Can You Save Money by Closing HVAC Vents?

closing hvac vents will not save you money

If you want save money on your energy bills this winter, get a hoodie. JK. In reality, turning down the thermostat is one of the only real ways to lower your heating bill. That still begs the question “can you save money by closing HVAC vents?’

No. Nope. Not going to happen. That is the answer, but if you want to know why, keep reading.

Physics, your HVAC System, and Your Home

Let’s say that you close the supply vents in the unused spaces and rooms in your home. It makes sense in your head that the heat you are paying for shouldn’t be wasted on unoccupied rooms. This is a common misconception though.

Two, or more objects or systems in contact with each other are always moving towards thermal equilibrium. In other words, all of the walls, furniture, and air are always moving towards temperature equilibrium. Additionally, the greater the temperature difference, the quicker the energy transfer.

Closing vents in some rooms and spaces makes these rooms colder (in the winter) making them act as heat sinks for the rest of your home. The different temperatures between the spaces and objects will accelerate the heat transfer from from the warmer spaces and objects.

Think of it like ice in a cup of water. If you put ice in cold water, then the water will transfer its heat to the ice much slower than ice in hot water.

Mold Growth

The cold air temperature of these rooms also promotes mold growth. The cold air and cold surfaces mixing with the warm air being drawn in, can cause condensation. This excessive moisture can cause mildew and mold growth.

Closed Vents Build Up Pressure

Your air conditioning and heating system consists of an air handler, your duct system (return ducts and supply ducts), and a heat exchanger (to absorb heat from the air, or transfer heat to the air). In the winter, the return vents pull cool air from the home. That air passes over the heat exchanger and gets heated. Finally, a fan in the air handler pushes that warm air through the air ducts to the different parts of the house.

pressure builds up when you close the ducts of an hvac system

Closing air vents builds up the static pressure in the system and that increased pressure has a number of negative consequences. The first effect of the added pressure is increased duct leakage. No duct system is leak free. The EPA, and estimate that the average homes ducts leak about 20-30 percent of the air moving through them. So, the extra pressure from closed vents turns small leaks into bigger leaks.

closing vents increases air leakage out of the ducts

It’s easy to see how closing a register can build up pressure and increase air leakage

The Blower

Secondly, the pressure build up from closing vents effects the blower in the air handler. The effect depends on the type of blower . There are blowers that are variable speed (ecm blower) and single speed blowers (psc blower). The increased pressure on blowers adds resistance. Accordingly, a variable speed blower will increase its speed to maintain the air flow. This of course increases energy consumption. A single speed blower will move less air low airflow to the rooms you were trying to increase airflow to.

Low Airflow and Your HVAC System

As established above, your HVAC system has a heat exchanger. This heat exchanger transfers heat (energy)to the air in the winter, and absorbs heat (energy) in the summer. Less air flow means less air is moving across the heat exchanger. Likewise, less heat is being exchanged. This also occurs when you have a dirty air filter.

Less air moving across your air conditioner’s evaporator coil (the heat exchanger) means its transfering less energy to air, and getting colder. Eventually, the coil will become a block of ice.

when your evaporator coil is a solid block of ice there is reduced air flow across it

Evaporator Coil Covered In Ice

Low air flow in the winter is even worse. This translates to less heat being transferred to air making the heat exchanger hotter. A heat exchanger maintaining hotter temperatures than designed for long periods of time can cause cracks. These cracks release carbon monoxide into the air. Carbon monoxide can be deadly.

closed vents can cause cracked heat exchangers

Cracked heat exchanger

Actual Ways to Save Money on Your Heating Bill

The number one way to save money on your heating bill is turning the thermostat down. Wear hoodies and socks indoors, and use heavy blankets when sleeping.

Windows are the next place we lose most of our energy. Making sure the exterior windows are caulked, and using thermal curtains can reduce energy loss through them. Thermal curtains also block sunlight in the summer.

Replace your HVAC filters

Get an energy audit. An energy audit will let you know where the rest of your efforts and money should be spent. You don’t want to blindly start sealing and insulating everything without knowing where most of your energy is being lost.

Bottom Line on Closing HVAC Vents

Closing your HVAC vents is a bad idea. It worsens duct leaks, offsets the balance of temperatures in your home, causes serious problems with your HVAC system, and can even cause mold growth. Instead of saving on energy costs, you’ll likely spend more and that is on top of costly repairs to your HVAC system.

Don’t do it.