Columnists: Alan Meier, LBNL

Published on: 26 Nov 2019

The Energy Costs of Moisture

Large parts of Europe have suffered from unusually wet, rainy conditions during the past year.  The floods in Venice may be the most dramatic—and tragic—consequence of water in the wrong place, but the subtle, ongoing impacts of moisture can be more extensive and expensive.  Moisture, liquid and vapor within building materials, droplets on surfaces, or appearing as vapor in the air, causes damage everywhere. This translates into repairs and renovations.  It also increases energy consumption. People don’t talk about a moisture bill in the same way as a bill for heating or cooling, but it exists and it’s large.

A moisture energy bill is complex because it is dispersed among many devices. One of the main components of a moisture energy bill would be the de-humidifier.  There isn’t much European data about de-humidifiers but about one fifth of American homes have them.  Operating patterns vary widely but, in the Mid-Atlantic states, they can easily run 2000 hours/year and consume 1000 kWh/year. That’s almost 10% of an average American home’s electricity bill!  De-humidifiers in basements need a sump pump as well; this too can add electricity consumption.

Excessive moisture in homes leads to mildew, mold, dry rot, and other issues that lead to odor and health problems. It also leads to poor comfort and can damage building materials, e.g., rotting wood and peeling paint.  Ventilation is a partial solution to home moisture, and thus becomes another constituent of the moisture bill.  People ventilate for odor removal and other reasons, so the hundred kilowatt-hours per year associated with bathroom fans can only partly be billed to moisture. 

Other elements of a home’s moisture bill are more elusive. Moisture reduces the effectiveness of insulation. Wet insulation translates into higher heating bills.  The problem may be confined to a single wall or corner, but the costs are nevertheless real.

Put all of these costs together and the moisture bill in some homes will approach the bills for heating or cooling.  And this doesn’t include the costs of material damage (or health complaints) from moisture-induced mold, mildew, and dry-rot.

How can a home’s moisture bill be reduced? Each home’s situation is different and there isn’t space here to detail all the options.  Installing a more efficient de-humidifier is a reliable first step, but more efficient ventilation fans and controls help, too.  Replacing wet insulation is a much bigger job but might be more easily justified for the health benefits rather than energy savings.   When internal sources of moisture are the culprit, targeted solutions, such as enclosing the shower, could be the simplest solution.

Providing thermal comfort and maintaining material integrity in a home is more complicated than just heating and cooling.   Creating a moisture bill is one way to highlight its complexity and perhaps raise the profile of drying out a home.

The views expressed in this column are those of the columnist and do not necessarily reflect the views of eceee or any of its members.

Other columns by Alan Meier