We are frequently asked some specific questions regarding Low Surface Temperature Radiators and High Output Natural Convectors. The first question being the most relevant in relation to the application of our products and should be borne in mind of the system designer at all times.

What is an LST Radiator?

At present there is no EN or BS Standard for the application of LST Radiators and the most relevant document is the Health Guidance Note; “Safe” hot Water and Surface Temperatures as published by NHS Estates, which states that “the maximum surface temperature of space heating devices should not exceed 43°C when the system is running at the maximum design output”. This document then goes on to emphasise that“there are no surface hot spots”. Whilst this document does not specifically mention outlet grilles, the NHS in Scotland has previously issued a safety action notice acknowledging that the outlet grille does exceed 43°C on some popular products which are claimed to be LST and concluded that these do not comply with the guidance note.

This guidance note effectively superseded the older DHSS Engineering Data reference DN4 which only considered the side and front surface temperatures ignoring that the outlet grilles will exceed 43°C, but is sometimes still referenced by some authorities and manufacturers.

Various other statutory documents reinforce the requirement of a maximum surface temperature of 43°C in the selection of heating appliances for specific applications which extends the requirements to premises other than NHS controlled, e.g. Care Homes, Schools, Prisons etc. Indeed anywhere where the building operator has a duty of care over users who may be young, elderly or at risk.

As we can see, the classification of LST Radiator is totally dependent upon the actual operating conditions, specifically the maximum design operating conditions.

Recent publications from HSE indicate that they will be using the NHS Health Guidance note as a guideline when evaluating any reports, therefore it would be wise to consider this to be a minimum standard of compliance with health and safety of the vulnerable.

What is the difference between an Autron LST Radiator and an Autron High Output Natural Convector?

An Autron LST Radiator will comply with the NHS Health Guidance note above and an Autron High Output Natural Convector is a higher output convector which is designed to be safe in most critical environments having a casing which meets the NHS Criteria but the outlet grilles may exceed 43°C if the mean flow/return temperature minus the room temperature is above 45° C. All units with the “H” Class emitters are considered to be High Output Natural Convectors whereas those that use the “S” Class emitter are LST.

Do Autron products comply?

Autron Low Surface Temperature Radiators using the Emitter prefix “S” have been designed and tested at BSRIA to be generally compliant with the Health Guidance Note; “Safe” hot Water and Surface Temperatures as published by NHS Estates when used with water flow temperatures up to 82°C and a 71°C return temperature by keeping all surfaces including the outlet grille to a maximum temperature of 43°C.

When High Output Natural Convectors using the Emitter prefix “H” are used with a maximum flow temperature of 75°C and a return temperature of 55°C then these will also be fully compliant.

With whatever emitter is used at flow temperatures up to 85°C, the side and front panel of the casing will not exceed 43°C which was considered the maximum temperature under the older DHSS Engineering Data reference DN4.

Where should a Low Surface Temperature Radiator be used?

In general LST Radiators should be used where there is a duty of care to a third party who may be vulnerable due to age or ability; particularly in all patient areas of NHS premises, Care homes and Special Schools. In addition to these, the local authority may have standard guidance or requirements which unfortunately are not standard across the UK. Also note that many disabled facilities would need the application of LST Radiators and the DDA may influence the consideration of LST radiators in some areas.

BB77 Design criteria for Schools that cater for children with special need will also influence the selection of heating product and it should be noted that most schools will have a number of children with special needs. Whilst it is the responsibility of the SenCo to ascertain whether LST Radiators are needed, this aspect should be considered at design stage.

With the surface temperature of heating equipment and safe water temperature being encompassed in the same guidance note from NHS Estates, it would be logical to assume that where ever temperature mixing valves are required for showers etc. there would be a requirement to use LST Radiators.

Whilst it is a requirement to have LST Radiators in Care homes, it is not yet a requirement for Sheltered Housing, however in our opinion, the distinction between Care and Sheltered is a grey area and greater regulation in this area is likely to make it a requirement in the future.

Can an Autron product be used on a single pipe system?

Yes, All Autron Low Surface Temperature Radiators and High Output Natural Convectors can be used on a single pipe system; however this will need the installation of diverter / swept tees on both the flow and return connections to the heating circuit and will need the application of low resistance valves. We recommend the use of Oventrop “AZ” valve inserts which are offered as standard on all “LR” valve options with DN20 connections and an optional extra on “LR” valves should be selected for DN15 connections. The “BD” valve options are not suitable for single pipe applications.

What is the maximum system pressure that an Autron product can be used on?

All emitters are factory tested to 7bar during manufacture for a typical operating pressure of 5bar, however we have tested the emitters on long term pressure tests up to 20 bar with no leakage.

The standard Oventrop valves work on a maximum 1 bar differential pressure. Options are available from Oventrop for higher differential pressures which may be experienced on very large systems or district heating schemes.

What is the warranty period and life expectancy of an Autron product?

As with any heating product, the warranty and life expectancy are dependent upon effective system maintenance. All Autron Low Surface Temperature Radiators and High Output Natural Convectors have a warranty period of 5 years if the system is installed and maintained in accordance with the General Installation and Maintenance requirements shown below, with the exception of the Valves which carry a 2 year warranty from Oventrop. The products have been designed to have a life expectancy of 30 years.

General Installation and Maintenance requirements

On completion of the installation, the entire system must be thoroughly cleaned and flushed to remove debris/flux residues etc. If a chemical cleaner is used, it must be thoroughly flushed from the system. Following this, the system must be dosed with a good eminence water treatment to prevent corrosion.

System design, flushing and dosing must be in accordance with BS 5449: 1990, BS EN 12828: 2003 and BS 7593: 1992

Notes on Valves: Hydrocarbons, including thread cutting oils/greases, will have an adverse effect on any EPDM components, such as valve seals, pump seals and flexible connections, in a pipework system.

Therefore it is essential that pipework systems are thoroughly cleaned of any residues, and that the use of water treatments containing mineral oils is avoided.