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Radiant Floor Heating Systems Information
A. Introduction to Radiant Floor Heat
B. Methods of Radiant Floor Installation
C. Tubing
D. Heat Sources
E. Controls
F. Flooring
G. Retrofits
H. Cooling Strategy
I. Baseboard and Radiators
J. Snow Melting
K. Contractor/Owner Preparation Information
Introduction to Radiant Floor Heat
In a hydronic radiant floor heating system warm water is pumped through the floor thus heating it to a few degrees above the air temperature. In this way the floor itself becomes a massive radiator sending out rays of heat, much like a wood stove or a wall that has been heated by the sun, into the room. These heat rays heat all the objects and people in room in a gentle, even manner. No more woolen slippers on winter mornings. No more cold toes and hot stuffy heads!
People who own radiant floor heating feel that the most important advantages are comfort and quiet operation. Radiant floor systems allow even heating throughout the whole floor, not just in localized spots. The room heats from the bottom up, warming the feet and body first. Radiant floor heating also eliminates the draft and dust problems associated with forced-air heating systems.
The human body has its own hydronic heating system. Heat is distributed to the body through blood pumped from the heart. The first priority of the body's heating system is to maintain central body core temperature. From there, blood is sent to the extremities. Since the feet are the farthest from the central body core, they are the last to get heat and the first to recognize the discomfort of a cold environment, with warm floors, you'll never feel even chilly.
Even heat distribution equates with lower heating bills. With radiant floor heating, you can set the thermostat several degrees lower than normal. Radiant floor heat also radiates heat for a longer period of time than a forced air system thereby eliminating roller coaster temperature swings. Another advantage is that radiant systems do not increase the infiltration of outside air into the house structure as forced air systems generally do. Radiant floor heating also allows lower boiler temperatures allowing them to last longer (a 45 year life is not unusual).
HEATING PERFORMANCE
There are two factors that determine the ultimate performance of a heated home: the manner in which heat is delivered into the home and the manner in which the home loses heat. A Thermacraft designed and installed heating system can cover the first factor, however, the control over the second factor is determined by the owner and builder. This is a very important issue in light of rising energy costs. Sometimes just a little bit of effort and a few extra dollars spent in improving a houses energy performance can make a major impact in energy dollars spent. We will gladly answer any questions you may have in regard to energy performance, you can make furthers inquire at the NC Solar Center, or secure the services of an energy performance specialist.
ADVANTAGES OF RADIANT FLOOR HEAT
Superior Comfort - Consistent, quiet, steady heat all winter long remaining near the floor where you are, there is no noise and no drafts. Beautiful wood and marble floors are even more enjoyable because they are now warm. Molds and fungus are less likely to propagate and dust is not blown into the air.
Higher Efficiency - with no wasted heat, thermostats are kept at a lower setting translating into energy savings of up to 30% over conventional forced air systems. Savings are even greater if a high-efficiency boiler is used.
Decorating Freedom - because the system is encased in the floor, furnishings can be place wherever you desire without concern for impairing heat distribution or hiding unsightly heating appliances. In addition, radiant floor heating systems can be installed under any type of flooring, including wood, tile, concrete and carpet.
Increased Equity - installing radiant floor heating in your home immediately increases the value of your home, radiant floor is becoming recognized as the most desired form of heat and is routinely found in higher quality homes.
Methods of Radiant Floor Installation
SLAB INSTALLATION
The most common, most efficient and most cost effective method installing radiant floor heat is to embed the radiant tubing in a 4" concrete slab. We attach our tubing to a grid of reinforcing bar that places the tubing exactly in the middle of the slab. This gridwork ensures that the heat will be delivered evenly, it safeguards the tubing by keeping it at a predictable depth and it strengthens the slab. The slab must be insulated around the perimeter and beneath to prevent unnecessary heat losses. Generally the tubing is placed on 12" centers except at the perimeter where it is run at closer spacing.
THIN-POUR ON TOP OF WOOD FLOOR
In situations where the floor is built with wooden floor joists, a common practice is to attach the tubing to the plywood subfloor on 8" centers and then pour a 1.5" thin-pour of gyp-crete, lightweight concrete or regular concrete over the tubing. This thin-pour provides a medium for heat delivery, it also strengthens the floor and provides sound-deadening and fire proofing properties. The floor structure must be designed to support the additional 11-15 lb. of additional dead weight. The floor must also be insulated below to keep the heat moving up wards. If a hardwood floor is desired, it is best to use a laminated, glued together "floating floor" or a solid hardwood flooring system designed for radiant floor heat thin-pour applications.
TUBING RUN ON TOP OF SUBFLOOR BETWEEN WOODEN NAILERS
This method works well for those who want to install a nail-down hardwood floor. The tubing is usually stapled down on 8" centers and then 3/4" nailers (commonly called "sleepers") are nailed down between the tubing. This results in a 3/4" thick system, if this is too thick, 5/8" sleepers may be used. If thickness is still an issue, 1/2" o.d. tubing and 1/2" sleepers can be used. For a really strong a (though thicker) floor system, 2x4 sleepers can be used. We prefer to use pex-aluminum-pex tubing or have a reflective radiant barrier applied to the subfloor in these applications for better heat delivery and greater longevity assurance. Thermacraft does not install the sleepers.
TUBING SUSPENDED BELOW THE FLOOR
In cases where an above-floor system is unacceptable, the tubing can be suspended below the wooden subfloors. Under floor tubing systems must run at slightly higher temperatures than thin-pour systems and usually cost more to install and is not the preferred method of heat delivery. Metal heat-transfer fins must be used unless the application is for comfort heating only. These systems must also be insulated very well from below including the use of reflective insulation. This is not a preferred method of installation because the system must operate at a higher temperature to deliver the same amount of heat and if there is a crawlspace below, it is very difficult to prevent some heat from being lost downward. This is sometimes the only available option in a retrofit situation or when radiant is decided upon late in the project.
WARMBOARD SYSTEMS
Warmboard is a proprietary structural subfloor replacement that is 1 1/8" thich with grooves every 12" on center for the piping and a thin sheet of aluminum covering the panel for even heat transfer. Warmboard comes in 4x8 sheets and installs just like your subfloor for a fast, responsive low mass radiant system. Warmboard systems are extremely efficient operating at a very low supply temperature.
PLYWOOD TRACK SYSTEMS
A special plywood/aluminum system has been developed that is only 5/8" thick. It goes right on top of the existing floor. There are grooves in the plywood and aluminum heat transfer plating. This system is excellent for retrofits where the new heated floor height must be kept to a minimum. This is an expensive system to install.
SPOT HEAT IN SMALL AREAS
Radiant floor can be installed in small areas such as bathrooms or kitchens. In these applications a gas tankless hot water heater supplies the heat.
Tubing
Cross-linked polyethylene, or PEX, has become the standard tubing used in radiant floor heating applications. This extremely tough yet flexible tubing was originally developed for radiant heat applications and is now also used in plumbing systems. It is extremely durable and does not chemically interact with concrete.
LONGEVITY
For technical information, visit the Radiant Panel Association. PEX has been manufactured for over 30 years and has been tested in a variety of ways. Tests that accelerate the aging process of pex have concluded that under normal conditions, PEX tubing will easily last up to 150 years. Most manufacturers offer a 25 to 30 year guarantee. Presently, there is a section of pex tubing manufactured in 1973 that has continually withstood 202 degrees F. temperature at 175 psi. When it was recently analyzed after 27 years of this extreme condition, it showed no signs of deterioration. In most systems, the pressure is 12 psi and the temperature averages 100 degrees F. in the winter.
In "wet" systems the tubing is surrounded by concrete and truly, it is not the tubing, but the integrity of the concrete that determines the lifetime of the tubing. In "dry" systems, where the tubing relies on the air around it to conduct the heat, we prefer to use composite or pex-aluminum-pex tubing for better heat delivery and the reinforcement of the aluminum layer to insure longevity.
BREAKS AND KINKS
Tubing is usually kept under pressure during the full construction process to monitor integrity, If the tubing is cut before a concrete pour, it must be replaced. Cut tubing that is not going to be embedded in concrete can be spliced using approved methods. If tubing is kinked during installation, most brands can be carefully heated up to remove the damage. Pex tubing has incredible resiliency.
SPACING OF TUBING
The tubing is spaced accordingly: In a slab: 6" to 12". In a thin-pour: 5" to 8". Under the floor: 8" to 12" ( two runs of tubing per joist space). In 1/2" plywood panels: 7". Closer spacing is used in areas requiring greater heat output. The 1/2" tubing is usually run in 250 to 300 foot lengths. One zone may have as many and 10 or 12 loops. These loops come together at a manifold placed in an accessible location. The individual loops each have a metering valve so that the flow rate through the loop can be adjusted if so desired. In some applications 3/8" or 3/4" tubing may be used, but 1/2" is the norm.
FREEZING
Pex is not designed to withstand continual freezing conditions, though in most cases it will survive a freeze, if not too extreme. If freezing conditions are anticipated, a 30-40% propylene glycol mixture should be used in the system. Homeowners in remote locations subject to very cold weather should invest in some form of backup electricity if they don't use glycol.
Heat Sources
BOILERS
Cast Iron boilers and systems using ferrous components must use PEX pipe with an oxygen barrier. This PEX has an additional layer on the outside to prevent oxygen from passing through the tube wall and attacking iron components in the system. Oxygen -barrier tubing costs almost twice as much as non-barrier tubing. Up until recently, all boilers were cast iron, however in the last decade copper and stainless steel boilers have been developed that usually have a higher efficiency rating and have a longer lifetime expectancy. They also cost more.
STAINLESS STEEL BOILERS
The most common stainless steel boiler and, one that we favor, is the Munchkin or Phoenix (combination unit). These 95% efficient hot water makers come in a variety of heat outputs, and are ideally suited for radiant floor heat. They can also provide domestic hot water at the same efficiency. High-efficiency heaters pull water out of the combustion gases therefore a floor drain should be located near this unit. We also install Lochinvar, Triangle Tube, Buderus and Viessman boilers.
GAS MODULATING BOILERS
The latest development in boiler design is the incorporation of gas modulation valves. These valves control the flow of gas being burned in response to the amount of heat required by the home. This is especially advantageous in mild weather when the heating requirements of the home are very low in comparison to the output of the boiler. The new Munchkin Vision 1 and the Lochinvar Knight controllers takes this improvement even further by providing two separate targets as well as tying one of the setpoints to an outdoor reset.
TANKLESS HOT WATER HEATERS
Tankless hot water heaters are very compact and relatively efficient (up to 93%), they are usually wall mounted and pump the heated water into a small holding or "buffer" tank. Water from these tanks can be used for floor heating and domestic use. These cost quite a bit less to install. We install Rinnai, Takagi and Navien units. When system costs must kept down and space being heated is well-insulated and less than 1500 sq. ft. in area, tankless water heaters (that are specified for heating systems) may be used. The tankless heater may or may not supply the dhw as well depending on system specifics. This is known as an "open" or potable system
POTABLE VS. CLOSED SYSTEMS
Most of our systems can be either potable or "open" systems or non-potable or "closed" systems. In potable systems, the same water is used for domestic hot water and space heating; these systems are simpler in design and cost less to install and usually we design the system so that any new water entering the hot water heater runs through the floors thus continually flushing the system with new water. The other choice is a closed system in which the heating water is separate from the domestic water. This is really a matter of personal preference and a cost consideration.
SOLAR
Solar energy makes an ideal companion to radiant floor and is discussed here: Solar Thermal Energy.
GEOTHERMAL
Radiant floor heat works well with geothermal systems which are currently the most efficient way to heat and cool your home. By taking advantage of the constant temperature of the earth a low consumption system can be achieved. Thermacraft works in conjunction with another HVAC contractor is able to install these systems.
ELECTRIC
Electric boilers are extremely compact and require no vent, but they are very expensive to operate. We have installed several of these units in both home heating systems (usually as a rarely used backup to a solar system) or in snow melting applications.
REVERSE CYCLE CHILLERS
Currently we are experimenting with a new technology- reverse cycle chillers. These units are similar to a heat pump in that they extract there energy from the air. The difference is they utilize water for heating and cooling. These units are highly efficient and can supply radiant heat and air conditioning from the same appliance.
WATERSTOVES AND WOOD STOVES
Large mass (500-1000 gallon) waterstoves allow homeowners to burn wood at full combustion in a short period, the stove absorbs the heat and delivers it for the rest of the day. In many cases, waterstoves are coupled with 6 to 8 solar collectors. These units heat the house and provide domestic hot water and usually have oil or gas burners for backup. Also, a small stainless steel heat exchanger is made that fits into wood stoves. Moving water must run through these units whenever a fire is lit - even if hot water is not needed at the time.
ASSEMBLY AND APPEARANCE OF PUMP MANIFOLDS
All of our pump assemblies are carefully built with copper pipe, they are firmly mounted on the wall and arranged in a neat and orderly manner. Everything is fully labeled and our larger systems come with operation manuals and in some cases, spare parts kits for emergencies.
Controls
There is a digital readout wall thermostat in each zone of the home which sends a signal to the appropriate zone valve or pump on the pump manifold which in turn sends heated water to the zone. In almost all of our systems there is some method of moderating the temperature of the water going to the floor. In our larger systems, the water temperature is continually being moderated in response to the outside temperature. As the temperature outside goes lower, the temperature of the water going to the floor is made higher. This is called a "weather responsive" control which produces extremely smooth, even heat conditions in the home, no matter how cold it is outdoors and prevents the home from overheating in mild weather. We also have thermostats that can sense floor surface or air temperature.
Flooring
Since the heat is delivered to the room by the floor, the floor coverings do have and effect on how well the heat is delivered. Tile, vinyl and hardwood allow for good delivery of heat, carpet is acceptable, but it must be as dense as possible and the carpet pad must be chosen with care.
TILE AND STONE
Tile and stone make for excellent delivery of heat. If the tile is covering a very large area over a thin-pour application, it is advisable to further stabilize the thin-pour with wire mesh, or to use a slip sheet between the tile and the heated substrate, this allows the substrate to move without affecting the tile above it. Some suppliers prefer to use a special rubberized trowel-on mastic. Brick pavers, which come in 2" an 1/2" thicknesses make for an excellent, long lasting floor. The 2" pavers can also double as thermal solar mass.
VINYL
Vinyl works very well with radiant floor, but it is always best to consult with the manufacturer beforehand. If the vinyl is being installed over a slab, the slab must be dry. There are some simple tests that the manufacturer may want you to make before installation.
HARDWOOD
Hardwood flooring works very well with radiant floor heat, but there are many things to be considered, since there are many kinds of hardwood. Maple and Brazilian Cherry are not compatible with radiant floor heat. Visit Launstein Hardwood Floors for radiant specific hardwood flooring.
LAMINATED
Laminated glue-together flooring that usually comes pre-finished and is glued together as one floating floor that lies on top of the heated subfloor is one of the best flooring systems for radiant floor heat. This floor is able to expand and contract independently of the subfloor below it. Also known as a "floating floor" system, this system can be refinished and in some cases can be installed unfinished and can then be finished like a regular nail-down floor.
GLUE DOWN
Glue Down wood flooring is an excellent choice for concrete floors. This flooring also comes in a variety of styles including laminated bamboo flooring from China.
STANDARD NAIL-DOWN
Standard Nail Down flooring can be used on top of wood floors with under floor tubing or it can be nailed to nailer boards (or "sleepers") laid on 8" centers on top of the floor. The tubing runs between the sleepers and is sometimes covered with gypcrete or concrete. The three important considerations with wood flooring are: #1) The wood should have a 12% or less moisture content and be allowed to acclimate in the home at least 3 days prior to installation (narrow widths do better than wide boards). #2) The temperature of the floor heating water should be controlled to stay below a temperature 125 degrees and, #3) The moisture level in the home should be kept stable in the summertime. Moisture is the culprit here. As stated above, maple and Brazilian cherry are not acceptable. Visit Radiant Panel Association for more detailed information on floor coverings, or call National Wood Flooring Assoc. at 800-422-4556.
CARPET
Carpet works best with radiant floor heat when it is kept to a minimum thickness and maximum density - usually Berber type carpet work best and high-pile, high loft carpets do worst. Another very important consideration is the pad. Natural jute pad is an excellent choice also acceptable is solid dense rubber padding. Avoid waffle and foam pads, they act like a blanket.
Retrofits
In most retrofits the new floor level cannot be raised very much, so usually a 5/8" thick plywood track system is used. If the ceiling below the floor in question is not finished, then the heat can be installed below the old floor. Retrofits in older homes can be expensive. In cases where the house already has a boiler in good condition, the cost is a great deal less.
Cooling Strategy
Today's better homes require some kind of air conditioning. It seems redundant redundant to have to install two separate systems in a home, one for heating and one for cooling. However, there are several options to consider.
First of all, a duct system designed to just cool a home, especially the upstairs areas, usually cost less than systems that are designed to heat and cool an entire home. In large homes with several stories, a popular strategy is to heat the basement, the main floor and the upstairs baths with radiant heat and to heat and cool the upstairs with an air unit that can also cool the downstairs in the summer.
Passive cooling design strategy takes into account the elements of house orientation, surroundings and heat reflective components to result in a home that is naturally cool, thereby requiring a lower cooling demand and a smaller cooling system. The North Carolina Solar Center has many pamphlets on this subject.
Several of our customers who have built solar homes with a great deal of internal mass, thorough insulation and proper window shading, just open their windows at night to cool the house off and then keep the house shut during the day. In hot weather they might use a dehumidifier once in awhile.
There are several "ductless/split" units that do not use ducts. The compressor is outside and compressed freon is piped to wall or ceiling-mounted fan units in the house. One central unit supports up to 3 fan cooling units that can be strategically placed throughout the house. Each unit is independently operated with a remote control. These systems work best in homes with large open spaces. Sanyo and Mitsubishi are two of the several manufacturers of these units. Also Multiaqua manufacturers a central outdoor heating and cooling unit that sends heated chilled water to any number of ceiling or wall mounted air handlers in each room or to a central air handler for ducted distribution. This unit can also use the heated water to provide radiant floor heating. Visit: Multiaqua
Baseboard and Radiators
Hydronic baseboard and radiators can be used in conjunction with radiant floor heat. These types of heaters require much hotter water than the radiant floor, thus making for a more complicated pump manifolds. Baseboard in usually less expensive to install, it usually is run along one or two outside walls of each room. European radiators have come a long way from those cast iron monsters of yesteryear, they are thin, sleek and very refined. Each radiator has its own thermostat which means individual room control. They are expensive though, and cost about the same to install as radiant floor heat especially in small rooms.
Snow melting
We have installed several snow melting systems in Western North Carolina, at Laser car washes and at private residences. Special moisture and temperature sensitive controls are designed to activate the snow melting systems when icing conditions exist. After the ice has been melted and the drive is dry, the system shuts down. These "smart" controls keep energy consumption down to a minimum.
Snow melt systems can only be incorporated in concrete. One customer installed the system in concrete and then covered it with asphalt. Snow melting systems usually cost in the neighborhood of $8.00 per sq ft (for approximately 2,000 sq ft) . The cost is higher for smaller areas or systems with more than one zone.
Contractor/Owner Preparation Information
CONCRETE SLAB HEAT
We usually suggest a minimum of 2" extruded polystyrene on top of the vapor barrier which covers the under slab gravel (or suitable R-10 or above under slab equivalent). The under slab insulation should be thicker in areas where moving ground water may be near the surface. An extremely important consideration is perimeter insulation: a 2 foot wide band of 1.5 inch insulation should be put around the perimeter, or be extended two feet down on the foundation wall. This perimeter insulation is sometimes difficult to incorporate into some slab preps, but it is a must - IT IS REQUIRED BY THE NORTH CAROLINA BUILDING CODE.
We prefer to use a contractor-installed grid of #3 (3/8") re bar on approximate 2 ft centers as a platform for our tubing. This grid is raised off the under slab insulation with small blocks of insulation. We then attach our tubing to this grid. This grid work is not absolutely necessary, but it is best way to install slab tubing and the best way to insure longevity of the tubing. It also makes for an excellent slab and minimizes cracks. We can also staple the tubing to the under slab insulation and the owner can use fiberglass or standard wire mesh reinforced concrete if he so desires with the understanding that he may be jeopardizing the life of the tubing.
As for the amount, we suggest that you multiply your square footage by 1.1 and get that many linear feet of re bar (1,000 sq ft = 1,100 lin. ft. rebar). The grid does not have to be exactly on 2 ft centers and there is no need to tie each crossing, every other one is enough. Usually we cut 1" insulation into 2" strips and break off little 2" squares to be placed under every other rebar junction. NOTE: For easy installation, elevate the rebar first and then tie it at every other junction where it is not supported. If the perimeter wall of your slab is formed by header block, be sure to run the rebar so that it rests on the block.
We will pressure test the tubing and keep it pressurized. If you puncture a pipe during a pour and can't get in touch with us, leave the damaged section of pipe exposed as best as you can and we'll repair it later. Ultraviolet light damages the pex tubing so schedule your pour to take soon after the tubing has been installed.
Please mark the location of expansion and control joints before we arrive so that we can account for them. After the pour, cover the slab with poly for as long as you can. Later on, when framing your interior partition walls be sure to use liquid nails beneath the bottom plates, a FEW 2" hard cut nails may be used to secure the bottom plates to the concrete - use as few as possible. We like to use the rebar grid to protect the contractor (by keeping the tubing at a precise elevation), to deliver the heat in the best manner, and to increase the stability of the slab.
THIN-POUR ON TOP OF SUBFLOOR
Whether the topping pour be Gypcrete or regular concrete, the floor structure should be designed to support an additional 15 lb.. per sq. ft. dead weight. To order a Gypcrete pour call Rich at K-Wall at (828) 628-9255 or Vince Carolina Flooring Systems at (803) 476-2692. Gypcrete is very smooth and level when installed and they prefer to install it after the sheetrock has been installed, finished and primed. Concrete pours are not usually as smooth as gypcrete, but they can be installed at any stage of construction. Since concrete shrinks as it cures, it tends to form cracks unless proper precautions are taken. If the poured floor is going to be the final floor, it should be at least 2.5" thick.
Some contractors prefer to double bottom plate the interior walls. Lay down all the first plates only and use them as a screed board guide. After the floor is poured, build the interior walls on top of the first plates. Another strategy is to use a 2x8 as the bottom floor plate with a 2x4 above it. This results in a small ledge at the base of the wall that can be used as a screed platform and for carpet tacking strips.
UNDER THE SUBFLOOR HEAT
We like to attach the tubing and under floor heat transfer plates to the subfloor as soon as the building is dried-in, the plumber and electrician should come in after us. It's best if the plumber himself marks out the location of all floor drains ahead of time. We will pressure test these lines.
Solid blocking gets in the way of our installation process, if you are using 2x10 floor joists, use 2x8 blocking flush to the bottom of the joist, or use metal cross blocking especially if you are using TJIs. Open web trusses make for the easiest under floor installation and should be planned for if this application is to be used. After installation, the joist spaces with this heat should be insulated with a minimum R-11 insulation.
It's not unusual for tubing to be punctured in the course of a job, however if more than 2 punctures are discovered on a job, the general contractor will be charged $40 per puncture for each puncture, so please remind all your subs to check before they drill. Any and all punctures compromise the integrity of the system so please mark all floors with red spray paint to alert forgetful subs.
BOILER ROOM SPECS
Most standard efficiency flue-type boilers need to have adequate provisions for combustion air. If the boiler will be in an enclosed closet or boiler room, certain sized openings will be required at the top and bottom of the room wall, in some cases the openings can be in a door or use a louvered door. If the boiler is in an open basement there may be enough volume to eliminate the need for any outside air source. There should be a drain near the boiler, especially if we are using an ultra-high efficiency boiler. The gas company should run any gas lines and be responsible for gas tie-in to the boiler. Thermacraft will run the vent. ALL MUNCHKIN AND PHOENIX INSTALLATIONS REGARDLESS OF SIZE REQUIRE 3/4 INCH GAS LINE ALL THE WAY TO UNIT.