Pipe fans

[mtarbert]

Greetings all,
I am thinking about installing a fan gizmo that fits in the stove pipe . The ads claim they gleen more heat from the heat that would otherwise go up the pipe. Any thoughts or problems from these will be appreciates.
Mike

 

[elkimmeg]

If one has taken note there is a lot of post concerning draft issues. Extracting heat from the system,
will reduce draft and increase cresote build up. Both of which reduce stove preformance. It is possible, such a unit could have a negative loss effect, less heat out of you stove due to poorer draft

 

[NFreiermuth]

Right on the money ELK!

I remeber the "Magic Heat" stack blowers that used to be on the Huge Steel "American Eagles". I also remember the creosote running down the stacks too. Gotta believe they cause MANY problems.

 

[Corie]

I would avoid these.

What kind of stove do you have? It seems if you think you're putting that much heat up the flue, you should probably consider replacing the old stove, since I bet it's an old unit.


If it's a Phase II newer unit, extracting that much heat from the flue is sure to make your draft performance suffer significantly, not only because of the heat removal, but also because the pipe heat exchanger seriously slows the flue gases.

 

[Rhone]

To clarify why they're not good, I only know for newer units. When you see a wood stove is 72% efficient the first thing that comes to mind is you're wasting 28% of your heat out the flue. That's not correct, that heat is needed to power your stoves draft and suck the exhaust out... it could be higher. There were wood stoves developed that were over 80% efficient, but they didn't allow enough heat to go out the flue to establish draft, fans had to be added to assist exhaust. Their R&D did some poking and came to the conclusion a wood stove that needs to be plugged in to be able to burn would be a flop, people would rather have a slightly less efficient stove that can run during a power failure so they removed some of it's transfer efficiency so more went up the flue. Also, the nightmare of trying to synch an exhaust fan with the variability and changes that happen during the burn of a fire and the added cost and design issue of dealing with a unit that's not safe to use without power but whose fuel will continue to burn. They'd have to invent and vigorously test a feature that extinguishes the fire if the power goes out (or exhaust fan fails). Much of what I say is incorporated in pellet stoves whose feed & fuel allows precise control. Over 80% efficient, power assisted exhaust, power out failure feature (when the power fails, the unit no longer feeds). They found the 80% efficiency mark is as high a wood stove efficiency can be and still have enough heat going up the flue to establish draft. That's why you see wood stoves teetering around the 71-76% efficiency range. Don't get combustion efficiency confused with transfer efficiency. Wood stoves can have over an 80% combustion efficiency.

So, I know with newer units the heat that's going up the chimney is just enough to power the draft and tapping it is dangerous, what's going up is the minimum to keep your unit working safe and effective, there's no excess.

 

[BikeMedic2709]

Thanks Rhone! I have been wondering for a long time about these things. I've been concerned about the creosote issue. This has made my decision!

 

[Gooserider]

Interesting, but one thing occurs to me, and this is PURELY speculation - I have no intent of trying one of these things, and on the primary stove couldn't if I wanted to since I don't have enough exposed pipe...

I grant the earlier comments about the modern stoves needing a certain amount of "inefficiency" to power the draft. It makes sense, but at the same time I note that they are also supposed to need a certain MINIMUM chimney height to get the required draft as well, and that taller chimneys provide more draft by their very nature. It would seem to me that someone with a high natural draft chimney could benefit from a "more efficient" stove since they wouldn't need as much to power the draft. However since the stove makers (IMHO quite reasonably) can't / don't make different efficiency models to fit differently drafting chimneys it would seem like some folks are "wasting" energy driving a draft that is already more than good enough...

I even see posts where some folks with extra tall chimneys complain about having too much draft and need to install extra dampers to restrict the flow further. If a person had such an extra-tall high draft chimney, might they be able to install something like one of these units (possibly with a bypass?) instead of using a more restrictive damper?

I'm thinking of a friend that has a geodesic dome house, his stove is near the center of the dome, the pipe goes up a good 3 tall floors before it goes through the roof to the outside, and I don't know how far above that. I'd expect his setup to pull a major vacuum at the stove before he even lights a fire, so how much heat does he really need to spend on driving the draft up the flue?

Gooserider

 

[suematteva]

Rhone;

Thanks for the explanation!

 

[Todd]

I can tell you from experience that those heat reclaimers reduce draft and create creosote. I tried it with 2 different stoves, one pre epa, and the other epa. Had the same results from both. Black dripping goo inside and outside the chimney. And even some dripping on to my hearth. Don't try it, you need that heat for draft.