Mao,

Any gas-fired device that has a pilot also has a thermocouple. It's a little metal rod that sits directly in front of the pilot flame. If the thermocouple gets cold it means the pilot is out and it triggers the gas valve to completely shut off as a safety measure. They DO wear out, and I've replaced several on boilers and water heaters over the years. It's a super-cheap part, and they're generally generic, meaning you might find a replacement at Home Depot for about $6. It's an easy DIY on a boiler but I can't say on your wall unit. Good luck-

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I'd contact the mfr. I do seem to recall directions to crack a window when using though. Maybe check the manual too.

Dear Brewster:

Thanks for your post.

The pilot on our units does not stay lit. Rather, one lightst the pilot through an ignition button and then one turns on the fireplace. Is there also a turn off mechanism for the fire if oxygen is low?

Incomplete combustion sounds right. Is it possible that a change in the atmosphere in the house which is now sealed significantly tighter than before, changed the efficiencey of the combusion? I should say that the soot was very very subtle and only in the corners of the room. What else might compromise the combustion? Do these simply wear out and need to be replaced?


Mao

Thanks for the helpful info. I have a similar situation in that it is a fireplace with a flu leading to an uncapped chimney. I was expecting that I would need to block the flu since it's been many years since the fireplace was used and I didn't want to deal with relining or create a fire hazard. No worries about my place being airtight either given it's age and the shitty window installation.

The fireplace is relatively shallow (as most of the ones I've seen in JC are, presumably since they burnt coal and not wood) and has an ornate wood surround and mantle (not original I presume?). I am concerned that the heat from the insert could be a fire hazard with the wood mantle? I could be totally off base on that. What do you think?

Did you do the install yourself? I'm definitely not up for running the gas line on my own. I can purchase the insert from a number of sources but need to find a plumber who might have some experience with this, Any recommendations? Again, thanks for the help.

Soot means you were getting incomplete combustion for some reason, not good. It wasn't shortage of oxygen, the pilot would go out in that case, as it's designed to. Unless because yours is a "fireplace" it doesn't go on and off so the pilot condition it irrenelevant. But I'm pretty sure they all have some sort of "oxygen sensor" system.

I've used a wall hanging unvented in my basement for 2 decades without a problem other than occasionally blowing clean the pilot light. They're 100% efficient since no heat goes up a flue at all, but the unvented thing freaks out the safety bugs.

Yes- I put them in five of the fireplaces in my house. I recommend them with the caveats mentioned below.
I purchased inserts that went right in to the fireplace. Initially, I had the flu opened. A draft would develop and most of the heat would go up the chimney. I was also concerned that my chimney needed to be relined. Then I closed over the flu with some flashing. The increase in heat generation was amazing. Turning on the fireplace would warm up the room in a matter of minutes. It is hard to figure out but I think it allows us to save on heating as we keep the house at like 60 degrees and then turn on the fire to warm up a room when we're in it.
Things seemed to go well for about nine years. Then a year ago, there were suddenly soot stains from the fireplace in the parlor and in the tenant's unit. It is sort of a mystery. Our best guess is that we got new windows and a set of interior doors for the front door so that the house was now sealed while it was sort of a sieve before. We think this changed the process as there would not be the endless supply of oxygen. So going on this supposition, we now crack open a window just a tiny bit when the fireplaces are on. We also have carbon monoxide monitors.
So far there has not been any soot but we really have not had it on that much.
There seems to be an intense debate about these online. Bob Villa of This Old House approves of them. Others vociferously warn of all kinds of dangers.
Good luck!

Anybody have experience with adding a ventless gas fireplace insert to an existing fireplace in an old house here in JC? Is it permitted by law in JC? Potential contractors?

Thanks