Moving my Fisher to 6"

[Yawiney]

Just got a 2nd Fisher for my shop/garage. it's the 2nd biggest. I think the grandma?
It's back vented and I just priced out everything in 8", and Ouch!
Would it work to go with an adapter to 6" and do everything from the elbow up in 6"?
Some say it will be bad for the draft and some say it's fine.
I have 8 ft single wall inside and will need another 7' double wall thru support box and above the roof. 15' total from the elbow out the back.

 

[bholler]

Just got a 2nd Fisher for my shop/garage. it's the 2nd biggest. I think the grandma?
It's back vented and I just priced out everything in 8", and Ouch!
Would it work to go with an adapter to 6" and do everything from the elbow up in 6"?
Some say it will be bad for the draft and some say it's fine.
I have 8 ft single wall inside and will need another 7' double wall thru support box and above the roof. 15' total from the elbow out the back.

Some people get away with it but it's generally not a good idea to reduce to 6".

In addition woodstoves are not allowed in garages by code in the USA and I believe a pre EPA stove cannot be installed in CA.

 

[coaly]

The reason you get conflicting answers is due to many factors. You are close to sea level, so have more atmospheric air pressure to work with, so that is a positive. You are in a warmer climate with less temperature differential inside and outside of the chimney flue, so that is a negative. With only one elbow, cap and spark screen, you have minimal resistance added, so that is a plus. The smaller diameter decreases capacity. How much reduction is acceptable is the question. Heated area square footage, desired temperature, fuel being used, heating from a cold building well below freezing or keeping it going at a lower rate are more factors.

The stove was designed with a larger outlet to be able to use an existing fireplace chimney. This has proven to allow expansion and cooling in the larger flue, requiring liner to decrease larger fireplace flue diameter to match stove to prevent creosote. It was also designed with the larger outlet for open door burning. Using a more efficient insulated chimney, closed doors for heating, with minimal resistance from pipe configuration you should not experience problems. I would add a baffle to reduce smoke as well. I would certainly install a 6 inch double wall so you can upgrade to a newer legal stove, unless you have a large area that will require a 8 inch vented newer stove.

If this is a attached garage, be aware any insurance claims for damages to home due to the stove installed in a garage will be denied . A unattached garage loss that doesn't affect home is your liability of garage loss only.

 

[Yawiney]

The reason you get conflicting answers is due to many factors. You are close to sea level, so have more atmospheric air pressure to work with, so that is a positive. You are in a warmer climate with less temperature differential inside and outside of the chimney flue, so that is a negative. With only one elbow, cap and spark screen, you have minimal resistance added, so that is a plus. The smaller diameter decreases capacity. How much reduction is acceptable is the question. Heated area square footage, desired temperature, fuel being used, heating from a cold building well below freezing or keeping it going at a lower rate are more factors.

The stove was designed with a larger outlet to be able to use an existing fireplace chimney. This has proven to allow expansion and cooling in the larger flue, requiring liner to decrease larger fireplace flue diameter to match stove to prevent creosote. It was also designed with the larger outlet for open door burning. Using a more efficient insulated chimney, closed doors for heating, with minimal resistance from pipe configuration you should not experience problems. I would add a baffle to reduce smoke as well. I would certainly install a 6 inch double wall so you can upgrade to a newer legal stove, unless you have a large area that will require a 8 inch vented newer stove.

If this is a attached garage, be aware any insurance claims for damages to home due to the stove installed in a garage will be denied . A unattached garage loss that doesn't affect home is your liability of garage loss only.

Thanks for that good info. I'm now in Oregon not as close to sea level as before, and it does get below freezing quite often in the winter..
The area size is just under 800 sq ft, so hopefully the 6" double wall would be enough for that.
I was planning to go single wall to the ceiling though.
Any recommendations on where to put the adapter? I was planning to put it right at the back vent and go 6" from there.

 

[coaly]

Oregon is the most restrictive state for emissions. That stove can’t be legally installed or sold there without decommissioning the stove for collector use. https://www.oregon.gov/deq/Residential/Pages/woodstovesFAQ.aspx

That said, most reduce right at the stove. By using 8 inch inside that slows the rising gasses in the larger area. This increases dwell time in pipe allowing more heat loss through pipe with greater loss to the inside of building. Good for heating, bad for chimney flue temps. You will be fine with that smaller area with the larger stove reduced. Colder ambient air temps outside are in your favor for increased draft. I would be more concerned about the stove police than reducing chimney size.

 

[Yawiney]

Oregon is the most restrictive state for emissions. That stove can’t be legally installed or sold there without decommissioning the stove for collector use. https://www.oregon.gov/deq/Residential/Pages/woodstovesFAQ.aspx

That said, most reduce right at the stove. By using 8 inch inside that slows the rising gasses in the larger area. This increases dwell time in pipe allowing more heat loss through pipe with greater loss to the inside of building. Good for heating, bad for chimney flue temps. You will be fine with that smaller area with the larger stove reduced. Colder ambient air temps outside are in your favor for increased draft. I would be more concerned about the stove police than reducing chimney size.

Thank you!