New EPA stove 8" vs 6" flue set up

[Radio]

Recently replaced a Vermont Castings Vigilant ('77) with Pacific Energy Vista. Since I had an 8" set up in place I put a reducer at the stove to connect. Seems to work well as long as the flow is high. However throttling back for a longer burn or decreased output there seems to be problem maintaining good flow. Is this my imagination? Is the design for the 6" set up really required for best efficiency across its operating spectrum? Manufacturer provided the answer that it would decrease efficiency. Not sure if thats a legal response since thats how it was designed.

Any insight greatly appreciated.

Radio

 

[begreen]

Welcome radio. The answer is, it depends. In a mild climate having 6" all the way can make a difference especially if there are complicating factors. Some of these would be a short flue, a couple 90 deg turns in the flue path, milder climate weather, or negative pressure in the house.

 

[Renovation]

How cold is it there now? How much exposed exterior pipe do you have?

One potential problem with a too-wide pipe is that its slower flow velocity and greater surface area makes the pipe more prone to cool down and stall, particularly when the stove is throttled back. If that is the problem, better insulation around your pipe (while maintaining combustibles clearances) could help.

EDIT: Changing interior stove pipe from single to double wall could also help keep gasses warmer and prevent stalling, particularly if your interior stove pipe is long.

 

[Radio]

Thank you. I have 6' of single wall and 6' of old triple wall each in the heated area and out. Climate is usually mild. The heated area is really my shop, a wide open area. The low flow in a large diameter pipe sounds like the problem when its drawn back. I don't know that spending the 600.00 to replace the venting will provide that much more efficiency.
Well I'll have to ponder that.
Thanks folks.

Radio

 

[Renovation]

Thank you. I have 6' of single wall and 6' of old triple wall each in the heated area and out. Climate is usually mild. The heated area is really my shop, a wide open area. The low flow in a large diameter pipe sounds like the problem when its drawn back. I don't know that spending the 600.00 to replace the venting will provide that much more efficiency.
Well I'll have to ponder that.
Thanks folks.

Radio

You're very welcome.

You have a pretty short chimney, and that combined with mild climate can mean poor performance with an EPA stove. Extending your chimney could help. You could add a piece of cheap singlewall to the top temporarily as a test--it might help.

HTH and good luck!

 

[begreen]

Thank you. I have 6' of single wall and 6' of old triple wall each in the heated area and out. Climate is usually mild. The heated area is really my shop, a wide open area. The low flow in a large diameter pipe sounds like the problem when its drawn back. I don't know that spending the 600.00 to replace the venting will provide that much more efficiency.
Well I'll have to ponder that.
Thanks folks.

Radio

Yep, that is the issue and you have assessed it correctly. You can try sticking a stub of cheap 6" vent pipe in the top of the flue to see what adding 3 ft will do. Just as a temporary test of course. I think you will notice the difference, especially in milder temps.

 

[Renovation]

Thank you. I have 6' of single wall and 6' of old triple wall each in the heated area and out. Climate is usually mild. The heated area is really my shop, a wide open area. The low flow in a large diameter pipe sounds like the problem when its drawn back. I don't know that spending the 600.00 to replace the venting will provide that much more efficiency.
Well I'll have to ponder that.
Thanks folks.

Radio

Yep, that is the issue and you have assessed it correctly. You can try sticking a stub of cheap 6" vent pipe in the top of the flue to see what adding 3 ft will do. Just as a temporary test of course. I think you will notice the difference, especially in milder temps.

Thanks BeGreen!

Actually, he has 8" pipe. You mean an 8" stub, don't you?