ussc 8500 fresh air kit

[slowlymakingprogress]

I've got a USSC 8500 pellet burner and it's been doing good and efficient after I have received tons of advice from a previous thread I started back in the other month and words or type couldn't express the amount of thanks for the help. All you all are incredibly helpful. Thank you. The pellet stove is doing good but there's been some overflow in the burn pot. I feel I got the draft fans set good(C6 at 20 and C7 at 110) where the door temps get about 250-300 on HR1 and about 625 on HR4 and exhaust is usually in 100deg (HR1) - 240deg(HR4) range with HR1 at 1.5pph and HR5 at 5pph. I've been starting to notice here lately the draft fan light'll flash for a second or to and than again it may not and according to the manual it does that to indicate a negative air pressure situation so adding a Fresh Air Kit is something I've been meaning to do just haven't done yet. I've got a good place(unused chimney flue) that's only about 8 feet or so away from stove where I can draw the air from and was looking into the USSC69FAK. Has anyone on here installed one of these kits on there's or someone else's 8500? let me know. Thanks

 

[Jeremy6500]

I've got a USSC 8500 pellet burner and it's been doing good and efficient after I have received tons of advice from a previous thread I started back in the other month and words or type couldn't express the amount of thanks for the help. All you all are incredibly helpful. Thank you. The pellet stove is doing good but there's been some overflow in the burn pot. I feel I got the draft fans set good(C6 at 20 and C7 at 110) where the door temps get about 250-300 on HR1 and about 625 on HR4 and exhaust is usually in 100deg (HR1) - 240deg(HR4) range with HR1 at 1.5pph and HR5 at 5pph. I've been starting to notice here lately the draft fan light'll flash for a second or to and than again it may not and according to the manual it does that to indicate a negative air pressure situation so adding a Fresh Air Kit is something I've been meaning to do just haven't done yet. I've got a good place(unused chimney flue) that's only about 8 feet or so away from stove where I can draw the air from and was looking into the USSC69FAK. Has anyone on here installed one of these kits on there's or someone else's 8500? let me know. Thanks

I have a USSC 6500, so basically and 8500 with just a few small differences. I don't have a FAK on mine, but I am I am considering it. If you install it let us know what your impressions are and post some pics.

My 6500 only has 3 heat ranges vs the 5 on your 8500. I am tempted to see if I can use an 8500 board on mine since all the other parts seem identical. I have my feed rates set almost exactly the same as you .I think my HR1 is set for 1.6 and HR3 set at 5. Mine burns well, but I always end up with unburned pellets around the burn pot. My burn pot doesn't overflow, so I think it is due to some pellets hitting the auger etc and bouncing out. I have seen where you can get a burn pot extender that fits over it to make it taller. I will probably end up getting one since it would keep me from wasting fuel.

 

[slowlymakingprogress]

I have a USSC 6500, so basically and 8500 with just a few small differences. I don't have a FAK on mine, but I am I am considering it. If you install it let us know what your impressions are and post some pics.

My 6500 only has 3 heat ranges vs the 5 on your 8500. I am tempted to see if I can use an 8500 board on mine since all the other parts seem identical. I have my feed rates set almost exactly the same as you .I think my HR1 is set for 1.6 and HR3 set at 5. Mine burns well, but I always end up with unburned pellets around the burn pot. My burn pot doesn't overflow, so I think it is due to some pellets hitting the auger etc and bouncing out. I have seen where you can get a burn pot extender that fits over it to make it taller. I will probably end up getting one since it would keep me from wasting fuel.

I'll certainly post pics of it if it gets hooked up. I was reading something or another somewhere that describes how it goes somewhere under or up inside the unit or what not to hook up but that's all I got. I'm hoping to find or get some pics of one hooked up or even a copy of the directions on hooking one up. My user manual for the stove has nothing, unless I over looked it, on the topic of where to hook up the FAK . I'm sure the USSC69FAK ain't the only kit on the market but it's the first one I stumbled upon. I called USSC and managed to talk to someone for a brief minute and they said 69FAK is the part number for the kit that belongs to the 8500 as well as other units. I have the stove hooked to a thermostat so I run it in auto mode and can't complain on how well the stove does as it keeps a 2700 sq.ft. house with upstairs warm on an AVERAGE of a little over a bag a day since first of December on southern Indiana weather. I too want to do a burn pot extension as I get pellets hitting the agitator and bouncing out but I'm thinking if I do that with the occasional overflow that it might stress the agitator a little more than it wants to be. I feel the draft is good as it produces a good flame when ramped up to HR4(current set point) and doesn't blacken the glass all the time(when defaults down to HR1 when thermostat is satisfied) but seeing the light that indicates a negative pressure is what has me knowing I need to do FAK. I know nothing about the 6500 other than it's a little smaller than the 8500 so I say go for the control panel change if the connections are the same and it doesn't cost too much but double check the return policy on panel in case it don't work out.

 

[Jeremy6500]

Glad to hear it heats the house well. I am up in northern Indiana. Mine was installed in the house I bought a little over a year ago, but did not run right. After replacing parts, hooking up a thermostat and tweaking the settings it heats well. The previous owner had it set up as a stove vs a furnace with the air just blowing into the room. Needless to say it is way too big to heat just a room. I can easily turn the back 2 rooms of my house into a sauna. Prior to next winter the plan is to move it to the utility room and hook it into ductwork for central heat.

I also have a PP130 pellet stove that heats the front half of the house. It works well with auto ignition etc, but between the 2 it uses a lot more pellets than the 6500.

 

[slowlymakingprogress]

Glad to hear it heats the house well. I am up in northern Indiana. Mine was installed in the house I bought a little over a year ago, but did not run right. After replacing parts, hooking up a thermostat and tweaking the settings it heats well. The previous owner had it set up as a stove vs a furnace with the air just blowing into the room. Needless to say it is way too big to heat just a room. I can easily turn the back 2 rooms of my house into a sauna. Prior to next winter the plan is to move it to the utility room and hook it into ductwork for central heat.

I also have a PP130 pellet stove that heats the front half of the house. It works well with auto ignition etc, but between the 2 it uses a lot more pellets than the 6500.

I'm not sure what kinda BTU's the 6500 is capable of but I'd imagine it'd be a bit on the warmish side of the thermometer in that application. I guess you could put a few palm trees in that room and it could be a vacation spot close to home‍♂️ I've got my 8500 hooked to existing duct work and it blows air throughout house nicely except upstairs don't get much airflow other than the heat going up staircase but it still stays comfortable. At this time any extra airflow upstairs is not a concern cause our kids aren't up there much anyway. We got this home back in May of 2020 and the 8500 was already installed as supplement heat to heat pump so previous owner ran it on manual mode and turned the door on 8500 white within first hour probably just to get that over with right off the bat. lol. Since than I installed the thermostat and I understand the whole tweaking the settings bit as did I have to do that as well but as I mentioned at beginning of this thread some of the members on this site helped me tremendously with that process and I could not thank them enough for that. I think moving the 6500 to utility room and hooking to duct work is a great idea!! I did more research on FAK/OAK and it seems it hooks somewhere by slide dampener?? I read a previous thread on here somewhere but don't remember the title of thread that had the info.

 

[slowlymakingprogress]

I'm not sure what kinda BTU's the 6500 is capable of but I'd imagine it'd be a bit on the warmish side of the thermometer in that application. I guess you could put a few palm trees in that room and it could be a vacation spot close to home‍♂ I've got my 8500 hooked to existing duct work and it blows air throughout house nicely except upstairs don't get much airflow other than the heat going up staircase but it still stays comfortable. At this time any extra airflow upstairs is not a concern cause our kids aren't up there much anyway. We got this home back in May of 2020 and the 8500 was already installed as supplement heat to heat pump so previous owner ran it on manual mode and turned the door on 8500 white within first hour probably just to get that over with right off the bat. lol. Since than I installed the thermostat and I understand the whole tweaking the settings bit as did I have to do that as well but as I mentioned at beginning of this thread some of the members on this site helped me tremendously with that process and I could not thank them enough for that. I think moving the 6500 to utility room and hooking to duct work is a great idea!! I did more research on FAK/OAK and it seems it hooks somewhere by slide dampener?? I read a previous thread on here somewhere but don't remember the title of thread that had the info.

I don't know how I did it but I put some sorta emoji in last post and don't know what it is supposed to represent?

 

[Jeremy6500]

The 6500 is rated at 50,000-105,000 BTU/hr and says for a house 1200-2800 sqft. My house is about 2200, so it should do well.

As far as the lack of airflow upstairs you mentioned, there are some videos on YouTube about the 8500 by a guy called LandAirMechanic that specifically addresses that issue. He found that it has to do with the cold air return opening being too small for the cfm of the blowers. He solves it by adding an additional 10” round duct to the side of the blower box and connecting it to the return.

 

[slowlymakingprogress]

The 6500 is rated at 50,000-105,000 BTU/hr and says for a house 1200-2800 sqft. My house is about 2200, so it should do well.

As far as the lack of airflow upstairs you mentioned, there are some videos on YouTube about the 8500 by a guy called LandAirMechanic that specifically addresses that issue. He found that it has to do with the cold air return opening being too small for the cfm of the blowers. He solves it by adding an additional 10” round duct to the side of the blower box and connecting it to the return.

I've watched the Land Air Mechanical videos at least that many times and he really seems to know these pellets stoves. I did go ahead and add the extra cold air return/air supply to the stove right under the control panel location and absolutely made a huge difference but I only used 6" cause that's what I had laying around. I suggest for anyone that gets one of these units for that to be if not the first thing to do certainly on the list of top two things to do right next to enabling the second blower to come at HR2 or HR3. I'll post some photos of unit hooked up and it's the way it blows air in a mostly straight horizontal line rather than like how the heat pump blows mostly vertical that slows air to upstairs but with closing some of the registers in main floor it forces more upstairs which at this time is sufficient since we don't use upstairs much. In photo you can see how at back of unit I made a box with 12" intake at top to hook to existing duct work to slide into tracks where the 10x20x1 filter goes and in that box I cut out a slide area for filter to go into than on hook up under control panel I take a filter fold it over (you can't see it or change it without removing side panel with pipe in it) and put it between panel/cover and fan motor to help filter air. Putting/squishing the filter in between fan suction opening and cover where I have 6"duct pipe cutout is likely not the greatest idea but it can't go anywhere or at least it hasn't but before next burn season I'd like to upgrade that pipe to a 8" or 10" than make an external box for filter so it's easier to change out when needed. The 8500 produces great heat and once I get some info (photos of what it looks like hooked up) on installing a FAK/OAK I think it will do heat production much more efficient and than I'll probably install a duct dampener or inline fan to get more air upstairs if we so choose to do so. What are you gonna do with the PP130 once you get the 6500 moved and hooked into duct work?

 

[Jeremy6500]

I've watched the Land Air Mechanical videos at least that many times and he really seems to know these pellets stoves. I did go ahead and add the extra cold air return/air supply to the stove right under the control panel location and absolutely made a huge difference but I only used 6" cause that's what I had laying around. I suggest for anyone that gets one of these units for that to be if not the first thing to do certainly on the list of top two things to do right next to enabling the second blower to come at HR2 or HR3. I'll post some photos of unit hooked up and it's the way it blows air in a mostly straight horizontal line rather than like how the heat pump blows mostly vertical that slows air to upstairs but with closing some of the registers in main floor it forces more upstairs which at this time is sufficient since we don't use upstairs much. In photo you can see how at back of unit I made a box with 12" intake at top to hook to existing duct work to slide into tracks where the 10x20x1 filter goes and in that box I cut out a slide area for filter to go into than on hook up under control panel I take a filter fold it over (you can't see it or change it without removing side panel with pipe in it) and put it between panel/cover and fan motor to help filter air. Putting/squishing the filter in between fan suction opening and cover where I have 6"duct pipe cutout is likely not the greatest idea but it can't go anywhere or at least it hasn't but before next burn season I'd like to upgrade that pipe to a 8" or 10" than make an external box for filter so it's easier to change out when needed. The 8500 produces great heat and once I get some info (photos of what it looks like hooked up) on installing a FAK/OAK I think it will do heat production much more efficient and than I'll probably install a duct dampener or inline fan to get more air upstairs if we so choose to do so. What are you gonna do with the PP130 once you get the 6500 moved and hooked into duct work?

The setup you have is similar to what I will have. My house is a ranch, so both the supply and return will be insulated and run in the attic.

I will have to get somewhat creative with the way the return hooks to the 6500. One of the big differences between 6500 and 8500 is that the exhaust comes out the back of the 6500 vs the side on the 8500. (see pics below). I don't know what the design engineers were thinking. In the manual for it, it specifically says that it is supposed to be used as a primary or add on furnace for your central duct system,,,,,but with the exhaust vent where it is if you put a cleanout T on it the bottom the T protrudes into the 10x20 return space.

My house is shaped like an L. At one end is the living room/kitchen etc. Then an L hallway with bedrooms off the halway. At the other end of the L hallway is a large family room area. Currently the 6500 is in the family room area and the PP130 is in the living room/kitchen area. The utility room is off the kitchen area. This makes the family room and 2 back bedrooms at the very end of the supply duct run. Doing all the CFM and duct sizing stuff says that I should still have plenty of flow there, but I am going to move the PP130 from the kitchen area and put it where the 6500 currently is. It will provide nice aesthetics in the family room plus supply some supplemental heat to that area of the house in case there isn't as much heat flow back there from the 6500 duct work.

 

[SidecarFlip]

The FAK (or OAK) kit will be cheaper from a specialty retailer like VentingPipe.com or Pellet head than it will be from any manufacturers website and both Selkirk and Simpson make them in various styles. I would however, stay away from the ones that employ the through the wall thimble as access to outside air simply because you don't want to preheat the outside combustion air at all. You want cold outside air for combustion. One it's more dense and 2, the fuel bed prefers cold intake air.

 

[Jeremy6500]

If your setup feeds the ductwork horizontally (blowing air down the run) vs perpendicularly in to it, I wonder if that could be what is causing some of your flow issues. By feeding it perpendicularly you can pressurize the system more evenly. I have never installed a pellet furnace, but I spent a number of years working with an HVAC contractor and installed a lot of forced air gas furnaces. I know with those you always deadhead the supply off the top and attach the horizontal duct run a few inches down from the top to aid in pressurizing the system. The pics below are from the install manual for mine and you can see the main furnace (pellet or otherwize) is installed this way. Your duct work sizing could also have a lot to do with it. It it is not sized correctly or doesn't step down in diameter correctly you lose a lot of flow towards the end of the run.

 

[slowlymakingprogress]

So is installing a OAK/FAK in an unused chimney flue that is next to the one that is being used (it's 25ft tall double flue each 8x12 clay lined) a bad idea even though there is blocks and clay liners "isolating them"? Or should I find a different, would be longer, route to take when I capitalize on the install of the OAK/FAK? I've not checked to see if temps in unused flue are the same as outside air at the cleanout door on bottom or if they are warmer. Any ideas/suggestions? Thanks

 

[slowlymakingprogress]

If your setup feeds the ductwork horizontally (blowing air down the run) vs perpendicularly in to it, I wonder if that could be what is causing some of your flow issues. By feeding it perpendicularly you can pressurize the system more evenly. I have never installed a pellet furnace, but I spent a number of years working with an HVAC contractor and installed a lot of forced air gas furnaces. I know with those you always deadhead the supply off the top and attach the horizontal duct run a few inches down from the top to aid in pressurizing the system. The pics below are from the install manual for mine and you can see the main furnace (pellet or otherwize) is installed this way. Your duct work sizing could also have a lot to do with it. It it is not sized correctly or doesn't step down in diameter correctly you lose a lot of flow towards the end of the run.
View attachment 273753View attachment 273754

I've got the same pictures in the manual that came with the 8500 as you posted and it does make perfect sense about doing the deadhead so it equalizes the air flow/pressure to each vent. I'm not sure if you can see it in the photos I posted but mine now is hooked up like the add on furnace picture. Had it not been installed already and I did the install knowing/learning more and more about these units as time goes on it would have been better to have moved it into more open area of basement and have it hooked like the primary furnace photo. However, with chimney location and cold air return duct location I can't blame previous owner for how they did it as it was to easy to hook it up the way it is at current time. This morning it was 11deg out and with thermostat (it's in main floor hallway) for pellet stove set to 68deg the upstairs was still 66 according to a thermometer with 8500 set on HR4 which is around 4ish pph. The burn pot was overflowed so I cleaned it up and certain I'll have that again this evening since the high today is in mid to low 20's. I'm hoping to get the FAK/OAK hooked up sooner rather than later to maybe prevent to overflow and keep things running as smooth as possible. I think if you move it and hook you're 6500 the way describe you'll be very satisfied with the results. I've burned 65 bags since the beginning of December but at first it was the getting things adjusted as good as could be so I burned probably 15-20 more bags than needed but it was a learning curve.

 

[slowlymakingprogress]

After a year as a newbie I’m impressed with how good and efficient my USSC 8500 is. Started this season about two weeks ago after a very thorough cleaning and seems good so far other than I didn’t install a fresh air kit as I hoped to. I watched video (Mudford guy) on how he did fresh air kit and it seems to work well for him but Is that about the only option or is there a kit for these 8500’s. Customer service told me of a kit(69FAK) but I don’t believe that kits made for the 8500. Any help or input is appreciated. Thank you

 

[Jeremy6500]

After a year as a newbie I’m impressed with how good and efficient my USSC 8500 is. Started this season about two weeks ago after a very thorough cleaning and seems good so far other than I didn’t install a fresh air kit as I hoped to. I watched video (Mudford guy) on how he did fresh air kit and it seems to work well for him but Is that about the only option or is there a kit for these 8500’s. Customer service told me of a kit(69FAK) but I don’t believe that kits made for the 8500. Any help or input is appreciated. Thank you

I will have to see if I can find the video you mentioned about the FAK. I have looked for a pre-made kit for my 6500 and have not found one. My air intake is through the front of my Ash box and then up through the firepot from underneath. It is controlled by the Auto/Variable draft fan and the amount I have the dampener open.

Do you still get pellets filling up and overflowing your burn pot? Once I figured out the way to clean all ash out and how to get to everything, mine does not over flow my burn pot. It usually stays below the agitator shaft and I am still able to see some of the holes in the burn pot.

 

[Jeremy6500]

I found the videos you were talking about. The OAK he made was interesting. I wonder if the length of the run and the multiple bends had a large negative effect on the flow rate.

 

[Jeremy6500]

After a year as a newbie I’m impressed with how good and efficient my USSC 8500 is. Started this season about two weeks ago after a very thorough cleaning and seems good so far other than I didn’t install a fresh air kit as I hoped to. I watched video (Mudford guy) on how he did fresh air kit and it seems to work well for him but Is that about the only option or is there a kit for these 8500’s. Customer service told me of a kit(69FAK) but I don’t believe that kits made for the 8500. Any help or input is appreciated. Thank you

Also, looking back at the thread.......prior to this season I did get the burn pot extender that we discussed. It has worked well. I still get some unburnt pellets bouncing out, but much less than before. The way it is running now I get almost no ash at all in the cleanout areas on the sides of the burn pot. It all goes down through the holes in the burn pot and in to the ash pan. A member on here mentioned they reversed the rotation of their agitator and I will probably do the same. Right now it rotates and tends to push the ash towards the back of the pot and dampener opening. Problem is there is a shelf at the back of the dampener opening under the burn pot so the ash piles up there instead of falling into the ash pan.

 

[slowlymakingprogress]

The video that guy made is good but I to wonder about the number of bends and I question if it needs to be insulated and all that. I do get some pellets bouncing out and I get decent heat that I can’t complain about but the flame is tall and lazy and Smokey when I open door to clean out everyday when in HR1 and it seems it’s not getting a complete burn. I think a fresh air kit would make a huge difference. I’ve not heard of reversing the agitator but it makes sense.

 

[Jeremy6500]

The video that guy made is good but I to wonder about the number of bends and I question if it needs to be insulated and all that. I do get some pellets bouncing out and I get decent heat that I can’t complain about but the flame is tall and lazy and Smokey when I open door to clean out everyday when in HR1 and it seems it’s not getting a complete burn. I think a fresh air kit would make a huge difference. I’ve not heard of reversing the agitator but it makes sense.

A lazy flame and not a complete burn is almost always related to not enough air flow. Are your C6 and C7 still at 20 and 110? According to my tech manual that would be way low and would explain the smoke. lazy flame and incomplete burn. I just checked my C6 and C7 to verify....mine are at 125 and 375. That is still a little below specs, but I was trying to keep more heat in the burn chamber and have no flame issues. Can you see your flame get pulled down some when the draft fan pulses? How far is your dampener pulled out?

See the pics of the manual C6 and C7 specs along with the pick of my flame on PR1. I opened the door for the pic, but you can see from the holes in my burn pot I dont have any incomplete burn or buildup.

 

[Jeremy6500]

I dont think the OAK needs to be insulated at all unless you are having some kind of condensation issue.

If you are referring to the duct work, I know we ALWAYS insulated both the supply and return for installs in unconditioned spaces. Attics especially.

I would always recommend insulating the duct work. If not you could be losing a lot of heat/cooling BTUs

 

[Jeremy6500]

Also wanted to make sure you didn't miss these ash cleanouts? Reason I ask is because I did for a long time and my flame was always lazy and pellets didn't burn well. I thought they were indicating the 2 slide doors on the bottom that drop the ash into the ash pan, but they weren't. They were pointing to 2 doors that slide up and allow access to chamber behind the burn chamber you can see. This is where the draft fan is hooked to and you get a lot of ash build up. Once I cleaned it the stove burned really well.

I also read your other thread about settings.

Here is a link to a thread I posted that had door/bonnet and exhaust temp readings. Keep in mind that I only have 3 heat settings vs your 5. I am still messing with mine and would like to get my exhaust temps down some. I may try dropping my c6 setting down some.

USSC and other setting info

FYI this thread has info about USSC/King/Ashley/American harvest setting. I did some searching for info and didn't find it, so I did my own experiment and am posting to help others. A couple of points: 1. My Stove is a AH6500. It IS NOT as stove. It is a furnace that is made to be hooked up to...

www.hearth.com

 

[slowlymakingprogress]

The photos of your burn pot and flame look really good and clean. I checked settings C6 @25 and C7@40. When I use these settings it keeps my exhaust temp down. I got HR1 @1.5pph and HR5 @5pph. When I keep draft settings low exhaust temps on HR1 stay about 120 and door is about 210 than when ramped up to HR3(current setting) exhaust is about 190 and door is about 490. Bonnet in HR1 maintains about 78 than when ramped up to HR3 it’ll be about 103. The door glass will blacken like this but wipes clean very easy. I noticed this morning that my pellets in hopper were hanging up on incline because of dust buildup. I’m starting to feel that could be quite a trouble and causing Smokey burn chamber. Maybe all along I should’ve been thinking pellet screening before I dump bag in hopper?

 

[Jeremy6500]

The photos of your burn pot and flame look really good and clean. I checked settings C6 @25 and C7@40. When I use these settings it keeps my exhaust temp down. I got HR1 @1.5pph and HR5 @5pph. When I keep draft settings low exhaust temps on HR1 stay about 120 and door is about 210 than when ramped up to HR3(current setting) exhaust is about 190 and door is about 490. Bonnet in HR1 maintains about 78 than when ramped up to HR3 it’ll be about 103. The door glass will blacken like this but wipes clean very easy. I noticed this morning that my pellets in hopper were hanging up on incline because of dust buildup. I’m starting to feel that could be quite a trouble and causing Smokey burn chamber. Maybe all along I should’ve been thinking pellet screening before I dump bag in hopper?

Your exhaust temps are definitely lower than mine. I checked and I am at about 160 on PR1 and 320 on PR3. I usually run on PR2. My door temp is about the same on PR1, but hard to compare because my door is glass. I read just above the door, which is probably a different location than yours. Bonnet on PR1 runs about 70*.

I tried lowering my CR6 settings by 10 down to 115 but it didn't seem to make any temp difference. I may try and drop it again. One thing I have noticed is that the factory settings on mine were completely jacked. A while back I reset my controller to start with a clean slate. Default had my PR1 at 5pph and PR3 at 13pph. That's crazy

I wonder if you already have a good natural draft so you don't need to do much with the draft fan.

I am curious how the person in your other thread was able to run PR1 on .75pph. I can't seem to go below 1.6pph. I tried 1.5pph and after it running on PR1 for a couple days it eventually burned itself down enough that it gave me a no flame code and shut down. Of course if it kicked up to PR2 every once in a while for a bit it would have kept burning fine, but the outside temp was warm enough that the thermostat never called for heat with the stove running on PR1.

Maybe if I turned the draft down a lot more it would slow the PR1 burn rate down enough to run a lower pph. It would be nice to be able to save the pellets if not needed.

I don't screen my pellets and never had them effect the burn.

My door setup

 

[slowlymakingprogress]

In one of my other threads how he ran such a low PPH the only I can think of is how he has his unit in a shed on side of house so when temps are cold it is constantly giving a short run(quick path) for cold outside air to burn rather than drafty basement air or in your case regular room air. I’d adjust your C6 and C7 settings down but only ten at a time and keep record of it so you can always go back. I’m foggy on which you should adjust first but some of the other guys in here I think(sorry if I’m wrong) said do low setting first. My exhaust is all 3” Selkirk from unit right into clean out T than about 12” vertical to a 45 than three foot run to another 45 than 24” run(horizontal) with 90 on end where it goes into 8x12 chimney so I think I got decent draft. I’ve tried doing 1pph on hr1 but had same results you got when lowering rate to much so that’s where I think the FAK would be useful. My pellets are good quality minus the sawdust but last year that happened on one ton but the other two ton I burned were fine.

 

[slowlymakingprogress]

So here is my version of fresh air kit. It’s a 25’ piece of 4” flex hose that has a wire in it to prevent collapsing under small vacuum. I ran it to a hole on basement wall that accesses a small crawl space that has a small hole to outside air. It may not exactly be a direct link to outside air but it drafts good colder air cause you can feel it flowing through where it connects(hangs by a wire from damper slide) to ash pan air inlet. I don’t believe it’s anything to be patent worthy but nonetheless it works really good so 8500 isn’t pulling in basement air for combustion and seems to provide a more complete burn. Anyone have a link to site where I could look into getting burn pot extension for ussc king8500?