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16
BCD Special Report on
Historic Churches
18th annual edition
preserves its historical climate, or departs
from it only slightly. Local heating is most
commonly used for small congregations
and building volumes, for example small
churches or specific parts of them which are
in use. The most popular systems are radiant
heating from infrared (IR) emitters located
overhead, on side walls or at floor level; and
pew heating using electric panels, tubular
heaters, water pipes or radiators, or heated
carpets (discussed in more detail below).
This type of heating system disperses
a small amount of heat in targeted areas,
while the building envelope and historic
furnishings or artworks are exposed to
little or no change in temperature. Outside
the moderately heated occupied area,
the RH remains almost unaffected.
Because it minimises the dispersion of
heat, local heating is suitable for non-energy-
efficient historic buildings thanks to the smaller
loss of heat. Less energy and therefore less
fuel is required. With local heating, people
benefit from a large proportion of the total
power supply – the system has high efficiency.
Heating solutions
The Friendly Heating Project demonstrated
that local heating was the best form of
heating for historic churches, but it was
necessary to conduct further research to
determine how best to reduce heat dispersion
and improve the limited comfort that local
heating typically provides. In recent tests
the best results were obtained with gentle
IR radiation emitted from low-temperature
sources including low-temperature heating
foils, heated glass units and heated carpets.
The gentle emission of mild or warm
air from fan heaters for example was quickly
excluded because warm air cannot be
buoyancy controlled: it rises quickly, escaping
from the occupied area and being dispersed
aloft, with little benefit for churchgoers.
In particular, churchgoers affected by
warm-cold fluctuations feel an unpleasant
sensation and they may prefer no heating to
draughts alternating warm and cold air.
Heating should be modular, that is: the
space to be heated should be divided into
independent parts that can be operated
separately, or together. For instance, in the
case of a few people attending a celebration,
the front pews can be heated independently.
Modular heating reduces the heat dispersed
into the church and reduces costs.
The Friendly Heating Project and related
subsequent research (see recommended
reading Camuffo (2007, 2010), Conference
on Energy Efficiency in Historic Buildings
(2011)) identified a number of different
solutions, each of them for a specific church
application, taking into account the different
architecture, lay-out and liturgy associated
with different religious communities, from
the pew arrangement typical of the Catholic
Church, to the box pews popular in the
Lutheran Church, or the standing congregation
typical of the Orthodox Church. Similarly,
account had to be taken of the position of
celebrants, choirs, organists and so on.
Heating foils
(Figure 2) proved to be a
particularly useful and versatile option. Wafer-
thin units can be used to provide pew heating,
to form horizontal, vertical or cylindrical
heating panels adaptable to any surface, or
under the altar-cloth. The heating foil is made
of an electrically heated layer of graphite in
microgranules deposited on a fibreglass backing
and then sealed between two plastic foils.
When an electric current is passed through the
conductive graphite layer, the electrical energy
is converted into heat energy and the layer heats
up. When the foil is heated, it expands and the
increased width increases the distance between
granules. As a result, the electrical resistance
increases with the foil temperature and
reduces the current intensity so the maximum
temperature of the foil is self-regulated at ‘built-
in’ pre-set levels. This self-regulation provides
a natural cut-out, preventing the risk of fire or
contact burns. A thermostat is added for further
fine regulation and safety, but is not necessary.
Pew heating is generally not very
comfortable, especially where the building
envelope is at a very low temperature. It was
found, however, that thermal comfort could
be improved with an ergonomic combination
of foil heat sources distributed in the part
of the church that is in use, fitted beneath
kneeling pads and seats, and on the back of
seats (Figure 4). Feet are the most sensitive
parts of the body exposed to cold, and the air
near the floor is the coldest, renewed every
time an exterior door is opened. A band
of heating foil was introduced under the
kneeling pad to heat the occupant’s feet from
the upper part of the shoe, which is the most
efficient solution. The heaters below the seats
heat the calves of the person sitting on that
bench, and the legs of the person sitting on
the pew behind. The heating foil band placed
in the back of the pews is designed to heat
churchgoers’ hands when they are sitting
and their chests when they are kneeling.
The heaters have been designed
to meet the physiological needs of the
various parts of the body so feet are the
first priority, then legs, and the torso last
as this should be adequately covered with
heavy clothing. The range of temperatures
achieved was between 40°C and 70°C.
All heating foils should be protected
against accidents and vandalism. The preferred
solution is a fine stainless steel mesh placed in
front of the foil and, on the back of the foil, a
reflecting aluminium foil and thermal insulation
to avoid back dispersion. The steel mesh
will reflect most of the radiation impinging
on it as it has a very low IR absorbance
(typically around 7%). The mesh will assume
an intermediate temperature between the
heating foil and the air, and meets safety
requirements by becoming warm but never hot.
Glass heating units
(Figure 3) can be
used on the back of pews, or in front of cold
windows, or mounted on the walls at the
level of a sitting person. In such cases, the
heaters below the seats are not necessary
and should not be used. The glass units are
made of very strong tempered glass which
Figure 3
These transparent but robust glass heating units (yellow arrows) provide a comfortable temperature to
the back and hands. Twin thermostat arrays are housed inside the marked boxes (green arrows).
Figure 4
Location and temperature of heating units
fixed to pews as part of the Friendly Heating Project