Efficiently heating a large space such
as a factory, warehouse or workshop
brings a number of challenges; many
such spaces make use of warm air space
heaters as the preferred heating technology.

As with other buildings, these
heaters need to comply with
the minimum net efficiency
stipulated by the Building
Regulations. The current
requirement is for a minimum
net efficiency of 91% and in
most cases this can be
achieved with non-condensing
warm air space heaters.

Looking ahead though, the
next edition of the Building
Regulations has already passed
through the consultation phase
and is due to come into force later this
year. While we don’t know the exact details
yet it is clear that higher efficiencies will be
required for warm air space heaters within
the next two to three years. It seems likely
that this will match the 101% net efficiency
that is already required for inclusion in the
Energy Technology List to qualify for
Enhanced Capital Allowances. I believe that
meeting this will require the use of
condensing technology.

In fact, condensing warm air space
heaters are not new to the market and as a
company that manufactures both types we
don’t have a particular axe to grind.

However, it has been estimated that around
18% of the world’s CO2 emissions arise from
non-condensing boilers and heaters, so a
move to higher efficiencies would certainly
be welcome from an environmental point of
view. There are also significant cost benefits
for building operators.

Condensing warm air space heaters can
be operated on natural gas or liquefied
propane gas (LPG) and are equipped with a
secondary internal heat exchanger. This
extracts residual heat from the flue gases
and transfers it into the warm air stream for
heating the space. The result is that the unit’s
heat output is increased without the use of
additional fuel.

Clearly inclusion of a secondary heat
exchanger results in a slightly higher cost for
condensing units, compared to noncondensing
units, but this is more than
compensated for by the reduced energy
consumption.

As this residual heat is recovered the
temperature of the flue gases is reduced and
this results in condensation, just as with
condensing boilers, so provision needs to be
made for safe disposal of the condensate via
a drain point, The volumes involved are
quite low, with typical condensate
production rates of 0.06L/kWh for natural
gas and 0.03L/kWh for LPG.

In new installations a condensate removal
system can be designed-in from the start
and will have a very small impact on
installation costs. Where non-condensing
units are being replaced with condensing
heaters, provision of pipework to carry
condensate away may be more complex and
cost a little more.

Nevertheless there are still cost benefits
that outweigh higher capital and installation
costs. This can be illustrated by considering
the running costs for a 140kW output gasfired
warm air space heater operating for 10
hours per day, 5.5 days per week during a
typical heating season (prices based on
commercial gas tariffs, August 2012), as
shown in table one.

It is also important to take installation
costs into account and
these will vary
considerably from one site
to another. For the
purposes of this
illustration, though, we
can consider a modern
well insulated building of,
say, 2500m2 floor area and
a volume of 13,500m3
requiring the above
140kW heater. Typical end
user customer installed
prices would be as shown
in table two.

The cost difference of £1400 could
therefore potentially be recovered in less
than two years when compared to a noncondensing
heater with minimum efficiency
levels. Given that warm air space heaters
should give at least a 10 year life – and many
of ours have lasted much longer – the
potential life cycle cost savings should be
attractive to any building operator.