I have a house built in 1951 with 3 separate flue stacks in the chimney - one each for fireplaces upstairs and downstairs in the basement, and one flue in the middle for the wood box in the brick right next to the upstairs fireplace. There is no smoke box; it is a straight flue.
First, why would a wood box have a flue in the first place? It is evident that nothing has ever been burned in the wood box. If there is a good purpose for the flue I'd love to know (and maybe it would be helpful for something).
Second, we discovered this had a flue after the first big rain - we could hear dripping in it. Turns out a previous owner put fabric over the flue and then just masonry over the fabric, so the fact there is a flue there is not evident from the top of the chimney. The chimney sweeps missed it too. The masonry is porous so water leaks into the flue and down into the wood box (which has a cover so the water just drips on there).
The chimney sweeps want to completely redo the masonry chimney cap to prevent the leak. Instead, I took asphalt shingles and used roofing caulk and construction adhesive to secure them to the top of the chimney over the flue. So far, no more leaking. Any reason this would be a bad idea?
Thanks in advance for any insight or advice.