Why Closing Vents Doesn’t Improve Energy Efficiency

12/31/2015

When it comes to saving money, lowering the thermostat in the winter saves you on energy costs, so it makes sense that heating only the room you need to keep warm would also save on energy wouldn’t it? It would be possible if closing vents adjusted how your furnace blower works.  Unfortunately, most blower fan motors are not designed to work that way, meaning your furnace is designed to run while all of the vents are open.

Why it Won’t Save You Money

Your furnace burns fuel at a set rate to generate heat.  Your furnace comes with two basic settings: ON and OFF.  If you have a multi-stage furnace, there’s an energy-efficient setting designed to help maintain the heat in your home, but it is simply a lower intensity ON state.  When your thermostat detects that the temperature has fallen below the set comfort level, it turns on the furnace and engages the blower fan to circulate air throughout the home.

Your furnace will shut off again once the room with the thermostat reaches a comfortable level. Closing the vents in another room is unlikely to increase how quickly the main room is heated.  Most of what’s accomplished by closing vents is an increase in back-pressure against the blower fan.  The motor in your fan continues to run at full force and, depending on the type of motor installed, will either increase the amount of energy used to maintain the force of air or will slow the rate of rotation as it becomes harder to turn the fan against that back-pressure.  Both of these will decrease the efficiency of your unit, losing whatever gains you might make from closing off other rooms.

What Closing Vents Will Actually Do

First, all of that extra pressure has to go somewhere.  It will leak out through gaps in the vents or it will escape through cracks in your ventilation system.  At best it will use existing leaks but it is likely that new leaks will form in seals and joins, leaking heated air into wall spaces.  These additional leaks mean a decrease in overall efficiency later when you reopen those closed vents.

Strain and extra stress are added to your heating system.  All of that extra air pressure will restrict airflow and increase the level of heat within your ventilation ducts.  Compound that with a dirty filter or air ducts and you end up with extra wear on your blower motor.  It has to work harder to force air through your ventilation, reducing its own lifespan and leading to costly repairs later on.

All of the excess heat ends up somewhere, and much of it will stay inside the heat exchanger. That extra heat will cause the exchanger to expand, meaning it can get hot enough to crack the exchanger.  Not only is that a repair you don’t want to have to make, a cracked heat exchanger can leak carbon monoxide gas into your home. Odorless and invisible, CO gas is deadly.  Which is why we always recommend keeping CO detectors in proper working order at all times.

What You Should Do

If you want to regulate heat in your rooms to save on energy, you should consider using a zoned heating system instead.  Ductless heating systems generate heat for single rooms, rather than for your entire house.  They’re more energy-efficient per room than a large scale heating system and will allow you to control each room independently for added comfort.  They are designed to be used independently, while a central heating system is designed to heat an entire home every time it’s turned on.

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