Clearing the air on radiant - (see our
list of research citations on radiant cooling and heating.)
Radiant heat is dry
Ok sometimes people
use wet heat vs dry heat to compare systems using
water, aka “hydronics” or without water, aka
“forced air” or "electric" but in this case they are referring
to the absence of moisture.
The thing is - heat is
a form of energy, moisture and air are not -
they are mass. Describing
“radiant heat as dry” would be like saying
energy is dry. There are no units in science to
describe radiant as dry. Yes we know it's done all the
time but that doesn't make it correct.
it this way; a characteristic of heat is
temperature, it and moisture are measured with
completely different instruments respectively a
thermometer and a hygrometer. The thermometer
indicates temperature as being between subjective
terms of hot and cold using units of
or K. The
hygrometer describes the moisture as being
and dry using units of kgwv/kgDA
or lbwv/lbDA, or
If you still don’t see the difference -
consider the warm and wet rain forest of Hawaii
and the hot and dry conditions of the Sahara
desert. Both locations are heated with
from the sun so using the incorrect logic of "radiant heat
is dry heat" - how can this be when clearly
conditions exists in Hawaii where it is wet? So now do you
see why radiant heat in of itself cannot be described as
dry? When people state, "Radiant heat is dry
heat" they are describing the coincident
condition of moisture and temperature. The way
to measure the coincident condition is with both
a black bulb thermometer (mean
radiant) and a wet bulb thermometer
(aka a sling psychrometer).
All of this is to point out that the moisture is
independent of the heating system be it radiant
or forced air – neither of these is wet or dry
just hot or cold until you add or remove
moisture. Now, further on you'll learn that
there is no heat in radiant just
With radiant you’ll have stale air because nothing is moving the air around, or you need to have a furnace to move air around, or you need to move air to provide thermal comfort.
I’ve never understood these comments since ventilation is required regardless of what type of HVAC system you have. Just because you have radiant doesn’t make you exempt from building codes – you still need to ventilate…and that takes air. So what radiant systems do is enable the use of balanced 100% dedicated outdoor air systems such as HRV/ERV’s. Such systems have the highest efficacy of all ventilation systems. When designers use exclusively a furnace to move ventilation air, the ventilation air efficacy is a function of the on/off cycles of the blower. When the blower is ‘on’ it is good – when it is ‘off’ it is less good – translation: if the indoor air quality system in your home is rendered useless by controlling thermal comfort it is IMHO dysfunctional. Also you don’t need to move air for thermal comfort. Is it a factor? Yes. Is it a prerequisite? No. Air movement it is not a prerequisite for thermal comfort. If air movement were a prerequisite for thermal comfort you would feel cold while sitting in the sun on a calm day...does that makes sense to you? Of course not..
Oy...there were so many
unbelievable statements at this eHow article
it's easier for us to advise readers to avoid
any article that mentions 'polyurethane' pipes
and 'floor furnaces' in the same breath. Pipes
aren't made of polyurethane nor are floor
furnaces even close to underfloor radiant
systems. This is just bad information all
around. Keep reading below for other amusing
statements and claims.
"On average, radiant
floor heating systems deliver only about a
maximum of 60% of their heat by radiation; the
rest is mostly by convection."
If 60% is the
majority - it is the "mostly" i.e. the
heat transfer is mostly by radiation. We find
the syntax in the
internet statement interesting...see this link
heat transfer coefficients (HTC)...this difference
between HTC values is based on the differences in
convection, and the amount of convection is a
function of the enclosure performance, room
geometry and surface temperatures and
orientation of the radiant panel (wall, floor, or
Here's what the ASHRAE Systems Handbook says, "A temperature
controlled surface is called a radiant panel if
50% or more of the design heat transfer on the
temperature-controlled surface takes place by
There are several
"authoritative" sites on the
internet which claim that radiant systems such
as floors are not radiant systems at all, further
they go on to state that these systems should be
called convective systems. We suspect the
authors have confused "baseboard" systems with
radiant systems where the former is
predominately convection and the latter by
ASHRAE definition a radiant system.
In the absence of forced drafts
(i.e., in space fans), radiant heating ceiling
systems and radiant cooling floor systems
provide marginal convective transfer ( <10%+/-) due to
reduced influence on air density, ergo they
transfer most of their energy by radiation.
Radiant floor heating and radiant ceiling
cooling exchange between 50% and 60% of the
energy via radiation ergo they, by ASHRAE definition
are radiant systems.
Handbook—HVAC Systems and Equipment, Section 6,
Figures 1 and 2
Fisher, D.E., Lindstrom, P.C. (1997) ASHRAE
RP876 Impact of Surface Characteristics on
Radiant Panel Output
"The floor material
then radiates off the heat into the cooler
"The air is warmed because
of the radiating heat"
"Radiant heat is
effective because it heats the air rather than
blowing warm air throughout your home."
"heated wires in the floor that warm the air in
the room above."
"With a radiant floor
heating system, heat is even and warms the part
of the room most used by people."
"it heats a
room from the bottom up".
"It is efficient
because it does not feature a fan blowing heat
around the room; it heats from the bottom up,
which warms the feet and body first."
real advantage of in-floor heating is it
radiates heat back to your body."
around you will be slightly cooler, but your own
body will absorb the warmth generated through
the heating system in the floor."
up the bottom half of the body making it
feeling more comfortable and reducing the
feelings of lethargy."
heat distribution over the entire surface of a
floor heats the lower half of the room,..."
"The warm or cool
surfaces then radiate heat to occupants"
For all practical
discussions outside of academia, the
exchange within a building does not directly heat the
molecules - it heats the surfaces in the room which in turn are in contact
with the air...ergo the air becomes warm
only because of the contact with warm surfaces
vis-à-vis the conduction and convection process.
The aggressiveness of natural
and stratification is a
function of the building enclosure, radiant panel orientation (wall, ceiling, or
floor) and whether it is heated (energy emitted) or
cooled (energy absorbed). For further discussions on
this topic visit our page on
heat transfer coefficients.
Furthermore, many people think radiant
floor heating heats the body but (sans
discussion on conduction heating the feet) this is not
case; radiant heating systems provide comfort by
warming the interior surfaces which reduces the
temperature difference between your clothing and skin and the
interior surfaces which in turn reduces the loss
of body heat via radiation. You see it's not
radiant energy you are absorbing - it is the heat
you are not losing which results in perceptions
The amount of heat
released via radiation for a clothed person at
various metabolic rates is covered in
Table 1. Representative Rates at Which Heat
and Moisture Are Given Off by Human Beings in
Different States of Activity.
Some people compare the warmth from
the sun to the warmth of a heated floor but the
sun and floor operate at
two completely different
electromagnetic wave lengths. Both provide
thermal comfort but in different ways.
Radiant cooling works in the opposite
direction of heating
by encouraging the loss of body heat via
radiation...it is the loss of heat from your
clothing and skin
via radiation which provides the cool sensation.
Learn more from our pages on
With regards to just
heating the lower half of the room...all we can
say is that has to be some very smart radiant
energy because the energy we know doesn't know a
lower half from an upper half - all it knows is
hot goes to cold and because of this there is no
"lower and upper half of the room" as it
pertains to radiant energy.
"...hot water is
circulated in the pipes and warms up the slab
and slowly radiates heat into the space."
thermostats, underfloor radiant systems also
overshoot your target temperature by an average
of 2.2ºF/1.2ºC since radiant pipes stay hot even
after the boiler has stopped heating."
First, it isn't hot
water - in fact in a
high performance home
with heating loads less than 10 Btu/hr/sf (32 W/m2)with
low VOC conductive floors
(tile, slate, concrete) and tight tube spacing
of 6" to 8" o.c.(150mm to 200mm), the average water temperature
is a nominal 85°F
(39°C) or very close to
and cooler than your
body temperature - tepid to warm water -
not hot water.
The cooler the fluid in
heating and warmer in cooling the better the
system efficiency through first and second laws
of thermodynamics (also see our comments further
exergy yes "e-x-e-r-g-y" it is not a
Second, the speed at which
the slab warms up is a function of the
building mass characteristics,
losses to grade,
and control strategy. With
proper designs and fabrication including passive and active controls there is
marginal differences in thermal comfort between
air and radiant based systems. For the range and
rate of temperature changes acceptable to
occupants see ASHRAE Standard 55 - Thermal
Environmental Conditions for Human Occupancy.
radiant energy travels at the speed of light -
there is nothing slow about it.
Discussion: when it
comes to "slow" to heat up...for some
bizarre reason people must imagine letting their
thermostat to drop to say 50°F
(10°C)before turning it on and then see themselves standing there with a
time clock to count how many hours it takes to
heat the room up to comfort conditions. This is
so far from reality it's almost silly. With one
run of the mill strategy, as soon as the
outdoor temperature drops below some preselected
outdoor ambient temperature, say 65°F
an outdoor reset control
from it's sleep mode and starts to monitor the
interior and exterior conditions and wakes up
the boiler controls...if it continues to get cold
outside and it shows up inside as drop in
temperature - then it starts to manage the system
fluid and heater by turning
it on and ramping up the fluid temperature.
With a well designed system with proper controls you can maintain comfort
all the way from 65°F
outdoor conditions down to
without having to "wait" for the system...that
is unless of course you actually enjoy starting up
system at polar temperatures.
"radiant heating is
"radiant cost a lot more than
"the most comfortable system
is radiant but it's a lot more money".
"The more robust the
enclosure gets, the more costly the radiant
system — the hundreds of feet of tubing, the
circulator pumps in every zone, the computer
components to monitor things…"
"Radiant heat can be
installed in an existing home, but it can be
" Typical costs for a hydronic system within a concrete slab are $6 to $10 dollars a square foot, and that’s just for the tubing."
Show us a big
inefficient home with whacked out geometry in an
extreme climate with wicked temperature
swings; a mechanical contractor who wants to do
a custom systems and
a builder who doesn't want to do the system, and we'll show you an expensive radiant system.
That's it - that's as complicated as the
economies get...price is always proportional to
contractor intentions, system complexity, building performance, climate
and builder flexibility and confidence (which comes with skill which
comes from practice).
the experienced designer and skilled contractor a high performance
enclosure (deals with the climate) with some normallacy in design
(simple geometries) and
we'll show you a low cost affordable radiant
based HVAC system.
The exception is when over
zealous designers and contractors use peoples homes as a blank
canvas to express their mechanical artistry ...
in this case - owners buy a 'one of a kind'
system for the 'one of a kind' price...talk
with us at the forum on how to prevent this
from happening to you.
Look, rather than
listening to the internet rif raff - do your own
homework...assume you have a 1400 sf basement
slab and call up a plumbing retailer and get a
price for 1400 ft of 3/8" air barriered PEX pipe, a
single 1/24 hp
circulator and a dual purpose water heater with
internal exchanger...it is obviously not the whole
list of equipment nor does it include labour
etc...but it'll quickly put pricing of components into
perspective. If you don't have the time let me say one retailer list its 3/8" PEXa for 0.65/ft...that would be 0.65 for each square foot at a 12" spacing...not sure where $6 to $10 a square foot comes from but it must be made of gold.
People who claim you
need lots of pipe and lots of pumps and lots
complicated computer stuff to support the
statement, "radiant is
expensive" are not living in the present or not
working with the right vendors or local
circumstances force them to deal with
service providers who have grossly inflated the
Lastly, the term
'expensive' is relative, circumstantial and
subjective - expensive to
one is affordable to another. Consider millions of
people stand in line at Starbucks day after day
to pay $5.00 for a boutique cup of coffee...others spend
thousands of dollars each year on jewellery,
clothing and accessories for their pets...and
some splurge significant cash on outdoor decks,
patio's and furniture trying to be more comfortable
outdoors rather than investing in their own HVAC
systems to be comfortable indoors where they
spend 90% of their time...expensive shmensive...it's all about
One final note...consumer
psychologist will tell you that when one persons
says to another an item is expensive what they
are saying is they personally can't afford
it...it doesn't mean that you can't afford it.
Where will your indoor climate system score?
How to "ball park" your budget for indoor
environments: Self assessment
Built to code:
What does it mean for thermal comfort?
The Total Comfort System - The "Un-minimum"
effective in energy efficient homes with really
small heating loads because even a small amount
floor heating can cause overheating due to the
thermal mass effect."
We often see this
statement associated with "popular science"
practices rather than on low load energy
proper controls and systems typical of well designed
projects mitigates overheating in all types of
buildings in all types of climates.
overheating in all buildings occurs with
various combinations of
performance, building mass,
solar control, control over
internal loads and control over the heating
systems (and all types of systems not just radiant). Poor control over one or
more of these elements can prevent
the occupants from shedding their internal body
heat at a rate fast enough to feel comfortable.
Your options: control the building
aspect ratio; and choosing the proper combination and location
insulation and mass; control the solar gain
internal gains; control the heating system or
preferably - all of
Since the finger is pointed at
radiant heating lets discuss the radiant by
first talking about controls:
In high performance
single zone homes with less than 10 Btu/hr/ft2 (32
W/m2) loads, and low to medium mass floor options; with proper
and glazing and with less than 20% window to
wall ratios, there is little demonstrated
benefit for having sophisticated radiant heating
controls. A simple non electric thermostatic
valve and analogue control on the heater or even
a simple pulse width modulated (PWM) thermostat
controlling the heat source is a suitable and
effective solution. In conventional
housing with multiple zones and dynamic loads it
is useful to
modulate the temperature of the system fluid
with in-space room feedback. Modulating the fluid temperature with what is
weather compensators or indoor/outdoor
controllers or reset controls is a tried and
true technology having been in existence for
decades - so this is not a "new" solution nor is
it "high tech" nor "sophisticated" -
as far as expensive, see previous comment...put it
this way,,,,weather compensators are like the
cruise control on your car...they regulate your
speed, control your fuel consumption and no
proper car would be without one...likewise with
radiant systems in some applications.
'Weekend engineers' who experiment
without doing the research or by
those who don't
want to invest the money in controls and then
blame the system for over and under heating tend
to be the same folks
who spend the rest of their life on the
internet telling everyone about how bad radiant
is. When you read this stuff on line what you
need to read is, "I'm a weekend
experimental engineer and
didn't do a proper job of researching building
science and radiant transfer nor did I pay
for a proper system design with suitable controls".
don't want to mess with solar gains then (hold
on - wait
for it) ...don't give the solar energy a place to
store itself... this is not that
complicated...keep the short and long wave
energy off and out of the building with external
shading, reduced glazing areas (20% or
less window to wall ratio's) with an
appropriate solar shading coefficient, improved
enclosure performance and use
readily available off the shelf low mass
100% of all over heating and under heating
complaints in homes heated exclusively with
furnaces did not have radiant floor heating to
"The heated pipes
radiate energy into the slab which then heats
"Radiant heat from the Pex hot
water tubes in the concrete slab is sent out in
a 360 degree pattern."
"This fluid picks
up radiant heat coming from the ground."
Embedded or buried pipes or
cables use conduction (not radiation) to heat the
mass...energy in the form of electromagnetic
waves are radiated (emitted) from or absorbed at
surfaces. There is no temperature in the
electromagnetic waves - only energy. In order for these electromagnetic
energy waves to be converted to heat (measured
by temperature) they must travel
through a transparent space until
they hit an opaque surface of a cooler temperature where
they are absorbed. The absorption of the energy
increase the molecular action in the surface
which raises the temperature of the surface and
through conduction heats the underlying mass.
overheating with very small loads, the slab has
to be no more than a few degrees above room
temperature which means the floor won't be warm
to the touch in fact it may feel cool to the
You have to
differentiate between "comfort" and "warm to
touch" or "cool to touch"...again decades ago, research discovered
that people wearing normal foot wear prefer floor temperatures in and
(24°C). In fact ASHRAE Standard 55 and
ISO Standard 7730 both state for comfort, floors
should be regulated between 66°F
(19°C) for cooling
(29°C) for heating with
(24°C) being the
For those in bare feet or
feet with light socks the limitations of the
floor are also a function of the flooring
itself. If 74°F
(23°C) is necessary for comfort
than this is a good thing. For further details
see this link on
floor temperatures and see this
discussion on having
warm floors in high performance homes.
it may be possible with floor heating to be
delivering excess heat causing overheating."
This is a twist on
what we have already addressed but lets explore
Have you ever placed
an ordinary thermometer in the sunlight inside
your home on a summer or winter day? What does
it read and what does this tell you?
Here's one example:
south facing double pane glazing, February 25th,
2011, Calgary, Ab., Canada - outdoor temperature
-8°F(-22°C), floor temp = 88.5°F
(31.4°C) WITHOUT floor
discussion on window performances, it should
tell you even without radiant floor heating the
floors will warm up - so long as the floors see
the sunshine the surface temperature will rise
due primarily to the short
wave solar radiation travelling through the
windows. Throw in the long wave energy emitted from
interior surfaces warmed by the short wave
energy and you have a room heated with radiant
energy without having embedded heating pipes.
Discussion: in a
properly controlled high performance home under
maximum load (no solar gain...middle of the
night...wind howling...nasty cold), the floor
temperature would be operated at a few degrees
above a room temperature of 72°F
(22°C), so lets say
calculation shows the floor to be between 74°F
(24°C) and if
maybe an average 80°F(27°C) fluid
core body temperature
and cooler than
skin temperature but still
comfortable ...recall you have
your own internal
heat source that generates at rest a nominal
- so in fact under normal conditions - you need
to get rid of heat to stay comfortable...and by
the way feet are a great place to shed heat due
to the blood flow and conductive transfer with
the floor...anyways the million dollar question
is, will you have that ooh ahh sensation
of a really warm floor? No but it will be
comfortable and warmer
than the floor in the same space heated with a
comes along and as soon as the sun hits the
(24°C) floor, it starts
to raise the floor temperature
but only those surface areas that "see" (absorb)
the shortwave morning sun radiation - as such the room
operative temperature of
(22°C) begins to rise as well...so what happens next? Well the thermostats stops
the flow of tepid water to the floor and after some period of time the
floor surface is at or
warmer than the fluid in the floor due to solar
gains. Since hot
travels to cold or in this case warmth to coolth
(yes it's a real word) ...the floor warming
system becomes a solar absorber and can cool the
floor by sending the solar gain ( a temperature
rise in the fluid) to a colder part of the
house...or you could turn the system off
completely and let
the sun take over the comfort in your space. All
you have to do is remember warmth travels to
coolth and if the sun makes the floor warmer
than the fluid in the pipes...the floor system
is not contributing to the overheating.
want to shed solar heat gain in winter...open up
the windows...it didn't cost you anything to get
it in the first place so it won't cost you to
lose it...the greenhouse people figured this out
centuries ago...if you don't want to manually manage
it...reduce your window area, reduce the windows
solar heat gain coefficient, use exterior
shading and low mass floors...but don't blame the radiant floor
...unless of course you didn't control
the incoming solar heat in which case it's still not
the fault of the floor.
100% of all over heating and under heating
complaints in homes heated exclusively with
furnaces did not have radiant floor heating to
systems transforms cold floors and furniture
into heat-omitting objects."
Heat is not
"omitted" from warm objects it is "emitted"
and can be absorbed,
reflected or transmitted. There is no thermal
effect of consequence from radiant
transfer between two bodies of the same
"...the heat travels
slowly upwards from the floor to the ceiling."
Radiant energy is not heat energy and it does
not 'travel slowly' it travels at the 'speed of
light'. The energy is only converted to heat when it
hits a solid object of a cooler temperature. Again, radiant floor heating operates in almost identical long wave infrared frequency as the human body meaning its not heat absorption but heat retention which provides the warmth perception.
"The best place for
radiant heating is on the floor because heat
"Will the heat
rise"? It's like gravity - it's physics."
"Heat rises so the whole room from floor to
ceiling will heat up..."
the heat where you are and not on the ceiling."
rise...hot air does relative to colder denser air
serving as the motive force...radiant energy travels
from hot to cold and in all directions...and
heats the entire room not just the first 6
feet (2m)...if you
don't get this basic principle try standing
under a heat lamp...heat rising? No...if heat
rose we would have to stand on top of the sun
and put heat lamps on the floor...so just exactly where is the top of
the sun? Radiant heating can be done from any
surface, floor, ceilings and walls.
"The best floor
covering is tile or concrete because of its
heat-conducting qualities. Wood floors or thick
carpeting are insulators..."
This is one of the
more predominate myths due to peoples confusion
with insulation, resistance which are conductive
elements affecting the heat transfer within the
radiant panel and emissivity and absorptance
which are radiant elements affecting heat
transfer from the panel surface.
The fact is the effectiveness of
a surface as a radiator has nothing to do with
its insulative qualities but rather with its
emissivity. 99.99% of typical
have very high emissivity's ergo they all make
The insulating qualities are
important but they affect
fluid temperatures and pipe spacing
and not the effectiveness of the floor covering
as a radiator.
"...radiant heat can crack or
otherwise damage fine wood flooring."
"Radiant heat will cause solid hardwood flooring
to dry out too much and cause it to crack and
Beans first law of
radiant heated hardwood: 100% of all hardwood
flooring complaints in buildings heated
exclusively with forced air did not have radiant
floor heating to blame.
The primary cause of
dimensional changes in wood is changes in moisture
content - not
heat. If this messes with your head, ask a
furniture craftsman or piano tuner schooled in the ways from
the old country. See below for the difference between heat
plastic tubing called "PEX" -- a polyurethane.."
PEX is actually
PE-X, an acronym for
cross (X) linked
polyethylene (PE). There are different types of
PE-X designated by a letter which is an
indicator of the method used to cross link the
molecules, for example, PE-Xa, PE-Xb etc...
"Comfort, in fact,
is the No. 1 advantage (with radiant floor
heating) with its warm-feet, cool-head
While it is
generally true, in heating people prefer a
warmer lower body and a cooler upper body it
should be clarified there is no single
floor surface temperature
for everyone and in all situations - as it depends on
the heat loss of the room, clothing including foot wear,
metabolic rate and the
conductivity of the flooring and the occupants
subjective view of comfort.
when wearing normal footwear -
floor surface temperatures are optimal around 75°F
(25°C) ...however keep in mind - air temperatures are not the
same as surface temperatures - when we talk air
- the smaller the
air temperature difference
between the ankles and head the more comfortable
people will be (favouring warm below to cool
above)...See our pages on skin and
comfort and temperature stratification.
"A wet system ..."
floors like concrete or gypsum based topping
systems - no one we know wants to live with a "wet system"....we suggest people use poured floor system instead of
"A dry system..."
systems installed under, in or on top of the sub
floor, - no one we know wants to live with a "dry
system"....we suggest people use subfloor system instead of dry.
Confusing the matter
further - some literature will use a "wet"
system in reference to a hydronic system and
"dry" in reference to an electrical system.
temperature are essentially the same thing..."
No they are not -
heat is a form of energy - temperature is not.
can have the same temperature but hold different
amounts of heat. Temperature is an indicator of
the speed of the molecules. You can apply more
heat to speed up the molecules i.e. raise the
temperature of the substance.
This is also a good
place to point out that in reality there is no
such thing as 'radiant heat'. I know it's used
all the time but in reality, radiant and heat
are just forms of energy...radiant is
electromagnetic energy measured by its wave length..heat is energy measured by its
temperature and comes from the stimulation of molecules in
a substance absorbing the radiant energy.
"The Romans invented
radiant floor heating..."
wrong...inhabitants of Asia
(Korea and China) were the first by several
thousands of years. Currently there are
archaeological excavations which have
also uncovered very old radiant system in the
Aleutian Islands of Alaska carbon dated to the
same period as earlier finds in Korea. Per building, Korea has the
most radiant heating anywhere in the world.
Northern Europe, Germany, Sweden, Denmark etc...
come in second.
"...the thicker the
slab, the more it will heat up and radiate..."
Slab thickness has
nothing to do with how well a concrete surface
will radiate - this is a function of its
Figure 16). A thicker slab (yes) will hold
more energy in the form heat but if the surface
temperature of the slab is the same as all the
surface temperatures in the room there will be
no radiant transfer regardless of how thick the
slab is or how much energy it holds.
"So, a lot of people
will install a foil double-poly reflective
insulation. They use a barrier insulation under
the slab and help keep the radiant heat moving
up, not down."
"the portion of
radiant heat being lost into the ground below."
What bubble foil S &
M folks are good at is creating a problem where
none exists so they can try to solve it with
their products. They have mastered the art of a
solution looking for a problem.
Fact: there is no radiant
heat transfer from the slab to the ground its
conductive ergo there is no need for a
reflective barrier. There is a long history of
reflective insulation scams dating back over 30
years and a list of successful lawsuits brought
by the U.S. Federal Trade Commission against
manufacturers and distributors of these types of
See our pages on reflective
barriers, paints and under slab insulation.
The piping can be
wrought iron, steel, copper or plastic,
including polybutylene and polyethylene. The
steel and wrought iron are typically only used
for floors. They are too heavy for walls and
Steel, iron, copper...these haven't been used in radiant systems for a
long time and polybutylene hasn't been readily
available in North America for well over a
"Warm air rises and
much is lost, making forced air heating less
energy efficient. Radiant heating works by
transferring heat to objects, so when placed
beneath wood flooring it heats the floor. Since
less heat is lost through the air, radiant
heating is more energy efficient than forced air
All things being
equal, radiant is more
effective at conditioning
people and spaces but it is not necessarily more
efficient. Efficiency is a complex discussion
because it involves other external systems and a
few other terms such a
something most people are not familiar
with...also there is an inverse relationship
between building performance and the need for
mechanical efficiency. The undeniable and
undisputable fact is - is
radiant is an enabler.
It enables higher combustion and compression
efficiency. But a lousy building with high
efficiency boilers and heat pumps can be less
efficient than a great building with mid
efficiency systems...ergo any statement about
radiant being more efficient should be
questioned for clarity - in most heating case it is
difficult to scientifically support the
statement unless there are mitigating
circumstances. However, there can be significant
electrical power conservation with radiant
cooling systems. See below for efficiency claims
and see this overview of
energy, exergy, efficiency, entropy and efficacy
or what we call the E5 factors.
floor heating is widely considered to be the
most energy efficient heating process currently
generated by combustion processes can have as
much as 70% losses between the point of
generation and the home...i.e. of the 100 units
of energy to produce electricity you get between
20 and 30 units at the plug -
far from being the most energy
efficient process. Hydro, geo or wind
generated power - now that's a
different story. See below for more efficiency
"brand x insulation
forces the heat from the radiant heat system up
to the floor's surface."
insulations help to retain the heat generated by
the radiant heating system blocking
it from escaping into the ground."
cold back into the ground."
Under slab insulation does not
force heat up to the floor surface nor block it
from going down nor does it reflect cold nor is
the heat within a concrete slab being transferred by
radiation...insulation is resistance...it slows
or impedes the flow of energy in the form of heat
travelling from hot to cold via conduction...radiation
only comes to play at the uppermost surface of the floor.
Learn more about reflective insulation scams.
associated with the use of radiant floor heating
range from 10% - 40% on utility bills."
saves 30 percent in energy costs"
heat can save up to 50% in total heating cost "
"can save up to 15% on heating bills ..."
"...saves 20 to 40 % on monthly heating ..."
"you can save 10-30 percent on your monthly
40% off your heating bill"
" can save
consumers as much as 50% in energy usage"
" radiant floor heating systems that should
be up to 80 percent more energy efficient."
"They are typically 40 percent more efficient"
of 30% to 50% over hydronic radiant heating
systems and even greater savings over
conventional forced air heating systems."
...and this next one is our
favourite claim of
"All radiant heat systems are 100
percent efficient at any capacity."
There is so much
anecdotal claims floating around you can pretty
much find whatever you want for savings
depending on what source you want to
believe...the reality is - there is no
formal independent scientific residential
research that we are aware of that conclusively supports any
of these claims...so here again are the
facts...radiant is an enabler...and by that we
radiant enables condensing boilers,
chillers or heat pumps to operate at their
maximum factory rated efficiency -
no one can dispute that statement.
If you have a
lousy house nothing is going to save you from
high energy bills but what you will get is
maximum performance from your radiant system
while the building loses lots of heat.
want to reduce your heating bills - first build a
high performance building and then get the
maximum efficiency from your hydronic heating system by
using low temperature radiant heating.
Caveat...in cooling - scientific
research and practical applications have
demonstrated significant electrical power
radiant cooling is used with
If anyone can
provide us a side by side identical comparisons
in peer reviewed scientific papers that
can support any of these efficiency statements we'll be
elated to revise our statement.
Please don't send us
anecdotal statement made in sales literature and
from product distributors websites nor send us
reports that fail to demonstrate side by side
identical comparisons. Nor are we interested in
the setting the thermostat lower argument (as
valid as it is) it is a subjective operator
Just so you don't go
chasing your tail, here's
a list of radiant based HVAC research papers
in our library...I've not found anything in
these papers that conclusively supports
the plethora of efficiency claims found in sales
and marketing literature.
Like I said, elated
to revise our statement if anyone can show me
the proof to support the internet efficiency
can insulate the floor also reduces or slows the
heat entering the space from the floor system.
This in turn increases fuel consumption."
should not be covered with carpet..."
This is only
partially true. Fuel consumption is a function
of many things including but not limited to building performance,
boiler over and under sizing, types of controls,
tube spacing and fluid temperatures. Floor
coverings and their corresponding R-value are
compensated for by tube spacing which influences
fluid temperatures (in heating, more tube = lower
temperature = better efficiency, in cooling more
tube = higher temperatures = better efficiency).
designed carpeted floor
can operate at the same effectiveness and
efficiency as a poorly designed wood or tiled floor.
"However, in humid
climates, problems with over-cooling the floor
could lead to wet slippery surfaces and fungus
the HVAC system, moisture must be controlled for biological
concerns (bacteria, viruses, mites and molds), for
hydrolysis and the
control of VOC emissions (formaldehydes, phthalates,
terpenes etc.), for the dimensional
stability of hygroscopic materials (woods) and for occupant
respiratory and thermal comfort; moisture must be regulated for
these greater priorities making the condensation on radiant
cooling panels a moot point.
sceptics conveniently forget, 100% of all
condensation problems in buildings conditioned
exclusively with air did not have radiant
cooling panels to blame (go figure). See our pages on
"The radiant floor
heating will save the most energy."
As pointed out by
the International Energy Association, "This
claim (saves energy)...conflicts with the first law of
thermodynamics stating that the total amount of
energy is conserved even though forms of energy
may change from one to another." In layman's
term you can't create nor destroy energy ergo it
cannot be made and saved like pennies in a bank - not even by radiant floor
At the end of the
day, energy can be preserved and conserved but
not saved. For a thorough study read about
entropy, energy and conservation ."
"It can lower the
allergens in your home by eighty percent!"
"Radiant heating will also keep your home
free of air-contaminants, bacteria and dust."
"There is no hot air being blown around as
with traditional systems, so no dusty sneezes."
While there are some
environmental benefits to using radiant, lowering allergens by
80% or keeping your home, "free of
air-contaminants, bacteria and dust" are not ones that we can find supported by
research. We love to know where
these came from...to get the facts read our
featured article on the
health effects of low
temperature radiant heating systems.
Also, every properly
designed and built building will need to have
moving air for ventilation purposes. Yes the
volume of air moved is considerably less with
radiant systems but it isn't zero as told by
"radiant heating is
only for new construction."
radiant is too difficult..."
" you have to
rip up floors to have radiant heating."
One of the lowest
cost, easiest and most effective ways of
radiant heat is to use the walls.
If that messes with your head ask yourself why
your cat or dog finds sleeping in front of a
window (a wall you can see through) so comfortable...hmmm
it might just be the radiant heat...who knew? Integrating radiant into
wainscoting is just one creative way of adding
the beauty of woodwork and the comfort of
radiant. See our pages on retrofitting radiant
into existing buildings.
"Floor heating comes
in three varieties: electric, hydraulic
(liquid), and air-based systems."
hydronic...semantics yes but this page is about
how myths get started and spread...people read
hydraulic from an expert and they think brake
fluid. Is "hydronic" any better - no...but it's
the correct term.
Glowing? Lets put
this into perspective, the surface temperatures
of a wood stove is over 400°F
interior temperatures over 1000°F
still these temperatures are too low to
glow...(pun intended)...floor heating operates
(29°C) surface temperatures...far below glowing
temperatures. We get what the writer is
trying to do - it's actually nice to think of
warm floors as glowing - but if the floor were
glowing - your house would be on fire.
"Heating the entire
slab may result in a condition known as "hot
foot". Your feet and ankles are not accustomed
to standing on a warm surface."
Another twist on the
above "glowing floor heating system"...once
again the control of floor heating temperatures
are specified in ASHRAE Standard 55 - Thermal
Environmental Conditions for Human Occupancy.
There is no "glowing floor" or "hot foot" unless
the system has been designed and installed by
amateurs. See this article on
do it yourself HVAC.
advantages of (radiant) are the absence of any
air flow from the outdoors that has to be
heated, as is the case with many forced air
We're not sure if the writer was
referring to exfiltration/infiltration (leakage) or
ventilation (to replace exhaust air from fans)
regardless both are heating loads which are
independent of the type of comfort system. See
"...uses a lower
thermostat setting as compared to forced air
system thereby lowering your energy bills."
All things being
equal, it is possible in standard construction,
to theoretically achieve comfort levels with lower thermostats
settings in spaces conditioned with radiant,
however there is a
report by CHMC stating that even though
people could use a lower setting few occupants
from the study actually do. Now I know some
people with radiant who do use a lower setting
but I also know people who also use a lower
setting with air based system. These are
subjective choices and hardly the basis for
carte blanche statements. Furthermore, in higher performing homes this argument becomes a moot point
the building enclosure solves the energy use and
minimizes the cold surface effect on the
heating...is costly to install, and maintaining
the system can be difficult."
The cost and
maintenance of any mechanical system is
inversely related to the complexity and
efficiency of the architecture. A high
performance home built to R2000 (Canada) or
Passivhaus (German) standards have very simple
and affordable systems that can use robust tried
and true components. If you want a difficult
system build a difficult building and use new
stuff designed and installed by inexperienced
"..if you set your
thermostat to about 68 degrees, the room will
likely heat up to about 72 degrees. This is
because the heat is sustained through the mass,
so the higher the surface is heated, the lower
you need to keep the boiler temperature."
Surface and boiler temperatures
are established from the tube spacing, floor
conductivity, fin efficiency and heat loss - it
has nothing to do heat being "sustained through
the mass".. A high
performance home with conductive floors and
tight tube spacing can operate at very low
surface and boiler temperatures resulting in very high combustion
floor heating systems use boiling water in the
pipes to generate heat..."
Water is not boiled
in a hydronic system. A high performance home
with conductive floors with tight tube spacing
the temperature of the water is similar to the
temperatures found in your own body, i.e. 85°F
floor heating systems are also environmentally
friendly as they have an option of recycling
your used water. In fact, it is also a part of
purifying your water where the water is brought
to a boil.
That statement is by
far the most bizarre statement we have come
across....Fact: hydronic radiant
floor heating systems do not recycle your used
water and are not part of purifying water for
domestic use. Read here about using
domestic water heaters for space heating.
"The heat energy
that is created by warm water, flows through
Heat 'is' energy and
its not created by warm water flow - energy in
the form of heat is transferred into the water
through the heat exchanger of the boiler or heat
"TLC points out
that while radiant heat is definitely more
efficient in smaller, snug homes with lower
roofs, it might not always be the greenest
solution in homes with bigger rooms"
Huh? Not sure what
this myth is based upon, but again all things
being equal, the larger the space the greater
the potential for increased system efficacy and efficiency. This
is due to a lower flux from a larger floor
surface area which affords the use of a lower
fluid temperature which increases the boiler
efficiency. There are countless examples of
large buildings with very big rooms using
radiant heating including aircraft hangars,
manufacturing facilities, warehouses,
towers, museums etc.
pairing a radiant heating system with an energy
efficient EnergySTAR-approved programmable
thermostat can indeed save households hundreds
of dollars a year on home heating bills "
The #1 mistake made
in the industry is trying to treat radiant
systems like air based systems including how to
operate them with so called, "EnergySTAR-approved
programmable thermostat". The optimum way to
control a radiant systems is use an
indoor/outdoor controller to adjust system water
temperatures but set the room thermostat to a
comfortable position and leave it alone.
"Radiant heat is
also very different in that the operative
temperature of the system (the actual average
temperature of the radiating surface) is
generally significantly cooler than a hot air
temperature is not the, “the actual average
temperature of the radiating surface”. The
author is mistaken with mean radiant temperature
or MRT. In its simplest form “operative
temperature” is the mean between the dry bulb
and MRT. For a greater explanation see our pages
MRT and Operative Temperature.
more to come...if
you want us to look at a questionable statement
let us know at the