Electric underfloor heating buyer's guide

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Everything you need to consider before purchasing an electric underfloor heating system.

Whether you've done hundreds of installations or if you've never installed electric underfloor heating before, this article will give you a one stop guide to everything you need to specify and purchase the correct electric underfloor heating system for your project. Let's get started!

Concrete substrates

Most properties have a concrete floor slab and new builds will have an energy saving sub floor insulation layer to stop heat loss through the concrete into the earth. If you install an electric underfloor heating system directly onto that concrete layer (insulated or not) you will spend money heating up the concrete slab before any heat makes it's way into your room. This is a waste of energy and you're wasting money heating a mass that does not really need to be heated.

The solution to this is to install a layer of insulation on top of the concrete substrate. Doing so will reflect the heat directly up into the floor covering and into the room giving you a fast response system that does not waste time and energy heating your entire concrete ground slab. Insulation boards typically range from 10 - 50mm thick and come cut to a convenient 1200 x 600mm sheets.

Various primers and insulation rolls are available on the market but HeatThat™ always recommend the use of a proper insulation board for its superior thermal properties and energy saving potential. If you're purchasing insulation boards you'll also need to buy a flexible polymer based tile adhesive to adhere it to the concrete substrate.

Timber substrates

Timber is a natural insulator so you wont lose as much heat through a timber floor as you will through a concrete floor. Timber floors do often require a certain level of stiffening and increased lateral stability to make sure they're suitable for tiling. If you're adding a board for stability we recommend the use of our coated insulation boards. These boards provide the perfect stable substrate for electric underfloor heating and tiling, as well as improving the efficiency of the heating system.

Installing coated boards is easy. You can cut them to shape with a sharp blade and simply fix them into place with fixing screws and washers at 30mm centres around each side of the board.


 

Choosing the right system for your project

HeatThat™ provide three different heating systems to suit different applications. Whether your project is a well insulated new build or a drafty old Victorian town house, we have a heating solution for you.

HeatThat™ 150W/m2 matting can be used as a primary heat source in a well insulated environment when covering over 85% of the total floor space in the room. The 150W/m2 matting system can also be used to provide an additional heat source and take the chill off the floor in a poorly insulated retro fit application.

HeatThat™ 200W/m2 underfloor heating mats are designed for use in areas with high heat loss, such as conservatories, that require a faster heat up time. It does not get any hotter than the 150W/m2 system, but will reach the target temperature faster and will not be affected as much by heat loss as the less powerful systems. If you're planning a conservatory or have a poorly insulated house, this is the system for you!

Adjustable output cable kits are designed specifically for use is smaller areas with awkward layouts such as shower rooms, ensuites and bathrooms. The variable layout makes it easy to arrange the heating cable around any furniture and the cable spacing can be adjusted to achieve your desired output. For a primary heat source (in a well insulated room) you should look to achieve 150W/m2 as a minimum. Anything less will simply act as a secondary heat to take the chill off the floor.


 

Simple manual thermostat

Every electric underfloor heating systems requires a thermostatic contoller to regulate the temperature and switch the power on and off. If it's simplicity that you want then HeatThat™'s Manual Thermostat is the perfect solution. It features a temperature dial and an on/off switch, That's it! In the box you'll find fixing screws and a 3m sensor probe which should be installed in the floor to regulate the floor temperature for maximum accuracy.

Touchscreen programmable thermostat

This thermostat also includes fixing screws and 3m floor sensor probe, but also features a fully programmable 7 day 6 event heating schedule and an LED backlit touchscreen display. A customised heating schedule will help you save energy by ensuring your underfloor heating is only on when you need it.


 

Tiling over underfloor heating

Electric underfloor heating mats are sometimes referred to as "under tile heating" and for good reason! It's really easy to tile directly over an electric underfloor heating mat, there are a couple of things to consider though...

Always install the matting wire side down where possible - this will help to protect the cable from snagging or any other damage during tiling.

Use a flexible polymer based tile adhesive and grout to fix your tiles. The flexible nature of this type of adhesive allows for expansion and contraction so it want crack or de-laminate when used with underfloor heating.

Carpet, timber and other floor finishes

It is perfectly acceptable to install electric underfloor heating under a wide range of floor finishes if the heating cables is concealed within a 10mm layer of flexible self levelling compound. This layer is essential to allow the heat to spread evenly before radiating into the room through the floor covering. When the self levelling layer is fully cured you can install carpet and under lay (up to 2.5 tog), timber, laminate or vinyl flooring. HeatThat™ always recommend that you check that your floor finish is suitable for use with underfloor heating before making a purchase. The flooring manufacturer will be able to tell you if it's suitable or not.


 

Ensure your electrical circuit can cope with the demand

HeatThat™ thermostats can cope with a load of up to 16A before you bump into any problems. As a rule you will be fine if you have a system under the areas stated below:

  • 100W/m2 system up to 36m2
  • 150W/m2 system up to 24m2
  • 200W/m2 system up to 18m2

If you suspect your system may be over 16A or any of the areas stated you will need to install a contactor/snubber to ensure the circuit can cope with the demand of the heating system.

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