Heat Exchange Tubes Modification

So, here's another idea that I've been considering. My Breckwell wood pellet stove has two rows of tubes that run front to back in the fire box about 8 inches above the combustion box. The convection blower forces room air thru them and most of the heat I get out of the unit blows out thru the tubes in the front. The first two pictures show the inside and outside.

My idea is to run a row of 1.5 inch tubes across my furnace above the coal bed between the loops of the water coils. Maybe about 6 of them in such a way they wouldn't obstruct normal tending and maintenance. On the outside of the fire box I would have a "cup" on one end of each tube to catch air that's being forced up thru the air jacket and direct it thru the tube. I would need to cut holes in the fire box wall and weld the tubes so they are completely sealed so air couldn't penetrate into the fire box. All thoughts and concerns welcome. What material would be best? And do you think the additional heat exchange area would produce valid results?

According to the math Area of a cylinder wall is (2)(pie)(radius)(height)
2 x 3.14 x .75 inches x 20 inches long = 94.2 square inches
94.2 sq in x 6 tubes = 565.2 sq in
565.2 sq in = 3.925 sq feet

So I would gain nearly 4 square feet of heat transfer area directly over the coal bed..
If I did that right

How efficient is your stove in its current state?

Make it so water coils can be pulled...

Would installing one end lower than the other help the air to flow naturally from the low end to the high end as it is heated over the fire or isn't there enough pitch?

Been done. It works!!! See the AK110 and AK220 from Leisure Line. Good photo's on their web site in the products section of what your proposing.

Rev. Larry

lsayre wrote:How efficient is your stove in its current state?

Being as honest as I can, I'm willing to say 75-80% heat transfer wise but that's just an educated guess.

CapeCoaler wrote:Make it so water coils can be pulled...

Yes, I would still be able to pull the coils forward and taken out thru the load door if needed.

titleist1 wrote:Would installing one end lower than the other help the air to flow naturally from the low end to the high end as it is heated over the fire or isn't there enough pitch?

Air is forced thru the furnace with blowers. I would put a "cup" on each end of the tube. The high cup would create a high pressure area at that end, directing air thru the tube. The low cup would create a low pressure area at that end, helping pull the heated air the same direction. Then the heated air would just follow the course of the rest of the air in the air jacket. The air in the tubes would gain extra heat, then just be distributed with the rest of the air.. See picture

blrman07 wrote:Been done. It works!!! See the AK110 and AK220 from Leisure Line. Good photo's on their web site in the products section of what your proposing.

Awesome! I like this idea because it gains heat transfer area overall where heat sinks rely on conduction from the opposing side of the fire box wall.

Maybe 1.5 black pipe. Hole saw for perfect fit. Half inch of thread on each end
and secured with thin nut similar to electrical conduit or could even be secured with bead of furnace cement.

Thanks Franco, I was considering having them welded because of all the positive pressure in the air jacket. Or maybe a nut on each side of the fire box wall.