Tag Archives: damper clamps

An open fireplace damper is like an open window

Money flying out of walletDuring these dog days of summer, many homeowners are making a very expensive mistake. Here in San Diego, homeowners are opening their SDG&E envelopes and getting sticker shock with astronomically high utility bills. What homeowners don’t realize is that by making a very simple change, they can save a great deal of money.

 

So here’s the tip: CLOSE YOUR FIREPLACE DAMPER!

What is a flue and what is a damper?

These terms are not interchangeable.

The flue is the vent pipe that allows gases, smoke, and heat to exhaust out of the home. The damper is a metal plate that opens and closes off the flue. When the fireplace is not in use, the damper should be closed in order to close off the flue.

Dampers are typically located at the bottom of the flue pipe, just above the firebox in the throat of the system.

Dampers typically have a rod or handle that you can push forward or backward. Other dampers move side to side, while others pull down or push up. It all depends on the type of fireplace you have.

In some cases, dampers can be located at the very top of the flue pipe with a chain that comes down and hooks in a bracket inside the firebox. These are called “top-mount” dampers. To close these dampers, you pull the chain down and hook it in the bracket. To open, you unhook the chain from the bracket and the damper plate pops open at the top because it’s spring activated.

Not all fireplaces have dampers but most do.

Why it’s important to close dampers

Here in San Diego, because our weather is typically very mild, many homeowners leave their dampers open all the time, not realizing that by doing so, their air conditioner is working overtime, costing the homeowner unnecessary money.

When the air conditioner is on and the damper is open, hot air from the outside is being drawn down the chimney and into the room. You’re actually sucking the hot air into your house. It totally defeats the whole purpose of using your air conditioner. In addition, if your chimney is dirty, you’re also sucking particulates of soot, which is a carcinogen, into the home. This is another reason to keep your chimney clean and your damper closed when the chimney is not in use.

It’s not just summertime that open dampers create problems. During winter time, when it’s cold outside, if your damper is open and you turn on your furnace, all you’re doing is sucking cold air into the home. This totally defeats the whole purpose of having your furnace turned on. So keep the damper closed during the winter time when you’re not using your fireplace.

How to tell if dampers are open

It’s not always easy to tell if your damper is open or closed. In fact, this is the #1 question when homeowners call me about their chimney. Unfortunately, because dampers open differently based on what type of system you have, I can’t give a conclusive answer over the phone. Here are several ways to tell if your throat damper is open or closed:

1) It’s actually easier to tell during the daytime than at night. One way you’re going to see more light from the sun than the other way. Keep in mind that because chimneys are not built straight up and down, you’ll rarely ever be able to see blue sky but one way you’ll be able to see more light than the other.

2) With a flashlight, look up from the firebox into the flue pipe. You should be able to see the metal damper plate in the throat of the system. When it’s open, you’ll actually feel more air movement than when it’s closed.

3) Light a match and blow it out. Immediately place the match close to the damper. The smoke from the blown-out match will indicate if the damper is open or closed.

4) Of course, there’s always the method that many homeowners use. Light the fire on a wing and a prayer. If it smokes out your house, then you know your damper is closed. We do not recommend this method due to the smoke damage to your home and to your lungs!

Here are examples of open and closed dampers.  This is looking from the firebox (where you make the fire) up the flue pipe:

Closed damper for masonry
Closed Damper for Masonry Chimney
Closed Damper for Pre-Fab Chimney
Open Damper for Masonry chimney
Open Damper for Masonry Chimney
Open Damper for Prefab Chimney

An Important Tip to Remember about Dampers

It’s not easy to remember, from season to season, which way the damper is open and which way is closed. To help me, I made a label and stuck it to the underside of the mantle which tells me which way to open. If I forget, I know where to look to find out easily.  Here’s the label I had on the underside of my own mantel:

Damper label

Not all dampers open this way so find out which way yours is open and make a label to place on the underside of your mantel.

Damper clamps

If your firebox is plumbed for gas, either for gas logs or a log lighter for burning with wood, then the damper has to be locked in a fully-open position with a clamp. You will not be able to close your damper. This is required by code in most areas of the United States. In this case, you may consider glass doors on the front of the fireplace.


Open window with curtainsRemember, an open damper is the same as an open window. Would you leave a window open when your air conditioning or furnace is on? Then why would you leave your fireplace damper open?

Fireplace Damper Clamps

Damper ClampThe issue of damper clamps can be confusing, not just to homeowners but to home inspectors, utility companies, government building departments and even amongst chimney professionals. In many cases, this issue rears its ugly head during the stressful time of purchasing or selling a home.

What is a damper clamp?

Damper clamps are also referred to as damper stops, damper locks or damper flue clamps, but the terms are all synonymous. They are typically a small C-clamp or steel beam clamp. The damper clamp is designed to lock the damper in a fully-open position. The damper is the metal plate that closes off the flue pipe. The purpose of the damper is to prevent heat loss from the home.

When is a damper clamp required?

damperwithclamp300x200
Damper clamp in position on a prefab fireplace to prevent closing the damper

A damper clamp is required by code when artificial gas logs  or a log lighter are present in an open fireplace. When gas logs are in use, the fuel (whether natural gas or propane) is going through the combustion process. The by-product from combustion is carbon monoxide, which is a colorless and odorless gas. If the damper is not open, the carbon monoxide cannot be exhausted up and out like it should, but instead will be drawn into the living area in which case the homeowners can get very sick and, in extreme cases, may die.

According to page 234 of the 2016 California Building Energy Efficiency Code for Residential and Non-Residential Building, Sub-Chapter 7/Section 150.0, 1C” When a gas log, log lighter, or decorative gas appliance is installed in a fireplace, the flue damper shall be blocked open …”

Why is a damper clamp required with gas logs?

If you’re burning wood in your fireplace and you forget to open the damper, you’re going to know it right away because the room will fill with smoke. If you’re burning gas logs and you forget to open the damper, you could become very sick or, in extreme cases, you can die because the gas loses its odor and is colorless, odorless and toxic and now spilling into the living area. For that reason, code requires the damper is locked in a FULLY-OPEN position so you can’t make that mistake.

Damper clamps are especially critical in the case of rental properties where the fireplace has artificial gas logs or a log lighter. If a tenant forgets to open up the damper and death results, besides the horrific loss of life, the heirs of the tenant will sue the homeowner and/or property management company due to the negligence of not having a damper clamp to lock the damper open.

Can the damper be locked partially open?

Manufacturers’ installation instructions for artificial gas log sets specifically say that dampers must be locked in a “FULLY-OPEN POSITION.” Some professional installers will lock the damper partially closed to reduce the heat loss from the home when the gas logs are not in use as well as to bring more heat into the room when the gas logs are in use. However, a partially-closed damper may restrict the draft enough to cause gas spillage into the living area when the gas logs are on. For that reason, gas log manufacturers specifically state that the dampers be locked fully open. Professional gas log installers may open themselves up to liability if they lock the damper partially closed.

With the damper locked open, how can I prevent heat loss from my home?

When not in use, a fully-open damper is like having an open window all the time and you will lose a great deal of heat from your home. This is a major disadvantage to gas logs or a log lighter. Even if you’re not using the gas logs and you turn on your central heater or furnace, it may actually draw the cold air down the flue and into the room, bringing the cold air in. To prevent heat loss, install glass doors in front of the fireplace. Keep in mind, in the case of prefab fireplaces, glass doors are not always available or listed with the system so glass doors may not always be a viable option for prefab systems.

Be very careful about putting glass doors on prefab fireplaces.  You can only put the EXACT glass doors that are SPECIFICALLY designed for that exact manufacturer and exact model of the system.  If you put on the wrong glass doors on a prefab fireplace, you will void out the listing on the system and can cause a potentially dangerous situation because the prefab system can overheat during a fire.

Is a damper clamp required with a log lighter used with wood burning?

There is a wide range of opinions on this question and the answer is that a damper clamp is still required with a log lighter. A log lighter is a round pipe under the grate, used to easily start a wood fire. You place the wood on the grate, turn on the gas and after about 10 minutes, turn the gas off. There’s no need for newspaper or kindling and it makes it very easy to start a wood fire.  According to the above-stated code, if there is a log lighter present inside the firebox, the damper must be locked fully open.  However, if the firebox is plumbed for gas but the gas is capped off, no damper clamp is required.


Having a damper clamp in place with gas logs or a log lighter is frankly a no-brainer, not only for the safety for you, your family members and/or tenants but for your liability as well. The lack of a damper clamp with gas logs or a log lighter WILL also be noted by a home inspector during a home sale.  Some local utility companies will “red tag” your system if a damper clamp is not installed.  A damper clamp is a critical safety issue when you have artificial gas logs or a log lighter!

One last caveat: Check your local jurisdiction to see what your local codes are for your area.  This above-mentioned code is a California Code.

[This blog was updated as of 3/27/18.]