wrote:
wrote:


Take two single-walled flue pipes of different enough diameters
and place one inside the other

that's a co-axial pipe. A dozen commercial products use it. Flue
gases flow out, exchanging heat with combustion air.


Some gas appliances and pellet stoves work that way.


Nick sounded as if (sometimes he posts without proofreading, I can
show you some posts where he confuses the dimensions of thermal
conductivity and thermal conductance)


Interesting. I don't recall those mistakes. I archive most of my postings at
http://www.ece.villanova.edu/~nick. If you send me a list, I'll fix 'em.


he was proposing a THIRD airflow that would bring vent air into the
living space.... a pipe inside a pipe, inside a third pipe.


No... just 2 pipes, with room air vs outside air flowing back to the
stove in the space between them.


And yes, George, it's not a "new" idea. He didn't claim it was.


It may be new, but it seems obvious to someone "skilled in the art."

It seems quite clear that Nick thinks it it "new" also "obvious" and the
fact that he is "skilled in the art"

By the way, what's YOUR track record vis-a-vis optimizing thermal designs?


George says he's an expert. Let's try an extremely simple test. If 10 cfm
of 70 F combustion air warms to 800 F before it exits a woodstove to enter
a perfect conterflow heat exchanger and 560 cfm of 70 F room air enters
the other end, what's the temperature of the room air at the other end
of the heat exchanger?

Where did I claim to be an expert, Nick. I asked you some very simple,
practical questions,

Remember this part;

Tell us Nick, What is the wall thickness of these pipes?

How much do they weigh?

How do you propose to support this weight?

With the forced air feed to the stove, how hot will the stove end of the
inner pipe get?

How hot can it get before it starts to slump under it's own weight?


Anyone can answer, but it would be fun to let Nick give it a try first.

You can see how Nick works. He just doesn't answer the questions.

All the theory in the world is not worth a pair of fetid dingos kidneys
if it is not practicable.

Now, I could go to the trouble of changing Nicks units to SI units, Dig
out the relevant books and answer Nicks question. Might even get it
right. Nah, it would be a pointless exercise.

The question is this: Is Nicks little day dream practicable.

Come on Nick. Is it practicable? Have you done this? Does it really work?

I'll give you a hint. It does work. It was as noisy as all get out. When
the contra flow fan was not running it was cooking in the heat rising up
from the stove.

In the end the simple solution was a nice quiet fan near the ceiling to
de-stratify the air in the room.

Had I done the maths, the result would have been the same. Not worth the
trouble.

Not a new idea. As obvious as all hell. I have the skill to build it.

Would I do it again? NO.

I opted for a Masonry Contra flow stove for heating. And no motors.