Can You Block a Heater Vent to Redirect Heat?

So you have unused rooms in your house that are being heated, and that monthly heating bill is a killer. You snap those vents shut, anxious to see your energy savings and looking forward to all that extra toastiness in other rooms. However, blocking a vent in an attempt to redirect heat, though commonly done, is actually ineffective and possibly even damaging to your HVAC system. There are much more beneficial approaches to the problem.

When you close a heat vent, airflow is not redistributed. The heated air simply flows into the duct leading to the closed vent, creates pressure and, to varying degrees, leaks out and is wasted. The Environmental Protection Agency's ENERGY STAR program notes that in the average home, 20 to 30 percent of the air traveling through ducts is lost due to holes, leaks and poorly installed ductwork. So creating pressure with closed vents is simply going to up that percentage, thus wasting energy and hiking your utility bill. This is probably not what you had in mind when you slammed those louvers shut.

Your heating cost can go up for several reasons. Furnace blowers pull return air and push it out through ductwork as heated air. Blower motors in high-efficiency systems can adjust speed to meet conditions. When excessive pressure is created, variable-speed motors accelerate to push for proper airflow. You lose efficiency and money.

The more common non-variable-speed motor loses its fight against increasing pressure and slows down. Internal heat builds, possibly cracking your heat exchanger and sending carbon monoxide into your home. So keeping your vents open is very smart. Heat exchangers are the most expensive component in your system, and carbon monoxide poisoning is bad.

Your heat system is most efficient and economical when the airflow is balanced. If you've noticed temperature variations in your home, you may want to consider having an experienced HVAC technician conduct air balancing testing and remediation to ensure even air distribution.

Your technician can, for example, spot and remedy ductwork that is loose, damaged, blocked or poorly configured. Fan speeds, thermostats and balancing dampers may need adjusting, or you may simply need to add dampers if your system doesn't include them. It's best to have a technician help you decide how many to add and where.

If you have manual dampers and can't afford professional air balancing, have your pro help you determine damper positioning that will redirect airflow to specific areas, effectively creating customized temperature zones. Such HVAC zoning can wipe out the temptation to close vents.

There are two ways to achieve zoning in your home: manually or through a programmed system. Both types make use of dampers, which are like valves inside your ducts placed close to the mouth of the air supply main trunk. Instead of closing a room vent, which allows the heated air to be wasted after traveling the length of the duct for nothing, you're creating control close to the main air distribution point.

Triggered thermostatically in a programmed system that provides a thermostat in each room, motorized dampers open in response to how much heated air is needed to raise the temperature of the room that a given damper's duct serves and then close to stop the airflow once the temperature is reached. Manual dampers are opened and closed by the homeowner simply by twisting a handle on the duct.

Many newer premium HVAC systems include this technology, but you can create programmed zoning with a preexisting furnace by adding a zone control panel, thermostatic control for each zone and zone dampers within your ductwork. Just keep in mind that to ensure the creation of an efficient system, planning it as a DIY project is probably not a good idea. Call an experienced, certified HVAC pro who will help you determine whether a zoned system makes sense for your home.