Making a wood burning fireplace more efficient.

September 19, 2007 6:26 AM

Fall is right around the corner. These chilly mornings have me thinking about lighting a fire in our fire place. I love the look, the smell, and everything else that goes with a fireplace. But efficiency wise? It sucks.

What are my options for getting more heat in to the room than letting it all go up the chimney? At this point I do not want to consider gas logs. Trying to stay with wood. Also it is worth noting that this is not our main heat source. Just a supplement and backup in case we lose power.

posted by jaythebull to Home & Garden (14 answers total)

You can get a blower setup that will move the hot air form the fireplace into the room. Alternatively you can put a big iron plate against the back of the fireplace that will heat up and radiate more heat out. I also saw a new kind of grate called the 'grate wall of fire' google it, that looked interesting.
posted by zeoslap at 6:36 AM on September 19, 2007

Blower/heat pipe link

Grate Wall of Fire
posted by zeoslap at 6:37 AM on September 19, 2007

We put in a wood stove a couple seasons ago and it is AWESOME. Super efficient (can't even see smoke out the chimney -- it all gets burned), blows enough hot air to heat the whole first floor, and a nice big glass on the door so you can see the fire.
posted by stupidsexyFlanders at 6:37 AM on September 19, 2007

forgot to mention the woodstove sits right on the hearth.
posted by stupidsexyFlanders at 6:38 AM on September 19, 2007

Various wood grates, such as The Physicist's Fire, aka the Texas Fireframe Grate, or alternative designs like the Grate Wall of Fire, try to re-arrange the burning elements of the fire to yield more radiant energy from the fire, but some of these put burning wood and hot gases higher in small fireplaces than is wise. Grate heaters are tubular devices that try to increase convective air flow into the room, pulling the heat of the fire out as warmed air. Neither does much to lower the loss of hot air up the chimney, but that is not their function.

To recover heat being lost up the chimney, you have to have a combination of efficient supply of outside air for combustion, and heat stack recovery. Woodheat.org is an excellent resource for learning about these topics, and the alternatives for improving your use of wood for heating.
posted by paulsc at 6:56 AM on September 19, 2007

If you already have a fireplace, then it is very likely to be a
cold air sucking hole. You can remedy this problem with a
fireplace insert (I have personal experience with an
earthstove BV400). For most pre-existing fireplaces, any
other solution is sadly inadequate.

A fireplace insert should give you complete
control over the amount of air the fire receives (you should be
able to extinguish the fire entirely by shutting down the
intake air), and gives you a heat exchanger (most likely fan
driven).

Proper installation is important for a fireplace insert. It may
be necessary to also install a chimney liner (which can be
something like a 6 inch diameter stainless steel flexible
steel tube, like a dryer vent hose) from your fireplace insert
through your existing flue to the top of the chimney. I
have personal experience with one of these.

There are fireplaces that are designed to be fitted with glass
doors, which are not airtight but greatly improve your air
intake control. The doors are not really glass as we know it
these days, and are much more transparent to infrared.
This will be cheaper than but inferior to a fireplace insert,
unless the fireplace was designed specifically for glass doors.

Installing an external air port into an existing fireplace is
also not likely to improve it much. It will alleviate the
problem of a fireplace sucking warm air out of your home,
but it will not make your fireplace any more efficient at
heating your room.
posted by the Real Dan at 7:31 AM on September 19, 2007

Get a wood stove! You will not regret it.
posted by lohmannn at 7:42 AM on September 19, 2007

You need to look at the shape of the fireplace. I have had fireplaces that would not, after hours of a blazing fire and a ton of glowing embers, raise the temperature of the room one single degree. This is happens when the fireplace opening is too deep, too low, and not in the classic "Rumford" fireplace shape, which is shallow and tall, with widely-angled sides.

If your fireplace doesn't look like a Rumford, you're out of luck. The blower ideas will make some difference, but the blower won't run during a power outage. Your best bet really is to invest in a stove insert, since this will be vastly more efficient than any fireplace possibly could be.
posted by beagle at 7:51 AM on September 19, 2007

The last place I lived in had a fireplace insert. It was fantastic -- you lit the fire, let things get good and hot, then closed a lever that routed all the smoke through a catalytic converter before sending it up the chimney. Closing the air control all the way let us get almost 24 hours out of a full load of wood (24 hours later there were still hot coals, and the stove was still putting out warmth, but not very much), and with the fan on "low" it easily heated a 1000 sq ft area.
posted by Forktine at 8:26 AM on September 19, 2007

Response by poster: Thanks everyone. It looks like an insert is going to be the way to go.
posted by jaythebull at 9:35 AM on September 19, 2007

You might need your chimney sweeping. If you are burning wood you are supposed to do it at twice a year (once with coal)... a sooty chimney can me your fire much less efficient (and making it much more likely that your chimney will catch fire as well!).
posted by fearfulsymmetry at 1:08 PM on September 19, 2007

Wood stoves are much more efficient than a fireplace. My dad used to joke that fireplaces would cook you on one side and freeze the other!

We installed a wood stove and we love it, but the dust and dry heat are not for everybody.
posted by msbaby at 1:16 PM on September 25, 2007

That is why we got an insert. These days they make them to look much better than the one we bought several years ago.

Just make sure your heat thermometer is not right close to it. Ours is just a few feet away and it makes the rest of our house cold when the fireplace is on.
posted by seekingsimplicity at 12:22 PM on September 28, 2007

My fireplace was smoky and didn't seem to give off much heat until I redid it using the Rumford design, essentially making it much shallower with slanting sidewalls. This cured smokiness and warmed the room faster and better with less wood. Plans and discussion by Rumford himself, circa 1796, found at http://www.rumford.com/chimneyfireplacesa.html
Before actually mixing any mortar, as I was a bit scared of the outcome, I got some extra large bricks and dry lay them in place and built a test fire. Improvement was very obvious. I then lay them up permanently, mortaring only the vertical joints, and backfilling with rubble and a bit of mortar. I used common brick, not firebrick and its fine after 3 years.
http://www.rumford.com/chimneyfireplacesa.html
posted by fkeese at 2:29 PM on January 31, 2008