< Expert Advice | 20.04.2017

Experts on Tap

Experts on Tap

Answers to your questions


Q: Sending my gas flue analyser away every year to be calibrated is such an inconvenience. How important is yearly calibration, and what can I do to minimise the inconvenience?

A: At some point in your analyser’s life cycle, the chemical gas cells within the unit will degrade and render the analyser unsafe. And an unfit analyser means you are no longer compliant with Gas Safe regulations. It’s these chemical gas cells that cause those unavoidable spikes in repair bills that will typically happen when your analyser is three or four years old.

Some manufacturers now offer cost-effective service packages to combat these big repair bills, with just a one-off annual repair cost. There’s plenty you can do to make your annual calibration easier, too. Avoid the pre-heating season rush by sending it away earlier in the year, and plan ahead so that customers aren’t kept waiting for commissions that can’t be delivered.

If your preferred manufacturer has yet to offer cost-effective servicing packages, you may want to consider completely replacing your analyser when that big repair fee comes in.


Q: A client wants me to install an underfloor heating system in an older property. When it comes to designing for performance, what do I need to consider?

A: Over the past decade, we have seen an increase in the use of underfloor heating in the UK. However, the actual performance of the heat emitter is often overlooked or unknown at the design stage. Underfloor heating systems were traditionally installed in newbuild properties within a 75mm-thick sand-and-cement screed, or more commonly a 50mm thick anhydrite flowing screed.

As underfloor heating became more popular, the market started to develop new systems to be used within retrofit applications (older houses). These new retrofit systems may be categorised as either ‘floating floor’ or ‘suspended floor’ systems, with an increasing emphasis on low-profile systems. The market as a whole has concentrated too heavily on designing systems that deal only with the practical application of the product rather than the actual performance and heat output of the emitting surface. This approach has led to a lot of confusion for both the plumber and the consumer.

A common mistake made by designers is creating a system without an intermediate layer, such as a 10mm plywood layer between a grooved dry-screed board and a carpet. Adding this structural layer reduces the risk of point load issues. However, it inevitably reduces the heat output of the floor. It is critical that a valid and accurate set of heat output data is known before designing or installing the complete underfloor heating system. This data also needs to take into consideration the impact that the materials you use will have on heat output. Designers also need to know the true heat loss of the building for which the system is to be installed.

Q: How should I calculate thermal output for a heated floor?

A: Industry relies heavily upon the BS EN 1264 Part 2 standard for calculating the thermal output of a heated floor, which sets out both a manual calculation and a procedure for carrying out live tests. Because of the number of variables present within a UFH system, the manual calculation for type B systems becomes inconsistent. Therefore other, more accurate, methods have been adopted, such as detailed computational fluid dynamics and conjugative heat transfer simulations, using the finite element method.

The overall heat output of a floor-heating system is affected by many parameters: pipe spacing, pipe diameter, water flow rate, water temperature, temperature difference between the flow and return, floor-covering resistance and the thermal properties of the heat conducting layers. As well as this, the fluid mechanics of both the air above the finished floor covering and the flow within the pipe can significantly affect and vary the overall result. Because of the complexity of these calculations, this answer only scratches the surface of this topic.

Do you have a query for our team? Email: editorial@plumbpartsmagazine.co.uk 


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