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There has been
much debate over low voltage radiant systems versus line
voltage radiant systems as radiant heat gains popularity in
North America. The aim of this article is to dispel
some of the myths surrounding the different kinds of
systems.
Myth 1: Low voltage radiant systems are safer than
line voltage.
Low voltage is
low, so it makes sense that it’s safer, right? While
this makes perfect sense initially, we have to take a
closer look to find out the real answer. If your
definition of safe is the chances of being hurt by
voltage during installation, low voltage will give you a bit
of a shock, but won’t cause lasting damage. The
real question we should be asking is how durable is
the cable against damage and how well is the cable
insulated. Both line and low voltage snow melting systems
are embedded in 4 inches of concrete, asphalt, or
under pavers. When installed properly the embedded
systems are not exposed and harmful. Some low voltage
heating wires are NOT designed for embedment. These have
only a thin layer of plastic and a heating element
that is THHN/THWN wire. This wire is intended for
interior use NOT in concrete, asphalt, or under
pavers. Low voltage wires do not have ground fault
protection, so electrical leakage can go undetected.
In contrast, line
voltage obviously has higher voltage, which is why line
voltage cables are built to withstand wear and tear, and are
much more difficult to damage. If you do manage to
damage a line voltage cable, don’t worry! Line
voltage systems are equipped with ground fault
protection (GFEP) breakers with a 30 milliamp trip. Which
means the system will automatically shut off when it
has reached beyond allowable leakage levels. What does
this mean? Well for one you don’t need to worry
about bodily harm, but you also don’t need to worry
about potential fire hazard from a damaged cable. The
bottom line: both line voltage and low voltage systems
are safe to use.
Myth 2: Low voltage radiant systems cost less to
run than a line voltage system.
It is true that
low voltage radiant systems consume a lower amount of
power, but this doesn’t mean it is less costly to
run. Low voltage systems can actually be more
expensive to operate because these systems generally
produce 20 watts/sq ft (which is below ASHRAE standards). By
producing less heat per square foot, it takes longer to heat
the same area, thus increasing the cost and the time
it takes to melt. Because of the decreased heat
output, during heavier snow falls low voltage systems
struggle to keep up with the snowfall, and have to remain on
much longer. For this reason, ASHRAE has set forth
watt standards for snow melting.
Line voltage
systems are designed specifically for the environment in
which they will be operating. These systems are made to
produce the necessary watts (that meet ASHRAE
standards) to melt snow in the most efficient time
possible.
 Some low voltage systems
on the market have some distinct advantages over line
voltage. Zmesh is low voltage, but does not rely on heat
cables to generate heat. Instead it is constructed of
a unique thin mesh that requires no embedding in
thinset and can be installed directly under carpet
pad, hardwood and even for use on your roof for snow and ice
melting. The biggest advantage of Zmesh is that you can
hammer nails into it without worry of damage!
Myth 3: Low voltage systems are easier to repair.
Both line voltage
and low voltage cables are easy to repair. Simply
remove the bad section of cable, add in a splice kit, cover
it back over with whatever surface it’s in, and
the system should operate as normal. You do not have
to replace the entire cable or rip out the entire
surface, only the area that is damaged. The location of the
break can be identified by using devices such as the
DEVItrace from Danfoss or a TDR, which uses radio
frequencies and a “wand” to locate the damaged
section of cable.
Myth 4: Low Voltage systems are more efficient.
Low voltage
systems are NOT more efficient. Since these systems have a
much lower output of heat per square foot; they take much
longer to melt snow, especially during heavy snow
storms and probably will not be able to keep up with
the demand. Further increasing their inefficiencies, low
voltage systems must have the electricity pass through a
transformer and very thick power leads (2 gauge),
which causes voltage to drop as it travels distance
before reaching the heating element. Line voltage cables
have the energy to go directly into heating, without the
loss of power. Overall, both line and low voltage
systems are more efficient than hydronic snow melting.
Myth 5: Low voltage systems offer a better warranty.
Some low voltage
warranties are very deceiving. They boast of a 25 year
warranty period, but when examined closer it is found that
the 25 year warranty only covers the heating wire. As
discussed earlier these heating wires are actually
THHN or THWN, which can be purchased relatively
cheaply at any hardware store.
Warmzone’s
line voltage cable manufacturer’s warranty (Danfoss)
covers up five times the cost of the original system
which is intended to cover the cost and time involved
in making repairs, not just the actual heating element
itself.
Myth 6: Both systems provide sufficient heat.
Low voltage
systems in most snow melting applications do not meet the
ASHRAE standards. The minimum watts per square foot ASHRAE
requires in North America is 32 watts per square foot.
Popular low voltage systems on average are designed to
produce approximately 20 watts per square foot and
with extremely tight spacing will max out at 30, still below
the standards ASHRAE has set forth.
Line voltage
systems are designed specifically for the environment in
which they will be operating. These systems are made to
produce the necessary watts (that meet ASHRAE
standards) to melt snow in the most efficient time
possible.
Myth 7: Both systems are UL Approved.
Most low voltage
snow melting systems are not UL listed. Warmzone’s
line voltage systems are UL tested and approved.
SYSTEM WEAKNESSES
- THHN/THWN wire was not designed for concrete
embedding. The outer jacket is soft and easily
cut which will shorten its life.
- Low heat output – Does not satisfy
ASHRAE requirements.
- Bulky and costly controls (transformer and
control box are 100 lbs per 200 square foot
zone).
- Warranty - only covers THHN/THWN wire. Control
box is 1 year, transformer is 5 years.
- Slow to install - the transformer and control
box are complicated and time consuming to
install.
- Noise – transformers emit noise and
location of them must be considered.
- Price – low-voltage systems are
typically double the price of a comparable line
–voltage system.
As radiant
heating systems have gained popularity, a lot of
fly-by-night manufacturers are trying to cash in on
the recent boom. This sparked ASHRAE to come out with
standards for radiant snow melting systems to prevent
abuse from manufacturers. Most low voltage radiant snow
melting systems don’t meet the ASHRAE standards
for quality and efficiency. Unfortunately, not all
consumers are aware of standards in the radiant
industry and purchase faulty products unwittingly and end up
with negativity towards radiant heating in general.
Rest assured there are plenty of efficient radiant
systems that will run smoothly for decades without
needing any maintenance. Make sure to do thorough research
before purchasing any products, which means checking
for proper safety certifications and standards, and
you won't regret it.
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