home > air
Air Heated Floors FAQ
or WATER COIL UNIT?
I have MCS (Multiple Chemical Sensitivities), and
I am concerned with what type of heating to use? Gas or electricity?
Electricity is cleaner for me, but more expensive than Gas.
Has anybody ever done a cost comparison between Gas and Electricity?
How much more would it cost to heat the same house with electricity
The cost difference between Gas and Electricity for conventional
forced air heating systems can be found at the following link:
With Legalett Air Heated Floors you will reduce the energy
requirements of your home by approx. 15-20% when compared
to conventional Forced Air Systems. Since the average room
temperature can be reduced while maintaining the same level
of comfort. In Ontario, Hydro One will be installing Smart
Meters before the end of 2010, which will enable you to purchase
electricity at off peak rates. For frequently asked questions
on Smart Meters in Ontario go to - http://www.oeb.gov.on.ca/html/en/tools/search.cfm
You have two heating units available, the 4000E &
the 4000W. We would like to know the benefit of each application.
We have an Electric heater and a Water Coil heater. The Water
Coil unit can be used when your heating source is oil, propane,
natural gas, solar-boosted, wood or geothermal. In the case
of oil, propane or natural gas, a domestic hot water heater
is all that is needed. In some areas where 2 tier electric
rates are available the Electric unit maybe more attractive.
I recognize that all forms of fuel are expensive,
but I'm not sure how using an Electric heating unit (or units)
could possibly be very efficient, and the addition of a boiler
in order to install the water coil unit would add considerably
to the initial cost. The Electric unit would obviously be
the better choice if it truly isn't too costly to operate,
would it not?
Electric is the most efficient method of heating since it
is 100% efficient. That does not mean it is the least expensive.
In some locations utilities provide multi tier rate structures
for electricity, because of this we see a greater demand for
electrical units for the reason you suggest (less expensive
to install). Bear in mind that the thermostats we supply have
built in timers, so when the demand for heat is present, the
heating unit will only come on during off peak rates. The
water coil unit requires a hot water heater and additional
costs for a pump and piping. On a small home, the additional
costs of a fuel-fired hot water heater may take many years
to pay back.
Do you know if there is a tankless hot water system
available that will handle both domestic hot water & heating
All tankless hot water heaters are well sized for domestic
but could be oversized for Legalett. Our 4KW heater when zoned,
could demand 1 KW only or about 100 L/hour at 60°C with a
return water temperature of 48°C. - this is much less than
domestic hot water demand.
Please note that domestic hot water supply would take precedence
over heating requirements. When choosing a tankless heater
ask about the minimum firing rate or turn down ratio to make
sure the unit is not oversized and cycling excessively.
How far can the boiler be away from your heat-exchangers?
Boiler can be as far as you want - there is no restriction
that we can think of outside of hydraulic issues with pressure
drop and line sizing.
I would like to learn more about heating sources
like oil burn boilers or wood fired boilers, can that be use
with your system.
Any energy source can be used. We have an electric or water
coil heater. The water coil heater can be supplied with hot
water from any heat source including geothermal, solar, hot
water heater, boiler (fired on natural gas, propane, or oil).
We have some installations where we have run piping through
a masonry fire place to pick up heat and distribute to the
or Air Heating System?
I have been looking at water heated radiant floors
and seeing your air system I am interested in a BTU comparison
of the two systems. Please provide me with any technical info
so I can compare the two systems.
Our standard supply is 10 Btu per hour per square foot -
this should be enough for most homes. Our system is a low
intensity system - which means we trickle energy into the
slab - the slab acts as a large radiator and is capable of
delivering a huge amount of energy into the building as required.
We maintain the system performance at a level where the floor
temperatures are comfortable.
We live in a desert climate. We would like to use
solar panels to help reduce heating and hot water costs. I
understand you design systems using air rather than water.
I would like your comments regarding using water or coolant
of some type.
Legalett uses air to heat the floor. However, to heat the
air we use a water or electric coil heater. If you are considering
using solar heat to supplement your hot water heating we would
be glad to work with your solar panel supplier to maximize
the efficiency of the system for Legalett. A Legalett water
coil heater would typically need say 55-60 degree C water
inlet and the return temperature would be about 8-12 degrees
lower. In a solar applications we would be most interested
in the temperature and quantity of water that can be heated
by the solar panel. If there is a temperature limitation -
we would need to know so that we can maximize the usefulness
of the system.
Would operation costs be comparable to hydronic in
Operation costs would be better than typical hydronic since
6 inches of EPS is used under the slab as compared to 3 inches
of EPS, as per the building code. Construction costs would
also be reduced due to the simplicity of assembly of the system.
Why are hydronic floors warmer than Legalett floors?
All else being equal, the floors would be the same temperature
for the given heat load.
However, many hydronically heated homes are not designed
with a goal of energy efficiency, so they tend to be over-ventilated,
and/or use air circulation systems with ducting in the attic
that are not well insulated, which suck energy out of the
living space. This over-ventilation and/or air circulation
losses into the attic require a higher rate of heating from
the floor to compensate for higher ventilation and heat losses,
and since the rate of heating (heat flux) is proportional
to the temperature of the floor, the floor temperature must
be higher in such a home. Since hydronic heating systems are
a much higher intensity heating system compared to Legalett,
this extra energy consumption goes un-noticed and the floors
simply run at a higher temperature. This of course, leads
to a much higher heating cost, because the energy is wasted.
Essentially it’s like you are cooling (ventilation & circulation
losses) and heating (from floor) the same space at the same
Legalett systems, on the other hand, tend to go into homes
designed with a much higher energy efficiency goal and thus
require a lower floor temperature to maintain the same level
of comfort heating, as less is wasted by poorly designed ventilation
and circulation systems. If such a wasteful ventilation/circulation
system is installed in a Legalett home, it is quickly noticed
as an energy-wasting mistake.
Can your system be used on the second floor?
Yes, we have a 2 inch system that is perfectly suited for
second floor applications.
I really like the concept of your system. Presently
we are using radiant hot water, which is good but expensive.
Planning next home and am wondering if your system can be
configured into an above ground slab on steel beams atop of
pilings? Site is steep with bedrock just below surface.
Yes, we have suspended floor systems. Typically we use either
Insul-Deck or Hambro structural systems for suspended floor
pours. In your situation it seems that you would most likely
use Insul-Deck as the stay in place form work (also to provide
insulation under the slab). As it turns out we are currently
working on a home in Ontario that is on steel columns with
What heat do you recommend for the second floor?
This is really the home owner’s choice. We have a 2 inch
system for suspended floors that work well with Hambro or
Insul-Deck ( or any other suspended slab structural system).
If you are considering wood frame you could consider a High
Velocity System for heating, cooling and air exchange. Legalett
can work with any system.
I have a second floor over part of the house. What
is the best way to heat that upper level?
Heating a 2nd storey can be done using the Legalett suspended
floor system with Hambro or an Insul-Deck type of product
or a more conventional construction method such as the Hi-Vi
system or simply add a water coil and air mover to your heat
recovery ventilation system. There are other alternatives
such as water or electric baseboards.
Can I build 2 stories of ICS with your floor system?
Yes, Legalett adapts very well to ICF - up to 3 stories is
no problem with our standard 8 inch slab/ 4 inch pipe design.
The problem now is that we don't know where to put
the heating system on my floor plans. Can I do it with one
furnace or do I need two of them? The garage will be heated
One of our heaters would cover approx. 1400-1700 sq. ft.
Legalett would locate the position of the heater box (s) during
the design phase unless you have a preference. We like to
locate the box in a central location - in a closet or under
a stairway if possible although not required.
From your website we are sold on your concept but
would like a little more detail on the furnace requirements
and placement etc.
We have electric furnace and a water coil furnace. The water
furnace can be supplied with hot water from a hot water heater,
The location of the heater box in the floor is also straightforward.
Ideally it should be located in a central location (but not
necessary), it can even go in the middle of a room since the
top access cover can be finished to match the floor covering.
However, we suggest a closet location for ease of installation
I noticed that some of your homes have smaller plastic
piping while others have metal ducting. Would you have some
written material with more detail that could be mailed to
us that we can study and plan with accordingly?
We have a 2 inch pipe system that is placed in a 5 inch slab
or an 4 inch pipe system that is placed in an 8 inch slab.
The 4 inch system is a little easier to install but the 2
inch saves 3 inches of concrete. The 8 inch provides for more
thermal mass and we would use it more for commercial/industrial
and larger home applications. However, allot of our installers
prefer the 4/8 inch system for it simplicity.
I am intrigued by Legalett's use of coiled ducting,
is this for structural compression loads?
Our 4 inch piping system uses a spiral wound pipe for two
reasons - first there is improved heat transfer since air
turbulence is increased, second structurally through the pour
the pipe maintain its integrity.
How about running pipes under the floor and out open
air ducts rather than closed loop?
Legalett is a closed loop system. The air you breathe is
separate from the air you heat with. When running an open
loop system with ducting through a slab, you would need to
be concerned about condensation, this scenario would require
a trap at each duct to remove any collected water from the
loop, otherwise the ducting would eventually rust and the
air quality would become a health concern.
Does the fan in the furnace box work with outside
air brought in ? (which would need to be piped in during layout)
The heater is completely enclosed and re-circulates air through-out
the slab. It is a closed system, you do not breathe the air
you heat with.
We have, in a previous project, piped a loop or two through
a fireplace hearth to pick up heat when burning with wood
as a supplementary heat source, but yet it remains a closed
How is warm air produced to heat the floors?
The electric inserts use electric coils to heat the air,
whereas the water coil units use air/water heat exchangers
to heat the air. For the water coil units a standard hot water
heater/boiler would suffice and a circulating pump would be
needed (grundfos) only -
Does the slab need to be heated all winter to prevent
damage from heaving?
Yes, the slab does have to be heated all year around to
prevent frost heave. If you are using a cottage for a week
or two in the winter, one can set the temperature lower when
not there, but it will take a couple of days for the temperature
to rise to comfort levels on arrival. If you lower the temperature
when not in use to say 15°C and then increase to say 19°C
when in use - you would arrive at a comfortable temperature
over 24 hours. Occupancy and use of building should be know
at the design stage. If you are not planning to use the building
over the winter then the slab design would change. Legalett
also supplies an unheated slab for heated buildings and an
unheated slab for unheated buildings, designed for cottages
that will freeze.
Can you use Legalett for cooling?
The simple answer is no.
Do you have examples of 'typical' heating costs for
new homes built/heating with your system utilizing the electric
It is very difficult to provide heating costs for electric
units - we have some data for water coil units in assembly
buildings. Electricity is used for cooking, hot water heating
( in some cases), lights, etc. - to monitor electric heating
costs would require a separate meter on the heating unit alone
- and if we had this data - what could we compare it to? -
We would need an identical home- with the same occupants with
the same habits during the same time period and weather.
We can say this: With a Legalett home - the building has
a completely insulated envelope - reducing energy losses to
the ground. Because of temperature stratification - the air
temperature at the ceiling is about 4-5°C lower than with
conventional forced air heating resulting in a lower delta
T across the ceiling and walls again reducing energy losses.
When your feet are warm the average temperature in the home
can be reduced by 2-3°C again saving energy. Now if we put
this together in an average year say in Ottawa, Canada this
would amount to about 15% minimum energy savings over the
I have plans to build an energy efficient and well
insulated, (R20 walls with additional foam sheeting on the
exterior & R50 in the attic, etc..), small retirement home
(1380 sq ft). Would one heating unit typically be sufficient
to heat a small home the size of mine or would I need two?
Do you design the system entirely using my house plans or
do I need someone else to first determine my heating requirements?
Our 4000 series heating units cover approx. 1400-1700 sq.
ft. at 10 Btu per hour per square foot. We basically sell
10 Btu's per hour per sq. ft. or more if the customer requests
it. We check the heating requirements for the building to
make sure the heating demand would be met with the installed
heater for conduction losses and a 0.12 Air Changes per hour
allowance for infiltration ( this corresponds to a well built
home - R2000 quality). We do not allow for any heat losses
due to ventilation and for this reason we do not take responsibility
for the total building energy requirements. Building codes
often require make-up air or exhaust air etc. usually through
HRV's . The building mechanical designer should take a look
at the total building heating requirements including ventilation.
Touch up heat is required for the ventilation air.
Since the system basically heats by means of thermal
mass, which takes considerable time to heat up, how well can
it handle the abrupt drops in temperature, which are increasingly
common anymore in the winter? All homes, no matter how well
insulated, have some heat loss and are subject to the outside
temperatures. Having an electric heating unit running non-stop
for a day or two, (or more), in order to 'catch up', and using
considerable energy in the process is one thing, but being
chilly and uncomfortable in the meantime would be extremely
frustrating not to mention inefficient and costly. Especially
when the temperature is likely to rise just as abruptly again
afterwards, and then do it all over again.
When using a radiant heated floor coupled with the thermal
mass that a Legalett foundation will give you - you will not
be subject to drafts or temperatures swings in your home.
When you open a door and get a blast of cold air coming into
the house - you will feel cold but when that door is closed
instantly you will feel warm again because the floor will
radiant the required energy to you. The outside temperature
may vary considerably - the slab will only impart the energy
that is needed to maintain comfort - it will not over heat
and it will not drop in temperature significantly to cause
you to notice -hence the benefit of radiant heat. We do not
recommend varying the thermostat once comfort level has been
attained whether the temperature outside changes or not. The
heat recovery ability of the system is sized for extremes
so the indoor temperature will not vary outside of the control
range. Legalett is a low intensity heating system - which
means we trickle energy into the floor slowly. You would not
normally notice that the heater is running due to the quiet
operation, but when the heater does come on it will stay on
for a few hours to replenish the energy in the slab.
Would I be able to use a woodstove as a secondary
heat source in that case as well as to offset some of the
cost of heating with electricity? The home that I've been
in that is built on a typical unheated but insulated slab
has surprisingly warm floors and is heated a considerable
amount of the time with just a woodstove.
Yes, wood can be used as a secondary heat source - we have
in the past run our piping up into a masonry hearth to extract
heat from the fireplace and deliver it to the floor slab -
if this is what you would like to do just let us know and
we will accommodate. The problem with heating with wood is
temperature control and most times the building becomes warmer
Would an attached garage require heat ducts in the
We design and supply both heated and non-heated slabs on
grade ( frost protected shallow foundations). You would have
your choice whether to heat the garage slab or not.
If there were three zones and water heat exchangers
were used in the in floor heating units, would there be one
circulation pump or three.
Each of our heaters have 4 zones or less. Zoning is determined
at the design phase. We would recommend one circulation pump
for 1 or multiple heaters for simplicity.
Do you design and size the system to different geographical
conditions? Or do you have some software to design?
Yes, we design the system to the weather conditions for the
building site. We follow ISO and ASCE guidelines for Frost
Protected Shallow Foundations. We have software programs that
model the frost line for different soil conditions. The science
is such that worst case scenarios are used to reduce the required
information from site. We perform an energy analysis for the
building as well as determine the air piping configuration
for zoning and heat load. Each system is custom designed.
Some of your pages say to use the construction heater
the same day as pouring, during cold weather, others say the
The construction heater can be used as quickly as you can
get onto the slab after the pour or if you install a construction
heater before the pour it can be used during the pour. We
do not recommend one way or another since the use of the heater
in this situation is strictly to benefit the builder when
doing cold weather pours.
How do you address the issue of recovery time for
the slab if the power goes off for 4 or 5 days? Last year
we had a 4 day power outage and long outages are common.
At design our heater would recover 2-3 degrees per day once
the power came back on and faster depending on heat load.
With our 8 inch slab during the ice storm of 1998 we had homes
without power for up to 11 days. The inside temperature went
from say 20 degrees C to say 14 degrees C. During an extended
power outage the slab acts as a heat source and sink. Because
of the thermal mass it will absorb energy during the day and
give off energy at night. Also, the heat flux from the slab
to the building fluctuates night and day and decreases as
the room temperature decreases. ---- It is not an easy answer.
So how long will someone be comfortable?
The Heat Storage Capacity of our 8 inch Slab: 0.44 MJ/(C-m2)
- at design (maximum heat flux) the temperature of the slab
will drop 1 C over 4 hours. This does not allow for solar
Realistically, the slab will gain or lose less energy during
the day and only require the maximum heat flux to the room
for very short durations. So in the peak of winter in say
Ottawa - based on 30 year climate norms for January - the
slab temperature would decrease approximately 2-3 C per day
when the inside temperature is 20 C and less as the inside
temperature decreases. So we go back to our experience from
the ice storm and can say that we would expect the inside
temperature to drop about 1-2 C per day over an extended power
According to Legalett Product Data Sheet 0528 (Electric
Heating unit), indication is such that the airflow rates include
a greater than symbol, are these maximum design rates?
Air flows are approx. and in most cases are greater than
specified. Design Air flow is shown on the PDS - the actual
Air flow can be different based on heater coverage, piping
design and design heat flux to the building. We basically
design for 10 Btu's per square foot per hour. This can be
done at different air flow rates and different water temperatures
for the 4000W. Our 4000W can produce considerably more than
4000 Watts. Our 4000E-24 is limited to 5000 Watts. We typically
try to keep the same coverage with our heaters - approx. 1600
square feet so that the water coil and the electric coil heater
are interchangeable ( if someone decided to change at a future
date). With a coverage of say 1400 square feet the air flow
rates are higher typically than stated air flows.
System for Additions
We are planning to build a 3 season sunroom, 14'
x 25'. Can we use the Legalett system instead of a wood deck
on piers? The finished floor will be approx. 12 to 16 inches
above grade as opposed to being at grade level as your illustrations
show. It would appear that the edge treatment would all be
Yes, Legalett can and has been used for many home additions
If the elevation is higher we would suggest to bring in
clear stone (after removal of the topsoil) to set the slab
EPS on. Our standard edge element is 14 inches ( 6 inches
of EPS and 8 inches of concrete) and we would like it buried
at least 6 inches. Depending on the heating requirements for
the sunroom or if you decide on a unheated slab we would possibly
skirt the room with EPS and would want the skirting to be
buried also. Some landscaping may be required.
Do you have any products for retrofitting an existing
home for radiant floor heating, furnace or other energy savers?
Legalett is not suited for retrofitting existing buildings,
unless existing floors can be excavated. The Legalett system
is suitable for;
- New construction and
- Additions to existing buildings.
System and the Building Codes
I am building in South Eastern USA and want to know
if your system is to code in the US. Bearing in mind that
I shall be building on a slope, will it support a two story
ICF wall house?
We have supplied our standard slab on grade warm floor system
to many states including California, Nevada, Utah, Michigan,
Pennsylvania and New York. Our standard slab on grade design
requires an engineer’s stamp in Canada as well as the USA.
We have available an alternate design that is IRC compliant
(International Residential Code) which has been adopted by
many states and would not require an engineers stamp. However,
most customer prefer our standard design because of its' simplicity.
Legalett is very well suited to ICF Construction for 2 or
3 storey homes. We have many back walk-outs on sloped property
- Legalett can be designed to suit the location.
Do you have CHMC approval for your system?
Yes, back in 1995 we had a CCMC evaluation report that we
let lapse in 1998. Our system falls under part 4 of the NBC
and OBC, which states that an engineer’s stamp is required.
System and Geothermal Energy
I live in Saskatchewan - -45 C. winters. Can this
system be connected to a Geothermal air heating unit?
Legalett has many systems in cold climates through out Canada
and the US. Yes, we can use/adapt the energy from a geothermal
Can your system connect to any geothermal heat pump
system or only to a specific manufacturer? If so which one
do you recommend?
We can adapt to any energy source and do not recommend one
technology over another. We simply need at required flow rate
at a set temperature.
on a Hill or on Uneven Terrain
My building lot (land) is not perfectly horizontal
but ia a rather flat outcrop with a slope of about 1 foot
per 10 feet, side to side (40 feet). I do not want to blast.
Can this slope be leveled with gravel?
Yes, legalett has been the system of choice when faced with
What is the load capacity of your system?
The Legalett system is designed for typical edge loading
of up to 5000 lbs. per linear foot. Legalett designers/engineers
can design up to 3 stories of ICF walls & suspended floors.
Is there any problem with a concrete wall on top
of the concrete slab? Your drawings show only a very small
setback from the edge of the slab.
We provide a complete design for building permitting. Our
designs fall under Part 4 of the NBC and are stamped by a
P.Eng. with a BCIN. All bearing walls are accounted for during
design for our slab on grade system.
Is there a detail of how the slab is used if there
are pier requirements or very large concrete support areas?
Each structure is custom designed - point loads, large bearing
areas and/or piers can be and have been many times incorporated
into our designs, depending on the structural requirements.
There is a low area along one side of where I am
going to build. The low area is about 4 feet below grade from
the surrounding area, which will be back filled. If I backfill
with rock, I will have to haul off dirt, otherwise I can push
the excess dirt into the low area. Your page says that your
system provides the structural integrity to bridge problem
soils, and holds up the house. Is this also true if I push
4 feet of dirt into a low area and build on that area as well
as on the solid area?
Our system has the ability to bridge poor soils and lies
very lightly on the ground - the resultant loads are very
light - in the area of 1000 psf or lower. However, this does
not mean that you should ignore good engineering practices
when building. It is important to have a uniform substrate
below the slab - either all dirt or all rock with a layer
of clear stone levelled when placing the EPS. It is recommended
to have a soils engineer provide some assistance to you knowing
the loading that legalett requires.
I have a high water table and am somewhat confused
about building without footings. Could you explain?
Legalett is a frost protected shallow foundation system.
Our most popular product is our heated slab on grade. We have
available non-heated slab on grade, basement and suspended
floor systems. High water tables are a nuissance when building
with a conventional basement, but are quite suitable when
building with the Legalett system.
We like hardwood floors. What must be done to use
your system under hardwood floors? Are some wood flooring
materials better than others?
Yes, many of our customers use hard wood flooring and today
with the engineered products available most are very compatible
What types of flooring do you recommend over the
heated slab? Looks like ceramic tile and hardwood are popular,
Any floor covering can be used. If you chose an insulative
floor covering such as thick carpet with a foam backing or
hardwood on sleepers we would like to know about it at the
Services & Warranties
Who backs the warranty? Legalett or installer?
Who services the unit should it need to be serviced?
A Legalett Service Rep or any licensed electrician or heating
contractor can service the unit.
Our uncle had your electric system installed in 1993
& we are inquring as to whether or not service is needed?
There is no regular maintenance required. Once a year the
cover and heating unit should be exposed and visually inspected.
What is a customer to do if your company goes out
of business? Are parts for the heating unit universal or are
they only made and sold by your company?
This question could apply to any heating supply company.
All parts in the Legalett heating unit are universal. Legalett
is supplied worldwide. In North America we warehouse complete
spare inserts as well as components. After market parts can
be purchased through our on-line Parts Catalog. We have units
in continuous service for over 20 years.
Do you offer the service of doing a heat loss calculation
and duct design for the HRV and/or cooling duct work?
Legalett is not a H&V design company. We do not do heat
load calculations as part of our supply.
We use our own proprietary software to evaluate transmission
and stated infiltration losses, as an internal check only
to make sure that the heating system sizing, as chosen by
the party who actually does the heat loss, is sufficient.
Ventilation and excessive infiltration losses are by others.
Ventilation varies from region to region and we do not supply
ventilation systems - for this reason we do not do whole-house
heat losses. We sell basically 10, 15, or 20 Btu's per square
ft. per hour - and perform an internal check for the Legalett
heated area to make sure that the system is sized correctly.
& Building Techniques
The slab heat system does not provide outside air
for the required ventilation. How do you provide ventilation
for public occupancy buildings and/or residences?
The air circulated by the heating unit does not enter the
living space. Ventilation air must be provided from a separate
ventilation system, especially for commercial or institutional
buildings where large volumes of fresh air are required for
occupancy loads The Legalett System is typically designed
to have a heat output to meet transmission losses and .12
Air Changes per hour for infiltration (R2000 Quality Construction
Heating of ventilation air (ie. ventilation losses) must
be done by external ventilation units. The magnitude of energy
required to heat the ventilated fresh air in an occupancy
building is typically an order of magnitude beyond what is
required to provide “comfort” heat. The slab cannot be used
to provide the heating of fresh air.
In other words, during periods of non-occupancy, when the
ventilation system can be shut down, the Legalett slab will
provide the heating needs, along with providing a comfortable
warm floor, by matching the transmission heat losses of the
building’s lower floor. Since the ventilation system is turned
off, there are no ventilation losses. During periods of occupancy,
the ventilation system has to be turned on, along with its
integral heating of the fresh air.