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Issues with airflow in pellet furnace hookup

Post in 'The Pellet Mill - Pellet and Multifuel Stoves' started by cgokey, Jan 29, 2013.

  1. cgokey

    cgokey New Member

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    I'm have some issues with airflow (more like lack off airflow coming out of many of my registers) in my hookup of a St. Croix SCF-50 pellet furnace. The diagram here illustrates the pipe coming from the furnace that hooks into the supply air and one thing that I notice is it goes in through the side. I see three potential issues with my setup:

    1) I've got mine hooking in the main trunk through the bottom of the main trunk near my oil furnace with a backdraft damper sitting in between the oil furnace and the supply plenum opening. Air just goes straight in through the bottom with no angle to try and direct it across the main trunk.

    2) I've got a pipe almost directly above the supply plenum where the hot air enters, so it might be directed up first and not across... I think that might be my issue as I might not be getting the pressure in the ducts that I need...

    3) The 800 CFM blower just can't handle the amount of duct work in the house and if that is the case, do I have any alternatives to make things work better... Stronger blower...? Blower in the duct work?




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  2. jrsdws

    jrsdws Feeling the Heat

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    I have a different furnace but a similar set up. I too have better flow at some registers than others. I've experimented a lot with closing registers in some parts of the house and even putting magnetic sheets over them to try to force more air down other trunk lines, etc.

    What I've found to work best for me is register booster fans.

    http://www.amazon.com/Suncourt-HC500-B-Flush-Register-Booster/dp/B001WT11Y2

    I'm sure there are others available but this is what works for me. I have one duct run to the kitchen that I need to install in-line duct booster fans in as the registers are under the cabinets and the register boosters won't work there.

    Next step for me will be some duct insulation to help alleviate heat loss on those long runs.
  3. cgokey

    cgokey New Member

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    Thanks you. I'll check this out. I'm curious did you setup your hot air supply from the pellet furnace directly to your regular furnace or did you tap in directly to the main trunk duct work?

    Another thought I had and I've heard some people do this is to hook your supply duct work directly to the cold air return of your furnace. Supposedly when the hot air heats up in there, it will turn on the oil furnace fan on, which is obviously much stronger fan than in my wood pellet furnace... The oil furnace fan is definitely strong enough and reaches all the registers. I read some people have set things up this way, but the manual for the SCF-50 directly says not to do this. Are they just covering themselves liability wise or is this really problems with this???

    "Follow all instructions when connecting to existing ductwork. Connecting the Warm Air Supply to the Cold Air return may cause harm to the existing furnace and may void the warranty of both the existing furnace and the SCF-050."

    Chris

  4. jrsdws

    jrsdws Feeling the Heat

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    Central Illinois
    My biomass furnace ducts directly into the plenum on my gas forced air furnace.

    I also use the gas furnace's cold air return system to the biomass furnace and installed a filter in it.

    I would assume that using your oil furnace's fan to distribut the SCF-050's heat would only cool it down before it reaches the registers. I've heard of a few people using their furnace fan to circulate stove heat, but I know mine blows far too hard for that.
  5. SmokeyTheBear

    SmokeyTheBear Minister of Fire

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    How well sealed are all of the joints in all of the ductwork?

    People chase air flow issues in hot air systems all the time only to discover leaks in the joints.
  6. 343amc

    343amc Feeling the Heat

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    I found out the joints in my hot air ducts were as solid as swiss cheese. A couple big rolls of foil tape and some duct wrap made a huge difference in airflow upstairs, and especially register outlet temps.

    I'm hoping the benefits carry over to the summertime with AC as well. My basement was always pretty darn cold in the summertime. Now I know why - lots of air was leaking out of the joints. Hindsight being 20/20 I should have sealed those joints years ago.
  7. jrsdws

    jrsdws Feeling the Heat

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    My guess is that mine is not so great either but I've honestly never given it any attention. I have no issues getting air to the 2nd story. I always just assume it was easier for that slow flow of heat to rise.
  8. DexterDay

    DexterDay Guest

    My Fahrenheit goes into the Duct just as yours does (straight in, no bend) and mine works great. But....

    I believe your problem lies in your #2 and #3 comments. The pipe directly above the plenum inlet and undersized for the amount of register ls.

    Have you thought about closing off that upstairs run (pipe above.inlet)?? Maybe the increase in pressure and heating below will set up a good convective loop? Especially if you have a return upstairs? A return will pull the wa air up (that naturally wants to rise anyways)?

    I only have 6 registers in my system. Would have 14 if it was the whole house (North trunk and South trunk), but just the North side works awesome. The heat naturally returns and migrates to the South side (convective loop). My entire system is also sealed well and insulated.

    Seal up the leaks, insulate the best you can, and close of some sections of the house. Experiment

    Oh and Jrsdws's furnace is a BEAST!! 2,000 CFM distribution blower and over 150,000 BTU (180k?) !! His house Glows when its running!!
  9. cgokey

    cgokey New Member

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    I agree, I can definitely reduce the # of registers. I've got two registers in the living room, two in a spare room, two in the kitchen, one in the downstairs hallway. I was thinking of just capping those and not using them. That reduces things by 4 or 5 and might help increase the pressure.

    I think that I'm going to move that plenum inlet from the main trunk, I may just do it right and pipe it directly into the side of the oil furnace... I'll need to think about a backdraft damper there, I imagine it will have to be much larger...
    Maybe for now, I can try just some sheet metal and see how things work.

    I just got a couple bags of HearthSide pellets from Lowes tonight, so I'm going to give those try, starting to get colder again here... Curious how much of a difference those make than my North American Pellets.

    I'll keep experimenting... Your idea of north/south side sounds like worth a try as well.

    Thanks for the feedback!
    Chris

  10. DexterDay

    DexterDay Guest

    Never heard of the pellets you just got, but North Americans are a Shoulder pellet IMO. Not the greatest

    Closing those 5 will help dramatically. I would even place magnetic covers on the tops of the registers upstairs, qlong with any manual dampers.

    As for extending the inlet. The father away you pipe it, the less Umph (read:power) that blower will have. Basically, adding another turn and 10 more feet of 10" duct may hurt more than help. ???
  11. exoilburner

    exoilburner Feeling the Heat

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    Try adjusting the majority of the registers ducted nearest the blower more closed. Maybe that will build up a little air pressure in the main plenum and balance out the air flow more evenly to all of your registers. Total air flow should still be the same but more balanced. If your registers are all wide open there will be very little plenum pressure and the air pressure to the furtherest register is going to be the looser. This is what I do to get the temperature balanced nicely in all my rooms. I tweak a couple of the registers when shifting from the pellet furnace to the oil furnace because they are not located closely.
  12. cgokey

    cgokey New Member

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    Yeah, not impressed with North American... Now, the HearthSide, what a difference in heat... They were almost the same price as what I paid for the North American and puts a LOT hotter heat. I've heard good things about the ash content too, bags says <.6% where the North American are < 1% so, I think that I'm going to pick up more of these, especially for the colder days.

    Yeah, I've thought about that, but I've got so many branches off the duct work that I think I may just run myself into more trouble if I just try and find another place... Anywhere I go, I've got a branch running just to the left or the right of where I plug the inlet in... I'm thinking that if I start at the end, plug up those registers I don't really need, I might be able to get a little more pressure in the main duct work... It is a short run from the pellet furnace to the oil furnace plenum, so that is probably a good thing.
  13. cgokey

    cgokey New Member

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    So cleaned the pellet furnace tonight.. What I found after using these pellets was a caked on amount of soot in the stove, especially near the heat exchange elements. Also the clinkers were pretty rock hard.. Yet, the heat that came out of the stove was noticably different and much hotter. Any idea what this means? I might have another variable here too and not related to these pellets. I changed the jumper setting on my furnace to wood pellets only from corn/wood pellets only, so it puts out a little more pellets, so maybe this might be the reason too.

    Chris
  14. DexterDay

    DexterDay Guest

    Pics??

    I cleaned my furnace today too (well, I emptied the ash pan and pulled the exchange rod :)) Not really a cleaning. LOL

    Have you cleaned this area before? Is the flame different? Is it active ??
  15. cgokey

    cgokey New Member

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    Yes, every week I remove the baffle plate just below the heat exchange rods. What I noticed this time and didn't notice last time was a caked on material (usually powerdy and just blows right off), literally had to scrape it off... No pics, I'll try to grab some next time. The flame is a lot stronger and fuller with these new hearthland pellets... Also clinkers I noticed a very very hard. I'm definitely getter more heat though from these pellets. It might be related to this new setting too switching from corn/wood pellets cycle time to just wood pellets, little faster distribution of the pellets. Just curious what sign caked on material means and if others see this.

    Chris
  16. cgokey

    cgokey New Member

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    Couple more questions.

    1) If I have the supply air from the pellet furnace going directly into the supply plenum of the oil furnace, when the temp rises in the supply plenum will the oil furnace fan turn on and help distribute the air (it has a little thermostat right in the supply plenum of the oil furnace)?

    2) Why does the picture state it needs a backdraft damper in the supply plenum of the oil furnace? All it is doing is pushing hot air into the oil furnace supply plenum, which I would imagine all it can do is help the oil furnace if I use them both in conjuction? How can hot air going in hurt the oil furnace where it pushes hot air in anyhow?

    Thanks,
    Chris


  17. 343amc

    343amc Feeling the Heat

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    One issue is an "air circulation loop" - hot air will go into the plenum of the oil furnace and circulate through the cold air return back to the pellet furnace, assuming you have both the hot air and cold air ducts connected.

    I read that the fan in the primary furnace could turn on if the plenum temp got high enough. Not sure what would happen short of two blowers possibly fighting with each other. My guess is the blower on the oil furnace would be blowing against the blower from the pellet furnace potentially causing an overheat condition in the pellet furnace.

    The backdraft damper I put in my oil furnace is a homemade one. I couldn't find a prefab one that would fit above the A coil for my AC unit. Its a sheetmetal plate I slide into the plenum. It will swing up if the blower in the oil furnace kicks in and let air flow through, then drop back down when the blower turns off. I can slide it out if I want to use the oil furnace or at the end of the heating season. Cheap and dirty, but it works. I have a round "butterfly" backdraft damper in the outlet of my furnace which will keep air from circulating through the pellet furnace come AC season.
  18. Ejectr

    Ejectr Minister of Fire

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    Did you check to see if the supply lines coming off the main feed trunk to the registers have dampers you can open and close to adjust the air flow to the register? Maybe if you do have those, some of them are closed or partially closed where you have low air flow.

    You installed the SCF to an existing furnace supply system, so maybe the dampers are there.
  19. cgokey

    cgokey New Member

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    I don't think hot air and cold air ducts are connected there is a piece of metal separating each space. Not sure if that is what you mean or not.. So if warm air gets piped in, I don't think it will enter the cold air return.

    As for two blowers fighting each other, yes/no, I do have a backdraft damper sitting between the oil furnace and the pellet stove, so no air should make its way toward the pellet furnace.

    So, if I just heat up the oil furnance plenum AND I'm not filling up the cold air return AND I do have a backdraft damper preventing the oil furnace fan from blowing into the pellet stove, I would think this would work, no?

    Chris
  20. cgokey

    cgokey New Member

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    Yes, I've even experimented by closing all manual dampers and leaving just one open... and I don't see much difference. I'm thinking my main duct work is just too large and the SCF-50 fan is just not large enough to push enough air in there to properly get pressure... I'm thinking about seeing if I can leverage the oil furnace fan by heating that plenum open and letting it push the air through, but I've read others think it will cool down the air too much, so that may not work either :(

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