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-   -   Looking for acurate Rumford measurements (http://www.fornobravo.com/forum/f36/looking-acurate-rumford-measurements-20055.html)

thijsatteiltje 10-22-2013 01:51 AM

Looking for acurate Rumford measurements
 
2 Attachment(s)
Hi all,

A recently found out about the Rumford design am very enthusiastic to use it for a smaller, outside fireplace using perhaps different materials than your normal masonry fireplace.

I have searched high and low and it is very difficult to get clear, complete and unambiguous scientific specs about the size, area and interrelations of the Rumford fireplace concept when disregarding masonry and building code restrictions or conventions for a moment.

My main questions are these:

1. What is the 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. Is the smoke chamber important at all for the efficiency of the fire?
or 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?


I have been experimenting with smaller Rumford fireplaces for outside and have
created a Rumford Calculator in Excel (click here to download) to help with different
sizes. I now realise the Calculator is probably off the mark
considerably.

I have included pictures of the first two quick trails and I am in the
process of building me first real prototype, roughly 21.5" (55cm) wide

You see, for the measurements I have gone of the plans that can be found
on Rumford Fireplaces, 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

brickie in oz 10-22-2013 02:34 AM

Re: Looking for acurate Rumford measurements
 
If you have read about the Rumford design you know what is required to make the fireplace work. :confused:

Dont try to reinvent the wheel. :D

thijsatteiltje 10-22-2013 04:09 AM

Re: Looking for acurate Rumford measurements
 
Al,

fully agree with you. Sorry if I was not clear.

My intention is not to experiment with the design, just with building materials (as availability and price are a factor, plus it is fun to come up with something unique)

But I have searched high and low and it is very difficult to get clear, complete an unambiguous specs about the size, area and relations of the different components.

I even have the old Count's papers somewhere but those also require some interpretation.

Someone might mention he uses a throat that is 4 inches deep, but then fails to mention how wide it is (not to mention most throats are trapeziod shaped)

So what I am curious about, are the design specification for a Rumford based on airflow, pressure, expansion of gasses, venturi effect and how the column of rising gasses in the flue behaves.

Cheers,

Thijs

stonecutter 10-22-2013 06:00 AM

Re: Looking for acurate Rumford measurements
 
Quote:

Originally Posted by thijsatteiltje (Post 164036)
Hi all,



I have been experimenting with smaller Rumford fireplaces for outside and have
created a Rumford Calculator...........to help with different
sizes. I now realise the Calculator is probably off the mark
considerably.



That is because an outside fireplace doesn't function like an inside fireplace, because of the infinite variables which effect draw outside.

Tscarborough 10-22-2013 06:43 AM

Re: Looking for acurate Rumford measurements
 
Rumfords are not really suitable for a true outdoor fireplace, although they work fine for a protected, covered outside area. Even then a modified Rumford will perform better than a true rumford.

seamad 10-22-2013 04:18 PM

Re: Looking for acurate Rumford measurements
 
Quote:

Originally Posted by Tscarborough (Post 164053)
Rumfords are not really suitable for a true outdoor fireplace, although they work fine for a protected, covered outside area. Even then a modified Rumford will perform better than a true rumford.

What mods ?
I'm planning on building an outdoor one, and will reduce the height of the opening slightly as per the rumford site.
Am also planning on casting my own throat and smoke chamber as postage to australia is exxy.
Would anyone with experience know what material would be best ?
Would a castable insulator be better than refractory material for example ?

stonecutter 10-22-2013 04:35 PM

Re: Looking for acurate Rumford measurements
 
A modified Rumford has different firebox dimensions ( ie: deeper wider firebox
) than a true Rumford, which is tall and shallow in depth. But it is not built like most modern, cavernous fireboxes built today.

Tscarborough 10-22-2013 06:36 PM

Re: Looking for acurate Rumford measurements
 
The entire Rumford design, both regular and modified can be built with standard firebrick, no need to cast anything.

For dimensions and design of both: Rumford Fireplaces

brickie in oz 10-23-2013 12:24 AM

Re: Looking for acurate Rumford measurements
 
1 Attachment(s)
Here is one I built for myself at home last year, no fancy cutting in the throat, it draws like a beauty and kicks out tons of heat.
FYI the opening is 1600mm wide and 900mm high at the the top of the intrados.

seamad 10-23-2013 12:41 AM

Re: Looking for acurate Rumford measurements
 
Quote:

Originally Posted by stonecutter (Post 164081)
A modified Rumford has different firebox dimensions ( ie: deeper wider firebox
) than a true Rumford, which is tall and shallow in depth. But it is not built like most modern, cavernous fireboxes built today.

My idea was for a rumford 900mm wide, 800mm high and 400deep with a 400 wide back wall. How much can I deepen and widen it ?


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