Q: I have a small, 100-year-old fireplace that I do not use because the chimney is unlined and I can’t afford to get it lined. There’s no damper either. I have decided to put a fake log and an alcohol gel burner (ventless) in there for the ambiance and a small bit of extra heat. I intend to block off the top of the firebox with a steel plate and fireplace caulk. This should keep air from going up the chimney, but will not stop heat loss via radiation.
Do you think, if I installed a Chimney Balloon 4 to 6 feet above the metal plate, it would survive? These gel burners put out 3000 BTU per hour per can, and I might at times burn 3 cans at a time, for a total 9000 BTU per hour. The flames would not be high enough to touch the metal plate. Thanks, ADH
A: Dear ADH, The Chimney Balloon will trigger its release at about 180-200 degrees Fahrenheit. I am certain it will only take about 5 minutes for a couple of rocket fuel… I mean… gel fuel, canisters to get the flue temp on the other side of your metal plate up to that temp. That metal will conduct pretty well once you get it cooking.
I do want to give you a fair warning about the adaptations you are planning to do to your fireplace. This type of DIY fireplace project is what makes home insurance agents get ulcers. When you self-seals a fireplaceflue with a metal plate in order to save heat you are definitely taking your chances. The heat will spill around the lintel of your fireplace and go right up to the mantle and be facing wall. When your mantel clock bursts into flames and your Hummel figurines neatly arranged on the mantle melt from the spilled heat it will be a bit too late to correct the error.
I’m being tongue-in-cheek here, but seriously, altering an existing fireplace to trap heat is not a DIY kind of thing. I don’t even know many fireplace professionals that will try it (unless it is at their in-laws). You might luck out and fix it up just right, and you might create a real safety risk. – Jason
Q: Jason, Thanks for your input about the chimney pillow and the concern about the fireplace adaptation. Before planning to do all this, I consulted specs from several manufacturers for ventless gas logs placed in existing fireplaces.
According to specs, ventless gas logs for this size fireplace, burned with the damper closed, can safely run at considerably more than 9000 BTU given the distance between the top of this particular fireplace opening (which has a hood) and the mantel. The metal plate will be in the same place a damper would be– if there was one– and dampers are metal, so I don’t see the problem. (It will only be touching firebrick and will be several inches back from the fireplace opening, also.)
A number of people in old houses here have had their fireplaces blocked off and big, honking gas logs installed without incident– seems to be standard practice around here anyway.
A: Dear ADH, I am very relieved to hear you researched it fully first, and it sounds like you covered your bases. Good luck with your fireplace project. – Jason