Air cooled flue with liner questions

[velvetfoot]

Please excuse me for not fully searching before posting (which I will do), but maybe someone knows this stuff off the top of their head.

I have an insert in a zero clearance fireplace that is vented by a liner inside the original sl300 fireplace flue. If I'm not mistaken, the SL300 is air cooled, but I'm not sure where it gets the cooling air from; I'm not even sure how it works. Early on, I stuffed up the air vent on the outside of the house because I thought it was for outside combustion air, which the insert does seem to need, from the way it's performed, and the general area in front of the tove felt cold. I wonder though, if cooling air for the SL300 came from there too? I recently looked at a big Quad zero clearance epa fireplace, and I believe they told me it used a dedicated air duct from the outside for cooling air. I've only been on the roof a couple of times (metal roof, height, etc), so I don't remember what it looks like up there.

Thanks for any insight. I'll be doing some searches as well.

 

[velvetfoot]

This link to the Heatilator install instructions helped:
http://hearthnhome.com/downloads/installManuals/28396.pdf


Since there was originally only one intake, it was probably for combustion air, since that seems to have been required.
The chimney air kit inlet, required in Canada, is up higher on the chase (6 feet).
The termination cap has vents to the annular space.
So, I would hope no chimney air kit would be installed, which would potentially be sucking out room air through those vents.

 

[DIYSAVE]

the air cooled chimney get the air from the termination cap. There is an air space at the top to allow it to breath. The function of the air gap is to cool the outside pipe from getting to hot. This allows the pipe to be in close condense to combustible building material. This would not provide the stove with ouside air. I don't believe the chimney air kit would suck out the room air. it would have a solid connection to the stove, provided the stove door is shut.

 

[Woodrow]

This a great thread, I have some of the same questions. I'm trying to learn this stuff so I can make the right decisions on chimney selection. Apparently the two choices are either an insulated or non-insulated/air-cooled chimney. Insulated keeps the flu warmer so it has better draft (the hotter the chimney the more readily smoke moves up and out). An air cooled chimney is much cheaper than an insulated chimney, so it has a price advantage. However, from what I've been reading here, some posters have discussed the disadvantages of an air cooled chimney. Not only do they not draft as well as an insulated chimney, the say they can cause cold air to draft into your fireplace and from there into your house when the fireplace is not being used. I think they called it a cold air "siphoning" effect.

I've looked at the manual for the zero clearance fireplace I'm considering (FPX 36 Elite) and it touts as a cost saving advantage an air cooled chimney. They claim to eliminate the disadvantage of cold air siphoning effect by installing these simple "P" tube hoses that apparently reduce or eliminate the siphoning phenom. And assuming the firebox itself is sealed and the manual air valve is closed, I don't see how air can get into the house. Unless the cooling air is routed to the heat exchanger instead of the firebox, where you may not be able to turn off the air to the house. Still not sure about those parts of how these things work. Hopefully someone can help clarify these issues, because it's an important thing to know about either way.

 

[Trail_Time]

This a great thread, I have some of the same questions. I'm trying to learn this stuff so I can make the right decisions on chimney selection. Apparently the two choices are either an insulated or non-insulated/air-cooled chimney. Insulated keeps the flu warmer so it has better draft (the hotter the chimney the more readily smoke moves up and out). An air cooled chimney is much cheaper than an insulated chimney, so it has a price advantage. However, from what I've been reading here, some posters have discussed the disadvantages of an air cooled chimney. Not only do they not draft as well as an insulated chimney, the say they can cause cold air to draft into your fireplace and from there into your house when the fireplace is not being used. I think they called it a cold air "siphoning" effect.

I've looked at the manual for the zero clearance fireplace I'm considering (FPX 36 Elite) and it touts as a cost saving advantage an air cooled chimney. They claim to eliminate the disadvantage of cold air siphoning effect by installing these simple "P" tube hoses that apparently reduce or eliminate the siphoning phenom. And assuming the firebox itself is sealed and the manual air valve is closed, I don't see how air can get into the house. Unless the cooling air is routed to the heat exchanger instead of the firebox, where you may not be able to turn off the air to the house. Still not sure about those parts of how these things work. Hopefully someone can help clarify these issues, because it's an important thing to know about either way.

If the FPX is installed correctly, using a "p" in the install of the cooling intake I have had zero cold air come in when the unit is not burning.

 

[mitchinpa]

My Northstar has 2 outside air ducts, 1 on either side of my chase. One is for the combustible outside air intake, which can be opened or closed manually (must be open during operation). The other is vented directly to the sl300 pipe, is always open, and used for cooling the chimney. No air from that duct can get into the unit. When the fireplace is in use, I can feel air being sucked into each vent, so I know the desired affect of the 2nd duct is present.

I have a pretty tall chimney (28 feet) and have never had any draft issues. I am a firm believer that most draft issues are either from chimneys that are too short, or from current weather conditions.