Quick Question on Draft for a Newmac multifuel wood/oil/coal CL86-96G, forced hot air

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Hobbyfromhome

Member
Jan 1, 2020
7
Maine
Good evening all. I've got a draft question. I've had the above furnace installed when my house was built about 9-10 years ago. Heating with coal was definitely a trial by fire... Took a couple of years and I finally figured it out with some help from some friends. Heating guy that installed it never knew how to heat with coal, go figure....

Anyway, my Mother had to get a new furnace last year which is a newer Newmac model Wood/Oil for forced hot air. You have two drafts on the furnace. One below by the ash pan which is supposed to be closed from my understanding at all times and this is the case for both my Mother’s furnace and my furnace and this is what the manual says as well. Is this supposed to be the case when burning coal and, or wood?

The issue that I have is when I was cleaning her furnace last week, I noticed that the upper draft that’s by the fan or maybe it’s an auxillary fan that blows air onto the wood or the coal until it reaches the desired temperature in the house based on the thermostat was only ¾ of the way open. This fan shuts off when the set temperature is reached and turns back on to stoke a fire when the temp drops below the set temp.

In the manual whether one is utilizing wood or coal, it states that that upper draft is supposed to be open or all the way to the right, but when one is utilizing oil only, it’s supposed to be all the way to the left.

The Heating/plumbing guy who’s been in the business for over 30 years said to leave it where it was set when I questioned him about my Mother’s furnace. He didn’t give me a reason why it was set that way and not all the way to the right when I asked, but that it was good where it was.

Well, this got me thinking. I know this guy and he knows what he’s talking about and even though he didn’t give me an explanation and my mother has a bigger house than mine, but can heat it really well; over 2000 sq ft with probably 6-8 cords of wood in Northern Maine which is pretty darn good.

I thought, what the heck, I’m going to try and bring my upper draft control to the ¾ position as I’ve had issues with heating my 1800 sq ft ranch especially when it’s below 0 Fahrenheit. I have to keep the fire box really full and heaping and the coals burning bright orange to keep the house warm. (I heat with Kimmel nut coal, but also have Blaschak nut coal as well) Both heat very well, although I've seen where it's been said that kimmel puts out a little bit more heat or btu output... Not a coal expert so I don't know how true that is.

I’ve noticed that my house heats better and the coal fire will last longer along with the house staying warmer and not getting really cold come morning when I wake up. In the past there could be a 10 degree difference by the time I wake up around 6am from the night before at 8pm-10pm. I fill it up with coal in the morning and at night going about 12-14hrs in between. Should I leave it the way it is, or bring it to half for better heat efficiency or return the draft as the manual says all the way to the right in the fully open position?

I always wondered if I had that upper draft open all the way to the right if it was causing most of my heat to go out the chimney. With the results I’ve had in the last week or so this almost seems the case and I’m using much less coal then I have in the past with fires lasting longer… They’re lasting like 16+hrs. Does this make sense to anyone? Any thoughts or guidance would be greatly appreciated.

I just had the draft and, or barometric damper checked as well before the beginning of the season and everything is in tip top shape just in case anyone was wondering….

Happy New Year to All!!!!
 
Not sure I follow the details of what is open/closed exactly...but in general, wood doesn't need any air from under the fire, but coal does...that's its main combustion air...then on some coal burners, they put a little (not a lot) air in over the fire to help burn off the coal gas. I tend to agree that have the upper control completely open sounds counterproductive...but it would also be helpful to know exactly what these controls do/where the air goes.
Have a model #? Or even better, a link to a manual?
 
Found this too...might help, maybe?
 
That's hilarious Brenndatomu... when I read the post that you said to look at for more information that was actually my post from many many years ago. LOL! I knew I had an account but I couldn't remember what it was so I had to make a new one. LOL! That is too funny.
 
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That is pretty funny!
Learn anything "new" after reading it again all these years later? ;lol
If the setting you tried recently is working better, I'd go with it...sounds like Newmac can't find their butt with both hands! Although I think they are owned by USSC now...not sure if that is a good or a bad thing...can't be great in my opinion, the one time I called USSC, they couldn't seem to even buy a clue!
That old thread was one of the first things to pop up when I googled your model #...they must not have sold a ton of them.
One thing that stood out to me when reading that old thread was that your were running 0.05" draft...sounds high to me for coal...I'd lean toward running -0.03" (manual specs -0.03 to -0.05") that will give the heat more time to transfer to the furnace/heat exchanger walls, and less up the chimney. Now by lowering the draft, you may need to run your adjustments open a bit more...maybe...might have to fiddle with it, the old trial n error.
But I also have limited coal burning experience too...ran some through my old Yukon Husky wood/coal/oil furnace...it worked pretty good after I figured it out, but since I had tons of "free" firewood here, I decided to stick with that instead of paying for coal.
Oh, and I don't think that running that draft fan (the one hooked to your thermostat) is going to do much besides blow heat up the chimney...it works better with wood, but not much. The one furnace I had that had the forced air draft like that, I just quit using the fan on it...used way too much wood when I did, better to just run it without the fan, more like a big ole whole house manually operated wood stove.
Anyways, not sure if any of this rambling helps you at all...