Question: My chimney will not allow the installation of a 6" liner. I'm considering a certain stove that has a 6" pipe, but the shop told me it would work well with a 5". On the other hand, the flue is currently lined with terra-cotta and is the correct size. However, I've been told that lining with stainless steel is the best course of action. I GUESS I WILL GET THE LINER, THE ONLY THING IS A 6 INCH FLEX LINER WILL NOT FIT THE FIREPLACE STORE SAID THAT A 5 INCH WOULD WORK FINE FOR THE MODEL I WANT PACIFIC ENERGY VISTA HEATS 1500 FEET 2.9 GRAMS HOUR. THE COMPANY SAID IT SHOULD BE FINE ALSO. Answer: Here's my take..keep in mind it is probably against the code and instructions to downsize a chimney: 1. As far as downsizing, it might work in this particular case. I say this from experience, not for a code standpoint. The reason that some stoves have a 6" vent is because that is the smallest common US size. As an example, many earlier models of European stoves inclusing Jotul and Morso used pipe sizes that were smaller than 5" (metric) . The only reason they were enlarged later is due to the popularity of 6" pipe in this country. 2. There are some companies and sweeps that will ovalize pipe for you. A 6" pipe cut down to about 5.5" would probably fit down....with the small oval, it would not be too wide to fit your 10" 3. your flue size is typical for what is called an 8 x 12 flue. Since that 8 by 12 is an outside dimension, the inside ends up being about 6.5 by 10.5 - or close to that. I have a new tile right here in my garage that is exactly 6 x 10 inside. 4. The reversal of your chimney is likely to happen whether lined or unlined. If I were buying the stove, here's what I would do- Assuming that my chimney was decent (two stories and had good draft while running), I would install the stove with only the short liner up to the flue tile and see how it works for a couple months. If I was happy, I'd keep it that way. If not, I'd figure out some way to line the chimney...preferably with 6" pipe that is slightly oval. On the other hand, if the chimney had always been a source of aggravation - smoking and downdrafting, I'd line it up front. That's only my personal opinion. I'm admittedly frugal..