I know this thread is 11 years old, but I would like to add that the culprit could be the toilet seat. I recently replaced our toilets, and they came with soft closing lids. We first notice the "soot" like residue on the seats. I believe that a small amount of grease is released as a fine dust. Several months later we noticed it on surfaces that emit air, such as our dish washer vent, and heat pump. We have used candles for years, but it was not until we replaced our toilets that the residue appeared. So it would be interesting to know how many find the residue on their toilet lids and of those how many are new installs and are they soft closing. Thanks

Hi Monica Thanks for your response. PlumbWorld does indeed carry the Roper Rhodes toilet seats, but they like all the other distributors I contacted only deliver inside the UK. I am trying to find out how I can possible buy one here in the US! We seem to have a dearth of decent wood toilet seats on this side of the pond! Would be a good niche for someone to fill.

Our old wood seat was Bemis and lasted 15 years. Didn't see Bemis at the store so we bought a wooden Kohler. Seat edge isn't rounded so paint will probably chip eventually, and hinges are cheap. Went looking for Bemis again and found out that Church is Bemis. I bought the soft-close Church at HD or Lowe's and am very happy with it. Mayfair is also Bemis and carried by Target. I don't know if their soft-close is the same quality as Church.

I have left side paralysis due to multiple sclerosis. Just yesterday I was able to swap my standard elongated seat for a Brondell Swash 1400. You can do it, but yes, you’ll need power. The water just t’s from your existing water line, then there’s a smaller water line to the new seat. However, while tightening the fitting to the threaded valve stem underneath the tank I turned it too hard and it broke! It’s plastic of course! So on top of the new seat, I now had to get a new flush valve as well. Strangely enough, I was not able the replace the new valve by myself so I had to call someone. Sorely disappointed and my pride hurt—but all’s well. Go for it!