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Why Closing Air Vents Actually Hurts Your Furnace

Closing air vents in unused rooms is a great way to cut down on heating bills, right?


In fact, it does the exact opposite and actually increases your energy bills. But, more importantly, closing air vents can also cause costly damage to your furnace and shorten its lifespan.

That’s not exactly the results you were looking for, right? Don’t worry. We’ll explain exactly why closing air vents causes so much damage and what you should do instead.

How your furnace blower works

Closing air vents forces your furnace’s blower motor to work harder, which eventually leads to expensive damage.

But why?

First, you need to know that your furnace’s blower system is responsible for 2 things:

  • Pulling air from your home into your furnace
  • Pushing heated air through the ducts and into your home

And that blower system is designed to work against a specific amount of pressure inside your ductwork. But closing vents (yes, even just one), increases the pressure inside the ductworks.

So now that you understand how your furnace blower works, let’s take a closer look at exactly how closed vents hurts your furnace.

How closing vents damages your furnace

If you consistently leave supply vents closed while your furnace is running, you’ll eventually be looking at expensive furnace damage. But the type of damage you’ll see depends on the type of furnace blower you have.

Here’s what we mean:

If you have an older furnace and close your air vents…

...the blower runs slower which leads to costly damageto your heat exchanger.

Older furnaces have “PSC” blower motors that only operate at two speeds: on and off. So, when these motors work against extra pressure, the blower runs at a slower pace. And if the motor can’t pull as much cool air over the heat exchanger (the part of your furnace that heats the air), the heat exchanger will eventually overheat and crack, leading to thousands of dollars in repairs.

cracked heat exchanger

If not enough cool air is blown over the heat exchanger, it can overheat and crack.

If you have a newer, energy-efficient furnace and close your air vents…

...the blower has to use more energy to keep up with the extra pressure, ultimately shortening the lifespan of your blower motor.

Here’s why.

Many newer, more efficient furnaces have “ECM” motors that offer variable speeds depending on the amount of output that’s needed at any given time. When ECM motors hit extra pressure, they can ramp up the speed to keep up. But working against that extra pressure strains the motor, shortening its lifespan as a result.

Other consequences of closing vents:

Closing air vents don’t just damage your furnace. Not keeping all air vents open can also lead to:

  • Increased energy use. if you have an ECM motor, your blower will constantly run at a higher speed to overcome the added pressure in your duct system. And the longer and faster the motor has to run, the more energy it uses.
  • Decreased comfort. If you have a PSC motor, your blower runs slower as it encounters additional pressure. And that means it can’t blow out as much hot air as it normally can, which makes you uncomfortable.
  • Increased duct leakage. According to energy.gov, most homes already leak about 20-30% of conditioned air out of holes in the air ducts. But the more pressure inside those ducts, the more conditioned air is forced out of the existing duct leaks. And that means wasted energy and higher heating bills.
closed supply vents

Closing vents can cause air ducts to leak

The solution?

Keep vents open. Yes, even in rooms you don’t use! The more vents you close and the longer you keep them closed, the more likely you’ll experience the problems above. Leaving vents open will also save you more money on heating bills and furnace repairs.

If you’re still struggling with higher-than-normal heating bills, though, you may have other problems such as air duct leakage or an inefficient furnace.

We suggest having a professional inspect your system to find the cause behind your high heating bills and suggest energy-efficient solutions.

Have questions on saving energy?

Just contact us. We’re happy to help you cut down on heating bills with our energy-efficient home comfort products.