Why Closing Air Vents in Unused Rooms Damage Your Heating/Cooling System

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“Closing vents in rooms we don’t use will save me money.”

Many homeowners think this, but it’s 100% wrong. It’s even worse than wrong; closing vents can actually cause your AC or heat pump to run inefficiently and eventually break.

We’ll explain why:

  • Closing vents does not save you money

  • Closing vents can actually damage your heating and AC system

Why closing air vents does not save you money 

If you close air vents, your air conditioning and heating system will not run less and therefore you won’t save money as hoped. 

Here’s why.

Imagine that you’re walking at a brisk pace, and you’re breathing by inhaling through your mouth and exhaling through your nose.  Moving air like this is how your HVAC (heating, ventilation and air conditioning) system works; the blower pulls air from the house through the return ducts and then pushes it back into the house through the supply ducts.

Now, imagine you decided to close one of your nostrils, but you continue to walk at the same pace. By doing this, you’re trying to move the same amount of air but have less pathways to do so. So, you either move less air (making you oxygen deprived), or you put in more effort to breathe comfortably.

Similarly, when you close a supply vent, you’re not causing your air conditioner to work less. All you do is increase pressure in your air ducts. Which is bad news for the blower because it’s designed to deliver a certain amount of air against a certain amount of pressure. 

Closing vents will cause different problems depending on the type of blower:

  • Permanent split capacitor (PSC) blower— Closing vents causes this blower to slow down because it can’t overcome the extra pressure. Thus your system becomes “oxygen deprived.”

  • Electronically commutated motor (ECM) blower— This blower can adjust its speed to varying conditions. When you close air vents it will ramp up to overcome the extra pressure. Meaning bigger energy bills for you.

How closing air vents can hurt your HVAC system 

OK, so now you know what happens when you close air vents. But how does that actually hurt the system?

Well, since a PSC blower (the most common type) slows down when you close vents, less air is delivered over your: 

  • Air conditioner’s evaporator coil (the part that cools the air). Low airflow causes the coil to get too cold, and sometimes turn into a block of ice. Eventually liquid refrigerant flows back to the outdoor unit’s compressor, destroying it.

  • Furnace’s heat exchanger (the part that heats the air). Low airflow will cause heat exchanger to overheat, possibly crack. 

And if you don’t have a warranty that covers these parts? You might as well replace the entire outside unit or furnace respectively because it would be more cost efficient than replacing those pricey parts.

Other issues with closing vents

So, we’ve covered the most important problem with closing vents: a damaged system. But there are a few other important problems closing vents can cause, including:

Comfort issues
Remember, a PSC blower delivers less air, the more vents you close. That means your home will take longer to cool down or heat up. 

Increased duct leakage
The average home loses 20-30% of the air blowing through it thanks to air duct leaks, according to ENERGY STAR. That means you’re paying 20% to 30% more than you should on your utility bills.

Closing vents worsens that leakage problem because the extra pressure forces MORE air out of those leaks. Think of it like jumping on top of a leaky air mattress. The mattress was already losing air, jumping on it just forces more air out of the leaks—and possibly making the leaks open even more.

Of course keeping vents open does not make the duct leakage problem go away. You would need a professional to seal the ductwork.

For the love of your budget, don’t close air vents!

Now, we don’t mean to be fear mongers here. Closing one vent isn’t going to instantly just ruin your system. But, we are saying that with every air vent you close, the above problems are more likely to happen. That’s all.

Have any other questions about the do’s and don’ts of cooling and heating your home? 

If you live in the Jackson, Tennessee area, contact us with your questions. We would love to help!