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add on harman furnace install

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by jakepursell, Oct 7, 2008.

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  1. jakepursell

    jakepursell New Member

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    im adding this furnace to my exsting furnace have a couple questions.im going to give this its own 18-8 return that will be ran from my panning about 12 feet to my furnace with a 20 -8 drop coming down to the wood furnace.my supply is 16-8 wich is going to come right off the plenum of the wood furnace and go into the 16-8 ductwork of my other furnace.this will be about 3 feet away from my gas furnaces plenum.one of my questions is do i need a damper it says nothing in the instructions.if running the ac is the only concern i can block off the wood burner in the summer. my other question is i bought a humidifier should i install this on my wood furnace or the gas?i plan on using the wood most of the time.my harman furnace does have b blower to.

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  2. jakepursell

    jakepursell New Member

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    i hope this is in the right section nobody is saying anything
  3. stee6043

    stee6043 Minister of Fire

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    I can't tell exactly what you're asking??? Two things - the way you're describing your duct runs sounds more like electrical wiring speak to me. 10-2, 18-8, etc. Second, you might need a diagram to help us out.

    My understanding of add-on furnaces hooking directly up to ducting is that they require a damper to do two things - force flow through the add-on furnace when it's on and prevent flow through the add-on when it's off. This is assuming you're using the blower of your existing furnace to do the work. If you have a built in blower on your add on furance you may need a damper to prevent flow in the "wrong direction".....I don't really know....
  4. jakepursell

    jakepursell New Member

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    i was asking do i really need a damper the only thing it will do if i dont is heat the basement i no i dont want the ac to blow in the wood stove so i will block it off.i also wanted to no if i should mount the humidifer on the wood stove or the gas.my wood furnace does have a blower.
  5. stee6043

    stee6043 Minister of Fire

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    In my limited research of the add-on furnaces before I went the gassifier route I do recall that there was a good reason the damper was required. You should probably call the manufacturer.

    I'd put the humidifier on your furnace. Keep it a litttle further away from the add-on furnace. But that's just me...
  6. Rattlesnake

    Rattlesnake New Member

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    I'm new here, just had a Harmon pf100 installed a month ago by the dealer. He did not install a damper, but my oil burner has one for each zone, located between the oil furnace and the heat outlet of the pellet furnace. Is it the correct way, who knows? I am in the learning process as well.
  7. laynes69

    laynes69 Minister of Fire

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    Yes, If I read this right, your 8x18 the return, your 8x16 is supply. If you are installing the furnace with a parellel install, then dampers need to be in place. I would assume this is what you are talking about. The heat from the wood furnace, could and would go backwards into the main furnace, if a diffuser or damper is installed, then it shouldn't. If its installed in series, then there should be a by-pass for your a/c to not run through the furnace. If you are using the blower of the main furnace to push air throught the wood furnace, then you don't need the dampers. Mainly because the air will flow in one direction. Sounds as if you are on track though with the install. Post some pics, and It will explain a little more.
  8. exoilburner

    exoilburner Feeling the Heat

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    I installed a Harmon PF100 pellet furnace about 10 months ago. Here is what Harmon's installation manual says.

    The PF100 warm air supply and the cold air return must be installed in a parallel arrangement. EXAMPLE:The warm air supply duct from the PF100 is to be connected to the warm air supply of the existing furnace. Also the cold air return duct from the existing furnace is to be connected to the cold air return duct of the PF100. Isolation dampers (2) should be installed in the ductwork. (1) in the warm air supply duct for the existing furnace and (1) in the warm air supply duct of the PF100 after or “downstream” of the high limit/fan control. These dampers can be manually operated or fully automatic. In either case, the unit that is not being used must be prevented from being operated. (This also can be done manually or automatically.

    The warm-air supply outlet of the PF100 shall not be connected to the cold-air return inlet of the central furnace because a possibility exists of components of the central furnace overheating and causing the central furnace to operate other than as intended.


    I am no expert but what I understand is, there are 2 types of dampers. One type is before the heat registers to keep the duct air pressure up and balance the duct system air flow. The other type is Isolation dampers in the hot air duct to isolate the two furnaces. Like the Harmon manual talks about.

    For manual isolation dampers I installed a sheet metal duct air filter holder assembly in the hot air output duct of each furnace just down stream of the high limit/fan control. Then instead of putting an air filter in them I made sheet metal blanking plates and slide them into the filter slots to isolate the furnaces. This way I wouldn't wonder if automatic dampers had shut completely or not. And they are much cheaper than the automatic isolation dampers. (The blanking plate from the operating furnace would be removed.) The high limit fan control in the furnace should prevent overheating if I forget to take out the plate.

    Hope this helps......good luck :)

    [​IMG]
  9. laynes69

    laynes69 Minister of Fire

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    Thats a perfect way to isolate the other furnace. The only thing is if you ever need the main furnace in case of a backup, then you may be in trouble. Can't stress the importance of a damper to block the main furnace to keep the woodfurnace or pellet furnace from backfeeding into the system. Thats a real simple solution.
  10. exoilburner

    exoilburner Feeling the Heat

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    laynes69,
    Both furnaces have this removable isolation damper downstream of it's "high limit/fan control". The picture was only the oil furnace to show what the damper looked like. I wired the 2 furnaces so that only a single furnace can be running at a time. Either furnace will heat my house well. I'm not an expert but running both furnaces at the same time seemed to have some questionable interactions. I would rather err on the side of safety. When I want to switch to the non-running furnace I just slide out it's damper and slide in the damper for the running furnace. It doesn't take much time to switch and has completely isolated both furnaces. I run the oil furnace when doing maint. on the pellet. Takes about 3 min to switch the dampers and transfer the electric power. Waiting for the running furnace shut down takes a little time.

    The Harmon PF100 pellet hopper will hold a 2 - 3 day supply of fuel.

    I agree with the importance of isolating one furnace when the other one is running. The residential HVAC eng. who checked mine out said there are issues with no isolation dampers installed. In a paralell install like mine, I would think the non running furnace ducting would bypass the house register ducting and steal some percentage of the air flow to the house registers.

    Harmon PF100 pellet furnace
    Outside air
  11. laynes69

    laynes69 Minister of Fire

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    I opted for a series install with my wood furnace. This way I had no dampers in the system. Before when dad owned the house, he installed this woodfurnace I have now. It was parallel w/o any dampers. When I purchased the house, I couldn't get the house over 68. Installed in series and I can get it 80 if I wanted to. Too much heat loss backfeeding through the LP furnace. I like the idea of having a piece to remove to access the damper. Makes life much easier.
  12. exoilburner

    exoilburner Feeling the Heat

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    laynes,
    That’s a pretty interesting temperature difference between the series and parallel installs. The old parallel must have had some pretty serious back-feeding going on without dampers.

    I thought about parallel and series installs. I decided on the parallel because in series it seemed to me the duct air flow would be going thru the duct fan of the non-running furnace. (and the Harmon spec said parallel) In your series install, does the non-running furnace duct fan appear to be an obstruction in the duct? Are you getting good air flow to your house registers from both furnace blowers? Your air flow must be pretty good with the house temperatures you get. What’s the CFM of the furnace duct fans?
  13. laynes69

    laynes69 Minister of Fire

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    I have some obstruction, I need to enlarge my duct going into and out of the wood furnace. But right now I have 3 8" lines going into the woodfurnace and 3 going out the top. I want at least an 8x18 in and out. I have a 100,000 btu Lp furnace that I use its blower. It goes through the LP furnace into the woodfurnace and out the top of the woodfurnace. No blowers on the woodfurnace its self. Its probably an 1600-1800 cfm blower. I have it set on low speed on the LP furnaces circuit board, this way its a little easier on the blower. Its also easier because right now I have no a/c on the system. Whats nice about the series, is I use the whole return air in the home. When the blower kicks on, the woodfurnace feels just like the regular furnace, and sounds the same. Only the Lp doesn't run, just the blower. If it calls for heat on the Lp, then the relay shuts off, the furnace fires, and back to the woodfurnace heat. I can load up for the night, and not worry about a thing if it goes out, or doesn't keep up. Instead of using the lp heat exchanger, the woodfurnace is my heat exchanger.
  14. exoilburner

    exoilburner Feeling the Heat

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    laynes,
    So your 1500 USStove Hotblast Wood/coal Furnace must be designed for a series install because it doesn' have an internal duct fan and uses the fan in the propane furnace. That kind of explains why you got the big house temp. improvement when you went series. My Harmon PF100 has a duct fan in it as big as the duct fan in my oil furnace.

    So I guess for the best air flow, when both furnaces have duct blowers its probably best to do a paralell install; when both furnaces use the same duct blower a series install is best. But I'm no expert; there may be other factors involved too.
  15. laynes69

    laynes69 Minister of Fire

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    It was meant to be installed in parallel with the Lp furnace. Originally had 2 500 cfm blowers on the back. But the manual showed a series install. So I modified the furnace a little and did series. Much better.
  16. exoilburner

    exoilburner Feeling the Heat

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    laynes,
    Now that you mention it I remember that my Harmon furnace did not come with a duct fan. It had to be ordered separate from the furnace. I wonder if thats why Harmon sells them separately. For a series install????? The dealer automatically ordered my fan with the furnace as though it was required, and the Harmon manual does say parallel only. :-S

    The series install would require some electrical control work to be done like you did so the pellet furnace could control the duct fan in the propane furnace.
  17. laynes69

    laynes69 Minister of Fire

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    I have a relay on the back of my woodfurnace to control my forced draft. I also have a limit/control for the woodfurnace. When the relay energizes, I have 2 wires on r and g on the relay and the circuit board on the LP furnace. That way it kicks in fan only mode, until heat would be needed from the LP.
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