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Under-Tile Heating Install – FAQ

What method of underfloor heating does Heatwell use?
Heatwell uses our Pro Series heating element.  The Pro Series cable is attached to the floor, a fibreglass matt 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 Tiler will love the flat level surface.
Heatwell only does electrical underfloor heating systems.  We no longer do water based or in-concrete installs.

How long does the self-levelling compound (screed) take to dry?
Please allow 24 hours. In cold conditions, drying could take more than 24 hours. Tiling or waterproofing should not be done if the floor is not fully dry.

When is the underfloor heating installed?
Underfloor heating is usually done just before the tiler.  The walls should be lined.  All gib stopping and sanding should be complete.  All painting should be done.

Is underfloor heating installed before or after waterproofing?
We can do either.  There will be no affect to the electrical element or our 25-year guarantee.  However, it is preferable that waterproofing is done after underfloor heating is installed.

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.
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.

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.  Strata Flex from Surtec is an example.  This option is probably the most expensive, however, it adds the least to the floor height.

Can underfloor heating be installed over existing tiles?
Yes.  However, no tile can be loose or broken.  The tile surface will need to be primed before underfloor heating is installed.  Mapei Ecoprime is an example.
You are adding significant height to the floor.  We would prefer that the old tiles are removed.

What condition does the floor need to be 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 have all the remains of the previous flooring removed.  Including glue and old tile adhesive.

Is there any wall prep required?
Yes.  We need to mount the thermostat / controller.  The cold tails that are attached to both ends of the heating element must come up from the floor to the thermostat mounting.
25mm holes need to be drilled through the wall nogs.  A 50mm wide and 25mm deep section must be checked out of the bottom plate of the wall.
A draw wire from the thermostat mount down to the bottom plate is essential.
The mounting box for the thermostat can be installed either vertically or horizontally.  Heatwell has thermostat options for both.

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 circuit breaker back to the board.
All our thermostats have a 15amp maximum capacity.
We allow 150-180W per m2

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, we need to know about it before we lay the underfloor heating!  Drilling a hole in the heating element will mean the whole flooring process will need to start again.
Please use a two-pot flexible tile adhesive and a latex grout.


258 Forrest Hil Rd
Forrest Hill

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Ph: 09 392 8533
Toll free: 0800 392 853

Email: info@heatwell.co.nz

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