Q. What is underfloor heating?
A. As the name infers, heat for the living
space emanates from below or within the floor. By heating the floor and
using it as a giant radiator a lower temperature can achieve the same
resultant warming effect over the larger surface area of the floor (when
compared to the higher temperature needed in more traditional radiator
systems to heat a room of the same volume).
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Q. How does underfloor
A. Heat is imparted to the floor which in
turn warms the room. It's as simple as that. The floor in effect becomes a
giant wall to wall radiator.
How the floor is warmed is a little more
complicated, but the most common methods include a 'wet system' that
involves circulating water that is warmed remotely through a run of pipe
secreted under or within the floor (timber floor or solid floor
respectively), or an electric cable run under or in the floor that warms up
as current is passed through - each warming the floor and in turn - the
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Q. How do you regulate the temperature of living space with underfloor
A. By regulating the amount of warmed water
passing through the pipework of a 'wet system' the amount of heat
percolating into the floor and subsequently into the room can be controlled.
By the same token, by regulating the
current either by amount or by switching that passes through an electrical
underfloor heating cable (a 'dry' system) the temperature derived within the
room can be controlled.
Regulating the amount of warmed water or
the electrical current (depending on which type of system you have) is done
by utilising a room thermostat (also known as a 'room stat'). The room stat
(positioned at about shoulder height on a wall within the room) feeds
temperature data back to a wiring centre, which in turn issues commands to
allow/disallow the flow of water or electrical current (depending on type of
system) so as to maintain the temperature set on/by the room stat.
Very large rooms or spaces may have more
than one stat controlling different zones within that space - enabling for
example a room to be set hotter at one end or place than another if so
In underfloor heating terminology, an area
controlled by a particular stat (room stat) is referred to as a zone. Whilst
a area may be split into multiple zones, a zone may contain and control
several heating coils (wet or dry) working together to heat the space. The
setup and layout of zones being dependent on size and desired control.
For example: An relatively small dining
room on a wet system may only need a small amount of heat to sufficiently
warm the area with the minimal amount of control. Therefore, a single room
stat communicating with the control (wiring) centre and single coil of UFH
pipe bring heat into the zone would suffice. A very large lounge however may
require more than one coil (or loop) of UFH pipe to bring in sufficient heat
to warm the area. Multiple loops of pipework could be configured to work
with one room stat (and therefore as a single zone) or configured to work
with more than one room stat, giving the area more than one zone to be
controlled. In reality, the large lounge would need to be very very large to
reap the benefits of multiple zone control (i.e. the potential to be hotter
in one place than in another).
The amount of heat imparted to the floor in
any one place may also be 'affected' by the design of the loops on a wet
system. Bearing in mind that the water travelling around the loop is
constantly loosing heat, the water in the early part of a loop is logically
hotter than it will be at the end. By concentrating early loops in a wet
system close together an 'uneven distribution' of heat can be achieved. This
for example can be useful if one wall of a room is totally glass or has a
much higher heat loss than other areas. By running more early coils within
that area more heat can be directed to colder areas - giving a means of
balancing heat against loss at the design stage. (Please refer to pipe
designs for examples)
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Q. What if I
have a leak in the underfloor pipework?
A. In short, leaks are highly unlikely.
In smaller and domestic installations it is unlikely you
will need to join pipes anywhere other than at the manifold. Pipes are
normally supplied in various coiled lengths that will enable you to run a full
continuous loop. If you have your layout calculated for you, it will become
evident from the plan how long each loop will be. Pipe coils in lengths
closest to your requirement/s will therefore be supplied as part of the
Should you need to join or repair pipes, special
fittings designed for underfloor heating are available.
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Q. It looks complicated. Is it ?
A. At a glance, underfloor heating can look complicated.
All those pipes converging on a manifold covered in actuators, cables, valves,
pump and thermostatic controls might look frighteningly complicated, but the
reality is somewhat more simple.
The manifold is only a simple way of connecting several
coils of water pipe to a single regulated heat source. Manifolds are supplied
in kit form and assemble easily to include all of the components required to
make them function. Full instructions are supplied and technical support is
available if required during the installation process.
Example: If you had a single pipe coil feeding to a
single zone things would look somewhat more simple. As the room stat calls for
heat, the actuator (an electrical solenoid valve) opens to allow water to flow
around the loop. The temperature of the water being fed around the loop is
regulated by a thermostatic valve so it does not get too hot. When the room
stat is satisfied with the room temperature it instructs the actuator to close
and flow stops. Simple - It just starts to look complicated when you have
several loops and zones on one manifold, but each zone is simply opening and
closing at the command of it's room stat whilst sourcing heat from a common
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Q. How can water in an underfloor heating system work at a cooler temperature
than the radiators in the rest of the house in a mixed wet system?
A. Wet underfloor heating systems actually use the
boiler's return water. In a heating system, return water (water returning to
the boiler having been around the system) is cooler than the flow (water from
the boiler that has just been heated). Providing the temperature of the return
water is adequate, this is adequate to heat your floor/s. Of course though, as
water passes through or under your floor it will continue to give up heat to
the floor and therefore cool. At this time, a sensor on the manifold detects
this temperature drop and if necessary automatically adds water from the
boiler flow (water that has just been heated) to ensure the required
temperature is maintained in the underfloor loop.
A very simple way to extract as much heat from your
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Q. Is it difficult
to install underfloor heating?
A. It would be fair to say more labour intensive, but
not difficult. It's still two pipes (flow and return to the manifold) but you
use the floor as the radiator instead of a wall mounted tin can.
Installing the manifold is actually fairly simple. This
complicated looking component is only a convenient way of connecting several
loops to a regulated hot water supply and presents no major problem.
Compared to hanging a radiator, which is fairly simple -
only requiring a pipe to and a pipe from - underfloor heating takes a little
longer, but still only requires two connections. You have a large coil of pipe
that must be laid in or under the floor which of course takes time. However,
there are many advantages (as described
here) to an underfloor system - not least of
all the savings that can be made in operating costs. So the time invested when
installing your system is recovered many times and in many ways throughout the
life of the building.
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Q. it is more expensive to install compared with a conventional wet radiator
A. Initially, underfloor heating is more expensive to
install than a conventional wet radiator system. It takes longer and there are
more components required. But it is a more efficient system to run, should not
require maintenance as with radiators and produces a more controllable
climate. So over a period of time will reduce running costs, maximise
available wall space and remove potentially hazardous hot surfaces from your
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Q. Are there
any drawbacks to underfoor heating systems?
A. The most obvious difference between a conventional
radiator system and underfloor heating system is the response time - both on
heat up and cool down.
It takes longer to heat up a concrete slab for example
using lower temperature water than it would to heat a small radiator with hot
water. Similary, a concrete slab (when warm) will take a considerable time to
cool down. This makes the response time to control input much slower. However,
underfloor systems are not really designed to provide instant heat control,
they focus more on providing a comfortable even climate with no local
Point of interest: A feature becoming common on underfloor systems is
'night set-back'. This works in the following way -
Take a concrete slab for example. This takes a
while to reach operating temperature so heating up every morning would also
take a while. The room stat is set say to 20oC during the day so
the system heats the floor to achieve an ambient temperature of 20oC.
When you go to bed at night you may not want to maintain this temperature, but
instead of simply switching your system off it enters 'night set-back mode'.
'Night Set-Back' (when
enabled) is a feature where the system allows the slab to cool down slightly -
typically by about 4oC. So the slab temperature will only fall
during the night to 16oC. Depending on conditions, this can take
several hours. The system remains at rest until it reaches it's set-back
temperature. When the morning comes the floor is not heating from cold, so it
only has to raise it's temperature by 4oC to return to the daytime
setting of 20oC. This of course does not take as long.
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Q. But what
about electric (DRY) underfloor heating?
A. In a DRY system an electric heating element replaces the pipes associated
with WET systems. The principle however remains the same, the floor becomes a
There is one subtle difference. The
electric heating element looks a bit like a cable but is in fact a flexible
heating element shrouded with insulation and mechanical protection. Due to the
properties of the heating element wire, heat is generated as current is passed
through it. The length of an electric heating element has a design calculation
to provide a specific number of Watts over a given area when installed to a
layout plan. An electric programmable controller energises and de-energises
the heating element/s in conjunction with a room stat or temperature probe
installed in the floor between elements (according to application) - this
allows you to regulate the floor/room temperature.
A common application for electrically heated floors is 'Undertile
Heating'. This is slightly different and should not be confused with
Ceramic tiles are becoming popular in
homes, especially in bathrooms and kitchens. A ceramic tile is however cold to
the touch - an unpleasant experience when walking around in bare feet,
showering in a tiled area or when climbing out of the bath. Undertile heating
is designed to warm the tile to a comfortable temperature and provide a cosy
sensation to the touch. Whilst it will have a warming effect on the room, it
is not the same as true underfloor heating and should not be relied upon to
heat the living space.
Undertile heating is often
no more powerful than the Wattage from an electric light bulb, so whilst very
cheap to run it should be used in conjunction with a supplementary heat
Advantageous points to Undertile
- Relatively cheap to buy.
- Relatively simple to install*.
- Cheap to run.
- Wet floors dry much quicker.
- Very thin element (2-3mm thick) means there is no
significant increase in floor level.
- Installs within the layer of floor adhesive
directly under the tile.
- Suitable for 'new-build', refurbishments and wet
- Programmable to provide several 'on' and
'set-back**' times throughout the day.
- Transforms cold tiles to a warm and cosy
- Temperature of floor is selectable with suitable
- Available in different sizes to suit the area to be
- Available as single strand or pre-formed mats for
ease of installation.
* An RCCD protected supply is required for reasons
of safety. All wiring must conform with IEE Regulations and Building
Regulations, and be installed and commissioned by a competent person.
** The 'Set Back' feature maintains a lower temperature
in the floor surface during 'off peak' periods of the day (periods when the
living space may not be used - when you're at work for instance, or
throughout the night) so the floor doesn't fully cool and warm-up times are
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should I lay out my underfloor heating pipework?
A. The installation of an underfloor heating
pipe can be determined by the type of floor into which you plan to install.
There is often less flexibility with how you
run a pipe in a timber floor due to the direction in which the joists run
and their proximity to each other. In timber floors pipes are run between
joists - passing through notches from one void to the next.
There is a degree more flexibility when
installing to a screed floor. Pipework in a solid floor can be laid in loops
or coils (or a combination of both) prior to screeding. A pipework layout
can be supplied if you have had a quotation once an order has been received.
However, the final layout can often depart from a suggested plan due to
various factors that require a different logic.
You should remember that the water leaving the
manifold is warmer than that returning. Therefore the water in the earlier
part of the run will be hotter than that at the end. This fact can be used
to great advantage if you carefully consider which parts of your room will
be colder than others. For example, if you happen to have patio doors or
large windows in a room it is likely that the area adjacent will be
generally colder in winter than say an inside wall. It therefore follows
that concentrating loops in the early part of the pipework run (with the
warmer water) in the colder zone may help to defeat the cold air causing the
localised cold spot. Having done so the loops can then change pattern to
however else logic might dictate - leaving the final part of the pipe run
(containing the cooler water) for the naturally warmer areas. There are
various different opinions and layout patterns on this subject, but here are
some of the more common solutions -
Q. What is an
underfloor heating manifold?
A. The term 'manifold' refers to bringing
several into one. In an UFH system there are often many loops of pipes carry
warm water from or cool water back to the start. This is achieved by using a
manifold. The many loops of pipe terminate at the manifold. The manifold is
equipped with valves that allow or disallow water to flow through each loop.
The valves open and shut in response to signals received from the wiring
centre as the room stats call for heat.