# New Ventless Gas logs in an old chimney. Now how to block the chimney?



## keyser soze (May 28, 2007)

I have a "real" fireplace and "real" chimney circa 1912. The chimney is in pretty bad shape so I had some ventless logs installed. Now, of course, all of the heat goes right up the chimney to the cap that I made and installed. I want to divert that heat out into the room but I'm not sure if I have the best plan or not. 

My first thought is to put some sort of insulation up there (is fiberglass with no paper okay?) then make a sheet metal (aluminum?) piece that will go at the top of the FP opening to seal off the fireplace from the chimney. That should keep a lot of the heat off of the insulation. I was thinking something like JB weld to attach the new shield to the fireplace since it has some metal trim pieces up there. It can handle the heat but I'm not sure Liquid Nails or something similar can. 

Is this a horrible idea? If so, what do other people do? Thanks a lot in advance all. :thumbsup:


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## Sammy (Mar 11, 2007)

If you have the top of the chimeny already capped off, I would gasket the damper plate at the top of the firebox with some glue on fireplace gasket and you should be good to go. 

Check for a cleanout door at the bottom of the fireplace leading to the outside. That may need sealing up also.


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## keyser soze (May 28, 2007)

Thanks a lot for the response Sammy. :thumbsup:

The damper idea would be great if I had one. There is nothing but air between my new logs and the cap. There's a good sized pipe coming out of the bottom of the pedestal in the basement but it doesn't seem to be leaking anything from the fireplace. I guess my chimney was made before they started using dampers? 

I'm going to the local stove and chimney shop tomorrow to ask about installing a damper. I can't think of any other way to seal it off correctly other than my sheet metal and insulation idea. Since I posted this I've been told that fiberglass insulation wouldn't be recommended for this purpose anyway. 

Bummer.


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## AtlanticWBConst. (May 12, 2006)

Roxul fire-proof insulation: http://www.roxul.com/sw34066.asp


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## keyser soze (May 28, 2007)

Very cool. Thanks a lot Atlantic. I'll track some of that down once I get the final plan worked out.


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## Bobhilltop (Dec 31, 2021)

keyser soze said:


> Very cool. Thanks a lot Atlantic. I'll track some of that down once I get the final plan worked out.


What did you end up doing to block off the firebox flue? Curious because I have the same issue


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## chandler48 (Jun 5, 2017)

It's a 13 year old thread, so participants may not be active. You may want to start your own thread or use the messaging system to contact the OP.


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## supers05 (May 23, 2015)

Bobhilltop said:


> What did you end up doing to block off the firebox flue? Curious because I have the same issue


Blocking the chimney is dangerous and shouldn't be done.


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## Bobhilltop (Dec 31, 2021)

supers05 said:


> Blocking the chimney is dangerous and shouldn't be done.


if I use a ventless log set and keep CO monitors nearby why is it dangerous?


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## roughneck (Nov 28, 2014)

Be careful when using ventless logs. They should not be used as a primary heating source. And when in use make sure to open a door or window to allow air into the house. 
They are dangerous enough they’ve been deemed illegal in some areas.


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## Bobhilltop (Dec 31, 2021)

roughneck said:


> Be careful when using ventless logs. They should not be used as a primary heating source. And when in use make sure to open a door or window to allow air into the house.
> They are dangerous enough they’ve been deemed illegal in some areas.


 Id appreciate better perspective on this topic. I can find 100 articles on why ventless logs are dangerous and 100 articles on how safe they are. I understand that CO could be an issue, but the Use of CO detectors counteracts the concern. What I’ve found is more liberal states have banned them, and even if these there are only a few. If they are as dangerous as certain groups claim why are they not banned everywhere and associated with multiple deaths? I’d appreciate perspective


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## roughneck (Nov 28, 2014)

I wouldn’t use them in my house. 
If the CO detectors are UL approved they will not go off until 70 PPM is maintained for 3-5 hours continuous. Most fire departments will not enter a structure without breathing apparatus above 35 PPM.


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## supers05 (May 23, 2015)

Bobhilltop said:


> Id appreciate better perspective on this topic. I can find 100 articles on why ventless logs are dangerous and 100 articles on how safe they are. I understand that CO could be an issue, but the Use of CO detectors counteracts the concern. What I’ve found is more liberal states have banned them, and even if these there are only a few. If they are as dangerous as certain groups claim why are they not banned everywhere and associated with multiple deaths? I’d appreciate perspective


They mostly illegal in places that are cold enough to need significant primary heating. CO detectors are the last line of defense. There's a reason why furnaces don't use the high limits for temp control. CO is very lethal and it doesn't take much before you lose enough cognitive function to respond to a CO alarm. IE. If it goes off while you're sleeping.


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## Bobhilltop (Dec 31, 2021)

roughneck said:


> I wouldn’t use them in my house.
> If the CO detectors are UL approved they will not go off until 70 PPM is maintained for 3-5 hours continuous. Most fire departments will not enter a structure without breathing apparatus above 35 PPM.


Low level CO detectors alarm at 25 ppm after 60 seconds.


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## roughneck (Nov 28, 2014)

Bobhilltop said:


> Low level CO detectors alarm at 25 ppm after 60 seconds.


Those are the ones you want. 
But I still wouldn’t want ventless. How much sense does it make to have to open doors and windows to use the fireplace? And in addition to the byproducts of combustion, it also discharges moisture.


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## Bobhilltop (Dec 31, 2021)

roughneck said:


> Those are the ones you want.
> But I still wouldn’t want ventless. How much sense does it make to have to open doors and windows to use the fireplace? And in addition to the byproducts of combustion, it also discharges moisture.


Thanks, I appreciate your comments. Other than the insanity expensive spring loaded chimney cap dampers what might be my options for a damper above the firebox? There wasnt one there when I removed the wood burner. This is a pic looking upjust above my firebox


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## chandler48 (Jun 5, 2017)

I"m going to swim against the current for a moment. We have a set of ventless logs, primarily for the frontal heat output. Compare it to a vented set, and all the heat of a vented set of logs goes up the chimney. I placed ours in a regular wood burning fireplace, had the chimney cleaned and left a block on the flue of about 1" to allow the gasseous smell out, while, I am certain bad stuff is going up, too. We don't lose a terrible amount of heat through the crack, but feel it is a good fail safe. Now, to disclaimer. I live in the South, not in Californya, so they haven't been banned, yet, and probably won't, until all the open fireplaces without flues in Southern Appalachia are required a retrofit


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## Bobhilltop (Dec 31, 2021)

chandler48 said:


> I"m going to swim against the current for a moment. We have a set of ventless logs, primarily for the frontal heat output. Compare it to a vented set, and all the heat of a vented set of logs goes up the chimney. I placed ours in a regular wood burning fireplace, had the chimney cleaned and left a block on the flue of about 1" to allow the gasseous smell out, while, I am certain bad stuff is going up, too. We don't lose a terrible amount of heat through the crack, but feel it is a good fail safe. Now, to disclaimer. I live in the South, not in Californya, so they haven't been banned, yet, and probably won't, until all the open fireplaces without flues in Southern Appalachia are required a retrofit


That’s actually a great compromise to provide partial venting. I could install a plate with a 1” gap. this is for. Hundred year old cabin as ambiance and partial heating in northern Michigan. We have an LG mini split for primary heating


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## gkreamer (May 8, 2020)

We have ventless logs in our fireplace and the damper is still intact. I was going to try and seal it but an HVAC tech advised just leaving it as is. Don't know how much heat goes up the chimney, but it sure gets this side of the house toasty if we want.


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## supers05 (May 23, 2015)

Bobhilltop said:


> That’s actually a great compromise to provide partial venting. I could install a plate with a 1” gap. this is for. Hundred year old cabin as ambiance and partial heating in northern Michigan. We have an LG mini split for primary heating


The 1"gap should be ok. Don't use it while you're sleeping.


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