Fireplace Efficiency and Inserts

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There is nothing like the crackle of a fire in the hearth and a blazing fireplace to create a sense of warmth and comfort.  And I know most of you agree because The National Association of Home Builders ranks fireplaces among the top 3 features desired by new home-buyers. However, there’s a major downside to the traditional wood-burning fireplace which is Heat Loss.  Fireplaces are, by nature, not very efficient- they pull warm air out of the room and into the fire.  A lot of that energy (heat) is lost up the chimney and through the material that surrounds it.  When temperatures drop below freezing, a fireplace exhausts more energy than it creates.  The Hearth, Patio and Barbecue Association rates older fireplaces’ efficiency at only 5-10%– that means up to 95% of heat energy literally goes up in smoke!


Heated room air is drafted up the chimney as well, so your main heating system actually works harder to keep the house warm.   And as a result, expect other rooms to be cooler due to escaping warm air.  I recommend avoiding using a traditional wood-burning fireplace as your primary source of heat.  A traditional type of fireplace can still be used for occasional enjoyment- like on special occasions and holidays.  Another option is to modify your traditional wood-burning fireplace and  increase its efficiency!  Many inventions have been made to maximize fireplace efficiency; including the use of a fireback, damper, glass/mesh door, fireplace grate radiator/ heater, and fireplace insert.

Firebacks have been used, in various forms, for hundreds of years.  They are made of heavy steel or cast iron and are positioned against the back wall of a fireplace.  In addition to protecting masonry of the back wall of the fireplace, a fireback heats up and radiates the heat of the fire forward into the room (instead of all the heat going up the chimney).  Firebacks can be decorative as well as functional.  Estimated cost: $75 to $350.


Having a good fireplace Grate can increase the efficiency of a fireplace AND make fires easier to start and tend.  They keep logs from rolling during burning, enhance your fireplace’s efficiency by allowing air to flow beneath your logs, and facilitate clean up by creating a central ash pile.  There are some new grate designs out there on the market that are specially engineered to make the wood fire radiate better into the room.  Estimated cost $25 to $200 depending on size and quality.

A Damper is the iron or steel trap door at the lower end of the chimney that remains closed when the fire place is not in use (preventing warm air from escaping up the flue and out the chimney).  To start a fire, you must have the damper in the full-open position. Some dampers are adjustable and after the fire has started, it is best to close the damper as far as possible without causing smoke to back up into the room.  Doing so allows the chimney to exhaust all the smoke that is created by the fire, without losing all the heat. Prefab fireplaces have built-in dampers which are often only open-close. These should not be modified or replaced as they are safety tested only in the stock configuration. Masonry fireplace dampers often have problems such as loose fit and missing handles. Most dampers fit snugly when they’re new, but can frequently warp within a year or two, producing a loose fit and allowing air to leak past them. One of the most pervasive causes of a stuck damper is rust, which can make operation difficult and the damper often sticks in one position.  Rust can be removed with a flashlight, a wire brush, and some elbow grease.

Glass Doors reduce the loss of room air up the chimney and still allow you to view the fire. The drawback is that the glass can also reduce the heat that reaches the room by half (even a mesh screen reduces radiant heat by 30 percent). The result is a small gain in efficiency- only to about 20 percent.  Fireplace doors are almost never tight enough to prevent cold air from back-drafts when the fireplace is not being used but they are better than not having doors. Beware that some glass doors need to be open during operation- the glass may shatter with high heat.  Always look into manufacturer recommendations. Estimated cost: $200 to over $1,000.

Fireplace Grate Heater/Radiator have been called many things: heatilator, hearth heater, fireplace blower, fireplace grate heater, Fireplace Furnace, tubular grate heater, etc.  Basically, a fireplace blower grate consists of an air inlet, metal pipelines or air tubes, and an air outlet. The inlet draws in cold air from the room. This air then passes through a series of tubes or chambers that pass through your fireplace. The air inside these tubes is heated by fire and is then expelled through the air outlet to heat the room.  A heat grate/heat ex-changer is a waste of money unless in is paired with a set of glass doors. The doors minimize the amount of excess combustion air consumed by the fireplace. An open fireplace (no glass doors) with a heat exchanger still has the problems of an open fireplace noted above.  Many are tempted to use these because they cost less than an insert but they are not nearly as efficient/reliable as an insert. Estimated cost: $410 to $615.

fireplace radiator, fireplace heat exchanger

And I saved the best for last… Fireplace Inserts!

Most Fireplace Inserts are designed to increase a fireplace’s efficiency. An insert is basically a fireproof box that’s surrounded by steel or cast iron and fronted by insulated glass, creating a closed combustion system. The steel or cast iron box helps to trap the heat. They use a heat exchange chamber with channels to allow room air to pass through and absorb heat. Some inserts have a blower that pushes the hot air back into the room through front vents.  Fireplace inserts usually require a full stainless steel flue liner, rather than simply connecting to an existing flue. The insert eliminates the excess combustion air, burns less wood more efficiently, and usually has a fan to blow hot air out of its vents. To make your fireplace truly efficient, you’ll want to install an insert approved by The Environmental Protection Agency (EPA).  An insert should also be installed by a factory-trained professional in order to ensure proper venting and best efficiency results. When properly installed, fireplace inserts can be a much more efficient supplemental zone heater than a traditional fireplace. According to the Lawrence Berkeley National Laboratory, a fireplace insert can make your fireplace up to 5x more efficient. The downside is the cost of an insert which can set you back about $2,000 to $4,000 (with installation) and also depends on the state of your existing chimney and the model you select.

But believe me- this investment pays for itself by improving efficiency and saving you money on heating bills.  Inserts can be powered by electricity, gas, propane, wood, pellets or coal.  However, since this is a website dedicated to firewood I will focus only on wood-burning inserts.

Wood-Burning Fireplace Inserts

The main benefit of a wood fireplace insert is that it gives you the beauty of an open fireplace with the performance of a state-of-the-art wood stove. The efficiency rating for wood fireplace inserts generally runs around 50% which is less than gas inserts but MUCH better than traditional fireplaces (which have 5-10% efficiency rating). The Environmental Protection Agency (EPA) certifies all wood fireplace inserts to ensure that they burn wood efficiently, safely and with less smoke.  When sized and installed properly, an EPA-certified wood fireplace insert will also reduce wood consumption and reduce maintenance of the insert and the chimney. The fireboxes of a wood insert run from 1.6 cubic feet (running hot, this size will kick out about 65,000 BTUs an hour) to 3.1 cubic feet (85,000 BTUs per hour). When loaded up with wood they can burn as long as 6-8 hours. The National Fire Protection Association requires a stainless-steel connector between the insert and the chimney’s flue liner, or a connector that runs all the way up the chimney (this setup is easier to clean). In many cases, some internal realignment of the chimney is necessary.

fireplace insert

Here are some safety and maintenance tips to get the best out of a wood fireplace insert:

  • If you smell smoke, your insert is not working right and could be dangerous.
  • Have your insert, chimney and vents professionally cleaned and inspected annually.
  • If using manufactured logs, use ones made from 100 percent compressed sawdust.
  • Remove ashes regularly, placing them in a covered metal container. Store this on a cement or brick slab, away from wood.
  • Burn only dry wood that’s been seasoned, sitting dry for at least six months.
  • Install a smoke alarm and carbon monoxide detector in the general vicinity of the fireplace.


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