"John" wrote in message
...
Ed Huntress wrote:

"Dave Lyon" wrote in message
news:tIApf.638866$_o.604585@attbi_s71...

That's interesting. I'll have to take a look sometime. The exhaust
sounds
like some of the modern gas furnaces. And stirring the corn sounds
almost
like burning in a fuidized bed. Does the air blow through the
burning
corn,
or over it?

The air blows through the corn.

Well, that is something like a fluidized bed, then. That can be a very
efficient way to burn things.


Also, the combustion air is piped in from outside the house.

That hurts your combustion efficiency because it reduces flame
temperatures,
but it reduces infiltration. In the tradeoff, it undoubtedly is a lot
better.

--
Ed Huntress

Any furnace should get its air from an outside source. You already paid
to heat the air inside the house at most a 95 percent efficency. The
outside air is part of the flame so it could be considered to be 100
percent heat transfer. You can get kits for your oil burner to burn
outside air. Also a guy I know put a kit on his burner and also a
damper to stop the air flow when the furnace isnt running to keep the
heat in the firebox and flue. He is working up data on the change of
efficiency now. He has to run it a couple of months to get some good
data.

Outside air avoids air infiltration, but burning with cold air reduces
combustion efficiency. It's an old engineering problem from steam- and other
subfields of combustion engineering. Preheated air makes for a more
efficient system.

In a house, using already-heated ambient air, as you say, is bad economy.
Also, burning inside air draws in air from outside -- infiltration, which
knocks the hell out of your overall heating efficiency.

I thought it was worth pointing out that there is an engineering tradeoff,
as there so often is, but that it works out in favor of burning outside air.

If you burn softwood, burning with cold air can really foul up your chimney
because of incomplete combustion of tars, unless the system is designed for
it.

--
Ed Huntress