How to install an Underfloor Heating System

Download Our Full Underfloor Heating Installation Guide or click the links below to read online

How to install an Underfloor Heating System Manual

Floor Constructions

Installing Underfloor Heating on Screed / Concrete Floors

Solid floors can be constructed in a number of ways:
Single pour concrete method
Under floor heating pipe work is fixed to insulation and concrete is poured over the top.
Screeded floor method
Concrete floor is already in place, insulation is laid on the top of the concrete under floor heating pipe work is then fixed to insulation and screeded over.
There are various variations of these methods. dependant on builders preferences

Installing Underfloor Heating in a Timber Floor using screed between joists

Build a subfloor (min 25mm from top line of joists) between the floor joists using a good quality dense board insulation supported on timber battens fixed to the side of the joist. Then fix the under floor heating pipe work to the insulation, screed the floor flush with the top of the joists. The floor will then require a structural board over once the screed has been allowed to dry. Note when using this floor construction method consideration needs to be given the added weight on the floor joists

Installing Underfloor Heating in a Timber Floor Using Aluminium Plates

Insulate in between your joists using either a board or quilt insulation. Then nail your aluminium plates to your joists leaving a least 200mm at each end of the runs where your pipe will turn. Then you run your pipe in the aluminium plates.

Installing Underfloor Heating - Floor Constructions

Building an Underfloor Heating Manifold

Inside the box:

  • Brass Manifold with Mixer Valve
  • Circulating Pump
  • Inserts for Pipe
  • Set of Ball Valves with washers
  • End piece with drain valves and pressure gauge
  • Thermostatic head

Build the manifold before fixing to the wall. Start by screwing in the end piece into the top manifold body. Make sure the pressure gauge is facing you once the end piece is fully screwed in. If adjustment is needed use the rotating nut to adjust then tighten back up.

Attach the ball valves to the manifold as per picture. Red on the right (Flow) and blue on left (Return). Make sure you use the rubber washers provided before attaching them to the mixer valve, then fully tighten.

Turn the circulating pump to the left so it is facing you. Then tighten the top and bottom nuts.
Now the manifold is ready to fix to the wall.

How to build an Underfloor Heating Manifold Instructions

Installing the Underfloor Heating Manifold

The Manifold unit can be installed directly on the wall or a suitable mounting board by securing it’s brackets with suitable fixings (depending on the kind of wall). These need to be inserted into the designated holes, the mounting surface should be flat and vertical.

The mounting bracket holes can be used to mark the fixing positions and the manifold unit screwed to the wall/ mounting surface using suitable fixings ensuring that the assembly is level. The pump should be turned to face forwards to avoid fouling the wall/ mounting surface where the Manifold Unit is to be mounted, check the overall dimensions of the Mixing Unit using the table and drawing below.

Ensure that there is room for the isolating valves and fittings below the mixing unit inlet connections and leave at least 300mm from the lower manifold rail to the floor to prevent damage to the pipes where they enter the floor.

How To Connect Underfloor Heating Pipe to the Manifold

Ensure you cut the MLCP pipe square with sharp plastic pipe cutters, It is essential to open the inner bore of the pipe with a pipe reamer tool to avoid damage to the O-rings when inserting into the monoblocco fitting. Insert the pipe into the sealing union until it is fully home, then turn the nut until the inspection slot lines up with the slot in the gripping ring and check that the pipe has been inserted all the way.

Note – To make insertion of underfloor heating pipe easier, if necessary wet the end of the pipe and/or the fitting with clean water only. Lubrication with oil or grease will do irreparable damage to the O-rings of the fitting.

Screw the nut onto the manifold and tighten with a 27mm spanner without using excessive force. When tightening pipe onto manifold fittings, hold fitting with spanner whilst tightening pipe nut. Once the pipe has been connected to the flow manifold, laid according to pipe layout drawing and connected back into the corresponding return manifold connection, it is now a complete circuit. When all circuits are fitted and secured, take time to check over pipe work and ensure the spacing’s are correct and there are no kinks in the pipe.

Fixing Rail Installation (Solid Screed Floor)

The fixing rail is used to make sure the pipe is installed evenly in the room or rooms. It is divided into 50mm spacings. So for instance if you are installing your pipe work at 200mm centres then you would clip the first pipe in 100mm from the wall then you leave three clips and turn the pipe back into the fixing rail and clip into the fourth clip this equates to 200mm. Insulation clips are used to fix rails in place

Fixing rail spacing
The top rail on the drawing where the pipe enters the room need to be 500mm from the top wall. The bottom rail needs to be 300mm from the bottom wall (see Fig 1) and then place a final strip in the middle of the top and bottom rails to keep the pipe runs nice and straight.

Remember to allow enough pipe to connect from the room to the underfloor heating manifold (the packs contain a small amount of excess pipe for connections).
It is important to bend the pipe in a “light bulb” shape to avoid kinking if anything less than 200mm centres are used.
Before installation please read the fitting, filling & commissioning instructions carefully, these are tried and tested to provide you with excellent results.

Underfloor Heating Fixing Rail Installation Instructions

*Typical screed floor with a depth of 65mm

Please remember that it is very important that the pipe is laid with due care and is not kinked when being installed. Electrical control wiring & Flow and return pipe work is required, ensure that this is in place prior to finishing work is carried out. (Please see drawings or Phone us on 0800 232 1501)

Installing Underfloor Heating using Screed between joists

200mm pipe centres
(Room up to current Building Regs)
When installing underfloor heating into a timber floor at 200mm centres pipe work is usually laid as 2 runs per joists (if joist are at 400mm centres). Notch the end of the joists about 100mm from wall this will carry UFH pipe coming into the room and the pipe work turning into the next joist .Clips should be every 1m-1.5m.

Installing Underfloor Heating between joists 200mm using screed

150mm Pipe Centres
(Room with High Heat Loss i.e. Conservatory)
When installing underfloor heating into a timber floor at 150mm centres pipe work is usually laid at 3 runs in each joist. Notch the end of the joists about 100mm every other notch should be big enough to take 2 pipes. Also you will need to notch the other end of the joists, every other joist should be notched at opposite ends to the notch where the pipe work comes in. Clips should be every 1m-1.5m.

Installing Underfloor Heating between joists 150mm using screed

Installing Underfloor Heating using Aluminium Plates

How to install underfloor heating using aluminium plates

Underfloor Heating throughout a Full House Layout

View Full House Underfloor Heating Diagram

About the Underfloor Heating Manifold

View Underfloor Heating Manifold Diagram

Filling the System

Once all the circuits are installed the system must be filled and pressure tested. For this you will need mains water supply and a garden hose, follow the step by step instructions below.

The manifold mixer has a built-in non return valve to ensure that the underfloor heating circuits can be simply filled from the drain and fill valves fitted to manifolds. To use the non-return valve the underfloor heating circuits must be filled using the drain and fill valve fitted to the upper rail only – it will not work if the lower drain and fill valve is used to fill the circuits.

To fill the manifold correctly you will need to isolate the loops. On the top manifold rail, work from right to left and close the flowmeters by rotating the red collar clockwise Fig 2. When you get to the last flowmeter make sure this one is rotated fully anti- clockwise Fig 3 for 3 and a half turns and then click the red collar down. Once the collar is down you then use the 19mm Spanner Flats Fig 4 to fully open the loop. (If this is not done you will not get any water into the loop).

On the bottom manifold rail again work from right to left and close blue isolators by rotating clockwise Fig 5. When you get to the last blue isolator turn this one anti-clockwise to open. Fig 6.

Once only one flowmeter and blue isolator are open on the manifold rotate the Red and Blue ball valves so the levers are horizontal.

Open the Auto Air Valve by rotating the grey Cap 1 turn anti clockwise.
Connect mains water to the top Fill valve, and connect a piece of hose onto the bottom fill valve and place the end into a bucket. Open the fill & drain valves by placing the opening tool attached onto the end of the fill & drain valves and rotate toward you to open. Now manifold is ready for filling.

Now turn the mains water on, once the water comes out of the bottom fill point this indicates that the first loop is fully purged. Isolate this loop and move onto the next and repeat the process using the steps on the previous page.

When the final loop is full open all the loops on the manifold turn off the bottom fill point. Use the mains water pressure test the manifold, once the pressure is stabilised shut off the top fill point and turn the hose off. In normal circumstances you should get at least 3 bar on the pressure gauge. If mains water pressure is lower a pressure testing pump may be required.

Plumbing using a Single Zone System

View plumbing diagram using a single zone system

Wiring using a Single Zone System

View wiring diagram using a single zone system

Plumbing using a Wiring Centre (Multi Zone)

View plumbing diagram using a wiring centre

Wiring using a Wiring Centre (Multi Zone)

View wiring diagram using a wiring centre

Commissioning your Underfloor Heating System

Once you have installed the underfloor heating, filled & pressure tested, connected the flow and return pipework to the manifold. If the floor is a solid screed floor before following these steps make sure that the floor has been allowed to naturally cure in accordance with the screed manufacturer guidelines.

  • Open Ball valves by turning red / blue levers inline.
  • Connect the thermostatic head to the mixer.
  • Set water temperature to low (20°c) on the thermostatic head.
  • Slowly increase the temperature over the next 4 weeks.
  • Remove all the white caps (if multi zone) on the bottom manifold body and attach the actuators to the manifold. If using a single zone system leave the blue caps connected and make sure they are turned fully anti clockwise.
  • Bleed any air out of the manifold that may have entered when you opened flow and return. Bleed air using the auto air vent located above the temperature gauge.
  • Turn on one thermostat at a time and check that the boiler turns on.
  • On a multizone system check that all thermostats individually open the right loops. The black tag of the actuator should lift. On a single zone system check the zone valve has opened.
  • Check the pump is running, the green lights should be lit.
  • Check the flowmeters are open and adjust flow rates refer to next page.
  • Hot water should now be running through the manifold from the top body into the floor and returning to the bottom body.
  • Check any other zones i.e. radiators/hot water that these are working correctly.
  • Turn off the thermostats and check the actuators, pump & boiler have turned off. Boiler may still run if other zones are calling for heat or boiler has a pump over run.

The initial warm up period will take a long time as the floor is cold and will remove all the heat from the pipe work. This will result in the water entering the floor (top body) will be warm as stated by temperature gauge & the water coming up to the bottom body will be cold.
The floor temperature should be gradually increased over a number of days as not to damage the concrete/screed floor.

Underfloor Heating Flowmeter Adjustment

How to balance the circuits using flowmeters
Flowmeters have a double regulating function i.e. they not only adjust water flow but also include an isolating function which can be opened and closed without affecting the flow setting. The flowmeter has an inner combined flow regulator and flowmeter, see Fig 7, and an outer red collar. The red collar, (1) is used for isolating the valve. The inner regulator is used to set the flow in the circuit, increasing or decreasing the flow by using the 19 mm spanner flats provided, see Fig 8. The change in flow can be read in the scale on the flowmeter tube. Check the valve is in the fully open position. To check isolating valve following the instructions below:

Turn the red collar anticlockwise approximately three and a half turns. You will see the whole of the flowmeter rotating and rising. If the valve is over-rotated – more than three and a half turns – then the internal plastic threads can become damaged and cause leaks. If you reach the positive stop please
rotate back half a turn.

You are now ready to use the flow regulating function. Lower the red collar until it touches the manifold (1). Then using a 19mm spanner, or your fingers, adjust the flow using the black spanner flats at the bottom of the flowmeter (2). You can read the required flow in litres per minute directly from the red indicator against the scale in the clear flow meter tube. When you have set the required flow rate, raise the red collar (1) again, until it is engaged against the black spanner flats at the bottom of the flowmeter (2), see Fig 9.

Cleaning the Underfloor heating flowmeter tube
Turn the red collar (1) clockwise, until the isolating function is fully closed. Remove the flowmeter tube by securing the black spanner flats, then using either hand pressure or a 17mm ring spanner, gently unscrew the flowmeter tube anticlockwise. Clean the tube and screw it back on. Turn the red collar (1) anticlockwise until the isolating valve is fully open again.

About the mixing unit

The unique design of the internal mixing valve components ensure that hot water from the heat source and return water from the underfloor circuit are mixed together in the valve body to produce a temperature range between 20°C to 70°C. This temperature range suits a range of underfloor heating applications from commissioning new floor screeds to operating with very thick screed in commercial applications. The following illustrations show how the mixing valve operates through its remote sensing thermostatic head.

How an Underfloor Heating mixer valve works

The Mixing valve is pre-assembled onto the manifold for time saving installation. At its heart is the Thermostatic Mixing valve which is a specifically designed mixing unit to ensure accurate temperature control of underfloor heating. The unique design of the internal mixing valve components ensures that hot water from the heat source and return water from the underfloor circuit are mixed together in the valve body to produce a range of temperatures from 20°C to 70°C. This range of temperatures suits the whole field of underfloor heating applications, from commissioning new floor screeds to operating with very thick floor screeds in commercial applications. The illustrations below show how the mixing valve operates through its remote sensing thermostatic head:

  • Initially the cool liquid in the remote sensing probe, allows almost all of the primary hot water from the heat source through the valve. Gradually the temperature of the probe rises as the underfloor circuits begin to warm up
  • Depending on the temperature setting of the thermostatic head, as the temperature of the probe rises, the shuttle starts to close off the primary hot water allowing return water to maintain the temperature set on the head, up to 70°C if required
  • Once the temperature set on the head has been reached at the probe, the shuttle balances the right amount of primary hot water and secondary return water to maintain this temperature. Depending on the thermostat setting, the hot water could be almost completely closed off allowing very low temperatures suitable for commissioning screed floors right down to 20°C if required.
  • The thermostatic mixing valve has a flow increase valve which allows return water to flow directly into the mixed water outlet. This cools the mixed water temperature sensed by the remote phial and causes the mixing valve to open allowing more primary hot water through the mixing chamber and raises the temperature to the setting on the head

Underfloor Heating Operating Instructions

There are two main elements of control for your underfloor heating; one is a programmable thermostat and the other is a thermostatic head.

Programmable Thermostat
This thermostat gives you the ability to set overall time control with two different temperature settings. As with a more conventional heating system the first temperature setting is used to provide a comfortable living environment (typically 21°C) for the time you spend in the room.

The second setting can be used to provide a facility called NIGHT SETBACK. Night setback is where the second temperature setting is at a much lower level (typically 16°C).

Setting the clock thermostat to the night setback temperature will turn the boiler and pumps off until the temperature programmable thermostat drops below 16°C.

The night setback stops the room from cooling right down during the night so that the room can be brought up to a comfortable working temperature quicker and more efficiently in the morning. To set the time and temperature on the programmable thermostat refer to the user instructions provided with the thermostat.

This piece of equipment is situated at the manifold and its purpose is to blend down the high temperature water from the boiler to a lower temperature suitable for underfloor heating.

The thermostatic mixing valve can be set on the thermostatic head from 20 to 70°C as follows:
1. Turn the knob of the thermostatic head, to set the required underfloor flow temperature
2. Allow sufficient time for the temperature to stabilise, then check the setting against the temperature reading on the mixed flow temperature gauge fitted to the mixer valve located above the pump

Temperature setting lock
The thermostatic head is provided with two setting pins, one red and the other blue. These pins are provided to lock the temperature setting as follows:

1. Set the required temperature as described above
2. Locate the black dot and insert one pin on each side of the dot
3. The head cannot be rotated.

4. NOTE – Floor heating is not a quickly responsive form of heating (like a gas fire) and can take some time to reach the desired temperature. The opposite is also true in that it takes a while for the floor to cool down. For example, if you want the room up to temperature by 8am set the higher temperature to 6am if you stop using at 11pm set the lower temperature setting to 9pm.

Additional Underfloor Heating Products and Assistance

We have tried to put as much in-depth information on our website as possible but if you require any further assistance or have any questions you can contact us here. If you are looking for any additional products please click here to visit our Underfloor Heating Shop.



Save & Share Cart
Your Shopping Cart will be saved and you'll be given a link. You, or anyone with the link, can use it to retrieve your Cart at any time.
Back Save & Share Cart
Your Shopping Cart will be saved with Product pictures and information, and Cart Totals. Then send it to yourself, or a friend, with a link to retrieve it at any time.
Your cart email sent successfully :)