HEAT PUMPS
MLCP – the pipe material revolutionising the way heating engineers are working
The effi ciency of air source heat pumps is a topic that is often debated, with the product all too often unfairly maligned. In this article, Matt Densham, Divisional Director - Building Services for Frankische UK, dispels such criticism, arguing that an underperforming system is often down to the incorrect sizing of pipes and choosing the wrong pipe material for the job when, in many cases, MLCP (Multi-layer Composite Pipe) would be the ideal solution.
"Physical benefi ts of MLCP pipe over plastic include the need for far fewer expansion loops,
brackets
and joints; it handles water temperatures up to 95o
pressures up to 10 bar."
C and
common misconception exists that heat pumps don’t produce enough warmth to heat larger homes eff ectively. This belief stems from anecdotal accounts which originate because of poorly designed or badly installed systems that fail to achieve the desired indoor temperatures. However, when the entire system is installed correctly, incorporating a suitable-capacity heat pump, the right-sized pipe bore and appropriate material, it should be every bit as reliable as a traditional gas boiler system and generate the desired room temperatures. A relative newcomer on the block compared to the long- established plastic and copper materials is MLCP, which is ideally suited to air source heat pump installations. Frankische manufactures its own brand of MLCP called alpex, which off ers numerous advantages over both copper and plastic, including ease and speed of installation. Its fl exibility allows installers to bend it easily by hand while
A
retaining its shape. And as MLCP requires fewer joints, there is a lower risk of leaks, whilst its smooth inner polymer layer resists corrosion and scale build-up, making it ideal for modern underfl oor heating and plumbing systems. Introduced in the 1970s, MLCP has become a transformative material within the plumbing and heating industry. Its popularity has gathered momentum over the last decade at the expense of plastic (including PEX-a) and copper. It is viewed by some as a ‘hybrid’ alternative, providing the fl exibility of plastic with the rigidity and strength of metal.
Restricted fl ow impacts system effi ciency An air source heat pump system – fi tted with incorrect diameter pipework - will inevitably lead to poor performance and the likelihood of greater ongoing maintenance and breakdowns. Such maintenance problems are likely to be a direct result of the heat pump having to work harder to achieve the preferred ambient temperature, whilst using more electricity in the process, thereby impacting on energy bills. One area of concern is when installers change the initial
32 July 2026 •
www.acr-news.com
project specifi cation. For example, a designer may specify copper pipes with an inner bore of 28mm, having calculated that the fl ow resistance and the volume of water passing through will be perfect for the given application. However, using 32mm MLCP not only gives the benefi ts of plastic pipes including corrosion resistance, fl exibility and point-to-point installation, but it will provide the same inner bore as 28mm copper (26mm). Yet, such sizing can be misconstrued by the installer or
contractor, who may decide to replace the copper option with 28mm plastic pipe, not factoring in that the inner core is the key dimension. Such a decision will impact system effi ciency as the plastic pipe will have a reduced inner diameter of perhaps 22.5mm through which the water can pass (over 13% less volume). There are usually two reasons for changing the specifi ed material: fi rstly, the contractor may be looking for a cheaper alternative to copper and, secondly, it may be a material they prefer to work with as it’s lighter to handle. Heat pumps are generally installed at the side of a house or in the back garden, but some householders try to hide them and position them away from the property. However, the resulting longer pipe run means there will inevitably be some heat loss sustained on the way back to the house.
The need for more training Seasoned professional heating engineers have the experience and knowledge to undertake the correct procedures when installing a heat pump system and will be aware of the impact of not selecting and installing the correct-sized diameter pipes. However, independent research shows that even some of those who have been in the business a long time still believe MLCP is primarily the same as plastic, and so there is a need to do more to educate the industry on this.
MLCP versus Plastic The most common pipe diameters used by heating engineers
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