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Old 10-22-2013, 03:24 PM   #1
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Rumford fireplace. Looking for exact measurements for


Hi all,

I have build some pizza ovens and fire pits in the past and I recently found out about the Rumford fireplace design. I am quite keen to use it for an outside fireplace.

But, I have been unable to find exact, scientifically accurate plans and specifications for a Rumford based on airflow, pressure, expansion of gasses, venturi effect and how the column of rising gasses in the flue behaves.

I have done quite some research but have trouble finding exact answers to:

1. What is the exact relation (ratio) between the INNER measurements of the
throat opening, the front of the fireplace and the surface area of the
smoke chamber and the surface area of the chimney?

2. What is the significance of the smoke chamber for the efficiency of the fire?
Is it merely an artefact from having to connect the wide fire place
to a smaller chimney, while still accommodating the narrow throat
opening?

3. Could one, in theory, completely do without a separate smoke chamber
and have the throat go over into a chimney straight away? Is a larger
area right about the throat required for the Venturi effect?
If so, what is the minimum ratio of throat-to-smoke chamber area to get
an effective fire?

A builder on a forum might mention "I use a 4 inch deep throat", but then fail to mention if this is an inner or outer measurement, a pre-made product, or not mention the width or shape to determine the surface area.


I am planning a Rumford fireplaces for outside and have created a Rumford Calculator in Excel (http://mercato.teiltje.nu/spool/rumford-calculator.xlsx) to help with different sizes. Warning! Do not use this version, it is probably off the mark considerably.
I would be keen to share it when the calculations have been corrected and vetted.

For the measurements I have gone mainly of the plans that can be found
on http://www.rumford.com, (http://koppclay.com/Rumford/plans/classicflyerplan.gif) combined with other information, comments and ratios found elsewhere.

The problem I now realise, is that most Rumford builders on the web approach the design from a builders
perspective, with the measurements of bricks, standard flue liners and building codes first in mind.

This is understandable of course, but for the most, the mention the OUTSIDE measurements of flue tiles and throat, which is not helpful when trying to figure out what the INSIDE measurements should be.
I would love to have more definitive INNER area measurements and the relationship between them. Also, because my fireplace will be on the small side, the margin of error is smaller and of importance i think.

As a part-time engineer and weekend-inventor, I am keen to get the measurements right.
I am very keen and willing to experiment with different materials to
make the fireplace as small and light as possible and have clear
boundaries for the thermodynamic principles at work would be essential I
feel.

If anyone would like to share the ratios and margins of error when it comes to throat, smoke chamber and chimney my fireplace will be a roaring (sorry) success and I am for ever in your debt and will sing the
praise of Count Rumford all this summer!

Cheers,

thijs
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Old 10-22-2013, 03:55 PM   #2
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Rumford fireplace. Looking for exact measurements for


Welcome to the Forum!

have you tried the Contact Us on the Rumford.com site? If not you may want to ask them your questions.

I use their information/specifications when designing a home with a Rumford fireplace, don't really get into it that much to be of any help with your questions.

Hopefully some of our more experienced members will be able to help you with your questions.

Good luck!

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Old 10-22-2013, 08:28 PM   #3
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Rumford fireplace. Looking for exact measurements for


Quote:
Originally Posted by thijs74 View Post
Hi all,

I have build some pizza ovens and fire pits in the past and I recently found out about the Rumford fireplace design. I am quite keen to use it for an outside fireplace.

But, I have been unable to find exact, scientifically accurate plans and specifications for a Rumford based on airflow, pressure, expansion of gasses, venturi effect and how the column of rising gasses in the flue behaves.

You need to find the papers/articles originally written by Count Rumford in the 1700's, I'm fairly sure they contain most, if not all of the info you're looking for. Orton is another "innovator" with fireplace from centuries ago who wrote extensively about solid fuel fireplaces.

I have done quite some research but have trouble finding exact answers to:

1. What is the exact relation (ratio) between the INNER measurements of the
throat opening, the front of the fireplace and the surface area of the
smoke chamber and the surface area of the chimney?

I'd have to do some serious digging to find any exact ratios at the moment, but if my memory serves me right, the throat opening is about 4.5" wide x 14" long (interior) on a Buckley Rumford one piece throat. The smoke chamber is ~20" tall, about 30" wide at the bottom, and 12" or so on the top, interior dimensions again. This is for a 36" wide fireplace opening.

2. What is the significance of the smoke chamber for the efficiency of the fire?
Is it merely an artefact from having to connect the wide fire place
to a smaller chimney, while still accommodating the narrow throat
opening?

It has a number of functions, including the reduction you mentioned. It alos allows an area large enough to provide space for a damper to operate. Probably it's most important function is to create a smoke shelf though, which helps keep strong winds from blowing smoke back down a cold chimney. It also aids in getting the smoke to roll on it's way out the chimney.

3. Could one, in theory, completely do without a separate smoke chamber
and have the throat go over into a chimney straight away? Is a larger
area right about the throat required for the Venturi effect?
If so, what is the minimum ratio of throat-to-smoke chamber area to get
an effective fire?

If you're goal is to save money by not buying/using a smoke chamber, you can craft you're own from two separate flues. That's pretty much all the Buckley Rumford smoke chambers are, but they are relatively cheap IMO anyways.....

A builder on a forum might mention "I use a 4 inch deep throat", but then fail to mention if this is an inner or outer measurement, a pre-made product, or not mention the width or shape to determine the surface area.

That's likely because professional forums are intended to be used by professional's. As a pro, I understand that lingo........

I am planning a Rumford fireplaces for outside and have created a Rumford Calculator in Excel (http://mercato.teiltje.nu/spool/rumford-calculator.xlsx) to help with different sizes. Warning! Do not use this version, it is probably off the mark considerably.
I would be keen to share it when the calculations have been corrected and vetted.

For the measurements I have gone mainly of the plans that can be found
on http://www.rumford.com, (http://koppclay.com/Rumford/plans/classicflyerplan.gif) combined with other information, comments and ratios found elsewhere.

The problem I now realise, is that most Rumford builders on the web approach the design from a builders
perspective, with the measurements of bricks, standard flue liners and building codes first in mind.

This is understandable of course, but for the most, the mention the OUTSIDE measurements of flue tiles and throat, which is not helpful when trying to figure out what the INSIDE measurements should be.
I would love to have more definitive INNER area measurements and the relationship between them. Also, because my fireplace will be on the small side, the margin of error is smaller and of importance i think.

As a part-time engineer and weekend-inventor, I am keen to get the measurements right.
I am very keen and willing to experiment with different materials to
make the fireplace as small and light as possible and have clear
boundaries for the thermodynamic principles at work would be essential I
feel.

If anyone would like to share the ratios and margins of error when it comes to throat, smoke chamber and chimney my fireplace will be a roaring (sorry) success and I am for ever in your debt and will sing the
praise of Count Rumford all this summer!

Cheers,

thijs

I would highly recommend doing some more research on Jim Buckley's site, as well as reading up on some of Ct. Rumford's and Orton's work. The information available is huge.

Plus, keep one thing in mind: When you visit the "Rumford.com" website, you're looking at nothing more than one man's rendition (Jim Buckley) of what he feels to be the optimum Rumford fireplace. Jim is an extremely intelligent man, and undoubtedly the biggest advocate for wood buringing fireplace alive. W/o him, there likely would be no wood burning fireplaces allowed in new construction in the majority of the states in this country. YES, he is trying to sell something and make a living as well, I'm not sure how much hard earned info he'll be willing to dish out for free. I will say I've done a number of Rumfords using his components, and he's been invaluable to me in the past.

Good Luck.....
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Old 10-24-2013, 12:00 PM   #4
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Rumford fireplace. Looking for exact measurements for


Mr. Buckley will help you all he can, give him a call.

The simple answer to your question is....there is no simple answer. You can either build a bunch of fireplaces and experiment or use the existing plans generously provided.

Technically, you do not need ANY commercial parts, throat or chamber, it can all be done with normal fire brick.
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