1 inches.

While a particular embodiment of a heating system and heated floor have been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects.