How to Install Underfloor Heating

If you want to install underfloor heating to warm up your home, look no further.

Doing it yourself is one of the biggest savings you can make on underfloor heating installation costs.

This guide will help you understand how to install underfloor heating, what tools and materials you may need, and how to keep safe during installation.

Let's dive in.

What Tools Do I Need to Install Underfloor Heating?

Before installing underfloor heating, you must ensure you have the right tools first.

Here's what you'll need:

• Pencil or pen
• Tape measure
• Scissors
• Cable puller
• Stanley knife
• Plastic trowel
• Saw
• Drill or screwdriver
• Bucket and mixing paddle
• Spirit level

What Safety Equipment Do I Need When Fitting Underfloor Heating?

You won't need specialist safety equipment to install underfloor heating, but some general safety gear is advised:

• Safety gloves
• Safety goggles
• Knee pads

An underfloor heating installation is quite a big job, so it can be beneficial to have someone else on board to help you during the process.

What Materials Do I Need to Install Underfloor Heating?

The type of materials you need for an underfloor heating installation will depend on the type of system you're having installed, either wet (water) or dry (electric).

Dry Underfloor Heating

Dry or electric underfloor heating consists of electric mats laid over the sub-base and connected to the electric supply.

This is ideal for use in single rooms, as it is usually cheaper to install as the installation tends to be easier, although running costs can be high, especially for a whole house.

For this type of installation, you'll need the following materials:

• Insulation board
• Plastering tape
• Screws
• Underfloor heating mat
• Levelling compound
• Thermostat and sensor
• Double-sided tape

Wet Underfloor Heating

A wet system or water underfloor heating is a series of pipes which are connected to a heat pump or boiler so warm water can flow through them to heat the room above.

This is best suited to entire home renovations and large spaces, as energy bills tend to be lower. However, it does take longer to install and is more expensive than dry underfloor heating.

Wet underfloor heating requires the following materials:

• Damp-proof membrane
• Pipework sheets
• Aluminium spreader plates
• Plastic piping
• Floorboards
• Adhesive
• Manifold

How to Prepare for Installing Underfloor Heating

To prepare your floor for underfloor heating, you need to ensure that you:

• Remove anything from the floor, including tiles, carpet, plaster, and anything else that may be covering the base.
• Brush away any dust, dirt, or debris that may be sitting on the floor base, so that you have a nice, clean surface to start work on.
• Check the subfloor to ensure it's in good condition. If not, you may need to hire a professional to come and make any repairs, or they may have to install a brand new sub-base.

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How to Install Electric Underfloor Heating: Step-by-Step Guide

Installing electric underfloor heating is the simpler of the two jobs, and most single rooms are done in 1 to 2 days.

Follow the steps below to install an electric underfloor heating system:

Step 1

Once the sub-base has been checked, you should lay down insulation boards in a staggered, brick-bond pattern and cut the boards so that they fit perfectly in the room.

Step 2

After the insulation boards are installed, you can then seal the joints with some plastering tape.

Step 3

Once the joints are sealed, you will then need to screw the boards into place, according to the manufacturer's instructions.

Step 4

You will then need to mark out where the fittings are going to go, including the thermostat position on the wall, the floor sensor, and the route the power lead will take up to it.

Step 5

Once you're sure of your layout, it's time to start fitting the underfloor heating. Some important things to remember are that the cables can't touch, they can't cross, and you can't cut the cable, so you need to make sure you get a cable that fits the room, measured without the areas under fixed units.

Step 6

The next step involves opening up the heating mat and checking it over for any damage before you begin to lay it, starting at the point where the controller is going to be.

Step 7

You should then start at the edge and roll it out. Once you reach the other wall, you want to then cut the mesh up to the wire.

Step 8

You can then turn your roll around and start rolling again in the opposite direction, securing the mat as you go with double-sided tape. For more difficult areas, you can remove the heating element from the mesh and work it around any obstacles.

Step 9

Once all the floor heating has been laid, the power lead needs to be fed up into the controller position. A qualified electrician must complete this step and connect it to the mains supply, checking the cable resistance before and after the levelling compound goes down.

Step 10

Once done, you need to create a channel in the insulation boards so that the cable sits flat. You can do this by using a Stanley knife and creating a groove in the insulation boards where the wires can lie flat.

Step 11

The floor probe needs to then be fitted in a conduit between two heating cables to ensure accurate readings.

Step 12

It's now time to add the levelling compound. Pour it onto the floor and spread it out evenly using a plastic trowel. Check the manufacturer's instructions on the recommended depth and drying time.

Step 13

Once the levelling compound is dry, you can then install your flooring over the top, leaving the heating switched off until it has fully cured.

How to Install Wet Underfloor Heating: Step-by-Step Guide

Installing wet underfloor heating takes longer than an electric system, at 2 to 4 days for a single room, as laying pipework and screed is a bigger job.

For those who are confident in their DIY skills, there are some basic DIY wet underfloor heating kits available. These are typically designed for areas such as a single bedroom or small bathroom.

Follow the steps below to fit a wet underfloor heating system (water underfloor heating):

Step 1

Begin by rolling a damp-proof membrane out across the entire surface of the floor.

Step 2

Once the membrane is in place, you can then lay out your pipework sheets on top of the damp-proof membrane. Cut them to size so that they fit across the entire length of the floor.

Step 3

You should then insert aluminium spreader plates into the pipework sheets. They should slot easily into the gaps on the sheet, and they will help to hold them together while you finish laying out the pipework sheets.

Step 4

You can then mark out the route that the pipes are going to travel, being sure to avoid routing them under any appliances. Mark this out with a pen or pencil, working back from where the manifold will sit, as this is where every circuit begins and ends.

Step 5

You can then re-lay your spreader plates according to your route markings, this time in their final positions.

Step 6

The next step involves installing plastic piping through the grooves according to your route markings. The pipes should be connected to the manifold only by a qualified installer.

Step 7

Once you've installed all of the pipes, pressure test the system, then cover with floorboards or a layer of screed, depending on the system type.

Step 8

Once you've laid all of the boards down, you can then add flooring on top of this as you wish, once any screed has fully cured.

What to Do After Installing Underfloor Heating

The job isn't finished once the flooring is down. Here's what you need to consider after installation:

Let the Floor Dry

With an electric system, the levelling compound is usually ready within 1 to 2 days, so you can walk on the floor and lay your flooring soon after.

With a wet system, the screed takes much longer, often several weeks depending on its thickness and type.

Check the manufacturer's instructions before laying anything over the top.

Switch the System On

Bring the underfloor heating up to temperature gradually over a few days rather than going straight to full heat, giving your new flooring or any screed time to settle without lifting or cracking.

Underfloor Heating Installation Mistakes to Avoid

Most problems come from preparation rather than the fitting itself, and they're much harder to fix once the floor is down.

• Cutting the Cable — The heating cable can't be shortened, so measure the room and buy a mat that fits the space you're covering.
• Testing the Cable Late — Check the resistance of an electric cable before and after the compound goes on, as damage is easy to miss and impossible to fix afterwards.
• Not Pressure Testing — Wet systems should be tested and left under pressure before screed goes down, so a leak shows up while the pipes are still reachable.
• Covering Fixed Units — Heat has nowhere to go under kitchen units and fitted wardrobes, and you'll lose access to the system if it ever needs looking at.
• Skipping the Subfloor Checks — An uneven or damaged base affects how well the system heats and is far cheaper to sort out before anything goes down.
• Skipping the Insulation — Without insulation boards underneath, heat escapes downwards, and the system works harder to warm the room.
• Forgetting the Floor Height — Insulation boards and screed both raise the floor, so check your doors will still open before you start.
• Turning It on Too Soon — Levelling compound and screed both need to cure fully first, or you risk cracking the floor.

Should You Install Underfloor Heating Yourself?

If you've never installed underfloor heating before, it's best to hire a professional to ensure your home and family's safety. Even if you do the job yourself, you'll need a qualified heating engineer or electrician to make the final connection to your boiler or power supply.

You may also have to arrange for approval from building control before the work starts if necessary, as a tradesperson can't self-certify work they haven't done themselves.

A survey carried out by a professional will help you select the best underfloor heating system and ensure your boiler can support the additional heating system.

Laying an electric system in a single room is manageable for most confident DIYers. Wet systems and bathrooms with stricter electrical work are more complex, and are better left to a professional underfloor heating installer.

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