Warming to condensing warm-air heaters

Published:  01 November, 2012

Space heating, ICOM Energy Association, warm air heater
Even without legislative drivers, the economic case for condensing warm-air heaters a good one.

While condensing warm-air space heaters are not yet mandatory, this is almost inevitable within the next few years. Phil Brompton of ICOM Energy Association considers the significant environmental and economic benefits they will bring.

It has been estimated that around 18% of the world’s CO2 emissions arise from non-condensing boilers and heaters, thus making a significant contribution to global carbon emissions. As a result, many governments are taking, or have taken, action to tackle this issue. The UK Government, for example, has already implemented legislation to make condensing boilers mandatory in domestic and some commercial applications.

As yet there are no similar requirements for warm-air space heaters. Part L2 of the Building Regulations currently requires a minimum 91% nett efficiency for warm-air space heaters, which can be achieved by non-condensing units.

However, recent changes to the Energy Technology List criteria mean that to qualify for Enhanced Capital Allowances (ECAs), warm-air space heaters will need to operate in condensing mode with minimum full and part load efficiencies of 101% (nett).

So while environmental responsibility or compliance with ECA criteria may lead a small percentage of specifications down the condensing route at the moment, there are clear indications that legislative pressure will make condensing technology mandatory in the UK in the next two to three years. This will be delivered through future versions of the Building Regulations Part L2.

Condensing warm-air space heaters can be operated on natural gas or liquefied propane gas (LPG) and have been on the market for over four years, so the technology can be considered to be proven. They generally achieve higher efficiencies by the deployment of a secondary internal heat exchanger, which turns the residual heat in the flue gases, which would be lost in a conventional heater, into useful heat.

As a result the rate of heat transfer into the warm-air stream is increased without additional fuel consumption. There is also a commensurate reduction in flue-gas temperature to below dewpoint, so liquid condensate is produced. As with condensing boilers, the condensate is collected within the heater and taken to a drain point for safe removal.

Condensate production rates are not excessive, typically 0.06 l/kWh for natural gas and 0.03 l/kWh for LPG. However, this does mean that if condensing warm-air space heaters replace non-condensing heaters in an existing installation provision needs to be made for installing pipework to carry the condensate away. Clearly this will result in higher installation costs compared to a new building where a condensate removal system can be designed in from the start.

Table 1: Comparison of running costs for a 140 kW output gas-fired warm-air space heater operating for 10 h per day, 5.5 days per week during a typical heating season (prices based on commercial gas tariffs, August 2012).

Even when not driven by legislation, there is a strong argument for specifying condensing warm-air space heaters because of the costs savings through increased efficiency, as well as the lower environmental impact. Consequently, the higher capital and installation costs of condensing warm-air space heaters can be offset by savings in fuel consumption.

However, it is important to take care when comparing efficiencies as some manufacturers may quote efficiencies at part-loads, which tend to be higher. For example, a condensing warm air space heater offering, say, 105% efficiency at part load may give less than 100% when operating at full load. Consequently, for a meaningful comparison, efficiencies should be compared at full-load conditions.

The return on investment can be illustrated by comparing the running and installation costs of the various types of warm-air space heater available (Table 1).

Installed prices will clearly vary significantly from one site to another. However, for a modern well insulated building of, say, 2500 m2 floor area and a volume of 13 500 m3 requiring the above 140 kW heater. Typical end-user customer installed prices for a condensing heater would be £7900, compared with £6500 for a non-condensing unit. The cost difference of around £1400 could be recovered in less than two years, compared to a non-condensing heater with CE minimum efficiency levels, and the savings over a 10-year life cycle are impressive.

Currently the timing of any move to mandatory condensing warm-air space heaters is unclear, but members of ICOM Energy Association that manufacture these units are gearing up for this to happen in the next few years. Certainly we welcome such a move, within sensible timescales, for the contribution it will make to reducing the UK’s carbon emissions.

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