Smokey Fireplaces
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Date: Thu, 11/24/00 To: Steve Hausz From: buckley@rumford.com Subject: Fireplace problem Steve, It sounds as if you are doing the right things. Multi-sided fireplace are temperamental. Have you run through the "Smokey Fireplace Checklist" on the website at http://www.rumford.com/smokey.html ? You say the smoke gathers in the hood which might indicate some restriction. In pic00003.jpg it looks as if the damper frame abruptly restricts the throat opening. You might knock the damper frame out completely and, if that helps, replace the damper with a chimney top damper. |
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Are the slots at the top of the chimney large enough? The total net free area of the slots should be at least four times the cross-sectional area of the flue to make up for all the extra surface areas and turns causing turbulence and restriction. Can you lift off the top of the chimney so the flue is unrestricted? (If so, you could also experiment with raising the chimney by temporarily setting a couple of flue liners on top.) If a restriction does not seem to be the problem, how about air pressure? Do you get an up-draft without gas, paper or a fire? If not, can you make a difference by opening a window? If the fireplace needs more air be careful where you introduce it so as not to cause too much air movement within the house that might cause the smoke to blow out of the fireplace before getting drawn into the throat. A remote mechanical room, cold air return, or laundry might be a good place to ad more exterior air. Wind makes a difference. Experiment in calm weather, make sure exterior air actually comes in the window you open and know that in a breeze the leeward side of the house will be depressurized and, if the intake is on that side, it may not work. Pump more air in with a fan if necessary. The fireplace will need at least one cfm of outside air for every square inch of flue cross-sectional area - maybe 300 to 400 cfm for this fireplace. I'd build tall tipi style fires directly on the hearth. Getting rid of a grate sometimes seems to help. Close any air intakes that may be in the firebox as they will not be adequate and often cause enough turbulence to make a fireplace smoke. I notice glass panels or screens on each side. Have you tried fitting one or both sides with tight-fitting panels? You could try this with sheet metal or plywood and duct tape before investing in glass. In general, eliminating interior drafts, raising the chimney and/or getting more outside air in the house, even if you pump it in, will help. I'd start with the easiest and least expensive first: 1) get more air in the house, mechanically if necessary, 2) open up the top of the chimney and remove the damper frame. Only if that doesn't work would I raise the chimney or ad glass side panels or lower the throat. Thanks for the pictures and please let me know if any of my suggestions help. Best, Jim Buckley
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Hi Jim! The endless remodel & addition is finally finished. Thanks again for your help with the fireplaces in the design phase. Soon, I'll get some good shots of them and e-mail them up to you. I have a favor to ask of you meanwhile. The 3-sided fireplace is being temperamental, as could have been predicted. My approach was somewhat accidental, as it took me a while to find out where on the property that he kept his stack of firewood. Consequently, 15 minutes or so elapsed between when I turned the log lighter on, and when I put logs in the fireplace. I theorize that this helped preheat the flue, and aid convection. I also stood the logs vertically, standing on top of the log grate. I did get a cloud of smoke gathering in the hood for a while, but either closing down the damper some helped, or the causitive factor may have been an open window, which I subsequently closed. In time, any cloud in the hood disappeared, as well as some smoke that had gotten into the room. I didn't have benefit of seeing the fire through to completion, and took the logs outside after satisfying myself that it was a matter of technique. My client complained that, even trying my suggestions, that the firpelace still smoked unacceptably. I met with him yesterday, and we built a fire together (sounds romantic, doesn't it?). Instead of running the log lighter for 15 minutes, he stuck a few sheets of newpaper above the damper and lit it. I don't think he had stood the logs upright either. The fire we built together seemed to work fine. It was however the warmest part of the afternoon, and calm. I don't know how much effect colder temps and a breeze might have.
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He seems to think that we should bring the hood down lower, or possibly
extend the flue. I suggested that the best first step would be to email
a sketch and some pictures to you to get a diagnosis and best course of
action. He has had some screens made, which are visible in the
pictures, though they are not as tall as the fireplace openings. I
wonder if there would be a benefit to backing the two side screens with
heat resistant glass, which would barely be noticeable, but might serve
to effectively make the fireplace opening smaller. Following code, and your advice, the flue does seem pretty cavernous, maybe it really needs more height relative to it's cross section. If we were to experiment with extending the flue, would it accomplish our goal to use some 24" dia. sheet metal duct as an temorary extension, or does the mass of a masonry flue influence its performance? I sure appreciate all the help you've been over the years. I can't thank you enough for giving me your feedback on this problem. My client seems to be somewhat accepting that it has to be expected that such an open fireplace is going to be more temperamental, but I hope I can do something to ease his concerns that it wasn't desinged correctly! Thanks, Steve Hausz
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