​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 a 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 machined 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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Are all engineered wood or composite wood the same?

No.  You will find that the cheaper engineered or composite wood products have not be 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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​​What method of underfloor heating does Heatwell use?

Heatwell installs both of our own Pro Series and Gold Series of underfloor heating cable.  The heating cable is attached to the sub-floor, a fibreglass mat 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 floor leveling 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 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 wood 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.
Installation over the top of particle board or plywood however 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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What condition does the floor need to be in prior to underfloor heating installation of engineered wood 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 checked out of 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.