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Hi all. I heat a huge farmhouse with a Newmac GAO, and grated coal and wood "add-on" furnace, and have been trying to figure out a way to design and install an improved baffling system to extract more heat. All it has now is a simple piece of plate installed horizontally 12 inches above the firebrick, and it seems to do little.
There is a barometric damper on the smokepipe between the furnace and chimney and I have it set as lightly as possible. Has anyone tried modifying the internal baffling in a Newmac?

I've also thought of installing a copper coil in the firebox connected to a taco pump to pump hot water to a distant upper floor in an addition that is not served by ducts - I'd just buy a salvage radiator and hook it up. Is there an expert on installing hot water coils in these furnaces on here??

Coal Jockey wrote:Hi all. I heat a huge farmhouse with a Newmac GAO, and grated coal and wood "add-on" furnace, and have been trying to figure out a way to design and install an improved baffling system to extract more heat. All it has now is a simple piece of plate installed horizontally 12 inches above the firebrick, and it seems to do little.

Is this it?
**Broken Link(s) Removed** It doesn't show any internals, can you scan your manual or post pics?

The baffle probably just creates a longer path for the gases to get out of the unit, sort of making it into a two pass unit. The longer retention time would capture more heat is the basic concept. I would not recommend playing with it without actually seeing it first

This is the big problem with a wood/coal combo furnace.. if you design the firebox and heat exchanger so that it burns wood well, then it is a compromise for coal...

A heat exchanger for wood MUST be simple and easily cleaned on the inside so that you can scrape the creosote accumulation off the surfaces. Without being able to clean it, it will soon be insulated by an inch or two of creosote and it will not exchange any heat at all to the house air. With a coal stove it is much simpler to make an efficient heat exchanger because the fly ash from coal will fall off most vertical surfaces or only accumulate an 1/8" thick or so.

All the above said,, the only way to increase the heat out put is to increase the surface area that the house air washes over on the outside of the furnace surface... You may be able to increase the temperature of the furnace body some by adding another baffle in the firebox, but the increast will be minimal.. you need a larger heat exchanger area..

That's where the water coil comes in... There are several threads about installing and plumbing a water coil to a hot water tank, and to hot water baseboard. Do a site search for 'water coil' or even 'coil' Each instalation is specific to the stove,and the house in question.

I think you are the only person owning and operating a Newmac furnace... So you will have to be your own 'guinea pig'. There are guys on the site who have been very creative and who have lots of welding and plumbing skills who have been sucessful with adding a water coil/heat exchanger system into a coal stove. You will have to search and sit back and read... If I run across suggested threads I'll come back and post links here.

What I would suggest,, and you probably won't like, is to find a good coal boiler. Made to burn coal.. if it is a hand feed and you only ocassionally burn VERY DRY wood, then you could burn wood in it too. But with a boiler, and some water to air heat exchangers in your heat ducts, you will have alll the heat you want and you can tap off hot water and add some baseboard in the remote parts of your house that need heat.

An actual coal burning boiler is what you need because it is designed to heat water, with coal as the primary fuel.. The eficiciency of the boiler will be many time that of a coil in a wood/coal furnace. The water to air heat exchangers can be purchased from the outdoor wood boiler guys... do an ebay search for 'wood boiler' or 'outdoor wood boiler' you will find lots of heat exchangers for sale in various sizes and capacities.. pick one that fits your ductwork and heat transfer needs.

As coaledsweat suggested in the previous post, a view of the Newmac furnace will help us help you..

Greg L

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Thanks, if you click on this and scroll down you'll see my furnace. I hesitate to replace it as it is only three years old. The furnace body panels stay cool as the oil furnace blower pumps cold air through it around the firebox. It has a plenum above it just like an oil furnace. There is no restriction inside the firebox besides the plate I mentioned. I was hoping to design a more elaborate system of baffles to really make the heat stop and think about things before whistling up the chimney - I have great draft. I can't post pictures because I have no camera and its a raging inferno. I'll keep searching as time allows.

**Broken Link(s) Removed**

You mentioned that you have a barometric damper set as light as possible.. Have you ever checked the actual draft?? If you have an exceptionally strong draft in your chimney you may need a larger or a second barometric damper to control your draft...
Do you have a thermometer either on or in the flue pipe??

Greg L

No thermometers anywhere. There sort of is "two" barometric dampers - in that the oil furnace has its own smoke pipe with baro hooked into the same chimney. Both operate when either furnace is burning. This may not be what you had in mind though. I've aldo considered making up a sort of heat reclaimer box surrounding the first 2 feet of the smoke pipe where it leaves the furnace as the cold air return duct runs just above it, and to hook into that and sort of "pre warm" the returning air and cool the outgoing exhaust all at once.
Anyhow, gotta run, late for work!!

Coal Jockey wrote:No thermometers anywhere. There sort of is "two" barometric dampers - in that the oil furnace has its own smoke pipe with baro hooked into the same chimney. Both operate when either furnace is burning. This may not be what you had in mind though.

Get two thermometers, one for the stack and one for the heat exchanger so you can tell what is going on.

How tall is your chimney and what size is the flue? It sounds like you need a bigger baro.

You should have a stack damper on the oil burner if its two pipes in one flue.

Hi coaled sweat,
My chimney is about 25 feet, 8" stainless liner in a cement block chimney. House sits on a ridge. She DRAWS!
The barometric damper I have on the Newmac is the one that came with it...

I'll have to research thermometers - where do you install them and what makes would you recommend?

What's a "stack damper"?

The oil furnace automatically fires up when the other cools off to a certain point - disabled person in the house who cannot walk, let alone do stairs to the cellar - so must keep the oil on standby always when I'm away.

This summer I'm going to dive in to the firebox and wirebrush the heck out of the surfaces - lots of goopy wood creosote etc that may be affecting heat transfer...although the coal fire is a pretty intense heat right now - how anything even vaguely combustible like creosote can survive in there is a mystery, maybe its burned off since I last looked in the fall.

If I could find an old handfired steam or hot water boiler and some salvage convectors or radiators, I'd consider replacing the hot air units. It must be CHEAP (as in free if I remove and haul it away etc) . I enjoy the rituals associated with tending a fire, and always have, and would rather shovel coal than fix busted stokers. My grandpa told me enough horror stories of his school janitor days trying to keep old stokers going with cheap slack coal and breaking dozens of shear pins. Just give me a shovel

Coal Jockey wrote:I'll have to research thermometers - where do you install them and what makes would you recommend?

What's a "stack damper"?

Get a cheap magnetic one for the stovepipe. You can watch the tempeture response when servicing and it will tell you how healthy your fire is by how long it takes to ramp up the temp.

A stack damper is an electric device that closes the stack when your oil burner isn't running, with two devices on one flue you may be siphoning heat through the oil burner up the chimney.