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Product category: Heating Systems, Controls and Management
News Release from: Encompas | Subject: Guide to underfloor heating
Edited by the Buildingtalk Editorial Team on 20 March 2008

Step by step guide to underfloor heating

Encompas explain installing underfloor heating is a relatively straightforward job following their guide.

Laying underfloor heating is a relatively straightforward job as long as you adhere to certain rules, prepare properly and take care with the components At Encompas we install underfloor heating every day and it becomes easier with experience

Proper Preparation Pays.

The first job is to install the insulation board over which you will lay the pipe-work.

Insulation is essential to stop any heat travelling downward and being lost - the better the insulation you use, the better the thermal insulation in your property.

TIP - Encompas always advises clients to install the best insulation they can afford - it will pay dividends in the future.

In this example we describe underfloor heating in a solid concrete floor but you can use underfloor heating in a joisted floor as well.

Before laying insulation ensure that the floor has been swept clean, as unevenness in the insulation will reflect in an uneven screed depth later.

TIP - The insulation boards should be laid tight together with staggered joints; it is often easiest to do this by laying full boards first and then go back filling the gaps in later.

Laying the Pipe.

Once the insulation is laid, run clip rail across the room at 90deg to the planned direction of the pipe-work.

The clip rail should be 1.5-2m apart with the last rail .5m from the wall to give enough room to turn the pipe and return it the other way.

The pipe is fairly flexible and a typical Alupex pipe will bend to a 150mm radius.

TIP! - It is best to warm the pipe to room temperature first as cold pipe is more difficult to work with.

Care must be taken when bending the pipe as it can be kinked.

A kink in the pipe can result in a break in the aluminium diffusion layer, potentially reducing the efficiency of the pipe.

TIP - When forming a bend in the pipe-work it is safer to form a bottle shape as this reduces increases the radius and any danger of forming a kink.

Start at the manifold and lay the groups of pipe-work working from left to right or vice versa.

Make sure that the start of the pipe has a clean cut to it; connect this to the flow manifold.

Pull the pipe-work slowly off the reel follow the pipe-work layout provided.

TIP - When you need to return the pipe to the manifold, it is best to lay the return pipe approximately 50mm from the flow pipe to avoid 'stripey' heating as the pipes will be at different temperatures (typically 8-10degc).

When back at the manifold allow a slight excess of pipe and make a clean cut.

Now align the pipe with the return manifold port you are going to connect to and make a final clean cut and connect the pipe.

Repeat the steps above for every group.

As you go around laying each group of pipe it is easiest to have a second person following you laying staples to give extra hold to the pipe (Fig 3) although this can be done afterwards if you are working on your own.

As a general rule 1 staple in-between each line of clip rail on a straight run should be sufficient with 3 staples at each bend (1 on the head and 2 at each end of the curve) although this will vary depending upon the type of insulation used.

Pressure Testing the Manifold and Pipe-work.

To fill the manifold and pipe-work with water it is ideal to use a pressure pump, however if this is not available mains water pressure is usually sufficient.

If you have access to a pressurising pump connect the flow from the pump on to the drain valve of the flow manifold and connect a hose from the return manifold drain valve into a large container (dustbin sized) of water and heating antifreeze.

Finally connect a hose between the large container of water and the supply for the pressurising pump - this should complete a logical circuit of flow.

Before switching the pump on, work through the manifold closing the isolation valves and all the groups on both the flow and return manifolds, except for 1 group at one end of the manifold.

Now turn the pump on and allow the water from the container to flow through the pump, pipe-work group and back into the water container for a few minutes to eliminate any air within the pipe.

Leaving the pump running close the open valve on the return manifold, now with a simultaneous action open both the flow and return valves on the next group of pipe to be pressurised.

Repeating the steps above work along the manifold one group at a time topping up the container of water with fresh water and antifreeze as required.

When you have completed all the groups on the manifold open all the valves on the return manifold and allow the water to flow for approximately 5 minutes through the whole system.

When the systems is running back into the container with a minimum of bubbles rising to the surface, leaving the pump still running close the drain valve on the return manifold and allow the manifold pressure to build to typically 4 bar or as high as the pump will go.

At this point close the drain valve on the flow manifold and switch off the pump.

It is recommended that you leave the system for 30 minutes before checking again to ensure that the pressure has held.

TIP - If you do not have access to a pressurising pump you will not be able to add antifreeze, which is not recommended for winter due to the danger of freezing.

To fill and pressurize from the mains directly, connect a hose from the mains to the flow manifold drain valve and a hose from the return manifold drain valve to a local open drain.

Following the process above, work through the manifold one group at a time, until you have pressurised each individual group.

At this point close the return manifold drain valve and again allow the pressure to build up to 4 bar or as high as the water mains will allow and then close the flow manifold drain valve checking back in 30 minutes to ensure the pressure has not dropped.

TIP - Finally once you have pressurised the manifold it is always best to check the tightness of your pipe to manifold adapters as the have a tendency to loosen under pressure typically 0.5-1 turn increase is enough.

TIP - Due to fluctuations in air temperature the manifold pressure may change over night, decreasing in the cold and increasing in the heat.

Also the application of screed adds heat to the pipe-work due to chemical reactions as the screed cures increasing the pressure.

Fluctuations are to be expected and there should only ever be cause for concern if the manifold pressure drops to 0 bar for longer than a 24 hour period.

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