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  1. #1
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    392

    Vent free in old wood burning FP

    Is there a code that requires that the damper to be blocked open with a damper clamp when installing a VF gas log set in a masonry wood burning fireplace?

  2. #2
    Join Date
    Apr 2007
    Location
    Rossland, B.C.
    Posts
    95
    Yes. Think about it. There is carbon monoxide in the exhaust. So you or the house sitter forgets to open the damper and you leave the log set on overnight. Lots of co in your place. eventually little oxygen left. Its part of the gas/ venting code. If you want heat and nice flames put in a good quality gas insert. When its off there is little or (with direct vent) no house air leaking up the chimney.

  3. #3
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    392
    I could understand your point if it were a vented gas log set, but I am referring to a vent free. Also, all vent free units have an oxygen depletion sensor that shuts the unit down when the oxygen levels get down to an unsafe level.

    The CO level is very minimal in a properly burning and maintained unit, even if left on for long periods of time.....though not recommended.

  4. #4
    Join Date
    Apr 2007
    Location
    Rossland, B.C.
    Posts
    95
    Tell us what brand and model of vent free you have.

  5. #5
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    392
    I service and repair them and I am looking for a response from the "elders" of this site. A home inspector says the damper needs to be blocked open with a damper clamp.

  6. #6
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,137

    Cool terminology

    A "vented" logset is one where it "vents" up the chimney. A "ventfree/ Ventless/ Unvented/ lungvented" set is one where it "vents" into the living space instead of a chimney. If you open the damper and the chimney is functioning as designed then the byproducts of combustion will escape up the chimney or "vent" thus making it a "vented" logset.

    There are many newer logs on the market that now carry a duel listing as "vented" (ANSI Z21.60) and as "ventfree" (ANSI Z21.11.2b). These logs have been tested either way. The problem comes in when you install logs listed only as ventfree then open the damper. Before you laugh at me, think about this: A ventfree log is tested without huge flows of secondary air or dilution air. All this air in a vented application tends to cool the flame mantel and distort the flame often to the point of impingement. Both impingement and direct cooling cause incomplete combustion and therefore carbon monoxide. One interesting thing about ventfree logs that is not part of their testing is the long term accumulation of CO2 in the combustion chamber. Carbon dioxide displaces oxygen. Whether in the combustion chamber proper or in the room, the air concentration of O2 can drop off right as the air enters the combustion reaction. This is where using a combustion analyzer can pick up on falling ambient O2 levels, which may be a harbinger for problems ahead.

    As for the practical side, since most homes in my area have some degree of depressurization in the CAZ, I usually see a downdraft with logs and sometimes, the unit setup venting out the front of the Fp and the downdraft remains, feeding the room venting only now the flame is begining to turn dirty from cooling. Most VF I've tested with open dampers were:
    a) not maintained and very dirty to start with and
    b) producing > 25ppm CO actively. Very few have a crappy old UL2034 CO alarm, much less a high quality unlisted CO monitor.

  7. #7
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    392
    Thanks for the response Hearthman. I agree with you that most of the VF customers that keep the damper open tend to have dirtier units than those which keep the damper closed. Leaves, pine straw, critters......all tend to dirty things up a little more and that is why those customers see my smiling face every Fall.

    When did ANSI establish that new classification of heaters, the lung vented?

    Seriously, there isn't a standard or code that states that a VF when installed in a masonry fireplace must have the damper open is there?

  8. #8
    Join Date
    May 2005
    Location
    Madison, WI
    Posts
    1,078
    Does this home inspector even know what a Vent Free logset is or how it works.... as in... NO VENT. I ran into one a couple weeks ago I had to look at. They thought the fireplace exhaust melted the siding, well the siding was melted on an adjacent wall (meeting inside corner wall clearances), a foot below the cap at a weird angle. Oh look... a Low E window... hmmm....

  9. #9
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    392
    These home inspectors really have a tuff job. They must have an understanding of every system of the house, plus they have to know construction codes, roofing, moisture issues, termites.......but that is why they get paid $300+ per inspection.

    Heck, I have been in the fireplace industry since 1999 and I STILL run across things I've never seen before !!!!!!

    jtp, I had an issue much like the one you describe. Last year a home inspector said the fireplace was melting the siding at about 5 feet off the ground. I pulled the siding off and took the temperature readings of the plywood and then, I let the unit burn for 45 minutes and took temperature readings again and they were within 5 degrees of the before temps (morning sun warmed things a little). It just so happened that the sun was reflecting off of a nearby window on the exact place where the siding was disfigured !!! Mystery solved !!!!

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