Is it OK to leave damper open?

Author: Cora Heidenreich  |  Last update: Wednesday, September 3, 2025

Leaving the damper open doesn't help hot indoor air escape up the chimney. Instead, outdoor air will flow down the chimney while the cool air from your air conditioner escapes. Your cooling system will work harder than it should, leading to an increase in energy bills and shortening the lifespan of your HVAC unit.

Should damper be fully closed?

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.

When should I close the damper on my fireplace?

Close the damper when the fire is extinguished. This will prevent the heated air from escaping through the chimney and will keep water and other debris out of the flue.

Should the fireplace damper be open in summer?

In the summer, a closed damper helps to keep cool, air-conditioned air inside the home where it belongs. 2. In the winter, when you're not using the fireplace, a closed damper helps to keep cold air from swirling down into the house.

Will leaving the flue open make the house cold?

Closing the flue in your fireplace reduces the amount of warm air leaving your home; and thus you don't have the cold air coming through the vent in your bathroom. The chimney is fine, it's not leaking- but the draft of cold air is normal when you have an open flue straight up the chimney.

What happens if the damper is left open on a gas fireplace?

What happens if you leave the fireplace damper open?

Many people are under the impression that opening the damper helps cool the house, because warm air rises and will travel up the true. This is simply not true. Leaving your damper open will actually allow hot outside air to draft in, negating the effects of your air conditioning system.

Can I leave the flue open overnight in winter?

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.

Do you get more heat with damper open or closed?

The handle to open and close the damper should be above the fireplace opening. To open it, slide it to the right. To create fires that produce more heat, open the damper as wide as possible when lighting a fire. A wide-open damper will increase the amount of air reaching the fire and improve combustion.

How should damper be in summer?

In the summer, it's critical to open the dampers on the upper level and block as much air from entering the basement as possible. If you have someone to assist you, one simple method to see whether the dampers are open or closed is to have someone go up and cover each vent with their hand.

How do I stop cold air from coming down my chimney?

Replacing the standard throat damper with a new top-sealing damper keeps the cold air out of the chimney entirely. The rubber gaskets surrounding the damper forms an airtight seal when shut. It also does a better job of keeping moisture, pests, and debris out of the flue too.

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.

What is the difference between a flue and a damper?

The damper and flue are two different parts, but they are related and involved in the same function. The flue is the inside tunnel of your chimney that brings gases from your fireplace out of your home, while the damper closes or opens the access to the flue.

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.

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.

Should I open my damper all the way?

Proper Damper Use

It's important to open the damper all the way when you're using your fireplace, a partially open damper can allow smoke and gases to escape, but can also cause a backdraft that can bring cold air into the home. When you're not using your fireplace, it's important to close the chimney damper.

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.

Should fireplace damper be open in summer?

Chimney dampers keep debris out.

Bugs and other pests can already be a problem during the summer months, so keeping your damper closed can help prevent it from getting worse.

When should you close your damper?

The damper is designed to be shut when the fireplace is not in use and can be easily opened when it is. It's common to forget to close the damper after a fire goes out, however, and that leaves a big hole through which heated or cooled air can escape the house.

What should my damper setting be?

What Damper Setting to Use. With a little experimentation, you will find the damper setting and drag factor that work best for you. We recommend starting out on a damper setting of 3–5. Really focus on technique, and as you improve, you may find that a lower damper setting gives you the best workout and results.

What happens if you leave damper open?

However, it can get damaged over time, creating an entry point for rainwater or pests. Leaving the damper open doesn't help hot indoor air escape up the chimney. Instead, outdoor air will flow down the chimney while the cool air from your air conditioner escapes.

How should dampers be set in the summer?

So, you'll want to adjust your dampers to provide less airflow upstairs and more airflow downstairs—because the warm air will naturally rise. In the summer, you'll want to do the opposite. (If you have a one-story home, simply adjust the dampers to provide more warm/cool air to the rooms you use most often.)

How to maximize heat from a fireplace?

Evenly distributing small pieces of wood throughout the fireplace will increase air circulation and speed up the burning of the wood. This creates a sustainable fire, but the wood burns faster. Placing large logs closer to the fireplace will keep the fire burning longer between refills, maximizing heat output per log.

Why does my house get smoky when I use my fireplace?

A smoking fireplace is the result of chimney draft issues. In this context, draft refers to how the air flows up the chimney. Indoor air pressure affects this air flow.

Do you want the flue open or closed?

Attached to the indoor fireplace end of the flue is a damper operated by a lever. The damper can be closed or open. The damper should always be open when a fire is burning in the fireplace. If a fire is lit and the damper is closed, the gas and debris have nowhere to go but into the house, causing a smoky situation.

Do you just let a fireplace burn out?

Fully extinguishing the fire in the fireplace before going to bed is crucial. It is also important to install and maintain carbon monoxide detectors near the fireplace and ensure proper ventilation. Regular chimney cleaning is necessary to prevent chimney fires and maintain optimal fireplace safety.

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