What filter is recommended for fine wood dust? You know, to keep the heat exchange surfaces from building up wood dust. I don't know if this makes any difference to your recommendation, but here in Canada, as of December 31, 2009, the minimum efficiency for natural gas burning furnaces is 90 percent AFUE. We can't get mid efficiency furnaces anymore, unless we go cross boarder shopping into the USA. Lets say I put in a condensing furnace in that wood shop, considering all the fine wood dust, it wouldn't be a good idea to go with the cheap fiber mesh filters right.