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Tuesday, September 30, 2014, 11:54 pm C.S.T.      
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Basements are difficult to keep effectively heated for many reasons. The natural properties of basement living space differ significantly in comparison to the main floor living area space. Basement floors are made of concrete and commonly referred to as slabs, cement slabs, or concrete slabs. Water vapor penetrates through the porous cement slab and walls, permeating the environment with dampness, moisture, and humidity.

Effective waterproofing systems, drainage systems, and sump pumps will decrease the threat of water seepage and flooding. However, they will not combat the infiltration of groundwater evaporation through the soil underneath the concrete slab and outside of the basement walls. A dehumidifier may improve the situation, but it is really better for improving indoor air quality.

Basement floor radiant heating systems are designed to heat a concrete slab, using it to conduct heat that is absorbed by the basement surroundings. If you have ever walked barefoot on a basement floor, you are familiar with the cold and damp shock that can be nearly unbearable to unprotected feet. With a basement floor radiant heating system, the floors will remain warm and dry, along with maintaining a consistently comfortable temperature throughout the entire basement living area.

Technological Advancements

Even though some manufacturers may claim that basement floor radiant heating is a new and innovative technology, it is not a novel concept. Radiant floor heating dates back to 60 A.D. when the Romans used the concept to warm enclosed spaces.

It is true that technology is continually being developed to improve the cost-effectiveness of basement floor radiant heating, installation, and operation. Systems are now offering advantages in terms of choice, energy efficiency, environmental considerations, and simplicity.

Understanding Heat-Transfer

Convective Heat

Think about the heat that radiates from fire. There is a difference in the main heat source between a fireplace and bonfire. The fireplace heats chiefly through convection because the air surrounding the fireplace is the main heat-transfer medium.

While the hearth absorbs warmth, the further you travel from the heat emitted into the air, the cooler it becomes. Often, the chimney flue will have cold downdrafts, creating a vacuum that sucks the warm air out through the chimney. The identical vacuum develops when the hot coals cool down.

In traditional convective forced-air heating systems, this process of air stratification, infiltration, and resulting exfiltration heat loss is known as the stack effect. When the heat-transfer medium is air, warm air rises to the ceiling until it cools.

Once the air falls to the floor, it returns to the furnace or fills the convective vacuum created by this process. As the outdoor temperature falls, the air infiltration and exfiltration increase in proportion to the rise in the inside temperature.

The superheated air from the convective system flows against the cooler exterior walls, drawing cold air into the home through any cracks and circulating with the heated air. Convective system thermostats take longer to equalize because of the time necessary to transfer the warmth where the temperature can be measured.

Radiant baseboard heating systems offer improved energy consumption compared to traditional forced-air systems. However, the heat generated from the baseboard radiators is not truly radiant. These types of radiant systems are still conveying the main heat source through the air, with the assistance of radiant heating elements.

Radiant Heat

Bonfires also heat the surrounding air, but the earth around the fire absorbs a majority of the heat. Once the firewood is burnt to the embers, the hot coals maintain their warmth and continue to heat the earth sometimes for days afterward. This is a true radiant heat because the earth is heated and absorbed by the surroundings, not through the air.

The energy from true radiant heat is known as infrared radiation (IR.) IR radiation is absorbed from every direction equally; it does not rise like warm air. Unlike forced-air heating, radiant heat is consistently even, eliminating drafts and cold spots.

With radiant systems, air infiltration, exfiltration, stratification and glass, heat loss is reduced by 10 percent to 25 percent over convective systems. The thermostat setting can typically be lowered by five to eight degrees Fahrenheit, saving energy consumption. The heat load of radiant heating systems is decreased by 25 percent to 40 percent.

A truly radiant system absorbs warmth from the heat source and is able to maintain more consistent temperatures. Once the target temperature set on the thermostat is reached, the temperatures will remain more consistently warm. The temperature differentials at the outside walls are lower, reducing air infiltration, stratification, and exfiltration.

Overview of Basement Floor Radiant Heating Systems

Basement floor radiant heating systems work upon the same principle as the warmth generated by hot coals from a bonfire. Just as the hot coals heat the earth, the floor is thoroughly heated and the surroundings absorb the warmth. These systems are efficient, economical, and cozy. Your home resale value can increase with the resulting comfort of the basement living space.

Typically, the majority of radiant flooring heat systems are hydronic. These types of dry systems can be installed both above and below the subfloor or underneath the concrete slab providing quiet, clean, and efficient heat, along with several other benefits.
  • Economical - Offers energy costs savings, amounting up to 40 percent in comparison to convective forced-air heating systems. Results in thermostat settings six to eight degrees lower than traditional heating systems with a reverse stratification of two to four degrees' difference between floor and ceiling level temperatures. Costs of installment are very affordable to the average homeowner.

  • Clean and Healthy - Eliminates drafts and circulation of common indoor pollutants through the air such as, blowing dust, dirt, and allergens. Reduces amount of outdoor pollutants through the conservation of fossil fuels.

  • Environmentally Friendly - Creates fewer greenhouse gases and can be assisted by the cleanest and most renewable energy source: improved solar energy technology.

  • Quiet - Abolishes noisy fans, popping ductwork, and pinging pipes of traditional convective systems.

  • Increased Living Space - Encourages you to live in and enjoy the previously cold and damp basement with consistent warmth with no cold or hot cycles and lower relative humidity.

  • Practical Investment - Increases long-term energy cost savings and greater interest in your home to potential buyers

Heated water or an antifreeze mixture is circulated in flexible tubing looped through a network above or below the subfloor. Most hydronic systems manufacturers find cross-linked polyethylene (PEX) tubing or rubber tubing with an oxygen diffusion barrier superior to the older soft copper or steel tubing.

Hydronic radiant floor systems pump the heated water through the tubing, effectively heating the flooring surface and radiating the heat to be absorbed by the surroundings. The PEX and rubber tubing are pliable and less susceptible to corrosion in pumping the heated fluid through the tubing past other metal components present in the pumps, fasteners, and couplers.

The flexible tubes are filled with water or an antifreeze fluid combination. This water is then heated by a traditional boiler, water heater, or solar collector and pumped through the tubing. The flexible tubes heat the slab, which then radiates the heat from the slab to the living area of the basement.

Types of Systems

Each type of system will have unique advantages and disadvantages. Deciding on a type of system will be a largely personal choice based upon your long-term goals, installation and energy costs, amount of product system research, any preparations needed for waterproofing or foundation repairs, and the recommendations of a professional installer. Perhaps the most crucial factor for making the type of decision will be based upon whether the system is being installed in an existing home or a new construction building structure.

No matter the type of basement floor radiant heating system you decide upon, there are a few things to keep in mind. Feeling the heat-transfer from a radiant floor heating system will take longer than a conventional forced-air system.

The rate of heat-transfer through the thermal mass of the floor takes longer than the heat-transfer through air. However, once the heat-transfer has fully penetrated the basement concrete slab, the consistency and elimination of hot and cold spots will far outweigh any inconveniences.

Above-floor systems can become costly and time-consuming when dealing with retrofits. Often, the existing finished floor may need to be removed and replaced afterward. Below-floor systems require drilling holes through the floor joists so that the PEX tubing can pass through.

The sections below should assist in deciding upon which basement floor radiant heating system is the best choice for your home. Seeking the advice and consultation of a contracted professional is highly recommended. You will be better able to weigh the advantages and disadvantages of the systems offered.

Above-floor Systems
Basement floor radiant heating systems are installed above the concrete slab subfloor and below a finished floor. Above-floor systems use grooved wood panels installed beneath the finished floor. PEX tubing is placed inside the panel grooves, setting flush with the panel surface.

The panel area and width dimensions vary according to each manufacturer. Accordion panels are offered by some manufacturers for larger areas. The manufacturers declare the panels will work under a variety of floor coverings: tile, marble, vinyl, wood, and carpeting.

Below-floor Systems

Basement floor radiant heating systems are installed under the subfloor. Below-floor systems involve attaching PEX tubing to the bottom of the subfloor or suspending it from the subfloor. This type of system is widely utilized for retrofits because installation is less costly than the Above-floor systems and hydronics systems. Below-floor systems have an efficiency disadvantage compared to Above-floor systems. A higher source temperature is required to achieve the identical heat load.

Dual-Function Panel Systems

This panel system, considered to have a Dual-Function panel, combines the structural requirements of a subfloor framework and a radiant floor heating system. The panel system is constructed in engineered comply tongue-and-groove. The top surface is engineered comply panel with a modular groove pattern on center. The panel is designed for PEX tubing with an alloy aluminum sheet conformed to the groove pattern and permanently bonded to the surface.

Hydronic Concrete Slab Systems

This basement floor radiant heating system is not the most economical or practical for existing basements, unless the concrete slab needs replacing. However, this type of system makes perfect sense for new home or building construction, as evidenced by the vast majority of homeowners choosing this type of system. It works most efficiently of all the basement radiant heating systems if properly installed.

Because the cost of the basement floor slab is already calculated in the construction costs, adding the basement floor radiant heating system only helps recuperate long-term energy savings costs more quickly. The system can be used alone or in conjunction with a traditional forced-air, baseboard heater, domestic water heater, wood stove, or water boiler.

Homeowners are pleasantly surprised at the quiet operation of the hydronic radiant floor heating system. Unlike traditional convective systems, there are no constant noises associated with blowers, fans, or creaking pipes. The water pump used to circulate the fluid through the flexible tubes is contained in the concrete slab.

Air currents are absent, unlike forced-air systems. The elimination of hot air coming out of the registers, eradicates dust from being blown about the house. Constant and even heat is achieved because there is no immediate cooling of the air in the room or blowing of cool air as the air is heated up with each heat cycle.

Installing Concrete Slab Radiant Floor Heating Systems

Crucial Insulation Factors

Installing the elements of a concrete slab radiant floor heating system changes the process of pouring a concrete basement floor very little from a traditional method. A 6 mil polyethylene vapor barrier is placed on top of the aggregate bed to prevent water vapor from permeating the concrete slab. Using vapor barriers has become standard in recent years.

A layer of insulation is laid on top of the vapor barrier and along the foundation wall edges to prevent leaching of heat through the cooler outside wall edges. This is the most crucial recommendation in the process. The insulation layer should be from one to two inches in thickness, according to the climate conditions.

Colder climates should start with two inches of insulation at the outside foundation wall and taper down to an inch toward the center. The length of the insulated area is recommended to 12 feet from the perimeter toward the center of the basement. In addition, ensuring proper foundation insulation increases the entire energy consumption efficiency of a home and will minimize heat loss from the concrete slab radiant floor system.

System Components

PEX tubing is then looped in between or on top of the concrete reinforcement material in circuits, controlled by a circuit manifold. The reinforcement material protects the tubing and directs the heat away from the tubing for faster heat transfer through the concreted slab.

Rod types of reinforcement are preferred to mesh types because of their durability. If rod reinforcement is used, it is recommended that half the reinforcement material be laid out on blocks, bricks, or other elevated surfaces. Then the PEX tubing is inserted and the remainder of the reinforcement material is placed on top of the tubing.

The flexible tubing is wire-tied to the reinforcement material in lengths less than 400 feet, depending on the thickness of the tubing. Spacing of the tubing varies between 6 inches to 18 inches depending on the climate, heat load, and areas more prone to heat loss. Interior areas are often spaced at wider distances, whereas doorways and along the perimeter are more concentrated.

Proper length in proportion to the pump capacity will lead to the lowest energy consumption. The tubing layout should be spiral and void of very tight turns. The goal is for gentle turns, which will assist in eliminating pump strain and conserving energy.

Pressure testing the PEX or rubber tubing for leaks prior to pouring the basement floor can save considerable hassles and time. This involves pumping the tubing to 50 psi and leaving it overnight. If the gauge registers 5 psi or lower, a leak is indicated.

Repairs are made before pouring the slab. Air is left in the tubing, while pouring the cement slab to help protect it. After pouring the concrete floor slab, another inspection is performed to determine if a leak has occurred.

To protect the PEX flexible tubing from damage, it is left in the bottom third of the concrete slab. At this depth, the tubing is most effective at thoroughly radiating the heat through the concrete slab. Care should be taken that the tubing does not breach through the bottom of the basement floor slab.

Energy Sources

Most basement floor radiant heating systems are called hydronic systems. This refers to the operation of the system, not the energy source itself. There are a number of energy sources available for these systems.
  • Natural Gas
  • Propane (LP)
  • Oil
  • Coal
  • Wood
  • Electricity
  • Heat Pumps
  • Ground Source Heat Pumps
  • Solar energy
The decision about which energy source to use is a personal one. Considerations include project budget, architecture elements, desired comfort level, regional climate, and the compliance of your local building codes.

Finishing Touches

After deciding upon the basement floor radiant heating system and the energy source, you are ready to select the finishing touches. Practically any type of flooring material is compatible with radiant heating systems. For more complete information on options, please refer to either or both of these sections: Basement Flooring and Hardwood Flooring.

Consulting with a basement floor radiant heating system professional is the first step in choosing the most economical and practical system for your needs. It may be beneficial to consult with a waterproofing contractor, foundation repair specialist, or with basement finishing professionals to ensure that any structural issues are resolved prior to installation.

With the proper information and professional recommendations, homeowners and their families can enjoy the most comfortable and cozy added living space at an economical cost!

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