Plan where to locate a fireplace to minimize backdrafting

Q: Our old fireplace always made the room smoky. Will the location of the fireplace in our new house we are now planning affect the amount of smoke? — Ron V. A:

A smoky fireplace can completely spoil the ambience and pleasure of a crackling fire. In many cases, the cause of smoke being drawn back down the chimney into the house is a result of poor fireplace design and construction methods. Today’s airtight house designs also exacerbate backdrafting and smoky fireplace problems.

It is wise for you to consider the location of the fireplace in your new home during the planning phase because its location also can affect how well the chimney draws the smoke out of your house. It takes only slight pressure differences between the top of the chimney and the interior of your house to suck the smoke back down into a room.

Since you are still drawing up the plans for your new home, try to locate the fireplace on the side facing the prevailing winter winds. In most areas, this is from the west and northwest. If your home will be located in a low area surrounded by hills, the wind direction may be different. The wind direction during the warmer weather is not a consideration.

The reason to locate the fireplace toward the prevailing wind is for combustion air. With today’s airtight homes, you should make provisions for outdoor makeup combustion air. This can be as simple as opening a window just a little or, even better, running an outdoor air duct to a register in front of the fireplace.

With higher air pressure on the side of your house facing the wind, the outdoor combustion air will be slightly pressurized. This air pressure difference will help force the smoke up the chimney. If the combustion air inlet were on the side away from the wind, the lower pressure could actually suck even more smoke down the chimney and into your room.

Try to avoid having tall trees between the wind and your fireplace chimney. When the wind hits the trees, it sweeps up and over them and becomes somewhat turbulent. This may create a downward rolling action of the wind as it passes over your chimney. This rolling action may impede the smoke from exiting the chimney.

It is also possible that the action of the wind over the trees can create a lower pressure area around your chimney and actually help exhaust the smoke. There is no way of knowing for certain which will happen, so to be safe, try to avoid locating the fireplace adjacent to tall, up-wind trees.

Locating the fireplace in the center of house is good for several reasons. The chimney will stay warmer, especially when there is no fire burning, than when it is located on an outside wall. This requires less heat initially from the wood to create the natural updraft (hot air is less dense than cold air) in the chimney.

Another advantage of an interior chimney is energy efficiency. Instead of losing all that heat from the hot smoke to the outdoors, the heat from the chimney stays indoors. This reduces the heating load on your furnace or heat pump and lowers your heating bills.