I can help with this.
I was both a Firefighter and a Licensed Chicago Mason Contractor.
(these comments pertain to Chicago metro area construction norms)
In most home built since the 50's, there are two types of chimneys.
The size of the pipe is determined by the size of the furnace or the
fireplace and the total height from the furnace/fireplace to free air.

A service chimney handles heaters such as furnace or water heater.
This type of chimney uses a round clay pipe flue.
this pipe is hard fired clay and has a shiny ceramic type surface.
This pipe is interlocking and resembles sewer pipe, usually 8" diameter for
average home.
Acids resulting from gas fired furnace/heaters would dissolve chimneys or
pipes without this protection.

A fireplace chimney is different and requires a different type of pipe.
The average fireplace only requires a rectangular pipe, also a clay product
but not hard fired.
This pipe is usually a soft orange/buff color and can break quite easily.
These pipe have no interlocking bells and is usually laid in a small bed of
mortar between units.
No acids result from wood burning fires hence a less sturdy pipe is
required.

While a chimney may contain both types of pipes, they must be separated by
masonry as to form multiple chimneys in one large unit.
In no way can heating and wood burning share the same pipe or the gases,
smoke, from one pipe be allowed to escape to the any other pipe.


And as for chimney cleaners. Pro construction people know that this is
RARELY NEEDED in today's modern era homes with the exception of possible
debris accumulation.

In older homes, and I mean old, where the clay liners were not used and the
chimneys were brick only, then a stainless steel liner is used for the gas
fired heating chimneys.
Some older homes that were coal or oil heated may not have the proper liner
and also require a stainless steel liner if conversion to gas fired takes
place.

So now I've given you far more than you need or probably wanted to know
about chimneys.....
Many many many questions on the masonry license exam are dedicated to
chimney construction codes.
Which explains why 'chimney shakers' can offer such low bids compared to
honest reputable contractors.

Carbon Monoxide leaking chimneys kill people in their sleep.
Improperly built or maintained fireplace chimneys result in severe damage..









"Brian Andrews" wrote in message
m...
We've been in our house for 3 years and have never used our fireplace
because a chimney cleaner told us that we need a new liner. We
didn't do the repair because it was low on our to-do list.

Now we are converting from an oil furnance to gas and a new chimney
cleaner has told us that we need to do the new liner.

First chimney guy quoted $2600 to install a stainless steel liner.

Second guy quoted $1275 to install an aluminum liner. He said this
was all we needed for our new gas burner.

So, I went with the aluminum. I wasn't pressured or rushed but when
speaking to the guy on the phone he assurred me that this was the
correct liner for the oil furnance, but I forgot to ask him about
burning wood in my fireplace.

I've now read that aluminum is fine for gas and stainless is required
for woodburning stoves or oil. Is SS also requried for having a small
fire in the fireplace? Does this liner even matter for using the
fireplace?

I know this is a dumb question because you all have never seen my
chimney, but is it possible that I have 2 flues and that one for the
furnance just needs the alumnium liner and the other for the fireplace
does not?

The house is a 1945 Cape Cod in northern NJ.

Thanks.