Questions for stove techs

[The Suburban Hippie Exper]

Hello,

So after like 10 or 12 years I decided to put an outdoor air kit on my stove. So the air intake is a weird size, it is 2.5" ID, but then right before the flapper, it goes down to what looks like less than 2"(I can't get in there to measure it)

So, the run from the back of the stove to the outside is only 18", so a piece of exhaust pipe would do it perfectly. I painted a 2 inch exhaust pipe black, and I ordered a 2" outside wall vent. Now before I installed the 2 inch, I tried to contact Harman to ask them if the 2" would be sufficient, with no answer. The outside wall vent is less than a 2" orifice because they made it to sit inside one of those flexible aluminum pipes.

So, the stove burns fine, but I am having a couple issues. On the 2" pipe, I was thinking since it was such a short run it would be fine.

So for an example of my thinking. Take a drinking straw, and suck air through it. Then cut it in half, and you will find you can pull air into your lungs much easier. I can't remember why, but I think it has something to do with fluid dynamics..

Okay, now that that is out of the way, I notice sometimes when the stove is off, and I turn it back on, just the combustion fan comes on, until I turn the temperature dial up a little and then the auger feeds pellets and it starts in short order (like 3 minutes)

I am thinking there is a temperature probe somewhere in the air intake, and I know there is a temperature probe in the exhaust.

I am thinking the control board looks at the temperature differential from the colder outside air(55 degrees) as of today, and the exhaust temp probe (probably at room temp of 74), sees a temperature differential, and the combustion fan comes on only because the control board thinks there was a fire in the stove, and wants to go through the routine to eliminate all the smoke like it normally would.

Is this correct?

Secondly, I am getting some whining from the combustion motor. So at first, I thought that the OAK was too restrictive, and making the combustion fan speed up and hit a certain resonant mechanical frequency causing the wine, so I unsealed the OAK so it could pull air through the 2" pipe and ALSO from the room, which should have made the intake unrestricted. That didn't seem to make a difference...

So, I went back and cleaned the dust out of the outside fan, and re cleaned the combustion blower, that didn't seem to to change anything..

So then, I turned the trim pot just to see if it would change the resonant frequency of the motor, and it seemed to help a little, but it still whines sometimes. As I said, the motor spins very freely, so the bearings seem fine.

I have ordered another combustion fan, which brings me to my 3rd question. Why do the replacement motors not have the second fan on the motor? The one behind the motor.

Is this a new design, or are the aftermarket motor makers, just cutting corners?

I don't want to just willy nilly change the motor out, as one, it seems like a bear to get the combustion fan off the motor shaft, necessitating cutting the shaft, and two, I would have to splice wires, which I can do, but if I don't really need to, I don't want to pull that motor out and ruin it.
By the way, the flapper is free. Nothing I did obstructs it in any way.

Here is a video I did of the DIY OAK

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[railfanron]

There is no temperature probe in the intake air. The stove relies on the vacuum switch to start the pellet auger. Proof of fire comes from the ESP probe in the exhaust duct. It seems from your description the intake air should be fine but Harman made it 2 1/2" for a reason and if it was me I would have gone the 2 1/2" or larger. When I installed my standby generator it had a 1/2" propane intake. I piped it in with 1/2" pipe and it didn't run right. I called the factory and they told me to pipe it in 3/4" as 1/2" didn't move enough propane. I did and it worked fine. Moral of the story is there's a reason they went to 2 1/2".
Ron

 

[DAKSY]

Harman stoves have no means of measuring incoming air pressure until
that air goes thru the burn pot & goes out the exhaust stream.
That's where the ESP is & it is temperature sensitive.
It will not turn the distribution fan on until it reaches 160 degrees F.
If it goes down to 90 degrees F it will shut off the feed motor.

 

[The Suburban Hippie Exper]

There is no temperature probe in the intake air. The stove relies on the vacuum switch to start the pellet auger. Proof of fire comes from the ESP probe in the exhaust duct. It seems from your description the intake air should be fine but Harman made it 2 1/2" for a reason and if it was me I would have gone the 2 1/2" or larger. When I installed my standby generator it had a 1/2" propane intake. I piped it in with 1/2" pipe and it didn't run right. I called the factory and they told me to pipe it in 3/4" as 1/2" didn't move enough propane. I did and it worked fine. Moral of the story is there's a reason they went to 2 1/2".
Ron

Thanks for the info. So any idea why my combustion fan would come on only, until I turn the stove temp up just a notch?

I would have installed an exhaust pipe of 2.5" OD, but the parts store simply did not have one. As for the outside went, it said 2" so I assumed that the opening was at least 2"

As for Harman making the intake 2.5" for reason, I got you. However, I think they did that for long runs. A longer run needs a larger diameter pipe to carry sufficient air flow. I was thinking 18" was short enough.

I don't know. The stove runs fine otherwise.

The combustion fan coming on by itself is weird, but if the stove detected there wasn't enough flow, I wouldn't think turning the temperature up a notch would make the auger and igniter come on...

The whining motor is irritating. I may just change it out one day, but as I said, I would have expected if it was the bearings going bad, the fan wouldn't spin so easily, but maybe that is just my hopeful thinking!