Unvented Gas Log Set in Vented Chimeny Question

andrelaplume2November 11, 2007

Ok, we had just about given up using the wood burning fireplace that came with the 20 year old home we bought. We simply do not like the smell or mess of wood.

A propane insert would be perfect. Not only would it give the ambience we want but it would throw off heat. Alas it is out of our budget at the current time.

A vented gas log set would be acceptable. No heat but a nice flame. Unfortunately law dictates that the damper must be locked in the open position all the time. When we do this now (with no logset) you can feel cold air coming in the house. Since my recliner is near the fireplace, I do not want a draft on me. Also, it seems foolish, like leaving a window cracked all the time. I could use the vented log set if I knew it were safe to insulate not only the sides of my glass door set but to somehow cover the upper and lower vents as well. In other words try to block the draft out when not using the logset. I am not sure this can be safely done.....thoughts?

That leaves an unvented log set. I know there is controversy here. We had a guy out. He said with our open floor plan moisture should not be a problem. We'd have the flame and heat of an insert for about 1/3 the cost. However, 2 of us have allergies so he reccomended against the unvented logset...though he could not explain why. Personally I think adding mositure to the room is abd idea anyway. Sounds like strike three!

So....could this be done. If I get an *unvented* logset the damper can be left closed all the time thus no draft. To eliminate the moisture / pollution issue, when I turn the logset on, what would happen if I open my damper? Would the logset function? I realize all the heat goes up the chimeney but we just want the ambience of the flame anyway. Could I do this? If I did would all the 'pollution' of the logset go up the chimeiney or would it still go in the room? Also, when the thing is not running I assume there is a pilot light lit...is that throwing mositure into the room too?

If the heatpump ever dies I'd have backup heat as well...even if the water vapor etc came into the room until it was repaired.


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I would recommend an unvented set with a fan. Open the damper when in use and let the fan circulate as much heat as possible. If the power goes out simply remove the fan( the heat will burn up the fan if it's not working) and open the damper partially to exhaust the odors that may upset your allergies, but let more heat stay in the house.

A vented set requires the damper to be opened and locked to allow a minimum opening, it does not have to locked in the fully open position. An unvented set can operate vented or unvented, but having it unvented gives you an extra option down the road if the need arises.

    Bookmark   November 11, 2007 at 10:40PM
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I am not concerned about adding heat at all. I am concerned about loosing heat when the log set is not lit.

I opened my flu a quarter inch last night. I flet no air permiating in aroind my glass door set anywhere. This morning there was air coming in. It felt like a window was cracked. I closed the flu and no more air came in. I really do not know why sometimes it comes in and sometimes it does not. I tried running fans and stuff in the house to see if something is sucking the air in but that did not seem to be the issue.

So, I really want that flu closed when no fire is burning. It sounds like I can do that with an unvented set.

I'll just open the flu when the unvented set is burning and the smell, mositure, pollution and heat all go up the chimeney right? Thats the big question.

If yes, when I am done burning the log set I will shut it and close the flu. Now the question is, how much junk is the pilot light burning with the flu closed throwing in my house?


    Bookmark   November 12, 2007 at 9:12AM
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the pilot is not even an consideration.

I think we should revisit this damper thing though. I guess I misread earlier but your second post clarifies what I misread perfectly. When you open the damper you should have air escaping through the damper, not air coming in from the damper. This means the pressure inside your house is less than the atmospheric pressure outside and opening the damper allows the house to suck in air to try to equalize the pressure difference. In other words you have a negative pressure issue. This also means that your house will suck in cold air from outside through any crack available, making it harder to heat, not horribly so, but still. I have no explanation for why this would be the case but it might be worth looking into on your part.

Take notice of what is going on when you can feel air coming in through the damper, is the central unit running...etc. I would also suggest posting this: "negative pressure causes" in the heating forum, and search the web some as well for clues.

    Bookmark   November 12, 2007 at 5:52PM
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Thanks all. Since I do NOT always feel the air coming in with the damper open, maybe its a bath fan or something that runs and creates the issue. I'll have to investigate. I guess when I am not feeling the air coming out, my heat must be going up snd out...not good either!

So is there a downside to using the unvented set AND just opening the damper when in use? Sounds like the pilot is not an issue.

I just want to insure two things. If I open the damper only when in use, all the smell/moisture (and heat) go up and out. I do not want any ill affect on our allergies or any excess mositure coming in.

Secondly, I want to be sure the flame still looks as good as a vented set...or at least close.

Thanks again!

    Bookmark   November 13, 2007 at 8:50AM
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If your main objective is a pretty flame, and not heating your room, but you worry about a draft caused by a damper locked in a partly open position, you might consider glass doors to seal the firebox when not in use. That should solve the draft problem. But good glass doors that do what you want will not be cheap. I would definitely NOT get unvented. I don't think they're safe because they use up oxygen in your home and adversely affect indoor air quality.

    Bookmark   November 13, 2007 at 1:46PM
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Yes. My door set is leaky. I took them off and noticed no insulation on the sides and top. Hopefully it is safe to add some. The tops of the bifold doors are a bit leaky too. I wonder it there is some thing I can put there to seal them better that is NOT flamible. Otherwise I think a better door set would solve my problem with the vented log set. You are right. I ran out at lunch to HD and Lowes and they have sets for $250 or less BUT the local fireplace store has them starting at $675.....thats out of our range! I am guessing there is a huge difference. Out set looks nice though my wife wishes it were black instead of bronze. In fact I was going to repaint them with high heat paint. Maybe I'll just try s set from Lowes....likely not as good as $&700 set but hopefully better than the 20 year old set on there now that needs to be insulated and painted!

Again, if I use the unvented set with the damper OPEN, I'd think I'd be eliminating the pollution issue but maybe not. If I knew it would eliminate that then I'd think they would be the way to go.

    Bookmark   November 13, 2007 at 3:44PM
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Last week we had a vent free log system installed in our existing wood burning fire place. Our clay chimney was in such bad shape that it made sense to cnovert the wood burning fire place to a gas system. The vent free logs were chosen because they provide an excellent source of heat, not just something pretty to look at. The vent free logs are used with the damper closed and they give out a ton of heat, we were shocked. If it gets too hot we can open the damper. However, one issue that we ran into was that the mantel was getting extremely hot so we are having a hood made to fit the opening of the fireplace. We had the gas line and log set professionally installed which I strongly recommend from a local fire place store. The vent free logs are very safe and can be researched on-line to answer all your questions.

    Bookmark   November 17, 2007 at 11:59PM
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