Damper stops & fesh air vent - InspectionNews

David Macy · #1 (**permalink**) 07-16-2007, 12:48 PM

I have a few questions pertaining to damper stops and exterior venting.

Does someone have the reference codes for damper stops?

Also pictured is a exterior vent for a framed pre frabricated chimney that vents to the exterior. Fireplace has a gas starter and is used for wood burning.

Glass doors that open. Damper controlled and flue goes to exterior.

The vent pictured is the 2nd question. Is this for intake air? Can someone explain the function of the vent?

I removed the insulation from the vent & damper and told the seller & buyer to not install insulation.

Thanks

Phillip Stojanik · #2 (**permalink**) 07-16-2007, 03:22 PM

Many of the pre-fabricated fireplace units have an air intake that is supposed to bring in air from the outside to aid in combustion and to help keep from depressurizing the structure and adversely affecting the flue's ability to draft properly. I have yet to see one that is supposed to be stuffed full of insulation material like the one in your photo.

The only damper stops I am familiar with are those on the flue damper that are required when a gas burning appliance has been installed in the firebox. Such appliances are UL Listed and are often shipped with a damper stop device that prevents the flue damper from being closed 100%. The intent is to have the damper always open at least some percentage to avoid the inadvertent introduction of carbon monoxide into the living space.

As far as the code goes...it is stipulated that gas appliances are to be installed per the manufacturer's specifications in order to maintain its Listing. If the installation instructions say to install the provided damper stop device then it is needs to be installed. Statements of this kind are typically found under the general provisions of the pertinent code section.

John Arnold · #3 (**permalink**) 07-16-2007, 04:03 PM

Try searching the archive. Bob Harper has written quite a few times about blocking the damper open. If memory serves, he has said that the damper needs to be blocked completely open.

Bob Harper · #4 (**permalink**) 07-16-2007, 04:47 PM

John, you're got me confused. If this is a woodburner, then it must vent vertically through the listed chimney. This appears to be a combustion air vent plugged full of bird nest detritus, which means the inlet screen is compromised. If the slinky to this vent is compromised, then you can have bird nests directly on top of the fireplace. I've already worked a fire case involving this mechanism.

As for damper stops and gas logs, the codes and log listing state the minimum permanent net free opening of X amt. based upon the input BTU rate. For most vented logs, this means 50 square inches, which equates to an 8" round flue blocked wide open year round or taken out. Now, gas log lighter pipes are unlisted and have no provision in the codes for damper clamps. The thought is, they are being used solely to ignite green wood. Woodburning requires the damper be opened fully.

The IRC now requires air kits installed on all fireplaces. It just doesn't require that you use them. ;-)

Do you have a pic of the Fp or make and model? ----you knew I was going there now didn't you John? [grin]

Bob

John Arnold · #5 (**permalink**) 07-16-2007, 05:57 PM

Sorry, Bob. I was attempting to respond to Phillip's:

"The only damper stops I am familiar with are those on the flue damper that are required when a gas burning appliance has been installed in the firebox. Such appliances are UL Listed and are often shipped with a damper stop device that prevents the flue damper from being closed 100%. The intent is to have the damper always open at least some percentage to avoid the inadvertent introduction of carbon monoxide into the living space. "

My bold, and probably my bad.

Phillip Stojanik · #6 (**permalink**) 07-17-2007, 05:05 AM

Quote:

Originally Posted by John Arnold

Try searching the archive. Bob Harper has written quite a few times about blocking the damper open. If memory serves, he has said that the damper needs to be blocked completely open.

If wood is being burned then the flue damper needs to be 100% open. I was referring to damper stops and installed gas appliances. The "problem" with a gas appliance is that it produces no smoke and little smell yet (unless its Listed as being ventless) does produce combustion byproducts that should not be exhausted into the living space. (We can discuss the virtues and detriments of "ventless" systems another time.)

When burning wood, a closed damper becomes readily apparent to the user as the sight/smell of billowing smoke out of the firebox into the living space (not to mention the sound of the smoke dectors going off) is a not so gentle reminder that one has forgotten to open the damper. This is not the case though with a gas buring log set and the damper stop is part of the "idiot proofing" (for lack of a better term).

Michael Thomas · #7 (**permalink**) 01-07-2008, 10:47 AM

What are the rules regarding sealing the damper and/or plugging or abandonment of a chimney in a previously wood-burning masonry fireplace which has vent-free log set installed?

John Arnold · #8 (**permalink**) 01-07-2008, 12:51 PM

Quote:

Originally Posted by Michael Thomas

What are the rules regarding sealing the damper and/or plugging or abandonment of a chimney in a previously wood-burning masonry fireplace which has vent-free log set installed?

Bob Harper, that know-it-all, has posted about closing up / sealing unused chimneys, i.e., that this is a no-no. I believe the idea being that the house changes hands and the new owner doesn't realize the flue is blocked, changes back to wood burning and ... yada yada ... he wakes up dead.