What happens if the damper is closed?

Author: Ms. Peggie Goodwin  |  Last update: Friday, June 6, 2025

You need to open the damper when you start a fire to allow for proper airflow and let the smoke out. A closed damper can restrict airflow and become a safety issue since smoke would fill your house.

Is it OK to leave fireplace damper open?

OPEN OR CLOSED? The damper should be kept closed when there is no fire or coals burning. Warm air from your home will not be lost up the chimney when the fireplace is not being used. Fully open the damper before your start a fire and keep it fully open until all embers and coals have burned out.

Does closing the damper make the fire hotter?

Use the Damper to Control Heat

Depending on how far open or shut you have the damper, your fire will be smaller and cooler (and burn for longer), or larger and hotter (and burn more quickly). The damper is usually located at the bottom of the stove.

Do you want the damper open or closed?

When you aren't using your fireplace, it should be closed to prevent heated and cooled air in your home from escaping. A closed damper also stops cold drafts from coming down the chimney. When you are using your fireplace, it needs to be open so that smoke can vent outside.

What does closing damper do?

When dampers are open, they allow airflow unimpeded. When closed, they restrict airflow. Thus, HVAC dampers play a role in regulating interior temperatures as they control the flow of hot and cool air to the various rooms of your house. HVAC dampers are usually inside your ducts, close to the main air handler.

Chimneys Explained #16 - Chimney Dampers

What happens if damper is closed?

A closed throat damper will cause smoke to fill your house immediately when you start a fire. If you have a chimney with a closed top-mount damper It might take a few minutes for smoke to start filling the house, but you will eventually notice that there isn't enough airflow.

How to tell if dampers are open or closed?

Place your hand near the air vent or register while your HVAC system is running. If you feel air flowing, the damper is open. If there is no airflow, the damper is likely closed.

What position should my damper be in?

HVAC Damper Open Or Closed In Summer/Winter

In most homes, dampers going to the upstairs are open in the summer and closed in the winter. By closing the dampers to the upstairs in the winter, it allows for the heat to rise naturally after first being introduced into the lower levels of the home.

How much to close a damper?

After you open the damper and light the fireplace, wait a few minutes for the fire to build into a productive fire. Then, partially close the damper about one-third of the way. This will retain more heat inside your home, leaving plenty of room for the fumes to vent.

How to adjust vents for winter?

Adjust Your Supply Vents For Maximum Heating in the Winter

Closing supply vents in higher locations by your ceilings while opening lower ones on floors or close to baseboards. Doing this will direct more warm air to the floor, where it will rise to heat the whole space.

Does closing a damper increase heat?

By not creating an airtight seal, these dampers minimize the strain on the system. In summer, you can close the dampers downstairs so cooler air reaches upstairs rooms. But in winter, closing upstairs vents halfway allows heat to rise.

How to properly use a fireplace damper?

First, ALWAYS ensure the damper is fully open BEFORE lighting the fireplace. Otherwise, you and your home may be covered in soot and ash if the chimney back puffs. The damper has notches, so you can partially close it (throttling), like a manual stick shift in a car.

What causes a fire damper to close?

They work when the fire's heat causes the room's average temperature to rise to about 165 degrees Fahrenheit. That heat causes the fusible link, which is holding the damper open, to melt and allows the damper to be closed. There are two types of fire dampers, dynamic and static.

What happens if you forget to close the flue?

If the flue is left open after the fire goes out, all the heat generated will escape. Closing the flue will keep the heat inside; you must be careful not to close it too quickly, otherwise you may trap smoke and carbon monoxide in your home. It's best to keep the flue closed when the fireplace is not in use.

How long does it take for a fire damper to close?

Actuator operated fire dampers are equipped as standard with a thermoelectric fuse, that activates the closing of the damper after the reaching or exceeding the ambient temperature of 72 °C. The actuator power circuit is interrupted and its spring closes the damper blade within 20 seconds.

How much heat is lost through an open chimney?

Warm air from your home naturally rises, and an open chimney provides an easy escape route. In fact, it's estimated that up to 30% of your home's heated air can be lost through an open chimney when the fire isn't in use.

Will closing damper put out fire?

No, never do this. The damper to your fireplace must be completely open when a fire is burning. If you close the damper even slightly, you risk allowing smoke and other dangerous contaminants from the combustion process into the house. And remember, the most dangerous by-product of combustion is carbon monoxide.

Should damper be open or closed in summer?

Closing your fireplace keeps your space cool.

If you keep your damper open, your air conditioner will have to work much harder to keep your space at a comfortable temperature. This can result in higher energy bills, and warm, humid air from outside can still make its way into your space.

Why would a damper be closed?

It connects to a lever that rotates to redirect airflow throughout your ductwork. For example, opening a damper allows the temperature-controlled air from your furnace or air conditioner to flow through that area of your duct system, while closing it restricts that airflow.

How do I know if my damper is bad?

If the damper is closed and you are feeling low airflow, or none at all, it is most likely a bad damper.

How do I know if my damper is open or closed?

A flashlight should illuminate a throat damper well enough to see if it's open or closed. For a damper at the top of the chimney, you'll have a chain that controls the device. If you can pull on the chain before it jumps back up, the damper is open. You can also start a small fire as a test.

What is the position of a damper?

A damper is usually placed near the end of each duct run and has three positions: closed, half-open, and fully open. The closed position blocks airflow completely, while the half-open allows only partial airflow. The fully open position allows maximum airflow out of the ductwork.

Is it OK to leave damper open?

One common myth about chimneys is that leaving the damper open during the summer helps “air out” the chimney. However, the opposite of true. Leaving the damper open just fouls up the rest of your home, and does nothing to clean your chimney.

Are dampers bad for HVAC?

Dampers are an important part of HVAC systems. Consider a dam, for example. When closed, a damper prevents the air from going across it like a dam does with water. HVAC dampers are an important part of your zoning system.

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