​​What method of underfloor heating does Heatwell use?

Heatwell installs both of its own Pro Series and Gold Series of underfloor heating cables.  The heating cable is attached to the sub-floor, a fibreglass mesh is placed over the top, a self-levelling compound or screed is poured over the top.  The result is a heating element that is encased and protected.  The final flooring installer will love the flat level surface.

 

Heatwell specialises in electrical underfloor heating systems, and we do not install in-concrete or hydro underfloor heating.

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How much height to the floor does the Heatwell method add?

Installing underfloor heating cable, with mesh and self-levelling compound over the top, adds approximately 4mm to the height of the floor.  Budget for 5mm to be safe.

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How much underfloor heating should be used under tile, slate, or stone?

Heatwell recommends that 180W per square metre be installed under slate and stone.  Slate and stone tend to be thick, at up to 20mm, so will need a greater degree of heating than tiles.

Heatwell recommends that 150W per square metre be installed under tile.

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Is there a maximum amount of Watts that can be installed per square metre?

Yes.  The maximum heating per square metre should not exceed 180W.  At 180W per square metre, the spacing between the runs of the underfloor heating cable is approximately 55mm.  Underfloor heating cable should never be closer together than 55mm.  The minimum heating per square meter is 100W under tile.  However, 100W per square metre under tile, stone and slate is not enough.  Heatwell recommends a minimum 150W and a maximum of 180W per square metre under tile, stone, and slate.

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Can an underfloor heating cable be cut to size?

No! Unlike most other electrical cable, underfloor heating cable cannot be cut to length.  All underfloor heating cables come premade to lengths that suit the size in Watt being installed.  The underfloor heating cable comes with cold tails attached and is sealed to be waterproof.  A damaged underfloor heating cable can be fixed, however, that is a job for a registered electrician.  Cutting the underfloor heating cable will void warranty.

Make sure that you buy the right size of underfloor heating cable.  Heatwell has a measuring app available that can help.

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How long does the self-levelling compound (screed) take to dry?

Please allow 24 hours. In cold conditions, drying can take more than 24 hours. If you are worried about drying time, a heater in the area will help. Tiling or waterproofing cannot be done if the floor is not fully dry.

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When is the underfloor heating installed?

Underfloor heating is usually installed just before the final flooring is installed.  The walls should be lined, all gib stopping and sanding should be complete, and all painting should be done.  Underfloor heating installation happens very late in the construction process.

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Is underfloor heating installed before or after waterproofing?

The answer is both yes and no.  Waterproofing must be completed after underfloor heating if there is going to be heating in the shower.  If there is no underfloor heating in the shower, then it can be installer either before or after.  A waterproofing patch will need to be used where the cold tails go up through the wall if underfloor heating is installed after waterproofing.  It is always best that waterproofing is done after underfloor heating has been installed if possible.

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Can underfloor heating be installed in a shower with tiles or slate?

Yes, underfloor heating can be installed into a shower, with careful planning, if the shower base is going to have tiles, stone, or slate.  Underfloor heating cannot be in the shower if there is an acrylic or stainless steel shower base.  The underfloor heating must be installed before waterproofing if going in a shower.  Heatwell recommends heating in a shower if the shower is going to be open with no door.

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Can underfloor heating be installed on a bathroom floor that falls to a drain?

Yes.  Underfloor heating should not go directly to the edge of the drain.  Heatwell allows for 80mm away from the edge of the drain.

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Does underfloor heating need to go under the whole floor or only where people walk?

Heatwell prefers to heat the whole room.  Full coverage of will generate radiant heat that heats both the floor and the air above the floor.  The majority of the cost of underfloor heating is the installation per square metre.  Extra cost for additional Watts installed per square metre is very small.

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Does tile, slate or stone thickness affect underfloor heating?

Yes.  The thickness of the tile, slate, or stone you are installing must be considered when planning underfloor heating.  The depth of where the underfloor heating cable is in relation to the surface of the floor is the issue.  Under a tile that is 10mm thick, the underfloor heating will be 15mm under the surface.  Under stone that is 20mm thick, the underfloor heating will be 25mm under the surface.  The deeper that underfloor heating cable is, the longer the surface will take to heat up, and the more heating cable you will need per square metre.  150W per square metre under 10mm flooring product and 180W per square metre under 20mm flooring product is recommended.

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Can underfloor heating be installed over the top of any type of floor?

Underfloor heating can be installed directly over concrete as long as there are no cracks, holes, or sharp protrusions.  Underfloor heating can also be installed over tile and slate underlay, insulation board, acoustic mat or self-levelling compound.  Installation over the top of particle board or plywood is not recommended.  Expansion and contraction of particle board or plywood is a certainty in NZ’s conditions.  Expansion and contraction risks cutting the electrical element where the flooring butts together.

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How should particle board or plywood be prepped?

There are three excellent options.  The most common is laying tile and slate underlay.
Another option is to lay 6mm insulation sheeting. Infinity from Tile Max is an example.  Insulation sheeting has the big advantage of improving the efficiency of the underfloor heating and will save you money in the long run.
The third option is to incorporate an anti-fracture rubber-based system into your waterproofing. This option is probably the most expensive, however, it adds the least to the floor height.  Please check with the manufacturer to ensure that self levelling compound can be installed over the product.

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Can underfloor heating be installed over existing tiles?

Yes.  However, no tile can be loose or broken.  The tile surface will need to be ground to take any glaze off the tile, and will need to be primed before underfloor heating is installed.  However, installing over tiles is adding significant height to the floor.  Underfloor heating adds a minimum of 4mm and tiles add a minimum of 12mm.  Heatwell and any other installer would prefer that the old tiles are removed.

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​What condition does the floor need to be in prior to the underfloor heating installation?

All floors need to be clean, free of dust, and free of paint.  They also need to be free of any cracks, holes or sharp protrusions.
A floor that is being renovated needs to have all the remains of the previous flooring removed, including glue and old tile adhesive.

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Is there any wall prep required?

Yes.  The thermostat controller will need to be mounted on the wall.  The cold tails that are attached to both ends of the heating element must come up from the floor to the thermostat flush box.  25mm holes need to be drilled through the wall nogs.  A 50mm wide and 25mm deep section must be removed from the wall base plate.  A draw wire from the thermostat flush box down to the bottom plate is essential.  The flush box for the thermostat can be installed either vertically or horizontally.  Heatwell has thermostat options for both.

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What does the Electrician need to know?

A 900W element draws 3.91amps and is 58.78ohms in total.  Any heating element 1000W or above needs a dedicated RCD, with its own circuit back to the board.  All of Heatwells' thermostats have a 16amp maximum capacity.  If there is more than one underfloor heating cable using a single thermostat, the total amps must be taken into account.

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Can a heated towel rail and underfloor heating be run off the same thermostat?

Yes.  Heatwell has the HT4t thermostat that has been designed to run both the underfloor heating and towel rail.  With the HT4t underfloor heating and towel rails can be run independent and have their own timing schedule.

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Can an Electrician repair a damaged cable?

Yes.  An underfloor heating cable has an inner and outer core.  The inner core is the heating wires.  The outer core is the earth wire.  The underfloor heating cable needs to be cut at the damage.  The heating cable will need to be crimped together then sealed with waterproof electrical heat shrink (Raychem).  The earth wire will then need to be crimped together.  A final layer of waterproof electrical heat shrink needs to seal the whole repair.  The heating cable and the earth cable cannot touch or be joined together.  Please note that a significant thickness will be added to the underfloor heating cable.  You will need to check out an area under the join for the repaired wire to sit flush with the rest of the cable.

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What does the Tiler need to know?

Please don’t drop anything sharp or heavy on the screeded surface.  Cutting of tiles should not be done on the screeded surface.
If any holes are to be drilled into the floor, a plan needs to be made before underfloor heating cable is installed.  Drilling a hole in the heating element will mean the whole flooring process will need to start again. 

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Can tile adhesive be used directly over underfloor heating without needing to use self-levelling compound?

No.  Don't even think about it.  The tile adhesive is often smoothed out with a trowel with a serrated edge. Using a serrated edged trowel over underfloor heating is never a good idea.  The tiler often has either too much or not enough tile adhesive under a tile.  Lifting a tile to do it again very likely to damage the underfloor heating cable. 

 

What adhesive and grout should be used over underfloor heating?

Any brand of tile adhesive can be used over underfloor heating.  It is preferable to use a two-pot flexible tile adhesive and a latex grout over underfloor heating if possible.  You will need to use a two-pot flexible tile adhesive and a latex grout if there is underfloor heating in the shower.  Normal grout can be used outside a shower.