Question: I have a growing concern regarding my existing fireplace. It is a standard, circa 1965 model. There has been much publicity in recent months regarding the health hazards of particulate matter emitted from older fireplaces such as ours. Can you tell me mow much particulate matter is generated per hour in an average open fireplace using a good grade hardwood such as oak? All new inserts and stoves are rated in 'grams per hour'. The articles I have read indicate that 10 microns and 2.5 microns in size are the two categories the EPA uses for hearth products approvals. Am I interpreting this accurately? If not, what is their current method of measuring particulate matter? Answer: The particulates they are referring to are put out the chimney, not into the room. An open fireplace can vary greatly as to pollutants, but if burned correctly - very hot with a good flame on the fire - the fireplace will burn much cleaner than an older (non-EPA) woodstove. The biggest problem with tars and particulates occurs when wood is burned in the absence of enough air...this does not usually happen in an open fireplace. EPA uses laboratory tests which trap certain particulates and tars from the chimney and allow them to be measured. This test only applies to air-limited stoves...not open fireplaces.