Alister Maclachlan:

Cater for all your customers or you might lose out

Published:  25 March, 2011

Guest blogger Alister Maclachlan, technical director of Vokèra, says: The market for SE boilers is still a viable and attractive one. But – should merchants continue to stock SE appliances?

It is estimated that around 300 000 homes in the UK have gas appliances that utilise a shared flue system, with SE duct or U duct being the most common type. The majority of these flue systems were constructed prior to the introduction of HE boilers, rendering them unsuitable for that type of appliance.

Even though the Building Regulations call for high efficiency condensing boilers to be fitted in upgrades, this is not always possible. SE ducts or U ducts, where a common flue system is shared, are perhaps the most typical instances where HE boilers are unlikely to be utilised. Prime examples of where this might be found are flats and apartments, where a single flue system or duct is shared amongst many appliances due to the layout and construction of the building.

Why are condensing high efficiency boilers not recommended for this type of installation? There are several reasons for this – one being that the flue system and materials used during construction are not generally suitable for condense fluid, the by-product produced by condensing boilers.

Another reason is that when these systems were originally designed, the relevant calculations would have been made based on standard efficiency appliances being utilised. The flue gas temperature from an HE appliance is usually much lower that that of an SE appliance and such a difference could have an effect on how the flue system performs.

When installers are looking to replace existing boilers that are connected to a shared flue system, they will need to ensure the new appliance is of the same type and input as the original appliance. For example BS 5440-1 stipulates that only a ‘type C2’ appliance can be connected to a SE duct or U duct, which means that if you remove an old ‘type C2’ appliance, it needs to be replaced with a new ‘type C2’ appliance of the same input. There is usually no issue as to whether you replace a regular boiler with a combi.

But, will all installers be aware of this? Perhaps not is my thought, as replacing an SE boiler is unlikely to be a regular occurrence for the average installer. It is for this reason that I believe merchants are ideally placed to offer advice and guidance that would complement current standards and regulations, ensuring their customers understand the nature of these installations.

Another consideration for merchants is that if there are 300 000 homes in the UK that will at some point need their appliance replaced, this would equate on average to 20 000 replacement units a year.

Should SE boilers be stocked as a standard product? Every branch manager in the UK will feel differently about this, and it may be that some locations have seen more requests than others for SE equipment.

If merchants don’t want to stock this type of equipment, then finding a manufacturer that can supply these boilers quickly will help should the need for one arise. This will ensure they don’t miss the opportunity for a sale, and potentially repeat business if installers know they can rely on the merchant to supply the equipment they may sometimes need.

I also believe that it is not just about offering SE boilers. If merchants can spare a bit of time to learn about the nature of these installations, then they are in a strong position to add value to their customers.

Those of us that have worked in the heating industry for a long time will probably know a thing or two about SE duct installations, but for the relatively new installers it might not be something they have yet had to face.


By giving installers an insight, merchants can demonstrate their expertise, help their customers to feel more confident about SE duct installations and hopefully, secure a sale of an SE boiler.

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