The smell is because of the creosote deposits in your chimney, a natural by-product of wood burning. The smell is sometimes worse in when it gets hot, when the humidity levels are higher and the a/c is turned on. A good sweeping will help but usually won't solve the problem completely.

This has become quite a common issue in modern air-tight houses where weather-proofing has sealed up the air infiltration routes. The fireplace in use exhausts household air until a negative pressure situation happens. If the house is tight, the simplest route for makeup air to enter the structure is often the unused fireplace chimney. As air is drawn down the unused flue, it picks up smoke that is exiting nearby from the fireplace in use and delivers the smoke to your living area. The solution is to introduce makeup air to the house so that the negative pressure problem is no longer a problem, thus eliminating not only the smoke issue, but also the potential for carbon monoxide to be drawn back down the furnace. Another solution is to install a top-mount damper on the fireplace that is used the least.

Yes! Despite the fact that gas is a cleaner burning fuel, the chimney can become non-functional from bird nests, animals, or other debris blocking the flue. Some newer furnaces can also cause many problems with the avg. flues made for older generation of furnaces. It is best to check the areas on gas and carbon monoxide to be on the safe side.

A complete chimney sweeping includes the chimney flue and smoke chamber. You will be able to visibly see the that the flue is cleaner. Ask for a report after the sweeping is done.

Liners for oil-fired and gas appliances do not require insulation to meet the manufacturers’ installation and warranty reqs. Due to the lower flue gas temperatures and lesser heat transfer they are less likely to get surrounding combustible material on fire. If combustible materials are in close contact with the chimney, there are provisions that allow the liner to be installed in what is called as a zero/zero install. It is more logical to insulate every liner serving a wood burning appliance. Even oil-fired and gas appliances that are vented into an outside chimney will benefit from liner insulation.