DEAR TIM: I've got both a fireplace and a free-standing wood heater spaced 15 feet apart from one another in my open kitchen and living area. The fireplace has a fresh air vent in the hearth. I've only used the fireplace twice in fifteen years because when I start a fire in the fireplace, it pulls a sooty smell from the wood heater. Surprisingly, I do not get the smell when I use the wood heater. I'd like to install gas logs in the fireplace. Will gas logs pull air from the wood heater and cause the same sooty smell? Jamie L., Gulfport, MS

DEAR JAMIE: I would be willing to bet money on my answer: Yes. Based upon your description, you are experiencing back drafting. When the fireplace is burning, it is consuming vast amounts of air each minute. It can easily be 250 to 350 cubic feet of air per minute. The fresh air vent in the hearth may be blocked or it may not be able to supply enough air to satisfy the appetite of the fire. The additional air to feed the fire must come from somewhere. Simple physics will tell you that the air will enter the room through the path of least resistance. In your case, it appears the air has decided to enter the room through the flue of the wood heater.

Back drafting is an enormous problem. It is a by-product of the constant push to make homes more energy efficient and air tight. The trouble is, homes are equipped with things that blast air, and lots of it, out of the living space. Have you ever stopped to think about what happens when you activate the switch for your bath fans, kitchen cooking ventilation fans and central vacuum cleaner? What happens when you turn on your clothes dryer? These devices exhaust air outdoors and in doing so create a partial vacuum in your home.

If you do not have an air inlet to re-supply the exhausted air, the replacement air will leak in through windows, doors, chimneys, water heater and furnace exhaust piping, cracks in the house exterior, etc. If several appliances are operating and the demand for air is great enough, exhaust gases from fuel burning appliances can be sucked backwards into your home. This can cause dangerous carbon monoxide to be pulled back into your home.

Many modern furnaces and water heaters have built-in pathways for the air needed to burn the fuel. In fact, virtually every residential building code mandates that combustion air for fuel burning appliances be supplied to fuel-burning appliances. But more air than combustion air is needed in the average home. For years, commercial and institutional building codes have required this extra ventilation or make-up air. This air creates a healthier interior environment, insures that plenty of fresh air is entering the building and that dangerous back drafts are avoided. It is in your best interest to provide this ventilation or make-up air.

This thinking is not new by any means. There are companies that actually sell sophisticated air exchange devices that provide some or all of this needed ventilation or make-up air. But I am not so sure that you need to invest in this equipment. If you do decide to investigate these appliances, be absolutely certain that you see a clear rate of return on your investment. In my opinion, there may be some more practical and far less-expensive solutions.