Buildings are normally heated to meet the requirements of their occupants. Second only to this fact is the need to know the likely cost of providing heating, either for a specific period or for the whole expected life of the building.

It is not intended to suggest that underfloor heating will inevitably hold the key to lowest cost, or be the most versatile in every instance. However, in view of current levels of interest in this method of providing thermal comfort, there is a real need for hard facts and figures.

The European Construction Directive places upon architects and designers the responsibility to ensure that a minimum lifespan of 50 years is achieved by careful specification, installation, and supporting maintenance.

Currently, it is not so easy to make an accurate prognosis of whole-life costs for a full 50-year period, as in that time innovation and development will make an impact. However, the thinking behind Private Finance Initiatives (PFIs) is that 30 years of operation will reach the realistic ‘half-life’ of a building.

The cost of providing a floor heating system cannot be effectively disassociated from the boiler or heat generator, as the energy it consumes has to be provided in some way, so this analysis is based on the cheapest energy option with gas-fired condensing boiler and weather-compensating control system. The resulting energy cost may be recalculated for other competing fuel systems.

The design criteria adopted is the same as that reported by Tony Cassidy of Cyril Sweet, one of the UK’s best known construction cost consultancies, in Building dated July 2000. The estimates were based on CIBSE ‘Codes and guide to ownership and economic life’, plus information from manufacturers. The report was modelled on a naturally ventilated community centre (Table 1).

Additional design criteria that apply only to underfloor heating are shown in Table 2. They include the cost of providing thermal insulation below the heating system to ensure that comparative operating cost differences with system, such as radiators, are minimised.

When all the costs analysed in Tables 1 and 2 are taken into account, the final total cost of the floor heating system is £55 000 — about 95% that of a radiator system.

Asset replacement in the 30-year period was analysed in terms of its present value, and the life-cycle value for any system will comprise at least the primary elements listed in Table 3. The figures for life expectancy share common values with original estimates, plus known estimates of potential life span of underfloor-heating products from actual records and experience of manufacturers and suppliers.

The cost of energy can only be determined by careful assessment of regional weather and prices obtained from the relevant local utility supplier.

However, in keeping with previous acknowledgments, the same values as the original report have been used, but extrapolated from 25 to 30 years.

The original cost of fuel, which was calculated as £43 000 over 25 years from 2000, becomes £51 600 for 30 years. However, In practice, the new Building Regulations 2002, will have reduced fuel costs for both periods equally by about 10%.

To retain comparison with year 2000 prices, no consideration has been given to any alleged improved system efficiency, or the effect of the new Building Regulations 2002 on reducing energy consumption.

The final costing of an underfloor heating system can be summarised as below.

• Prime cost —£55 000

• Asset replacement inside 30 years —£17 500

• Energy costs over 30 years — £51 600

• Preventive maintenance (5% a year.) — £3000

These 30-year figures add up to £127 100, or £3.92/m2 per year.

Comparison with the original Cyril Sweet article shows that the predicted 25-year cost for an LPHW steel-panel-radiator system is £130 000. A simple extrapolation of this cost to 30 years gives a sum of £156 000 for a radiator system, which for the 1080 m2 building in Table 1 equates to £4.81/m2 a year.

That long-term cost for a radiator system is about 25% more than for an underfloor heating system — which could be expressed as underfloor heating consuming only 80% of the final cost of a radiator system.

Without further calculation, it can be shown that there are other factors behind the savings achieved by underfloor heating, which manifest themselves in the installation, operation and maintenance of the system.

Such factors will certainly include the following.

• 40% faster installation period, generating savings in site preliminaries.

• Liquid floor screeds reduce construction time by another 10 days.

• Screed pre-heating fuel costs can add up to about £1/m2 to the contract. However, pre-heated floors advance the installation of the floor finish by up to a month and can ensure main contractors progress by eliminating delays.

• No maintenance on the floor heating system itself — only the boiler plant.

• No costs are attributable to painting and decorating, or health and safety risks.

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