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#292791 - 09/19/16 06:34 AM Re: Count Rumford [Re: logtroll]
pondering_it_all Offline
veteran

Registered: 02/27/06
Posts: 7886
Loc: North San Diego County
It certainly does not look like most fireplaces, in terms of the shape. Just how efficient is the Rumford fireplace supposed to be? (I know normal ones actually lose more heat pulling in outside air than they put out the front.)

Doesn't matter much in Southern California. The outside temperature is usually too high for a flue to draw.

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#292798 - 09/19/16 02:49 PM Re: Count Rumford [Re: pondering_it_all]
logtroll Offline
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Registered: 04/26/10
Posts: 8872
Loc: New Mexico (not old Mexico)
That's a question with no clear answer, that I can find. It also shines some light on a little acknowledged knowledge gap in the bigger subject of building heating and cooling, which is substantially based on affording air heating and cooling more weight than the other heat transfer dynamics.

Heat is transferred in three different ways; conduction, convection and radiation. For some reason, most of our attention is on air and conduction, which has resulted in a pair of "common sense facts" - that 'heat rises' and that insulation works by 'trapping air'. But these two facts are only true about air... hot air rises and air is a good insulator, unless it is moving. But air is worthless when it comes to impeding radiant heat transfer.

Our skin senses heat and cool, and it tracks both through radiance and conduction. But it may be more sensitive to radiation - think of sitting in the shade with an air temperature of 50 degrees vs sitting in the sun at 50 degrees. In the first case you would be cold, the second you would be comfortable (in the absence of a breeze).

A Rumford fireplace works on the principle of radiant heat transfer, not the heating of air. It is known that buildings with radiant heating systems will be comfortable at air temperatures of 5-10 degrees lower air temperature. Radiant heat also heats up objects, which then both re-radiate heat and heat air. Radiation moves equally in all directions (until something is in its path), unlike heated air, which rises (the ceiling zone is warmer than the floor zone).

Wood stoves often heat both air and radiate heat, though they are known best for standing next to on cold days to get warm fast (that would be the radiant component at work).

Given these characteristics, it could be said that radiation is a more efficient means of heat transfer than air, though our basic methods for evaluating heat efficiency (and heat loss, btw) primarily measure air heat transfer. Heating appliances, like a gas boiler, can have their fuel conversion efficiency measured, but that sheds little light on their end use heating efficiency. All of the data I could find in a 20 minute internet search was about appliance fuel conversion efficiency.

The only way to evaluate comparative building heat efficiency would be to conduct complete building system monitoring of the same structure using different heating appliances. I don't think that has been done to compare fireplaces to furnaces to boilers - of course, the heat delivery system variables would also need to be tracked. Pretty complicated.

That didn't answer your question, but I hope it was interesting. Incidentally, I did read that most fireplaces are positive contributors to space heating. I was under the impression that most are negative.

http://www.rumford.com/articleRumford.html
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"You can't fix a problem until you understand what the problem is." Logtroll

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#292816 - 09/19/16 07:27 PM Re: Count Rumford [Re: logtroll]
pondering_it_all Offline
veteran

Registered: 02/27/06
Posts: 7886
Loc: North San Diego County
Any fireplace will deliver radiant heat and heat the air in front of it. I think standard fireplaces are overall negative because they suck in cold outside air through windows and vents to replace air going up the flue. So they add heat right by the fireplace but cool the rest of the house.

But maybe people want that. Makes the fireplace a good place to hang out on a cold night. Humans have enjoyed radiant heat since the domestication of fire.

I think the shape of the firebrick walls and their proximity to the fire will make the Rumford fireplace radiate more heat out the front. The surface of the firebricks will get very hot but very little of that heat goes into the bricks, because they are such good insulators. So it gets reradiated out the front. I bet it provides twice the radiation of a standard fireplace.

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#292827 - 09/19/16 11:14 PM Re: Count Rumford [Re: logtroll]
matthew Offline
newbie

Registered: 03/24/16
Posts: 353
'
My fireplace alone is enough to heat up my whole ground floor (1500 sq. ft.) within two hours.

Power of radiant heat !
.
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#292996 - 09/25/16 03:42 PM Re: Count Rumford [Re: matthew]
logtroll Offline
veteran

Registered: 04/26/10
Posts: 8872
Loc: New Mexico (not old Mexico)
First fire in the Rumford! Working on the mantle today, still got a lot of finish plastering to do...

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"You can't fix a problem until you understand what the problem is." Logtroll

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#293026 - 09/26/16 04:22 PM Re: Count Rumford [Re: logtroll]
Spag-hetti Offline
member

Registered: 09/10/08
Posts: 1662
Loc: Middle, USA
"I am the god of hell fire and I bring you:

Fire!"

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Just a Missouri school teacher ... stubborn as a mule and addicted to logic.

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#293027 - 09/26/16 05:14 PM Re: Count Rumford [Re: logtroll]
Greger Online   content

Pooh-Bah

Registered: 11/24/06
Posts: 14201
Loc: Florida
What I love about the Rumford firebox is how tall the fire can be.
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#293175 - 09/29/16 11:28 PM Re: Count Rumford [Re: Greger]
logtroll Offline
veteran

Registered: 04/26/10
Posts: 8872
Loc: New Mexico (not old Mexico)
Made the mantle and got it installed. The finish is catalyzed tung oil. Now I can get back to the lime plaster.

_________________________
"You can't fix a problem until you understand what the problem is." Logtroll

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#296168 - 11/13/16 08:55 PM Re: Count Rumford [Re: logtroll]
logtroll Offline
veteran

Registered: 04/26/10
Posts: 8872
Loc: New Mexico (not old Mexico)
Nearly done. Needs the soapstone hearth and custom blacksmithed fire screen.

_________________________
"You can't fix a problem until you understand what the problem is." Logtroll

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#296180 - 11/14/16 02:25 AM Re: Count Rumford [Re: logtroll]
Ujest Shurly Offline
newbie

Registered: 10/16/16
Posts: 349
Loc: Sterling Heights, MI, USA
Looks nice.

May you have many days to enjoy it.
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