My Fireplace is Sucking the Heat Out of My House!

My Fireplace is Sucking the Heat Out of My House!

I grew up in an 1880’s Victorian house in New England that was built, coincidentally, right about the time central heating systems began finding their way into American and European houses. Before that time, most houses wereDylan CHalk House Talk heated by burning wood and coal in fireplaces. Our old house reflected this technological transition because it had both an antique boiler as a central heating system and the legacy of fireplaces in nearly every room with multiple masonry chimneys lofting from the roofline. By the time we got to live in the house, many of the old fireplaces had been covered up and were no longer in use, but it was neat to see them scattered about the house; relics of times gone by. Here is a YouTube video of the house now; all fixed up and lacking the peeling paint on the exterior which characterized our ownership. You can see all the old fireplaces if you look.

(This is a great example of how looking at houses works; once you know what to look for you start to see things differently… you start noticing all the old fireplaces.)

In the 1980’s when I was living in this house, heat came from an antique boiler system that fed steam to cast iron radiators which would knock and ping so loudly that at times I would awake at night convinced that an intruder had broken into the house and was whacking away on the iron pipes with a crowbar. This was a very big house, with large single paned windows, virtually no insulation and tall ceilings. After buying our first few tanks of heating oil, in our first winter in the house, my father quickly realized that a new strategy was needed for winter comfort: keep the thermostat for the central heat just high enough to keep the pipes from freezing and live in the family room with the wood burning fireplace going constantly.

This did the trick for us. When we were in winter’s grip I recall cozy evenings in the family room punctuated by jarring cold sprints for the bedroom where we would burrow under a mountain of blankets for the long winter night. This was how I learned to live in an old house and use a fireplace for comfort. Imagine my surprise when I started learning more about houses and building science and I learned that fireplaces are horrible heat sources and really just suck all the heat out of your house!

This is true. Wood burning fireplaces make no sense in a modern home with central heating. What you do when you light a fire in a fireplace is suck the heat out as quickly as possible – the heat in your home literally goes up the flue. Building scientists call this the stack effect. Don’t believe me? Here is a great picture of it in action:

Information on fireplaces as heat for homes

After a holiday party, the flue damper was left open in the fireplace and as the owners slept, air and heat was sucked out of the house up the flue, dragging the holiday balloons along with it. This photo shows how the owners found the room in the morning after the party.

My family and I were able to make the fireplace work in our old Victorian house by conceding comfort in the rest of the house, but for most modern American families who appreciate a more sophisticated level of comfort, such as heat in the whole house, the traditional wood burning fireplace is not your friend. If you love a beautiful wood fire in the winter, as I do, this is dispiriting news. But here are a few options for using fireplaces as an efficient heat source or at least to minimize heat loss.

Wood Stoves: One thing that separates wood stoves is the ability to run a duct from the exterior, to the combustion air inlet in your wood stove. This allows you to use exterior air for combustion – so you are not using the warm air inside your house for combustion. In modern wood stoves, there is also a secondary combustion air which makes wood stoves more efficient than fireplaces. Some modern wood stoves are so efficient you can even use them during burn bans. If you live in an area where wood is abundant, a well-installed high efficiency wood stove can be excellent and inexpensive heat source.

This photo shows exterior air being ducted into the combustion air port on a wood stove

This photo shows the secondary combustion air on a modern wood stove – this helps make them more efficient.

Combustion air and glass doors. Modern fireplaces come with small ports built into the firebox. These can be opened when having a fire to allow combustion air to enter the firebox from outside. If the fireplace also has glass doors, this can reduce the amount of heat loss in the house and still allow you the joy of a wood burning fireplace. This set up is likely not as efficient as a well-installed wood stove with outside combustion air, but it is a vast improvement over the old-fashioned fireplace.

Here you see a modern fireplace with glass doors and inside the fireplace – those small vents are to allow combustion air to enter from the exterior.

Pellet Stoves. Pellet stoves have combustion air integrated into the flue pipe, so they do not use interior air for combustion.Pellet stoves are often one of the cheapest cost / BTU because the fuel source is made from waste wood scraps. These appliances do not have the charm of a roaring Yule log fire, but they can be excellent heat sources.

I hope this article helps clear up some confusion around wood burning fireplaces. Stay warm everyone!

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