# Opinions - Flue Pipe Heat Sink...



## Peter B. (Jan 30, 2009)

I posted something similar in the Hearth Room awhile back, but thought I'd give the Boiler Room a try as well.

I'm heating with an antique parlor stove to which I've made some modifications for improved efficiency and safety... or at least I'd like to believe they're improvements.

At a fairly normal 'cruise', the flue pipe internal temps run close to 500*, with the stovetop (surface) a roughly corresponding temperature.  For the most part, the performance of the stove is steady and reliable, but I'm inclined to think I'm wasting heat up the flue.

I'm already using a manual pipe damper, and do NOT have any interest in the available flue pipe heat 'reclaimers' (due to their creosote production and difficulty to clean).  Nor do I want to add the noise of a fan.

It occurred to me that an 'honest' heat sink - say 18-24 inches of extruded aluminum with radial finning - that fit snugly around a length of 6" flue pipe might extract some of the waste heat.

But I'm surely no engineer, and have no way of estimating what - if any - gain I might get from such a 'device'.

Almost certainly, it would condense more creosote, but the flow through the flue pipe proper would not be impeded (as it is with the reclaimers), and the pipe could still be readily brush cleaned when necessary.  Conceivably, some kind of open shroud over the heat sink with a deflector above to direct the convection downward might help... I haven't thought that far yet.

I'm afraid 'prototyping' the heat sink would be very expensive, but also thinking the per piece unit cost thereafter might be survivable.

What I'm asking is whether some among you think an appreciable amount of heat could be extracted this way... or am I just whistling in the dark?

Thanks For Your Time.

Peter B.

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## Eric Johnson (Jan 30, 2009)

"Efficiency" and "Round Oak Stove" don't belong in the same sentence. If you want to burn wood efficiently, get a modern stove and polish the RO up and admire it for what it is--a beautiful antique. There have been so many advances in woodburning technology over the past 100 years that just about any stove you could find--with the possible exception of a Franklin Stove--would be more efficient and safe.

I'm not trying to rain on your parade, but that's a fact.


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## Peter B. (Jan 30, 2009)

Alright, forget my errant use of the word 'efficiency'... forget I'm burning in a Round Oak.

Is there any benefit to be derived from the flue pipe heat sink as described?

Peter B.

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PS - If I described the internal modifications I've made, you might actually acknowledge I have done the old RO some good.

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## Eric Johnson (Jan 30, 2009)

Without a fan, I think it's doubtful. I'm not aware of anything like that commercially available, and you'd think there would be if it worked. The thing that makes the conventional "heat saver" stovepipe inserts work to the extent that they do is the fact that they obstruct and slow the smoke to some degree, allowing it to be absorbed by the device and dissipated into the room. With only a damper to modulate the fire, I think you wouldn't experience an appreciable gain. OTOH, it might be fun to experiment with if you have the skill to build one and field test it.


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## Eric Johnson (Jan 30, 2009)

You should buy my used 8" add-on catalytic combustor. That would do what you want, plus eliminate most of your creosote.


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## Peter B. (Jan 30, 2009)

Eric Johnson said:
			
		

> You should buy my used 8" add-on catalytic combustor. That would do what you want, plus eliminate most of your creosote.



Thanks... I already have a catalyst installed in-stove.

Peter B.

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## Fred61 (Jan 30, 2009)

You are obviously burning wood for fun and not for efficiency because you are not getting your money's worth out of your wood. There is a safety issue. Round oak stoves are a beautiful work of art but they have burned a lot of houses. Be sure you have plenty of clearance from combuttables especially at the thimble to the chimney.

Stretching several springs around the pipe would scavenge some heat heat as they would act as fins out in the air. The hot stove is pumping air upward and the hot springs would turbulate the air. I don't know how long a spring will stay a spring after prolonged heating.


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## Peter B. (Jan 30, 2009)

Fred61 said:
			
		

> You are obviously burning wood for fun and not for efficiency because you are not getting your money's worth out of your wood. There is a safety issue. Round oak stoves are a beautiful work of art but they have burned a lot of houses. Be sure you have plenty of clearance from combuttables especially at the thimble to the chimney.



Sheesh... so many nay sayers and not one useful answer.

I've been burning the same stove off and on for over 30 years.  I wouldn't say that was recreational use.

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I surely didn't want to argue whether my stove was efficient or not (though I could debate that to the death).  Just wanted some sort of meaningful answer to the posted question.

If there was *nothing* to be gained by it, why would so many devices use heat sinks to dissipate heat?

I'm at the point of saying 'thanks, anyway' but if someone actually wants to try to answer the original question, I'm all ears.

Peter B.

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## Eric Johnson (Jan 30, 2009)

I like the internal catalytic combustor. Does it work well?

I thought my observation that nobody makes a version of what you're proposing--which ought to tell us something--was a legitimate response to your question. Given that it would be much easier to install and maintain than a traditional heat saver insert, I think they'd be all over the place if they worked.


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## Peter B. (Jan 30, 2009)

The internal cat moves forward and back in a slide... it's bypassed in the retracted position.

In concert with a fairly elaborate internal baffle and a supplemental air feed to the firebox, it works fairly well... though the catalyst currently in use is a little tired after x years of use.  (I have a fresh one in reserve.)

The stove vents from the top... after all exhaust passes through the baffle and catalyst.  I make some creosote in the black pipe sections, but overall, I think I'm doing reasonably well... given the stove.  With a good, hot fire the smoke downwind (outside) smells sweet and clean... with no 'off' odor.

Springs might represent an inexpensive trial... thanks for the suggestion.

I'd be inclined to think the simple economics of my idea are what might have prevented adoption.  I bet (even after prototyping is complete), one of the suggested heat sinks would still retail over a couple of hundred dollars.

I have an inquiry in the works with an aluminum extruder outfit.  If they have the patience to respond, I'll post what they have to say re: cost.

Peter B.

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## Peter B. (Jan 30, 2009)

CZARCAR said:
			
		

> how about a tee atop the stove with 2 pipes to a second tee above which rejoins pipes into 1 flue.



I've done that in years past, but don't (now) want to introduce something that isn't *easily* cleanable.  I'd have to break down the tee 'loop' to clean it... and it wouldn't be that easy to clean itself... just like a Magic Heat or similar.

Peter B.

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## Peter B. (Jan 30, 2009)

CZARCAR said:
			
		

> MH HAS scraper plate & fan. 4tees + 2 elbows would allow easy cleaning thru capped elbows.



Hard to visualize this without a diagram...

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I'll let my original question float for a while yet... and would welcome additional input.

Thanks.

Peter B.

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## sfriedri (Jan 30, 2009)

Peter,

Sounds like a good idea from a theoretical standpoint.  What is the orientation and length of your stove pipe?  If the stove pipe is vertical I would assume you would plan to mount your fins so that they are oriented vertically to take advantage of convective air flow over the fins.  However, I would think that if your pipe is anything less than say 5' you would not get much extra heat off the pipe.

The biggest problem as you mentioned is that by extracting any extra heat you would increase creosote buildup in your chimney.  Having a flue temp of 500F is actually right in the ideal range from the standpoint of minimizing creosote.  By reducing flue temp you will also reduce your draft.  Does your stove pipe feed into a double wall stainless chimney, or just a masonry chimney?  If it is the later, I would not try anything that reduces your flue temp.


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## Peter B. (Jan 30, 2009)

SWF said:
			
		

> Peter,
> 
> Sounds like a good idea from a theoretical standpoint.  What is the orientation and length of your stove pipe?  If the stove pipe is vertical I would assume you would plan to mount your fins so that they are oriented vertically to take advantage of convective air flow over the fins.  However, I would think that if your pipe is anything less than say 5' you would not get much extra heat off the pipe.
> 
> The biggest problem as you mentioned is that by extracting any extra heat you would increase creosote buildup in your chimney.  Having a flue temp of 500F is actually right in the ideal range from the standpoint of minimizing creosote.  By reducing flue temp you will also reduce your draft.  Does your stove pipe feed into a double wall stainless chimney, or just a masonry chimney?  If it is the later, I would not try anything that reduces your flue temp.



SWF:

Thanks for this...

Yes, I thought it would be best suited for a vertical run... but I only have about 3' feet total (at present, on the first floor) to work with.

I was at least partially aware of the increased creosote and decreased draft problems.  I did NOT know that my typical (present) flue temps were in a 'good' range with respect to minimizing creosote.

The black pipe feeds into Class A... and the total run from stovetop to sky is... what (?)... maybe 25'.  (I made the installation 20 years ago and never thought to measure the total height.)

I guess I'll pursue this unless or until I get a quote from an extrusion outfit (or two) that turns the idea into expensive pixie dust.

But, meantime, I'll keep bumping the thread...

Peter B.

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## waynek (Jan 31, 2009)

Peter,

A couple of individuals in the Boiler Room sandbox here are not playing very nice...trash talking your Round Oak Stove. I really admire your ingenuity and the research and development modifications you have done to your stove. Philo Beckwith could of used you years ago in his R & D Department.

Maybe some day your efforts will produce a drop-in adaptation for all the Round Oak cylinder stoves that are still burning out there and the stoves yet to be burned again.

Don't pickup your toy in the sandbox and go home. Keep the ideas coming.

Thank you and best regards,

Jackpine


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## Peter B. (Feb 1, 2009)

jackpine said:
			
		

> Keep the ideas coming.



Jackpine:

Thanks for your encouragement...

I haven't heard back from the extrusion company as yet, but I'll get after them next week if they don't reply.

I actually think it might be possible to design a (nearly) 'drop-in' retrofit package for certain Round Oaks... but even after twenty years worth of tinkering with my own stove off and on, I don't consider I have the perfect recipe by any means.

Meanwhile, with this weekend's break in the weather, I was able to clean the chimney and the catalyst, and install a somewhat improved secondary air supply.  A quick and dirty experiment for the moment, but it should help me dial in the sizing needed for a more permanent version.

I have other ideas I'd like to pursue one day, but the stove is typically in use almost 24/7... though tonight being mild (mid-20's), I let the fire burn out.

Next year I'll have a shop set up (for the first time in a long while) and should have more time to spend with additional improvements... but I think I may be done for this season.

Round Oaks were certainly built well, and were highly thought of in their time.  The D-16 was my first stove, and at this point, it seems likely to outlive me by a good margin.  I doubt many modern stoves could provide over a hundred years of service.

Peter B.

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## Duetech (Feb 1, 2009)

Peter B.,
Your concept has been tried before and works at least the fins. I had a furnace man look over my old wood furnace who recommended the fins only made from galvanized sheet metal. There is an addition to the creosote and it will boost your cleaning frequency. I used 2" 22ga galvanized bent at 90 deg. with the "fins" cut at about 1/2-3/4" which allows you to wrap the finned strap around the pipe. You probably won't need over 6' as too much heat extraction would really cause creosote buildup. It's relatively inexpensive and does gain a little in output as the creosote is testimonial to though I don't know as it is that much gain. As the creosote builds the effectiveness of the fins diminishes though they do still transfer heat. Mine was never in a shroud but that would have been an easy fix. Instead of using 2" galvanized use 1 3/4" and use the 3/4" for the fins then use an 8" pipe for the shroud. There are various collars you can use to secure the shroud to the black pipe. There are also some very quite duct booster fans that could be used from a  2 x "T" configuration so you could force the heat downwards but them a ceiling fan/light would look better and gain you more across the seasons functionality.
Also 400 is the minimum you should go for stack temps in ideal conditions 450-500 is a better safety/work margin.


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## Peter B. (Feb 1, 2009)

Cave2k said:
			
		

> I had a furnace man look over my old wood furnace who recommended the fins only made from galvanized sheet metal.



That certainly sounds like an economic way to at least test the theory in basis, but I concede I'm not highly skilled with sheet metal work.

Most of my other modifications have relied to some extent on the catalyst 'doing its job'... but much of the heat it produces is still at top of the stove, near the flue outlet.  Perhaps I should concentrate more on trying to promote improved combustion in the flue box proper... which the added secondary supply is hoped (in part) to do.

I think it has made a difference, but so far, I have only a single 3/4" feed tube... and the intake air is probably not heated as much as necessary to support continuous secondary combustion.

I enjoy futzing with the stove, and in fact it's my primary source of heat, so I'll likely keep trying to make incremental improvements.

Thanks for the input.

Peter B.

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## waynek (Feb 4, 2009)

When you examine the shape of your stove is it possible that Round Oak modified the cylinder to dissipate heat. A clean cylinder radiates heat outward and heat rises straight up to ceiling. The cylinder shape of the Round Oak stove is interrupted first by the cast iron ring above the fire pot and secondly by the cast iron dome and seperate ring. This interruption causes turbulence and to a certain extent stops the immediate rise of a specific volume of heat, possibly radiating heat towards the floor. To extract additional heat from the stove burn, my direction would be to address it at or near the fire, which is the sheet metal stove body.

To support my point I will share an experience with infrared thermography. A neighbor is a professional building inspector and he brought his infrared camera over to my home a couple of years ago to map heat loss room by room. I asked him to shoot the Round Oak stove...very interesting.

Design a crescent moon shape fin device to be placed around the body of the stove. Knock some rivets out of the door frame and bolt a bank of fins to the frame. If necessary, attach a support vertical piece at the back of the stove. You would have about 16 to 18 inch high sheet metal surface to work with.

Jackpine


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## Peter B. (Feb 5, 2009)

jackpine said:
			
		

> The cylinder shape of the Round Oak stove is interrupted first by the cast iron ring above the fire pot and secondly by the cast iron dome and seperate ring. This interruption causes turbulence and to a certain extent stops the immediate rise of a specific volume of heat, possibly radiating heat towards the floor. To extract additional heat from the stove burn, my direction would be to address it at or near the fire, which is the sheet metal stove body.



jackpine:

I missed this post yesterday...

Here is a pic of what I've used on my stovepipe as a deflector for a number of years.  Crude, and likely not very effective, but in fact I can see cigarette or incense smoke roiling around the edges when the stove is hot.

You may be right that I'd have more luck trying to extract heat from the stove body.  I guess what I really should do first is see if I can find a nearly SILENT fan I can tolerate... and see if that a) moves the heat through my rooms any better, b) seems to bring down overall stove temps a little.

Anyways...

Peter B.

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## waynek (Feb 7, 2009)

Peter B,

You continue to amaze me in stove modification to capture more heat. The stove pipe add-on device is another example. Now if you would expand the device to a 16" diameter size and put a couple around the stove cylinder you would be close to what I suggested...placing fins around the cylinder.

As a side, I have a couple of questions. That is an interesting stove pipe damper. Is the damper body oval shaped rather than round and does the damper handle say round oak on it?

In addition, what can you tell about the object sitting on the stove lid? it looks like a stove grate or a corn planter plate.

Thank you and best regards,

Jackpine


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## Peter B. (Feb 7, 2009)

jackpine said:
			
		

> As a side, I have a couple of questions. That is an interesting stove pipe damper. Is the damper body oval shaped rather than round and does the damper handle say round oak on it?
> 
> In addition, what can you tell about the object sitting on the stove lid? it looks like a stove grate or a corn planter plate.



jackpine:

The damper is indeed oval... made of heavy tin.  The handle was originally part of a finial and yes, it says Round Oak on it.  I wanted the damper as close to the stove outlet as possible, and opted to use a more 'stylish' handle.  (The finial wasn't complete anyway.)

I believe you're right... the object on the stove is from a planter of some kind.  I don't recall where I found it.  I tried to use it as a grate at one point, but it cracked readily and was 'demoted' to a trivet.

Peter B.

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