greeNEWit Mythbusters Edition: 2 Home Energy Efficiency Myths

April 30, 2015 Written by  Comments Print
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There's a lot of information out there about home energy efficiency. And while much of it is true, there are some concepts that sound plausible but are actually false. In this blog, we're on a mission to bust these myths once and for all! Keep on reading to learn about 2 home energy efficiency tips you may have heard that are actually myths, as well as how a home energy audit in Maryland can help make your home more energy efficient!


2 Home Energy Efficiency Myths


#1 – Get new windows to solve draft problems and save money on energy bills.

Sounds logical enough, right? Old windows are drafty and let air in and out of your home, so that conditioned or heated air goes right out (around) the window.

However, there are two flaws with this statement. The first concerns where most drafts come from, and the second, the cost-effectiveness of new windows.

Convective Loops

Most drafts actually come not from air leaking into your home, but from what are known as convective loops. Here's how a convective loop works:

Heated air in your home rubs up against the window glass, which is cool. This causes the air to cool, which makes it more dense, which makes it fall to the floor. Warm air around the floor is displaced by the falling cool air, and moves up to the window. Here, it is cooled, and falls to the floor. This creates a cycle known as a convective loop.

You perceive a convective loop as temperature loss in your home, so you turn up the thermostat to compensate. However, this just causes you to use more energy. The source of the problem, the cold window glass, still exists.


The second problem with our first statement is that new windows are rarely cost-effective. While they can reduce drafts and convective loops, the cost to purchase and install windows is often much more than what you'll get in energy savings. Unfortunately, new windows are often marketed to give consumers the impression that they will realize a significant return on their investment on new windows in energy savings. The Securities Exchange Commission is cracking down on window energy efficiency claims to ensure consumers in Maryland are given an accurate estimate of the real potential for energy savings.

#2 – Close off supply registers in rooms you don't use to save money on utility bills.

Why send cooled air to your home office when you're not in it? Closing off the supply register in the room prevents you from wasting that air, and in turn, wasting money. Right?

Actually, what usually happens is increased duck leakage and energy usage.

Under Pressure

Your HVAC system has a blower that pushes air through the supply registers and then pulls it back into the system to be filtered and cooled through the return registers. Most blowers are permanent split capacitors (PSC), which operate at one speed. Newer systems may have an electronically commutated motor (ECN), which can operate at variable speeds.

Both blowers want to push against a maximum pressure difference of 0.5 inches of water column (iwc) to work most efficiently. When you close off the supply registers to a room, this increases the pressure the blower has to push against.

An ECM blower will respond to this increase in pressure by speeding up, which uses more energy. A PSC blower is not variable speed, so it won't respond to the increase in pressure, but it won't be able to move as much air. In addition, the increase in pressure increases duct leakage, because most ducts aren't sealed. This means conditioned air is leaking into unconditioned spaces like crawlspaces.

So, the end result of closing registers is higher systemic pressure, leading to increased energy usage or decreased airflow, and increased duct leakage.

Keep up with greeNEWit's blog for more home energy efficiency myth busting! Call us today at 866.966.7630 to learn how a home energy audit can increase the energy efficiency of your home in DC, Baltimore, or Columbia.

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