Boiler heat exchanger location

MNfarmer Posted By MNfarmer, Jul 23, 2017 at 11:29 AM

  1. MNfarmer

    MNfarmer
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    Sep 28, 2011
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    I have an indoor boiler that's piped to a forced air heat exchanger above the wood furnace but with that set up we have no back up heat. I picked up a used gas furnace and I'm wondering if the heat exchanger can be installed between the furnace filter and the furnace it's instead of in the hot air plenum? My thinking is that way if the are ever gone and the gas kicks in it won't be blowing through a cold heat exchanger? Any thoughts or recommendations? The boiler is an old Royall 6526.
     
  2. maple1

    maple1
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    Sep 15, 2011
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    Not sure I understand but wouldn't it be blowing through a 'cold' exchanger anyway - just in a different place?

    Also if the wood boiler is out, it's water should not be circulating, so the heat exchanger won't be very 'cold' - it will be the same temp as the hot air around it in short order. But I'm not sure I'm reading right - you have both a wood boiler, and a wood furnace? Seems odd to have two wood burners.
     
  3. MNfarmer

    MNfarmer
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    Sep 28, 2011
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    I am only using the wood furnace for the blower. Sorry for not being very clear. I'd like to replace the wood furnace with a gas furnace and have a backup heat source. I didn't know if putting the heat exchanger on the cold air return side would help with efficiency when the gas kicks on. Another question is if it would make the air too hot going into the blower motor? Thanks for the reply
     
  4. maple1

    maple1
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    Ok - a backup is very good to have.

    I don't think doing that will do anything for efficiency. Might hurt it if anything - the heat would then have to travel through the backup furnace before it gets delivered to the house, and there could be some heat loss out the LP chimney/vent. Too hot going into the LP furnace may also be a concern but not sure. I think the generally accepted place to put it is where it sounds like you have it now - but some may have also done what you were thinking about. Maybe you'll get more feedback - I don't have any first hand experience with this.
     
  5. Bad LP

    Bad LP
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    Nov 28, 2014
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    In a former house I had (1996) it was built running a Williamson oil fired hot air furnace into a Dover (Sangerville, Maine made IIRC) wood furnace with no ill effects. Matter of fact if you ran it hard it would send you outside on a -30F night wanting to cool down.

    I'm sure if I still owned it and had this resource I could have got it working properly. The positive side was when the wood went out it returned to oil on it's own. It could not have been very efficient.
     
  6. MNfarmer

    MNfarmer
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    Sep 28, 2011
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    Thanks for the replies! So what would you all recommend then, above the furnace or in the cold air return? I see the plusses and minuses both ways. Would it waste much heat being blown through a cold heat exchanger, obviously the exchanger will warm up but will it siphon through the boiler and keep warming up cool water?
     
  7. maple1

    maple1
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    Sep 15, 2011
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    I would put it above.

    Not sure on the pluses putting it in the return - don't think I saw any? I think the ones I read about doing it, did it strictly for space limitation reasons.

    The siphoning possibility you're picturing should be less with it up higher - heat exchangers are more apt to convect naturally when they are mounted lower. Been there, with a sidearm.
     

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