Installation of insert into fireplace : Throat of damper too small 4 vent

frederic · Oct 14, 2012

I am just venturing into the world of stoves and inserts after putting up with a conventinal fireplace (built 1955). I am considering a century cw2500 for it's price and seemly decent reviews. Fireplace measures 36" by 28" and 22 deep at the bottom with the back curving to just 11" from front to back at top. First problem:

The throat of the damper is too small for 6" vent by at least 3/4". Looks like removing it would be nearly impossible. So anyone ever ground or sawzalled damper throat to achieve clearance? I figure a good welder could repair it if anyone was out of their minds enough to convert back. Comments please.

Second, the hearth extension is level with the floor and the manual staes that in this case, the R value of the extension should be at least 1. It is 1" thick tile with according to the table doesn't even come close. Any advice on would could be done?

Any comments on the century cw2500 insert would be appreciated. Thank!
Fred

begreen · Oct 14, 2012

An angle grinder will work much better than a sawzall here. Wear a mask, ear and eye protectors.

The hearth will need insulation. For the lowest profile put down 1/2" of micore, 1/2" of cement board like Durock NextGen, then tile.

frederic · Oct 14, 2012

begreen said:
An angle grinder will work much better than a sawzall here. Wear a mask, ear and eye protectors.

The hearth will need insulation. For the lowest profile put down 1/2" of micore, 1/2" of cement board like Durock NextGen, then tile.

I looked up micore 1/2 " board which has an R value of just over 1. That should be suitable for the hearth extension with tile over it? I am trying to keep it level with the floor. Cement board, micore and tile will be too high. Thanks BG!

begreen · Oct 14, 2012

You can not tile directly onto the micore. It's too fibrous and makes a poor substrate. They do make it in 3/8", but that may be harder to find. I'd just put a nice sloping picture-frame curb around the hearth made of wood or tile bullnose and it will be fine.

frederic · Oct 14, 2012

begreen said:
You can not tile directly onto the micore. It's too fibrous and makes a poor substrate. They do make it in 3/8", but that may be harder to find. I'd just put a nice sloping picture-frame curb around the hearth made of wood or tile bullnose and it will be fine.

BG: So if it is raised a 1/2" or so the hearth becomes higher than the fireplace floor. Won't this be a problem with insert installation? Thanks a million from a firebox newbie!
F

webby3650 · Oct 14, 2012

A grinder will work well, but I often need to use a sawzall as well, the grinder won't cut deep enough sometimes. Don't worry about ever reusing it, a lock-top damper/cap can be installed in the event that someone wants to use the fireplace again. You would want to raise the hearth as well as the fireplace floor, this way it's all the same level. Are you sure the hearth isn't solid masonry? The hearth should be part of the fireplace structure, but it isn't always. Can you get under it to see if it steps out to carry the hearth as well as the fireplace? If it's all masonry, there no need for R-value.

cygnus · Oct 14, 2012

I 'ovalized' my 6" liner through my damper so it remains fully enacted. I had to narrow it down a lot more than 3/4" and it works great. Just a consideration for resale. I could rip everything out and put the fireplace back the way I got it with no problem.

Here's a pic of the rig I used to help guide and pull the liner from the bottom as my buddy fed it from the roof. I ovalized the leading 4-5' as shown just to get thru the damper then straightened out the end to fasten to the insert.

rwhite · Oct 14, 2012

If you seen the amount of creosote and other such junk hiding behind the smoke shelf (ready to burn at any time) I think you would not hesitate to cut the thing out. Even removing the damper which was 7" was not enough to clear the liner because the bend it must make. I had to remove 2 brick deep as well. If you cant find micore locally hit the used building supply or thrift shop. Office cubicle panels are made of them. It will look almost like pressed newspaper but will have Micore 300 written on it. I already had a tiled hearth but it didn't provide the clearances so I built this to just sit over it. The insert sits on 2" concrete pavers to bring it all level

Here is the link into my venture of installing an insert and building out a hearth.

https://www.hearth.com/talk/threads...t-it-installed-and-running.75933/#post-971461

And here is a link showing damper removal.

https://www.hearth.com/talk/threads/what-i-learned-while-removing-my-damper.76609/#post-971457

webby3650 · Oct 14, 2012

cygnus said:
I 'ovalized' my 6" liner through my damper so it remains fully enacted. I had to narrow it down a lot more than 3/4" and it works great. Just a consideration for resale. I could rip everything out and put the fireplace back the way I got it with no problem.

Here's a pic of the rig I used to help guide and pull the liner from the bottom as my buddy fed it from the roof. I ovalized the leading 4-5' as shown just to get thru the damper then straightened out the end to fasten to the insert.

You can also order the liner ovalized at the end. Sometimes it still won't fit through the damper, and is often too far forward in the fireplace to make the connection. Ovalizing can also cause draft issues, especially if the chimney is short.

begreen · Oct 14, 2012

frederic said:
BG: So if it is raised a 1/2" or so the hearth becomes higher than the fireplace floor. Won't this be a problem with insert installation?

Not if the firebox floor is shimmed to match the final desire height. This can be done with a layer of cement board if necessary.

cygnus · Oct 15, 2012

webby3650 said:
You can also order the liner ovalized at the end. Sometimes it still won't fit through the damper, and is often too far forward in the fireplace to make the connection. Ovalizing can also cause draft issues, especially if the chimney is short.

I ovalized with a 2x6 working it very slowly down to size. The few feet to get through the damper probably took about 10 minutes and figured I just do it myself instead of adding to cost. I did slightly ovalize the full length also just to be sure it wouldn't get hung up on any joints in the terra cotta during the install. I think that was a good decision as it slid right down.

Draft may be affected but I think it's very limited. My liner is 30' and insulated so I have lots of draft and don't really think the ovalizing affected it much at all. The area of the oval is very close to the full area of round liner and the most oval portion is just a few feet to get through the damper. Without pulling out my Fluid Mechanics books, I can't see how it would be any worse than a 90 degree, or maybe a 45, in stove pipe. Air control, insulation and dry wood are MUCH bigger factors in chimney performance than a short length of moderately ovalized liner.

frederic · Oct 15, 2012

webby3650 said:
A grinder will work well, but I often need to use a sawzall as well, the grinder won't cut deep enough sometimes. Don't worry about ever reusing it, a lock-top damper/cap can be installed in the event that someone wants to use the fireplace again. You would want to raise the hearth as well as the fireplace floor, this way it's all the same level. Are you sure the hearth isn't solid masonry? The hearth should be part of the fireplace structure, but it isn't always. Can you get under it to see if it steps out to carry the hearth as well as the fireplace? If it's all masonry, there no need for R-value.

No, the hearth extension is just tile and mortar with the subfloor below. If I raise the hearth and retile what is used on the fireplace floor to get it to the same level as hearth? Is fireplace tile available from a good seller of stoves and inserts? Thanks!

thechimneysweep · Oct 15, 2012

Next time you're having a milk shake, try pinching the straw even the teensiest bit, and you'll get an idea why we don't advocate ovalizing the liner. Ovalizing also increases the odds you might get a brush stuck when sweeping. Enlarging the damper opening is the better option.

Many fireplaces have a drop-down of an inch or more from the hearth to the fireplace floor. Most inserts have rear leveling legs to compensate.

sksmass · Oct 15, 2012

Here's a thread all about this:
https://www.hearth.com/talk/threads...tting-the-damper-ovalizing.69998/#post-936874

Cutting the damper out is pretty common. I did it with an angle grinder. Just save the piece in case anyone wants to weld it back. No one ever will.

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Installation of insert into fireplace : Throat of damper too small 4 vent

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