Underfloor Heating Installation

Contents:

• How water underfloor heating works
• Tools & materials
• Water underfloor heating: Step-by-step
• Electric underfloor heating: Step-by-step
• Common mistakes
• FAQs

In this guide, we’ll look at how to install underfloor heating, including both water and electric underfloor heating systems.   

Installing underfloor heating is a big job. It’s important you plan everything very carefully before you do any fitting work. You need to get a professional to help with at least some parts of the work as well.  

There are two main types of underfloor heating: Water and electric. Fundamentally, both types work in a similar way. They are laid as a network of pipes or cables under the floor, and this heats up and delivers radiant heat upwards through the room. The main benefits of underfloor heating are even heat distribution, warmth under your feet, better air quality, better household heat control and space savings (no radiators).

There are some things to think about at the planning stage, however. The cost of underfloor heating varies between types, in both purchase costs and energy bills. Installation methods vary between types as well. Some types are much easier to install than others. The type of room it’s being installed in also affects system choices and installation methods.

Water (hydronic) underfloor heating works with a network of flexible polyethylene pipes that are laid underneath a floor. Warm water flows through the pipes, just like with a radiator, and the pipes deliver heat upwards through the room. 

Here are the benefits:

• Even heat distribution and warm feet.

• Compatible with any fuel heating system, including gas, LPG, solar heating panels and heat pumps.

• Efficiency cost savings - 40% more efficient than a boiler and radiator system.

• Space savings – no need for radiators.

• Better air quality – radiators create air currents that disturb dust.

• Divide heating into zones throughout a property for better heat control.

The main disadvantages are the initial underfloor heating cost at purchase and complicated installation. Installation is more difficult if you are retrofitting a property.

Find out more in the underfloor heating guide.

Here are the tools you need for the basic stages of installing water underfloor heating:

• Cleaning equipment – dustpan, brush and hoover.

• Marking and measuring tools – tape measure, spirit or laser level and marking pen.

• Pipe cutter – a plastic or copper pipe cutter, for accurately cutting pipes.

• Panel saw and utility knife – for cutting insulation.

• Safety equipment – work gloves, eye protection and knee pads.

You may find you need other equipment, depending on circumstances. Some stages also have to be done by a suitably qualified plumber or electrician, and these need specialist equipment.

You also need an entire underfloor heating system. This will include the insulation, pipes, pipe fittings, pipe clips or fixing track, a manifold and a thermostat at a minimum.

Be careful to wear your personal protective equipment when you need to, and work carefully.

Installing water underfloor heating is a big job. Most DIYers should only do the basic stages of the process. In some cases, it’s actually better to leave everything to a professional. Professional fitters will often offer guarantees for their work, which is one big advantage they offer. 

If the system is going to be connected to a boiler, the final connection must be completed by a certified Gas Safe engineer. There is also some electrical work involved to connect the system to a thermostat and programmer. This must be carried out by a qualified electrician who is part P or NICEIC certified.

In some cases, however, DIYers will want to do some of the work themselves. It might be possible, for instance, for an experienced DIY enthusiast to fit the damp proof membrane, insulation and piping for their water underfloor heating system. Some people might even want to lay their own screed and flooring as well.    

In this section, we’ll explain how to fit water underfloor heating. Here are the stages:

1.  Planning and design

2.  Prepare the subfloor

3.  Install damp proof and insulation

4.  Lay the pipe track (if included)

5.  Install the manifold

6.  Lay the pipes

7.  Pressure test the system

8.  Lay screed and flooring

9.  Connect the system to the mains

If your water underfloor heating kit is supplied with fitting instructions, these should always be your first source of information.

 

Step 1. Planning and design

You need to pick the type of system you use very carefully, making sure it suits your property and the room. You also need to make a layout plan. There are several considerations at this stage. The best thing is to ask a professional for advice to plan and design your system.

There are regulations in the UK that apply to underfloor heating systems. Always check with your local building authority to see which regulations apply to you. We also recommend seeking professional advice to ensure that you stay compliant.  

Here are some of the important things to consider in system design:  

• Room size and heating requirements

• Floor structure – you need to lay onto a structural floor

• Finished floor level

• Fitting damp proof, under-insulation and edge insulation for the underfloor heating system

• Pipe layout

• Manifold positioning

• Thermostat positioning

• Flooring compatibility

• System controls and zoning (if multiple systems are installed in a property)

Careful planning will help you calculate your underfloor heating cost.

Be aware that retrofitting water underfloor heating is more difficult than installing it in a new build. 

Another thing to be aware of is that, once the underfloor heating is installed, accessing pipes, cables or other things underneath the floor might be very difficult. As such, it's worth checking if there is any other work required beneath the floor before you start the process.

 

Step 2. Prepare the subfloor

The first practical stage of fitting an underfloor heating system is preparing the subfloor. You should install your heating system on top of a structural floor. Concrete or a suspended timber floor with floorboards are both fine.

Once you’ve stripped the floor back to the bare surface, clean it thoroughly. You need to ensure there are no jagged edges that could damage the pipes in your heating system or cause it to be unlevel.

If the floor has any damage or significant areas of unevenness, they should be repaired at this stage. Self-levelling compound might be needed to level uneven floors.

 

Step 3. Install damp proof and insulation

You only need to install a layer of damp proof if you’re laying your system on top of a concrete floor.

Here’s how to fit underfloor heating damp proof:

1.  Lay the sheet out along the entire length of the room.

2.  Pull it up at one end, so it runs up the wall for about 10 inches – ultimately it should form a tray that holds everything including the screed laid on top of the system.

3.  Cut it at the other end, so it extends the same distance up the wall.

4.  Make sure it fits at the sides in the same way.

5.  If you need to lay more than one length, overlap the joint by 150 mm and tape the sheets together with polythene joint tape.

Insulation is crucial for efficient and effective heating. All water underfloor heating systems should be installed with a layer of insulation underneath and against the wall at the edge. The installation process depends on the insulation you use. Here are some things to know:

• Insulation boards should be joined together with the correct tape - aluminium foil tape for aluminium-backed boards.

• Some insulation boards have in-built grooves for piping – these boards need to be arranged in the correct pattern.

• Always fit a layer of insulation around the edge of the entire room – this should extend up just higher than the layer of screed.

• You may need to attach insulation boards to the floor with screws and washers or adhesive.

 

Step 4. Lay the pipe track

If your system comes with a pipe track for arranging your underfloor heating pipes in the correct layout, install it at this point. Refer to the instructions that come with your track for correct fitting. Be careful not to damage your insulation while you’re working.

 

Step 5. Install the manifold

You need to install the underfloor heating manifold before you lay the pipes to keep things organised and so the pipes are all laid correctly. You should have chosen a good location at the planning stage.

Fitting a manifold is a job for a professional. Manifolds are normally supplied with fixing brackets. They should be fitted in a location with sufficient ventilation, that allows access for maintenance and with sufficient clearance for attaching the pipes.

 

Step 6. Lay the heating pipes

Next, you should lay the entire underfloor heating pipe system.   

Here’s how to install underfloor heating pipes:

• Start from the manifold.

• Lay the pipe according to the plan – follow the track for tracked systems and follow the piping plan manually for other systems. Pipes normally need 200 mm clearance from each other and from the edge of the room.

• For non-tracked systems, clip the pipe in place with purpose-built clips. Make sure it is held firmly.

• Be careful not to twist or kink the pipe while you’re working.

One planning consideration you shouldn’t overlook is that you need to leave space for any floor fixings that will come later. In a bathroom, for example, you might need to leave room for a shower, sink outlet or to secure bath feet.

 

Step 7. Pressure test the system

Next, a qualified plumber should attach the system to the manifold and pressure test it.

The entire system should be pressure tested at this stage to make sure it’s working before the screed and flooring is laid on top of the pipework. This is a job for a professional.

 

Step 8. Lay screed and flooring

Note: Screed should always be laid with the heating pipes under pressure.

Once the system has been pressure tested, you can lay the screed on top of the pipes and then lay your finished flooring. The pipes should be under pressure when the screed is laid to prevent pressure expansion causing problems later on.

Laying screed is a big job in itself, but it’s a job experienced DIYers can do with the right preparation.

When the screed is fully cured, you can lay your final flooring. Be aware that the type of flooring you choose has to be compatible with underfloor heating. Materials with high thermal conductivity are best. The best flooring types for underfloor heating are tile and stone, engineered wood and vinyl flooring.    

 

Step 9. Connect the system to the mains

The final step is to connect the system to the mains. If the system is going to be connected to a boiler, the final connection must be completed by a certified Gas Safe engineer. There is also some electrical work involved to connect the system to a thermostat and programmer. This must be carried out by a qualified electrician who is part P or NICEIC certified.

With electric underfloor heating, adhesive-backed mesh mats with pre-installed electric heating cables are laid under the floor. They should be laid on an even structural floor at the base. Normally, this is a screed floor that has been installed to provide a solid and level surface. A layer of insulation is laid on top of the screed to ensure the heat travels upwards into the room. Then the electric underfloor heating mesh is laid on top of that.

They are then covered with the chosen flooring, usually with a self-leveling compound on top of the heating mats that acts as a base for the flooring. As with water underfloor heating, flooring that conducts heat well is best.

Once laid, the heating wires are connected to the mains electricity and are controlled with a thermostat and programmer.

Electric underfloor heating is often used in small rooms, in particular in bathrooms. Tiles make a good choice of flooring, and electric underflooring works well in bathrooms with tiled floors. It can be used in conjunction with radiators to provide extra heat.

Electric underfloor heating installation is much easier than water (hydronic) heating installation. Here are the main steps to install electric underfloor heating:

1.  Plan the layout and gather tools

2.  Prepare the subfloor

3.  Lay out the heating mats

4.  Install the floor sensor and test the heating mat

5.  Fit the floor

6.  Connect the system to the mains

If your electric underfloor heating system is supplied with fitting instructions, these should always be your first source of information.

All electrical work, including wiring and connecting the underfloor heating, thermostat, and programmer to the mains electricity, must be completed by a qualified electrician who is part P or NICEIC certified. Do not connect the system to a power source yourself at any point during installation.

Find out about efficient and convenient heating in the smart heating guide.

 

Step 1. Plan the layout and gather tools

You should pick the type of system you use very carefully, making sure it suits your property and the room. It’s often best to ask a professional for advice on the correct choice of system.

Wattage is a key consideration with electric underfloor heating. The wattage you need depends on the size of the room, how well insulated it is and the flooring type used below and above the heat mats. You should aim to choose a system that will provide adequate heat as efficiently as possible. Large rooms are often too expensive to heat with electric underfloor heating.

Some other things to consider are:

• Will you remove existing radiators or run underfloor heating in conjunction with radiators – in bathrooms, people often have both.

• Finished floor level.

• Thermostat positioning.

• Flooring compatibility.

• Future room features that should not have heating underneath, such as a shower in a bathroom.

You also need to make a layout plan.

Tools and materials needed to fit electric underfloor heating

Here are the tools and materials you need for electric underfloor heating installation:

• An electrical tester - for testing resistance

• Scissors and a utility knife - for cutting the heating mesh

• Adhesive tape – for securing mesh in place

• Underfloor heating insulation boards – for insulating underneath and around the underfloor heating

You also need an electric underfloor heating kit. This should include a heating mat or loose wire heating cables, a digital thermostat and a floor sensor with conduit.

 

Step 2. Prepare the subfloor

Electric underfloor heating is normally installed on top of a layer of screed. This screed layer provides a clean and level surface for laying insulation and electric underfloor heating. All you need to do is make sure it’s clean and free of debris, ready for laying your insulation.  

There’s no need to lay damp proof on a screed floor with damp proof protection underneath it.

The method for how to install underfloor heating insulation depends on the type of insulation you have. Refer to the manufacturer instructions that come with your product.

Here are some key things to know:

• Insulation boards should be joined together with the correct tape - aluminium foil tape for aluminium-backed boards.

• Do not fit a layer of insulation around the edge of the room for electric underfloor heating.

• You may need to attach insulation boards to the floor with screws and washers or adhesive.

 

Step 3. Lay out the heating mats

The next step is to lay your heating mats. Make sure you refer to the instructions that come with your product for the exact installation procedure.

Do not connect the system to a power source at any point during installation.

Electric underfloor heating is normally supplied in rolls of mesh matting with an adhesive backing. You roll them out, sticking them down completely level as you go. When you need to turn a corner or turn 180 degrees at a wall, you cut across the mesh (without cutting the wires). Then the mat can be bent around back on itself to complete the turn.

Here are some other things to know about how to install electric underfloor heating:

• Start from beneath where your thermostat will be located, with your connection wires directly beneath it.

• You must not cut the cables.

• You must adhere to minimum clearances between cables and walls.

 

Step 4. Install the floor sensor and test the heating mat

Next, fit the floor sensor beneath the thermostat location and make sure the system works:

• Install the floor sensor in the middle of two pieces of wire in the underfloor heating. It should be installed in a conduit pipe (provided with most kits). The conduit should run directly beneath the thermostat.

• Tape the cable for the floor sensor and any other cables to the wall directly beneath the thermostat.

• Use an electrical tester to check the underfloor heating system is correctly connected and functional. This is an important step because the next step is to cover the entire system with your flooring.

 

Step 5. Fit the floor

The next step is to fit the floor.

Before you start fitting your flooring, check there aren’t any raised patches in your electric underfloor heating. If you find any, make sure they are securely held down with tape.

Most floors are laid on top of a layer of self-levelling compound. A common alternative to using self-levelling compound is specially designed flooring underlay materials. The first step is to lay your self-levelling compound or alternative base for your flooring. This is a difficult job in itself, but it’s a job DIY enthusiasts can do with the right preparation.

After you’ve finished this stage, you can lay your flooring. Remember that you have to use flooring that is compatible with underfloor heating. Tile is a good choice for bathrooms. Some good alternatives are stone, engineered wood and vinyl flooring. It may be possible to use carpet with underfloor heating, although most carpets aren’t the best type of flooring.

 

Step 6. Connect the system to the mains

The final step to installing underfloor heating is connecting the system to the mains. This is a job for a suitably qualified electrician.

All electrical work, including wiring and connecting the underfloor heating, thermostat, and programmer to the mains electricity, must be completed by a qualified electrician who is part P or NICEIC certified.

After your electrician has finished, you’ll have a nice underfloor heated room.

After you’ve installed an electric or water underfloor heating system, you need to be careful about how you use the heating. If you turn the heating up too quickly, in particular, you might cause problems with the screed or your flooring.

Here are some things to be careful of:

• Give screed or self-levelling compound time to fully cure before turning on the heating system. This can be as much as 28 days. Check the instructions with your product.

• Avoid rapidly heating a new system - Gradually increase the temperature over several days when you first turn it on to prevent cracking in the screed or problems with the flooring.

• Check if there are maximum heating temperatures for your flooring.

• Check what maintenance your heating system needs and stay up to date.

• Careful with work to the floor in the future – Remember not to drill any holes into floors with underfloor heating.

Mistakes in fitting underfloor heating can mean difficult and expensive repairs. It’s important you take the time to plan everything very carefully and you do all the work correctly.

Here are some of the common mistakes:

• Failing to design the system correctly – make sure all the important design calculations are made and you choose the right system.  

• Failing to properly prepare the subfloor – make sure the subfloor is clean and level before you start.

• Not clipping water pipes down properly – make sure all the pipes are firmly clipped down.

• Skipping the pressure test – never skip the pressure test with a water system.

Troubleshooting common challenges with installing underfloor heating

If you are installing your own underfloor heating, make sure you research and plan each stage of the process very carefully. There are many different points at which you could make a mistake. The best approach is to research and plan everything very carefully, without exception.

Understanding how to fit underfloor heating correctly without experience can be difficult. Don’t be afraid to ask for professional help at any stage of the process if you’re unsure.  

Underfloor heating is great. It’s more comfortable, it’s much more energy efficient, and it means you can put furniture anywhere in the room you’d like. Pets also love lying on a warm floor, if you have any.

However, fitting an underfloor heating system is a big job. Working out how to install electric underfloor heating is easier than water systems, but installing underfloor heating is always something you need to be careful about. Mistakes are difficult to correct if they’re found after the floor’s been laid.

If you do decide to fit your own underfloor heating, make sure you take the time to properly prepare and you’re careful when you’re working. Don’t be afraid to ask for help and advice as well. You can also do your own research to find out more.

You can install an entire underfloor heating system with tools and materials from Screwfix.