AHG Solutions Guide_Edition 2.7

Contents
Condensing Boilers
How does a condensing boiler work?
Like conventional boilers, a condensing boiler burns fuel
to heat the water in a metal heat exchanger. A condensing
boiler uses an extra-large heat exchanger (or sometimes
two) to maximize heat transfer from the burner and recover
useful heat from the flue gases. In condensing mode the
flue gases give up their latent heat and can exit the flue in a
visible plume of water vapour at 70-90°C – they’re usually
180-200°C in a non-condensing boiler. At the same time
condensate, is produced which must be drained away.
Are they only efficient when in
condensing mode?
A condensing boiler is always more efficient than a
conventional non-condensing boiler, due to its larger and
more efficient heat exchanger. The rating represents the
average annual efficiency the boiler can achieve in typical
conditions, making reasonable assumptions about how
it’s used, the climate, controls, and other influences. This
indicates how efficient your boiler will be taking into account
its efficiency in condensing and non condensing mode.
Is it worth changing a five-year-old
conventional boiler for a new
condensing one?
Gas prices are rising, so efficiency is crucial. To comply
with new building regulations, new or replacement boilers
must have an energy gross efficiency of at least 90%.
Condensing Boiler Vapour Plume
They produce a visible plume of vapour when they are
operating, so the flue terminal needs to be sited carefully to
avoid the steam creating a nuisance.
They produce an acidic condensate that must be passed
through a condensate neutraliser and plumbed into a
suitable drain.
CONDENSING &
CONVENTIONAL BOILERS
Latent Heat of
Evaporation 10.2%
Fume
Latent Heat of
Evaporation
Fume
Insulation
and loss
through
convection
& radiation
< 1%
CONVENTIONAL
BOILER BOILER
Latent Heat
Losses 2%
Condensing
CONDENSING CONDENSING
BOILER BOILER
Rated Thermal Efficiency 78% Rated Thermal Efficiency