18
BCD Special Report on
Historic Churches
19
th annual edition
Underfloor
Heating
John Minter
P
laces of
worship come in a wide variety
of shapes and sizes and have evolved
to suit local needs. Generally, however,
they adhere to relatively standard forms of
construction, subject to some regional variation,
and while the following article is based on the
installation of underfloor heating in a typical
Anglican parish church, this guidance is
generally applicable to other places of worship.
Church heating (where it exists at all)
usually comes in two forms. The most common
type of system uses cast iron radiators or large
pipes, often located against the external walls
but less frequently against internal partitions.
Pipes (either elderly cast iron or modern ‘finned’
pipes which release heat more efficiently) are
also commonly found beneath cast iron grilles
which run down the aisles. These are usually
fed by gas boilers in a semi-underground
chamber. Occasionally this is supplemented
by the other widely used system, electric
radiant heating coils fixed beneath the pews
or on the walls. These are often used as a
primary heat source in smaller churches.
Old churches are seldom insulated and
often have large expanses of single glazing.
Some heat radiates from the appliances but
reaches only a small proportion of the floor area,
while the rest circulates through convection
currents, and most of the benefit is lost as it
cools in the upper voids of the building. Much
of the perceived warmth tends to come from
the body heat of the people in the congregation,
who are usually dressed in outdoor clothing.
The 21st-century parish church has often
lost its nearby meeting room and in order to
best provide for the needs of its community,
the church building must be adapted to suit
new functions, such as a meeting space,
concert or arts venue, as well as providing
facilities for youth groups. One option is to
replace the pews in all or part of the building
with more flexible seating. Although this
solution is unthinkable in some fine historic
interiors, in many lesser buildings it provides
a once-in-a-lifetime chance to resolve a
number of building problems in one go.
Underfloor heating is usually considered
in churches where there is a need for an
uninterrupted expanse of flooring and a
desire to reduce energy consumption. With
a low surface temperature of around 29°C,
the primary advantage of an underfloor
heating system in a church is that heat is
provided evenly across a broad area, enabling
an ambient temperature of around 18°C to
be maintained up to two metres above the
floor and emanating from directly beneath
the congregation. This means that the
visitors readily perceive warmth on entering
the building and can shed their coats.
Conventional radiators also have the
disadvantage of drawing moisture through
the fabric due to the increased evaporation
that occurs from the masonry to which the
radiator is fixed. If the underfloor heating
can be used alone in a particular area, this
problem is avoided. However, the time taken
for the floor to reach optimum temperature
on a cold Sunday morning will never be as
rapid as the appliances in a conventional
central heating system, so a few radiators are
sometimes retained to provide local pockets
of warmth while the building warms up.
Considerable fuel savings can be achieved
by installing a dual-fuel system where a
ground source heat pump (GSHP) can run the
underfloor heating, and gas, where available, can
heat the radiators. GSHP is a viable source of
energy even at sites with sensitive archaeology
as it is now possible to extract heat from ground
below the archaeological threshold by using
radial boreholes, avoiding long trenches for
pipes in the churchyard. The possibility of GSHP
as a heat source should be considered early on,
however, as the water temperature is likely to be
lower and the spacing of the underfloor heating
pipes needs to be designed with this in mind.
Underfloor heating can also work with
solar thermal energy as a source, provided
there is space for a large thermal store of
warm water, but there are almost always
difficulties (ethical and aesthetic rather than
practical) associated with installing solar
panels on the roof of a historic church.
Insulation can also be installed under the
floor at the same time as underfloor heating
and, in a historic building, this may be the
only place where it can be introduced.
Construction options
There are many underfloor heating systems on
the market and each needs to be considered
with the substrate that goes underneath it
and the desired floor finish. The common
types of system are described below.
Conventional screed
Underfloor heating
may be incorporated in a conventional screed,
on either suspended beam and block or a solid
concrete slab. Properly designed, this provides
a firm and level base for a new floor finish
and can take high imposed loads. However,
generally the heating is slow to respond and
the structure as a whole is deep and more
expensive to construct, and installation is very
St Mary the Virgin, Ashford, Kent (Grade I listed) following a major re-ordering programme including a new
limestone floor with underfloor heating installed in 2010/11 using a dry system developed in co-operation with
Jupiter Heating Systems Ltd (Photo: Robert Greshoff)
