The removal of heavy snow and persistent ice often requires more than just manual labor like shoveling. When mechanical removal is insufficient, people turn to active melting methods that accelerate the phase change of frozen water. These methods fall into three main categories: modifying the snow’s chemistry, applying concentrated thermal energy, or utilizing the liquid state of water itself. Understanding each approach’s function, limitations, and potential risks is important for effective and safe winter property maintenance.
Chemical Methods for Lowering the Freezing Point
Chemical agents melt snow and ice by manipulating freezing point depression. This principle dictates that adding a dissolved substance (solute) to water (solvent) decreases the temperature at which the solution freezes. This occurs because the dissolved ions interfere with the ability of water molecules to arrange into the rigid crystalline structure of ice.
The effectiveness of a chemical agent relates directly to the number of particles it releases into the water. For instance, the common deicer sodium chloride (rock salt) releases two ions and is effective down to approximately 21 degrees Fahrenheit. Other compounds release more ions, allowing them to work at much lower temperatures.
Magnesium chloride can depress the freezing point to around negative 5 degrees Fahrenheit, while calcium chloride is effective even lower, near negative 25 degrees Fahrenheit. Calcium chloride is potent because it releases three ions when dissolved, further disrupting solidification. The dissolution process also releases a small amount of heat, which helps accelerate the initial melting.
Applying Thermal Energy to Melt Snow
Active snow melting is accomplished by directly applying sustained heat to the surface. This thermal energy approach involves either permanent systems installed beneath the pavement or temporary, surface-level devices. These systems work by increasing the surface temperature just above the freezing point, allowing snow to melt on contact and preventing ice from forming.
Permanent installations often use a hydronic system, which circulates a mixture of heated water and antifreeze, typically propylene glycol, through PEX tubing embedded in the concrete or asphalt. A central boiler heats this fluid, and the warmth radiates upward to the surface. These systems are highly automated, often using sensors to detect moisture and temperature before activating to conserve energy.
Alternatively, temporary electric snow melting mats rely on resistance heating. These portable mats contain embedded electrical heating elements that generate heat when plugged into a power source. They are placed directly on walkways and stair treads, and some can melt snow at a rate of up to two inches per hour.
Using Liquid Water for Snow Removal
Liquid water itself can be used to melt snow, but its application requires careful consideration of temperature and purpose. Pouring hot water directly onto a frozen surface provides an immediate melting effect by transferring thermal energy to the ice. However, this method is impractical and risky in most winter conditions.
The rapid cooling of the hot water against the cold pavement or air quickly causes the resulting runoff to refreeze. This process can create a layer of extremely slick and transparent ice, often more hazardous than the original snow cover. For this reason, hot water is avoided for clearing large, open areas.
A more effective use of liquid water is in creating brine solutions for pre-wetting solid chemicals. When solid salt is sprayed with a liquid solution, such as a salt brine, the water immediately begins the chemical dissolution process. This liquid coating accelerates the formation of the melting solution, allowing the deicer to lower the freezing point faster than dry granules. Pre-wetting also helps the solid material stick to the pavement, reducing chemical loss from vehicle traffic and wind.
Safety and Property Considerations
Each active melting method introduces specific risks that must be managed to protect property and ensure safety. Chloride-based chemical deicers pose a threat to infrastructure due to their corrosive nature. Chloride ions penetrate porous materials like concrete, where they can reach and corrode the steel reinforcement bars.
Corrosion causes the steel to expand, leading to internal stress that results in cracking and spalling (flaking) of the concrete surface. Additionally, these chemicals accelerate the oxidation of metal components, such as vehicle parts, railings, and drainage grates, causing rust. Users should select deicers formulated to be less corrosive, or use them sparingly on vulnerable surfaces.
Thermal melting systems, while non-corrosive to surfaces, involve electrical power or pressurized heated fluid. Electric mats require proper outdoor-rated connections and must be used according to manufacturer instructions to avoid fire or electrical hazards. The most common safety hazard across all methods is the increased risk of slip and fall injuries caused by the refreezing of melted snow. The water created by melting must be able to drain away completely, or it will turn into a sheet of ice once temperatures drop, especially if hot water was used.