Vent sizing

[brianMA]

First time posting and first time with a pellet stove! I just installed a new Castle Serenity a week ago. I looked on related threads but can't quite find the info I'm looking for. My question is more general, however.

In a bit of a rush to get the stove in as we completed renovations, I used 3" pipe since it was available at the local big box. Due to constraints on where I could place the thimble, I needed to run a stove adapter, 45, 90, 90, and a 1' straight pipe (in that order) to get out to the exterior. From there, it's a clean-out tee and will (eventually) run vertically up 7-8' to get the proper clearance above a window. At the moment, it's 3' up from the tee.

The stove seems to work well (still tuning the damper and blower settings) but based on other threads, it's perhaps not as hot as it could be. In any case, I'm wondering what (if any) effect changing to a 4" exhaust will have? Everything I'm reading says I "need" 4" pipe with that many turns/length, but I'd rather not shell out $300-400 worth of 4" pipe. Even if I'm burning at a more optimal rate, it seems like it would take a long time to recoup those costs. However, I'm also concerned that the additional 4-5' of vertical pipe in the final configuration might be the straw that breaks the camel's back in terms of allowing the stove to exhaust well. Thoughts? Thanks!!

 

[Lake Girl]

Not exactly sure what the EVL max is for the Serenity ... looks like you will be 18 EVL. Usually 15 ish is when you move to 4" exhaust. A pic might be helpful to see if there is any way to re-route for less elbows. Vertical piping is the least restrictive 1'=1/2' in EVL. 90*=5; 45*=3; 1' horizontal=1' The biggest problem with the elbows will be a requirement for more frequent cleaning as ash will collect in those elbows. Not sure what long term effect it may have on exhaust blower longevity.

Did you install an OAK?

 

[Pelleting In NJ]

Compared to 3 inch diameter pipe, 4 inch pipe gives you 1.77 times more flow area (less restriction).

 

[brianMA]

Not exactly sure what the EVL max is for the Serenity ... looks like you will be 18 EVL. Usually 15 ish is when you move to 4" exhaust. A pic might be helpful to see if there is any way to re-route for less elbows. Vertical piping is the least restrictive 1'=1/2' in EVL. 90*=5; 45*=3; 1' horizontal=1' The biggest problem with the elbows will be a requirement for more frequent cleaning as ash will collect in those elbows. Not sure what long term effect it may have on exhaust blower longevity.

Did you install an OAK?

I'll see if I can get a picture later when I'm home. It's a corner install, which prompted the 45. The stove exit is quite low to the floor, so I had to place the thimble higher to clear my baseboard. I didn't necessarily want to look at the venting, and the two 90s did the trick (at least to get it out the wall, maybe not the most efficient solution...). Hindsight is 20/20...

So, it seems like a restrictive exhaust might just make the blower work harder with not a huge detriment to burn temperature?

No OAK at the moment; install guide says it's only required in mobile homes and suggested in tight homes. The flame seems lively and bright yellow, although it seems a bit smaller in comparison to videos of other Serenity users. The stove is in a pretty tight addition (which has an open floor plan to the rest of the house), but the rest of the house is drafty (circa 1890). It's not a HUGE deal to cut another hole in the house as it's just sheathing for the moment.

thanks for your help!

 

[Lake Girl]

You might feel those drafts less if you install the OAK... need to pull combustion air from somewhere. W/o an OAK, you are pulling cold outside air through areas that are not air-tight which usually is around windows, doors, transition areas like rim joist. Makes the house drafty. You're also throwing pre-warmed air outside through the exhaust. If you go with an OAK, it needs to be below the exhaust outlet. You may want to insulate the line as it does get cold and will frost with the difference of temperature between outside and inside temps.

 

[rich2500]

As per the manual it should be 4" pipe.with that being said because of the design of the Serenity it moves a lot of air through it quickly so I highly doubt you would have burn issues the way you have the vent, but you would want to keep on top of your vent cleaning more frequently.

 

[Nvnv]

I just went through this same thing a couple weeks ago when I installed my Serenity. I didn't see the blurb in the manual about using 4" for anything over 2500' elevation and I'm at 4800'ish. Although it ran fine like that I still swapped it out for 4" pipe to be safe and make sure I was to code/minimum specs. The only thing I have noticed is the bigger pipe is slightly cooler to the touch. But it seems to burn the same.