Metals also vary in their thermal conductivity. Thus, they tend to cause water vapor to condense. Inspectors can be aided by a rule of thumb that states that a metal's ability to transfer heat (and, therefore, create condensation) is roughly equal to that metal's electrical conductivity. Electricians and some inspectors may know that, of all metals, copper is the second-best conductor of heat and electricity, meaning that it's more likely to respond to a brief burst of cool water or air than other metals, such as steel or lead. The metal with the greatest conductivity is silver, but it's far too expensive to be used in ordinary construction. Condensation is more of a problem in older homes, which often lack a vapor barrier or sealers in the concrete. In this instance, moisture in the ground is forced through the foundation and masonry, which is why condensation is commonly found in the basements of older buildings. The two strategies used to reduce condensation are to lower the relative humidity of the air and to keep surfaces from becoming cold. These strategies can be practiced in the following ways:
- Use a dehumidifier. This is a simple, effective appliance used to lower the humidity of the air, as it forces water vapor to condense into a water tank so it cannot condense elsewhere. An air conditioner can also dehumidify the air.
- Remove plants from the home. This will decrease relative humidity, as their transpiration of moisture is a significant source of water vapor in homes.
- Insulate cold surfaces. Insulation will keep surfaces from becoming cold, and it can easily be applied to water pipes and water pressure tanks. Fiberglass insulation should be avoided, as it's ineffective when wet and it can be the source of mold growth. Plastic foam wrap is an adequate material for this purpose. Keep in mind that by adding thermal insulation to water pipes, they can no longer be counted on to supply radiant heat to their surroundings.
- Ventilate the basement. However, this tactic might be counterproductive if the outside air is more humid than the indoor air.
- Add heat where condensation is a particular problem.