Wet underfloor heating
In previous articles we’ve looked at boilers and radiators. However, the heating
market is looking toward a different future - and this seems to have been led by
the self-builder!
Demand for underfloor heating has rocketed in the past five years. What was a small
part of the heating spectrum is now rapidly expanding. There are now very many heating
companies across the UK solely installing underfloor heating - which would have been
unimaginable twenty years ago.
In addition, companies supplying all the parts that make up the system have sprung
up to meet the demand. Currently this seems to come from abroad - where installers
are less hung up about technology and innovation than their British counterparts.
UK plumbers are notorious for sticking to conventionality, and plastic plumbing took
years to have an impact in the UK. Even now, there are thousands of plumbers sticking
rigidly to soldering copper pipes together. Take a look at them; they look for all
the world like stone-age bearded men trying to start a fire with two sticks! They
have yet to discover that you can even glue mains-water pressure pipes together now!
Underfloor heating comes in two forms: wet (heated from a boiler) and dry (electric).
We’ll be discussing electric underfloor heating in the next issue. Wet underfloor
heating is simply a continuous coil of tubing looped around a room. It is connected
at a station known as a ‘manifolds’ - with all the other loops from each room. Obviously
there are two ends to this loop. The flow end is connected to the flow manifold and
the return to the return manifold. The flow manifold is fed by a large pipe from
the heat source - usually a gas or oil boiler. However, there are also electric boilers.
Systems that should be avoided are those that join tubing together under the floor
with connectors rather than having a one-piece loop. It is simply not good practice
and you could find yourself in a depressing struggle trying first of all to actually
locate a leak, let alone repair it.
Wet systems suffer from two flaws in the very idea - water and boilers. Your entire
home will be ringed by water pipes. No screws or nails can ever be driven into the
floor, lest you want a major upset! And don’t think, as have been suggested, that
this might act as a sprinkler system in the event of a fire. The actual water content
is low. Still, the incidences of leaking underfloor heating pipes is rare. Any installer
worth his weight in salt will diligently check the system by pressurising it upon
completion of the installation - so showing up any possible leaks. The only likely
leak source should be at the manifolds.
Wet underfloor heating also needs a heat source - a boiler. This then is a potential
unreliability factor. Even boilers that only have to heat a simple loop system are
complicated enough. They will almost certainly also be required to heat the hot water
- usually via a mains pressure unit. The manifolds have a circulating pump and a
thermostatic mixer valve. This combines heated water with water returning from the
loop having given up its heat to the floor.
There is also a question of control. An underfloor heating system, like all others,
needs to know when and where to switch on. Incredibly, I see many systems use a central
room thermostat - just like a conventional radiator system - that controls the entire
heating system.
With individually-looped feeds to rooms there is a golden opportunity to have individual
room heat-control. A room thermostat needs to be fitted in each room. When calling
for heat it sends a signal out to a small valve located on the manifold. The valve
opens and allows heat to go to that one loop if necessary. The downside to this is
that because each room has its own control you then have perhaps twelve air stats
in an average home, and twelve valves - all waiting to go wrong! The valves are mechanical,
and prone to failure just like everything else that moves.
Wet underfloor heating installation is not something I would usually recommend to
a diy-er. It is fairly specialised and will therefore require the expertise of an
experienced installer. And don’t let your plumber do it if he has never done it before!
The vast majority of heating engineers have little or no experience of underfloor
heating yet - it hasn’t been around long enough.
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