It's Done. My Chubby Stove Heat Exchanger Retrofit.

I built a heat exchanger/blower as a retrofit to my Chubby Stove. The design requires no drilling, cutting, or modifying the Chubby Stove in any way. The heat exchanger is a 6" diamter tube (fabricated from regular steel flats) with a 6 3/4" lip that sets in the 6" opening in the top casting of the Chubby. I have some 3/8" stove gasket in place around the lip. I used steel flats instead of aquiring 6 inch steel tubing because it was way cheaper than custom ordering the tubing. The tube has a divider runing down to the last 1 inch of the tube. I constructed a round manifold on top of the tube that channels air around in a circular pattern and then down one side of of the tube down into the firebox. The air comes up the other side of the divider and straight out the top of the manifold.

I thought I'd have a high temp fan mounted directly on the rectangular intake of the manifold, but it turns out these fans are too heavy at 5-6LB. Instead, I fabricated a round-to-rectangle adapter and have 4" aluminum duct running out of it down to a fan. I'm going to paint all the duct work black to match the stove. What's shown is actually a fan in a plywood box I was using for ventilation in a hydroponics system. The box just provides baffling of the fan noise. I am still looking for the right, quiet fan for this application that doesn't cost a fortune. The super quiet type fans cost over $100. I'm leaning towards using a 6" inline duct booster ($30) and a reducer to 4". Unkown yet how the sound will be and what kind of baffling is needed to eliminate unwanted rattles and noise. A stove blower should be silent or at least an unoticeable white noise in the room.

So how well does it work? VERY WELL. It got down to 50 this weekend at night, so I burned a small wood fire to test it out and cure the paint. Out the top of the exchanger comes a blast of extremely hot air at a good rate (the fan right now is 165 CFM). The manifold itself is completely cool to the touch even with the stove at 425 degrees for 2 hours straight. I had to shut off the fan in order to get the manifold up to temp to cure the paint. I would assume that is a good sign that the heat is being srubbed off the manifold and down through the heat exchanger.

Couple things not yet done:
Find the right fan setup.
Paint all the duct work black.
Add a small deflector over outtake opening to direct the air out into the room rather than straight up.
Bolt or screw the lid shut more tightly and with some flat gasketing to prevent leakage around the rim.
Run it more on cold nights and see how well it circulates air in the room.

wow... A+ on the efforts bro!

are you anywhere near the south shore of MA? Larry might have a chubby (or 20) sitting around his garage with heat exchanger tubes built in and a fasco blower sitting around you could swap and offer him a lil' money to make up the diff???

dcrane wrote:wow... A+ on the efforts bro!

are you anywhere near the south shore of MA? Larry might have a chubby (or 20) sitting around his garage with heat exchanger tubes built in and a fasco blower sitting around you could swap and offer him a lil' money to make up the diff???

I paid $400 for my Chubby on Craigs and bought a couple hundred in parts from Larry and other materials like paint and sandblasting to refinish it. The bimetal draft regulator I configured was more money on top of that, but they don't even come with those. In the end it would have been slightly cheaper to buy a reconditioned unit from Larry, I have family on the south shore and could simply drive there to pick it up. But, I was in it for the project and learning exercise. It was fun. The blower model new is $2000. I would love to get a brandy new Chubby, but there would be quite a diff there to pay into. Someday maybe.

Congratulations on thinking different. Measure the smoke pipe temperature before and after using your fan to see the difference. Would be even better to measure with your unit detached from the stove and then attached.

franco b wrote:Congratulations on thinking different. Measure the smoke pipe temperature before and after using your fan to see the difference. Would be even better to measure with your unit detached from the stove and then attached.

Are you referring to measuring the stack temperatures?

JRLearned wrote:

franco b wrote:Congratulations on thinking different. Measure the smoke pipe temperature before and after using your fan to see the difference. Would be even better to measure with your unit detached from the stove and then attached.

Are you referring to measuring the stack temperatures?

Yes, the stack temperature when using your unit and without, to get some idea of effectiveness.

If stack temp comes down slightly when using your rig it means that you are gaining Btus into the living space that would otherwise be going up the chimney.

Lightning wrote:If stack temp comes down slightly when using your rig it means that you are gaining Btus into the living space that would otherwise be going up the chimney.

I didn't think I was going to gain any BTUs, but I'd be glad if I did. I just thought it would help circulate the heat rather than it sitting in that one area where the stove is. I'll have test the temps and see, if it gets cold one night soon.

I agree partner. Even if there is minimal BTU gain at least the circulation should be dramatically improved

A box fan would have done that...... But I realize you are having fun fabricating all this stuff. We all do the same thing.

Kevin

KLook wrote:A box fan would have done that...... But I realize you are having fun fabricating all this stuff. We all do the same thing.

Kevin

Box fan, shmox fan! :punk:

You sure took to welding in a hurry! Looking good!!!

I don't know how well your design will work but I think it clever and a different approach. Anything that increases the air flow over heated surfaces will increase the heat transmission of that surface, as for instance a box fan. This design is different as it adds heat exchange surface within the stove as does the Chubby design with blower. I am not a fan of the bulk, but this is a prototype and not necessarily a finished design. It's to prove a point. It should lower stack temperature as well as improve circulation. There is also the baffle effect of the tube extending into the stove that might direct gasses into closer contact with the stove sides and improve heat transfer.

franco b wrote:I am not a fan of the bulk, but this is a prototype and not necessarily a finished design. It's to prove a point. It should lower stack temperature as well.

Agreed. If I were to build it again right now, I'd make the manifold shorter: more of a skillet than a dutch oven in size. Also would have designed the intake round from the start. I would compact the whole manifold. As for effectiveness, I can just tell from operating it that the air coming out of it is HOT. Much hotter than with a fan blowing on the stove surface. A few tests/measurements like you suggested and we could probably put together a model to prove some tangible benefit.

Also keep in mind I have one radiant and one fan powered floor vent/duct with a big heat collector above the stove: http://www.amazon.com/gp/product/B0085UZ8EK/ref=w ... UTF8&psc=1. So getting the hottest air up to the ceiling helps heat the upstairs better.