Installing Old Mill Fireplace insert - couple questions

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eggsPR

New Member
Nov 1, 2021
8
PA
Hello all,
I purchased an Old Mill fireplace insert, originally manufactured by DeVault Fab in SE PA. The model is O.M. 45 or 55, built around 1980 I think. I’ll include photos (the photos of it looking nice with white brick, was where I bought it and removed it).

I’m looking to DIY install and have some questions about the chimney liner.

Q1 The exit hole is 8”, but my flue opening is 6”. Knowing the brand/model, is it a definite no-no to reduce the 8” to a 6”, then run a 6” pipe all the way my 25” chimney?

Q2 If Q1 is no, can I bend the the 8” circular tubing for the 6” flue gap (the oval should still have the same area for emissions. Or use a pre-fab 6” oval connector to the 8” pipe? If not, that’s ok, I can just use 8” for the whole chimney, if needed.

Q3 I’m not a chimney expert, but I THINK my chimney can accommodate a 8” chimney liner (firebox flue aside). I took some photos of the outside of my chimney, it looks like it turns a bit. But, given the measurements I took, would it seem as if the chimney would be big enough to instal 8”? My house was built in 1978 if that helps, though unsure if chimney was original.

Q4 I heard that corrugated stainless steel is NOT good. Apparently it’s harder to clean and collects more creosote than smooth. If i was to buy smooth stainless steel chimney liner, where the best place to go to buy? I feel Amazon quality for this kind of thing is suspect, but have no clue who could provide the highest quality product for a decent price (even in this high-price environment).

Any help would be appreciated thanks!

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john26

Minister of Fire
Oct 27, 2008
755
Wildwood MO
The damper can be cut out and removed for more room. What is the inside dimensions of your clay tile? Also the liner should be insulated.
Just a little friendly advice I suggest finding a modern EPA insert with a 6" flue this insert will chew through wood and the window will be black most time.
 

begreen

Mooderator
Staff member
Nov 18, 2005
92,798
South Puget Sound, WA
The damper area can be cut to clear the liner. You'll need an 8" insulated liner in that chimney. Looks like it will fit, including the liner. The corrugations on a decent liner are not an issue for a rotary cleaner like the Sooteater. Avoid 2 ply, smooth wall liners. If you want better quality get a medium-duty one. Rockford Chimney Supply has decent liners. Woodland sells Champion (Olympia) which is of pro quality. You can get their preinsulated liner for an easier install. If the liner that is purchased is directional pay attention to the correct install direction.
 
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eggsPR

New Member
Nov 1, 2021
8
PA
The damper can be cut out and removed for more room. What is the inside dimensions of your clay tile? Also the liner should be insulated.
Just a little friendly advice I suggest finding a modern EPA insert with a 6" flue this insert will chew through wood and the window will be black most time.
Hi thanks for your reply. My questions regarding the oval was to prevent destroying the damper. Because what if, 20 years down the road, somebody maybe would want the damper if they got rid of the stove insert. I always know I have option to destroy the damper and surrounding brick to make the opening wider. Just asking if using a smaller oval was an option.

Are you asking what are the dimensions of the clay tile inside the Old Mill stove insert? Because I’m not even aware that my chimney had clay tiles. How would I obtain inside dimensions of clay tiles?

This insert cost me $100, but you may have a point. I was thinking that the windows would always be clear. When you say “chew through wood” do you mean that it ain’t burn the wood slowly? Meaning the technology of more modern inserts has advanced since the 80s to become more efficient?

6” insert would certainly be easier to install, since 8” would be a squeeze I’d say.
 

begreen

Mooderator
Staff member
Nov 18, 2005
92,798
South Puget Sound, WA
This is done all the time. If a notch is cut out of the damper to clear the liner, then a plate could be welded back in 20 yrs down the road, assuming open fireplace burning is permitted in 2040.
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
28,178
central pa
Hi thanks for your reply. My questions regarding the oval was to prevent destroying the damper. Because what if, 20 years down the road, somebody maybe would want the damper if they got rid of the stove insert. I always know I have option to destroy the damper and surrounding brick to make the opening wider. Just asking if using a smaller oval was an option.

Are you asking what are the dimensions of the clay tile inside the Old Mill stove insert? Because I’m not even aware that my chimney had clay tiles. How would I obtain inside dimensions of clay tiles?

This insert cost me $100, but you may have a point. I was thinking that the windows would always be clear. When you say “chew through wood” do you mean that it ain’t burn the wood slowly? Meaning the technology of more modern inserts has advanced since the 80s to become more efficient?

6” insert would certainly be easier to install, since 8” would be a squeeze I’d say.
Cut the damper frame out nicely. Throw the part up on the smoke shelf it can be fixed later if need be. And yes stoves have come a very long way in the past 40 years.
 
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eggsPR

New Member
Nov 1, 2021
8
PA
Wow thanks for the replies. My mind is pretty blown right about now.

Here I was, thinking that the older the stove, the higher quality and warmer it would be, plus the fact that the older one would have more character. But it seems the opposite is true at least on the quality/efficiency part.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,178
central pa
Wow thanks for the replies. My mind is pretty blown right about now.

Here I was, thinking that the older the stove, the higher quality and warmer it would be, plus the fact that the older one would have more character. But it seems the opposite is true at least on the quality/efficiency part.
A modern stove will give you much more heat from each piece of wood and make much less creosote. You will also be able to see the fire through the window
 
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eggsPR

New Member
Nov 1, 2021
8
PA
A modern stove will give you much more heat from each piece of wood and make much less creosote. You will also be able to see the fire through the window
Ok thanks for this feedback. While i don’t want to stray too much off thread (we’re talking about older inserts), but are there any recommendations of newer inserts that are reasonable priced? In other words, are there any new high quality inserts for less than $1000?

Or, if I search in the used market, is there a certain year/vintage when inserts became more modernized? Or brands that are tried/true where, if bought after a certain year that you can’t go wrong?

The more I type, the more this 8” Old Mill May go back to FB Marketplace.
 

eggsPR

New Member
Nov 1, 2021
8
PA
Also, is it possible to quantify the efficient loss from a newer insert to this old insert?

How much time would each insert take to burn through “a single load” of wood of the same type?

Same question applies to creosote buildup? Are we talking 3x per winter season of cleaning on an old stove versus 3x per decade on a newer one?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
28,178
central pa
Ok thanks for this feedback. While i don’t want to stray too much off thread (we’re talking about older inserts), but are there any recommendations of newer inserts that are reasonable priced? In other words, are there any new high quality inserts for less than $1000?

Or, if I search in the used market, is there a certain year/vintage when inserts became more modernized? Or brands that are tried/true where, if bought after a certain year that you can’t go wrong?

The more I type, the more this 8” Old Mill May go back to FB Marketplace.
There is nothing new under 1000 that I know of. Drolet has a nice budget option package with a liner that is pretty cheap and good quality.

As far as used the real improvements started in the mid 90s. If you find something used ask about it here. Some were not great
 
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bholler

Chimney sweep
Staff member
Jan 14, 2014
28,178
central pa
Also, is it possible to quantify the efficient loss from a newer insert to this old insert?

How much time would each insert take to burn through “a single load” of wood of the same type?

Same question applies to creosote buildup? Are we talking 3x per winter season of cleaning on an old stove versus 3x per decade on a newer one?
Burn time isn't a factor of efficiency it is just a factor of how much wood the stove holds and how low you can turn it down. The lower you turn it down the dirtier it will burn. Old stoves like yours will burn without leaving much creosote in the chimney but in doing so they send very large amouts of heat out the chimney. The lower you run it you get some efficency gains but you also start making much more creosote.
In general going from a basic steel box like you have to a modern stove you will save between 1/3 to 1/2 the wood.
Cleaning frequency will depend upon operation and wood moisture content. I know some people with old stove clean weekly. Others easily make it a year. But really the same goes for modern stoves if burning wet wood incorrectly they will make a big mess as well
 
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