There has been quite a furor over gas stoves (how they worsen human health along with cooking (far) less efficiently and safely than magnetic induction stove tops) over the past few months. During cold winter snaps, one can see and smell the signs of yet another indoor air quality disaster: wood-burning fireplaces.
ACTION ITEM NOTE: Open wood fireplace dampers are an energy inefficiency disaster. When not using the fireplace, seal the flu either with a DIY plug or buy something like a Fireplace Draftstopper. You’ll save money and have a more comfortable home.
The Washington Post‘s Allyson Chiu, amid the WashPost’s ramp-up of its climate coverage, wrote an article about fireplace issues and how to address them that appeared in the January 3rd Health & Science section as “How to light a greener blaze in the fireplace” (online 23 Dec). Amid a generally good laydown of issues with chimneys and fireplaces along with ameliorative options to those problems, this opening paragraph on “wood-burning fireplaces” go so much right and something quite fundamental wrong by implication:
A traditional open wood-burning fireplace “emits the greatest amount of pollution and is typically the least efficient,” according to a spokesperson with the Environmental Protection Agency. Most of the heat goes out through the chimney, making it a poor way to warm a home.
What is so right there?
- Wood-burning increases, significantly, indoor air pollution (with significant health impacts) and is a major contributor to outdoor pollution in many places.
- And, they are highly inefficient. When being used, a very good open wood fireplace might hit 25% efficiently but more often is 10 percent or less.
As to what is fundamentally wrong? Any implication that wood fireplaces actually contribute to warming a home. Traditional fireplaces are actually disastrous as home heating systems
Field trials conducted by the Combustion and Carbonization Research Laboratory (CCRL) of fireplaces in Canadian homes, in conjunction with other combustion equipment, have shown that in all but one case, on cold winter days, use of conventional masonry fireplaces actually resulted in an increase in fossil-fuel consumption for heating. The fireplaces actually had a negative energy efficiency during the tests.
In the exception where a fireplace did reduce fossil-fuel consumption, the fireplace was situated opposite from the house thermostat. Without glass doors, the fireplace’s infrared radiation fooled the thermostat into thinking the house temperature was satisfied, while allowing the rest of the house to become quite cold. The owners had just arrived from Great Britain and were used to cold bedrooms, so they thought nothing more about it. The thermostat cutback did save energy, but the fireplace itself was still very inefficient.
But that is just the start of the equation, as that only considers the energy equation while burning wood rather than the full open wood fireplace efficiency equation. Far too often, efficiency analysis isn’t systems of systems. Let’s take a simple example, car fuel efficiency standards are miles per gallon for the gallon that makes it into the gas tank. That doesn’t account for the (significant) energy requirements (rough rule of thumb, additional 20 percent) to get that gallon to the car’s tank. When doing full systems analysis, both during fires and the rest of the year (or just the heating season), it becomes clear that open wood fireplaces are not simply inefficient but actually are wasteful and negative in terms of what it takes to deliver the useful energy of a heated home.
A brief review of the system-of-systems issues that turn open wood fireplaces into energy-wasting systems:
- The chimney effect: Unless using a relatively rare top-mounted damper, the chimney is open to the outside temperature: cold in winter and hot in summer. “Whether it is hot or cold, the air temperature in the flue often affects the temperature in the rooms surrounding the chimney, causing the heating and cooling system to work harder to keep the entire home at a consistent temperature.”
- The wood sourcing challenge: How much energy is required to get the wood into the fireplace, ready to burn. Relatively few fires, especially in urban areas, are supplied by Paul Bunyan-like cutting down trees and splitting logs by hand tens of feet from the fireplace. Instead, the trees are cut up and delivered with fossil-fueled systems. The energy from that, alone, sometimes can be greater than the embedded energy of the delivered wood logs.
- A draft reality: A fire is sending heat primarily up the chimney. That hot air is replaced by air being pulled from the house. “The draft can actually draw more warm air from inside the house up the chimney, which makes the inside colder than it previously was. Experts estimate that open fireplaces can draw up to ten times as much air from the room than is needed to build the fire.”
- The damper problem: A built chimney (with embedded energy) sits unused most of the year with a metal damper providing zero insulation and a very leaky barrier (a damper is generally just a metal plate that is resting on a typical-uneven masonry lip inside the chimney. The damper really does little to protect the house from winter’s cold and summer’s heat. And, that is if it is closed which too often isn’t the case. Thus, “an open or unsealed damper in a well-insulated house can raise overall energy consumption by up to 30 percent.”
Considering all of this, a typical open wood-burning fireplace is a negative return from primary energy (the energy in the tree before harvesting) in terms of useful energy (a heated home) delivered. That is true when burning the wood (the draft problem) but the equation worsens when considering the full picture.
Each of these challenges can be addressed.
- As per above, a top-mounted damper can end the chimney effect.
- If you source your wood in the neighborhood from fallen trees and split wood by hand (as I do for my wood stove), you can actually reduce fossil fuel (no diesel miles driving the wood out of the neighborhood) while shedding pounds.
- As discussed by Chiu, a stove insert can flip the energy equation in part because it comes close to ending the draft and make this systems-of-systems turn from an outright negative into something positive. Going with a wood stove can be a pricey investment and ameliorates, but does not solve, the pollution impacts inside and outside the home from burning wood.
- As to solving the damper problem, a simple solution: When not using the fireplace, seal the flu either with a DIY plug or buy something like a Fireplace Draftstopper. You’ll save money and have a more comfortable home.