When we purchased our current home, the furnace situation was a bit of a mess. The furnace was an old oil-burning monster that had been converted to burn natural gas. The exhaust running through the crawl space was full of holes, and instead of a fabric air filter, it had an electrostatic precipitator. In theory, this was cool – precipitators use a negative charge on large plates to effectively remove particles from the air.
However, the precipitator didn’t work, and when we replaced the furnace with a much newer gas furnace, we asked the installer to remove the precipitator. He didn’t, saying it still worked and was good thing to have. Sadly, he was wrong about it working. So air just passed through it to a reusable filter below.
Then, when we remodled the basement, we built a wall around the entire unit to quiet the whole operation down. I left access panels on both sides for the filter and to access the furnace proper. It really quieted things down, which made the basement a much more pleasant place to be. Then, last winter, the furnace started acting up. Twice, the unit died. Once, the ignition element cracked, and the second time, the board died. On the service visit, Todd Morrison (who is awesome) recommended removing the precipitator because he felt there was some restriction on the airflow. I cleaned out what I could in the precipitator from below, but the top portion was now closed in by the wall. (whoops)
Yesterday I pulled out the fabric filter, grabbed the sawzall, a drill, and some tin snips and started taking apart the precipitator plates. It was dirty and slow. But then I hit the motherload. Atop the two metal plates (the positive then the negatively charged panels), I found a screen mesh that was clogged with suety, gross lint and nastiness. See.
I fired up the furnace, and the airflow was immediately improved. The air stunk of burnt oil, so I ran the unit for a while while everyone was gone with all the windows open. Now we should be in for a cheaper, warmer winter.