Direct vent draft setting

Wxtrendsguy · Post by **Wxtrendsguy** » Mon. Nov. 08, 2021 10:23 am

We have a used Alaska Liberty stoker stove near Allentown, PA. Basically the same as a Channing 3 but not as pretty to look at. We have it connected to a direct vent fan (NOT a SWG power vent) and then out a 90deg elbow, 2' vertical straight pipe, 90 deg elbow, 2 feet horizontal pipe, 45deg elbow. With everthing fired up we are seeing a draft of approx -0.09" H2O on the calibrated Magnehelic manometer. Open the stove door and it drops to 0 which is expected. I believe the -0.09 that we are seeing is too stong a draft and basically sucking the heat right out of the stove.. Combustion blower seems to be functioning correctly. I have already moved the direct vent a little closer and a little further away on the stove collar and no change.
So applying some logic if the stove is seeing more negative pressure than expected, there are only 2 options, either the combustion fan is not supplying enough air (already well cleaned and the console has been well cleaned) or the direct vent fan is too strong due to the relatively short length of vent pipe.

I think I will get a rheostat like the one below to control the direct vent motor. Any other suggestions are welcome. Or come see it your self at the winery and say hi. Cheers
https://electricmotorwarehouse.com/kb-electronics ... k177-1005/

McGiever · Post by **McGiever** » Tue. Nov. 09, 2021 8:04 am

Just a guess, but does the DV have a tee handle or something that you could "throttle" the output flow?
If it doesn't then your motor speed control should get the job done.

Do you have the "fume switch" wired in to kill stoker power if should DV system not perform properly and allow raw exhaust to begin to spill out into the space? IT IS "VERY IMPORTANT"

Wxtrendsguy · Post by **Wxtrendsguy** » Tue. Nov. 09, 2021 9:50 am

McGiever wrote: ↑
Tue. Nov. 09, 2021 8:04 am
Just a guess, but does the DV have a tee handle or something that you could "throttle" the output flow?
If it doesn't then your motor speed control should get the job done.

Do you have the "fume switch" wired in to kill stoker power if should DV system not perform properly and allow raw exhaust to begin to spill out into the space? IT IS "VERY IMPORTANT"

There is nothing to slow the direct vent down...

Yes we have a fume switch and everything but the convection fan is supplied from that.

Next step might be to clean or replace the combustion fan to ensure its 100%. If still too much draft then it will be time to throttle back the direct vent with a rheostat.

McGiever · Post by **McGiever** » Tue. Nov. 09, 2021 1:55 pm

Fume switch does Not ever control the convection fan as you have described.
It is to kill the FIRE with degraded draft as in fly ash build up inside reducing flue capacity or any other restrictions to the free flow of exhaust from combustion.

Wxtrendsguy · Post by **Wxtrendsguy** » Fri. Nov. 12, 2021 8:57 am

McGiever wrote: ↑
Tue. Nov. 09, 2021 1:55 pm
Fume switch does Not ever control the convection fan as you have described.
It is to kill the FIRE with degraded draft as in fly ash build up inside reducing flue capacity or any other restrictions to the free flow of exhaust from combustion.

Thats correct the Fume switch plugs directly into the wall and the other cord from the fume switch connects to the combustion fan and direct vent with a 3 way outlet. This leaves one outlet on the 3 way free which is used to run the convection fan, I don't think its that much of an issue if the convection fan is also plugged into the 3 way plug....it will just shut off when the fume switch trips like the rest of the fans on the stove. There is a hand written drawing in my manual by the original installer that shows all 3 fans being fed by the fume switch. I guess I could envision a situation where the convection fan should be independently powered to help draw residual heat away from the stove in the event of a fume switch trip.

McGiever · Post by **McGiever** » Fri. Nov. 12, 2021 10:06 am

Okay I missed earlier of your claim to have stoker/fan plug in…no mention of the 3 way plug before.
Killing the convection fan does not save a life is all I was getting at.

Wxtrendsguy · Post by **Wxtrendsguy** » Fri. Nov. 12, 2021 12:51 pm

McGiever wrote: ↑
Fri. Nov. 12, 2021 10:06 am
Okay I missed earlier of your claim to have stoker/fan plug in…no mention of the 3 way plug before.
Killing the convection fan does not save a life is all I was getting at.

No problem you can never be too safe....the good thing is this is out in our 4 season porch in another building that is not connected to living space.

Wxtrendsguy · Post by **Wxtrendsguy** » Wed. Nov. 17, 2021 8:10 am

Apparently my stove is happy with my choices....running with feed rate set to 3 and pressure at -0.03" in H2O.

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McGiever · Post by **McGiever** » Wed. Nov. 17, 2021 10:47 am

That’s Great!

So how did you slow down the direct vent?

Wxtrendsguy · Post by **Wxtrendsguy** » Thu. Nov. 18, 2021 10:50 am

I swiped the rheostat from the circulating fan and placed it inline from the fume switch to the direct vent fan. The circulating fan now just runs full blast. I plan to get a rheostat like the one in my OP. Just wanted to test out the theory and see if it would indeed improve things....lets just say it did. I do find that I am going to need some sort of cap on my pellet pipe to battle when the wind blows right at it.