I had the opportunity of discussing open fireplace issues with Fred Schukal at Sleepy Hollow Chimney Supply, Ltd. when we both were asked to speak to the Natioanl Chimney Sweep Guild in April, 2007.

Fred is clearly a believer in his Rosin and, like me, one of the few interested in open fireplaces. Among his admonisions are:

1) Fireplaces should be small. (I agree)

2) The entire fireplace and flue should be insulated. (I agree.)

3) The parabolic fireback of the Rosin directs heat back into the fire to concentrate the heat, burn cleaner and radiate more heat. He criticises the Rumford for having a smoke stained straight fireback indicating that it doesn't get hot enough. (Sounds good except there are plenty of pictures of Rosins with smoke stained firebacks too.)

4) Advocates top-down fire starting and doesn't like tipi fires. (Logical consequence of the shape of the firebox.)

5) The Bellfires stainless steel throat is a transition from the Rumford throat he modeled after ours directly into the round SS flue with no smoke shelf or smoke chamber. Claims small unit can be vented by 5" flue. (I agree with Rumford that the abrupt temrmiation of the throat and the smoke chamber volume will discourage sudden downdrafts. If, in fact the Bellfires can be vented by a 5" flue I think it might be more likely due to the smoothness of the SS throat.)

It would be interesting to do some comparative testing.

Jim Buckley, 4/07

Fluid Dynamics
Date; 2/20/05
To: Buckley
From: Charles Riggs

Comment on the venturi effect discussion. I think the round concept question ignores a difference in objectives. In the fireplace you don't want the streams to mix. In a carburetor you want to maximize mixing effects.

Follow up question on the air space question. In the firebox, do you mortar the firebrick to the back up brick? Is so, what type mortar?

New question: Should the chimney be topped with a rain cap? If not, where does the rain water go? Do you leave weep holes in the outer shell?

Charles,

Answer 2/20/05

I suppose that a carburetor is not an adequate analogy - maybe not even a very good one. I hoped that it would be something familiar to someone who never heard of Bernoulli and couldn't spell venturi.

But I think your comment about objectives is just a matter of focus. Where exactly - before or after the nozzle - you are focusing? The air intake of a carburetor is designed to keep the flow of air laminar and to maximize it's volume and speed through the narrow part of the venturi because it's main function is to draw in fuel by the reduction in pressure created in the venturi. Then, as the mixture of air and fuel exits the carburetor into the manifold and certainly by the time the mixture is drawn into the cylinders, you want the streams to mix turbulently for good combustion - especially in the cylinder - which is one reason why the Chrysler Hemi engine was so good.

Like a carburetor, the flow of air into the curved Rumford throat is laminar. That's the main purpose of the Rumford throat so we focus on it. The intake to a carburetor does the same thing but it's not the main objective and not where we focus. Does flow through the Rumford throat create a partial vacuum that helps to draw the smoke through the throat? I don't know, but it's not where we have focused. The analogy may be lacking since the main function of the Rumford throat is to keep the flow laminar until the mix is shot into the smoke chamber while the main function of a carburetor is to create a reduction of pressure to draw in fuel. However, in both a carburetor and a Rumford throat, the flow into the venturi is laminar and the flow out of the venturi is turbulent.

You don't say so but I suspect you know a lot about fluid dynamics. Maybe you'd be interested in a related issue and tell me what you think.

Most combustion engineers argue that they want turbulence in the firebox for better combustion. In an open fireplace, too much turbulence in the firebox will make the fireplace smoke. We do want turbulence in the neighborhood of the fire but then we want those turbulent products of combustion to stop being turbulent - or at least be confined - so that they flow into the throat without mixing with the dilution air flowing into the Rumford throat. We think we know that the flow into the throat is laminar but the devil is in the details. Is the layer of combustion products turbulent but overwhelmed by the sheet of laminar flowing dilution air? Can we make the throat smoother to reduce turbulence with the result that we can make the throat smaller and reduce the amount of dilution air? Or do we want to add spoilers in the firebox to increase the local turbulence within the fire for better combustion efficiency?

I think Rumford got it right - or at least pretty good - and that modern science (the part that hasn't moved on) probably can only expect to make minor improvements in the best solid fuel radiant heater ever developed.

On to the mundane........

Yes, I like to build a composite firebrick/backup masonry firebox. The firebrick I lay fast with weak corner-to corner joints between the fireback and the covings without taking the time and effort to cut the firebrick and weave it in the corners. Then I back the firebox up with at least 4" of solid masonry laid with Type S mortar, taking care to weave the back up units in the corners to make it strong if not pretty, and slush the half inch or so between the firebrick and the back up masonry solid with mortar. I leave an air space or bond break between the composite firebox and outer masonry shell of the fireplace. Other masons take time to make the firebox stronger and leave the air space or bond break between the firebrick and the rest of the masonry but I find that takes more time, isn't as strong and often the vertical joints between the fireback and covings don't look as good.

The vast majority of American chimneys are wide open at the top. It's certainly better to keep rain out of the chimney and to protect the top of the chimney from weather. If you don't it will lead to more maintenance. Where does the rain go if you have no rain cap? Generally it's absorbed in the masonry which, by ASTM standard can absorb up to about 12 % of its weight in water and still meet the "severe weather" (SW) standard. Clay flue liners are only allowed to absorb 8% of their weight but that's still a lot of water. Masonry "breathes".

Best,
Jim Buckley

Comment on Orton Rumfords
See also "Which From: "John Harrison Jones"
To: "'Jim Buckley'"
Subject: RE: Rumford Fireplaces
Date: Mon, 31 Oct 2005

You bet. I always love to learn something new. Orton's book was loaned to me by a client about 12 years ago. They wanted the Rumford in their house. WE built it exactly by the Orton book. It was very difficult to build with the fire back pulled forward as he illustrates. Keeping the center of the throat over the center of the firebox is damned near impossible. IT has smoked ever since. Since then I have modified them in our details to counter the smoking problem. This was before we learned about Superior. We are on the same page. Thanks for coming in. I am flattered by your visit and I appreciate your kind comments about what we are doing.

Maybe I should put a link on our website to you!

See you soon.

JJ

From: Jim Buckley [mailto:buckley@rumford.com]
Sent: Saturday, October 29, 2005 2:52 PM
To: john@johnjonesarchitect.com
Cc: Allan Trustdorf
Subject: Rumford Fireplaces

John,

It was a pleasure to meet you last week once Al Trustdorf and I found your offices. I've also enjoyed looking over your website - lots of traditional homes with proper chimneys and masonry fireplaces.

I hope I wasn't too hard on you about proper Rumford design but at the same time I hope I irritated you enough to read Rumford and see why the Orton version is wrong even though it has been picted up by Graphic Standards and the BIA.

Start with the article at http://www.rumford.com/articleOrton.html and move on to Rumford's original essays available at any good academic library or on line at http://www.rumford.com/chimneyfireplacesa.html if you don't believe me - or need a little help getting to sleep.

Keep in touch. I really like your work.

Warm regards,
Jim Buckley

Jim,

Well, another dose of true enlightenment; thanks again.

My first "Orton" is over twenty years old and really does work beautifully. the only smoking we get is when something is just too far forward. The other is about six years old, and is further deviant in that I was forced to angle the chimney backwards to miss a beam. but that one works beautifully also.

My family owns a children's summer camp in upstate new york, and we have over fifteen other fireplaces. The "Ortons" work far better than the others, which range from Heatilators on the really low end to the odd ideas of thoroughly uneducated stone masons. But some of the stone work is beautiful.

Really looking forward to building a real Rumford, now more than ever.

Thanks again,
Richard*

.........

Richard,

We've had some anecdotal testimony that "real" Rumfords perform better than "Ortons" but maybe not from people who have two Ortons and 15 other fireplaces. I'll be interested in your evaluation. We may have something of a statistically significant sample and an objective comparative analysis going here.

Best,
Jim Buckley

...........

Jim,

Thanks for your quick response; we hope to be pouring the foundation in about two weeks, so I need to have the details ready.

I appreciate all you've done in forwarding the "Rumford" cause. I've built two previous rumfords, but neither with your system. I built them based on the specifications in Vrest Orton's book, and both are terrific, but I've gotten older and my back tells me that using the superior clay items you designed will be a lot easier and faster.

And your website is a goldmine. So thanks for everything.

Richard

............

Richard,

Thanks for the kind words. And, you might add, our system is more authentic and will work even better than the Orton Rumfords. See our evaluation of Orton's book at http://www.rumford.com/articleOrton.html and read Rumford in the original so you don't have to take my word for it at http://www.rumford.com/chimneyfireplacesa.html

Happy building and thanks again,
Jim Buckley

Back to Orton

Radiant Heat
For a general discussion of radiant heat see the Radiant Heat section of this website.

Conversation with Gerald Maxwell - PhD with a Rumford

Comments on Balanced Ventilation
From: TopHatSwp@aol.com
Date: Thu, 2 Feb 2006 21:44:56 EST
Subject: Balancing Ventilation System
To: buckley@rumford.com

Thanks for spelling this out so well. I've been sending clients with odor and draft problems to your site because sometimes it seems they understand better reading it from someone else other than me just telling them.

I noticed you have a new date of 1/5/06. Did you change what was previously written? I didn't save a copy of the previous writing.

My only suggestion is to mention attic doors being sealed well as this seems to be a problem area in our area.

I just heard about a product called the attic tent which appears to be a good product but I have not had any experience with yet. I would be interested in reading your thoughts on it. www.attictent.com

Thanks again!
Sweep's luck,
Ron Rust
Top Hat Sweepers
CSIA # 1694
NCSG Member
SC Guild Member
Columbia,SC