​Can underfloor heating be used under any wooden floor?

Unfortunately the answer is no.  Heating under natural timber is not recommended.  Natural timber will warp and twist if not fixed directly to the floor joists.  Nails and underfloor heating are not a good combination!  Underfloor heating cannot be installed under existing wooden floors without significant cost.

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Are there options if we want a natural wood flooring finish?

Yes.  Happily, most wooden floors now are an engineered wood or a wood composite. Engineered wood or wood composite usually has a thin layer of natural wood on top with a plywood or composite backing.  A well-laid engineered or composite wood floor will look as good and last as long as a natural wood floor.

The engineered wood or composite wood does need to be the clip together style. The floor will expand and contract. If the engineered wood or wood composite is not clipped together you will develop gaps between planks. You do need to be careful that there is no insulation attached to the engineered or composite wood, otherwise the heat will be trapped under the insulation. Ask your flooring supplier if your choice is suitable for underfloor heating.

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Is Bamboo flooring suitable over underfloor heating?

Yes.  The bamboo flooring must be a composite.  It cannot be 100% bamboo.

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Does engineered or composite wood need to acclimatize before laying over underfloor heating?

With poorer quality engineered or composite wood an acclimatizing period is often required.  The problem is often moisture.  Underfloor heating can reduce moisture and cause shrinkage.  High quality engineered or composite wood will be able to be laid without an acclimatization period.  However, the screed over the underfloor heating must be 100% dry.  You cannot trap moisture under the engineered or composite wood. 

You must talk to your final flooring provider about underfloor heating before you install.

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Are all engineered or composite wood the same?

No.  You will find that the cheaper engineered or composite wood products have not been designed to take expansion and contraction into account.  Expansion and contraction is not good over underfloor heating as cracks between planks will develop over time.  Quality engineered or composite wood has used materials that minimise expansion and contraction.  Please ask your flooring specialist if your chosen final flooring is suitable over underfloor heating.

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Is there a maximum temperature underfloor heating can be under engineered or composite wood?

Yes.  Heatwells' maximum recommended temperature under engineered or composite wood is 27 degrees Celsius.  Anything over 27 degrees may result in the engineered or composite wood delaminating.  Please check with your final flooring provider for underfloor heating recommendations.

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Can a maximum temperature of 27 degrees be set on a thermostat?

Yes.  Heatwells' HT4 and HT5 series of thermostats both have the capacity to set a maximum temperature that will not vary between manual and program modes.

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​​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 engineered or composite wood?

Heatwell recommends that 120W per square metre be installed under engineered wood and composite wood.

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

Yes.  The maximum heating per square meter should not exceed 180W.  180W installed under engineered or composite wood is too much.  The minimum heating per square meter should be 100W per square metre.  100W installed under engineered or composite wood is not enough.  Heatwell recommends a minimum of 120W and a maximum of 150W per square metre under engineered or composite wood.

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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. Installation of engineered or composite wood 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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​Can heating under engineered or composite wood 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 if installing engineered or composite wood?

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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Can underfloor heating be installed over existing engineered or composite wood?

No.  All existing engineered or composite wood must be removed.  All glue and other remnants must be removed.  The subfloor must be striped back to its original condition. 

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What condition does the floor need to be in prior to underfloor heating installation of engineered or composite wood?

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.

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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 remove 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 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 is needed 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 final flooring installer need to know?

Please don’t drop anything sharp or heavy on the screeded surface.  The installer needs to remember to allow a small gap between the edge of the flooring and the wall to allow for expansion and contraction.

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Can engineered or composite wood be glued down over self-levelling compound, or must it be floating?

Engineered or composite wood can be either glued down or left floating over self-levelling compound.  Again it depends on the quality of the engineered or composite wood.  High quality engineered or composite wood that has minimal expansion and contraction can be glued.  Poor quality engineered or composite wood will need to be floating.  Ask your final flooring supplier before installation.

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Can underlay be used under engineered or composite wood over underfloor heating?

Yes.  Often engineered or composite wood is sold with an underlay product attached to the bottom of the board.  A thin standard underlay can also be used.  However, the underlay cannot be an insulator.  Insulated underlay will trap the underfloor heating and will not allow the heat to radiate upwards.  Again check with the final flooring supplier to ensure the underlay is suitable for underfloor heating.