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Rumford Technical Discussion The Skinny on Fireplace Doors To ask technical questions or contribute to the discussion click here |
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Glass or metal fireplace doors block radiant heat but don't block air loss. Requiring glass doors for radiant heating fireplaces like Rumford fireplaces is counter productive. Glass doors block over 90% of the radiant heat while not preventing heated room air from escaping up the chimney - just the opposite of what most people expect. Glass doors will not transmit the THERMAL infrared wavelengths from 8 to 12 microns, although they may transmit the short wavelengths around 1 micron, which we do not feel as heat. The glass will heat up, however, due to its absorptance and then will radiate out with an equal emissivity and at wavelengths determined by its temperature and Planck's Law. In other words, glass is not transparent in the infrared. You get some heat from a fire through the glass only because the glass gets warm and re-radiates some heat. You'd get more heat through solid metal doors because metal conducts heat a little better than glass. According to the Stephan-Boltzman Law radiant heat is proportional to the fourth power of the absolute temperature. The radiant heat output of an open Rumford fireplace with a typical 1600 deg.F wood fire will be sixteen times the radiant heat output of the same fireplace with glass doors closed on the fire if the doors reach a temperature of 540 deg.F. Even very hot glass doors block well over 90% of the radiant heat. See the calculations. Besides blocking nearly all the heat, glass doors leak like a sieve - on purpose. Manufacturers almost universally provide glass doors with tempered glass rather than expensive high temperature neo-ceram glass. Room air is "washed" up the inside of the glass to keep it cool so it won't shatter. Closed down as far as possible, most doors still let in plenty of air so they don't cause the glass to break or the firebox to over heat and create a fire hazard. Glass doors, with all the vents closed, leak about as much as an open damper. They block most of the radiant heat but not any of the air - just the opposite of what most people expect.
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An alternative to doors in Washington Valid criticism from another "expert" |
How it Really Works in California Blocks all the heat Even high temperature glass blocks heat |
Discussion
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Jim, Well our 48" Rumford is complete (see attached JPG) and now my mason tells me he thinks maybe Thurston County, WA will require glass doors. Since they were not built into the masonry like your site shows is this a problem?
Dennis Hamblet
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Dennis,
Your Rumford looks great! May I use it on the website?
The Washington Indoor Air Quality Code requires "Tightly fitting glass or metal doors, or flue draft induction fan or as approved for minimizing back-drafting."
We've been successful at eliminating glass doors in western Washington by arguing that, if the space is designed to have positive indoor pressure (as are most commercial buildings, lots of high end homes and any home on the upper floors), then, in essence, we do have a "flue draft induction fan or as approved for minimizing back-drafting" - only our fan is in the mechanical room (or wherever) not at the top of the chimney.
In Spokane, building officials will approve Rumfords without glass doors provided the house does not exceed 8 Pascals negative pressure (the limit on our guarantee).
Here, I think, are your options:
1) Install a damper in the cold air return of your heating system so the air handling fan can be used to control the indoor pressure or install some sort of fan (like a kitchen fan) backwards to blow outside air in the house and argue that you have a "flue draft induction fan or as approved for minimizing back-drafting."
2) Appeal the decision to require doors based on the argument at the top of this page that fireplace doors are counter productive.
3) Make a cheap sheet metal cover since the code permits metal or glass doors and says nothing about hinges.
4) Install one of our glass or metal frameless aftermarket doors that are designed to be "visually minimal and easily removable".
Best,
Jim Buckley
Hi
I have had a beautiful Rumford Fireplace built in my new home. I'm not moved in yet but could not resist having a few fires already! Because of building codes here in Washington State, I had to have glass doors installed. They seem to make all of the heat go straight up the chimney and negates the whole purpose of my Rumford.
Tracy Knizek
Mr. Buckley,
On occasion our office receives questions from code enforcement personal about the Washington State Ventilation and Indoor Air Quality Code requirements for fireplaces. My office does not agree with a number of the recommendations you're company has made for meeting this code. They are work arounds, not specifically noted in code. Interpreting these recommendations on an individual basis puts the code enforcement personal in an awkward position.
At a minimum, every three years the State Building Code Council accepts proposals to change the state codes. This year applications are being accepted until Feb. 28. If there are sections of the code (s) you object to, you should submit a proposal for changing it. To obtain forms for submitting code changes, go to the State Building Code Council web site.
Respectfully,
Chuck Murray
Thank you. That's a good suggestion. Never mind that my "work arounds" have merely been passed on to me by customers, the responsible thing for me to do is to submit a code change proposal. Time is short but I will make an effort to submit a code change proposal by the Feb 28th deadline.
Regards,
Re-reading Mr. Murray's email message, I asked him specifically what recommendations I have made that his office does not agree with and why. I hoped that maybe he and I could find agreement and together propose changes that would make the VIAQ code better. By the 28th he had not responded so any change I would propose will have to await another opportunity.
In the meantime Section 402.3 of the Washington State Ventilation And Indoor Air Quality Code is pretty vague, the intent is not clear and it is at odds with the ICC codes. But it may be better to live with a vague and unenforceable code we can work around than to unintentionally help bring about a more rigid code with no room for interpretation.
Jim Buckley
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