Anatomy of a fireplace

[Max]

Hi Folks,

I have 3 photos that go along with this post:

http://www.bodoin.com/images/fire1.jpg

http://www.bodoin.com/images/fire2.jpg

http://www.bodoin.com/images/fire3.jpg

Our fireplace has 2 things in the firebox. One is a plate that lifts up and allows access to the ashpit. This is located near the back of the firebox. The other thing is ???. Can anyone tell me what it is by looking at the pictures? The last picture is probably the best even though it's not quite in focus. I have no idea what it is used for. There is a little screw on the front plate of it that connects to a wire and which connects to piece of metal inside it. I'm just wondering if it's something that I need to maintain to keep the fire in good working order. We have had problems getting it to light without the smoke coming into the house before.

Cheers, Max

[Max]

I think it might be an outside air intake, I just need to figure out how to clean it because it looks full of ash (that's if I have correctly identified it I mean).

[Max]

Although I am not a scizophrenic (sp?) I'm just gonna keep on replying to myself.

Got the vent cleared with my shop vac (suck then blow) so that's great.

However, we still run into problems with smoke coming in the house when we 1st start the fire. I've done lots of searches on the net and found lots of advice but I'm curious to hear what works for you. Now just to answer myself again, I think we've got the problem nailed. It looks like we have to burn one of those fake logs first just to get the flow going then we can add real wood. The reason I have a problem with that theory though is that when we go to our friends house they just chuck in some newspaper and a pile of logs and the whole thing burns great with no smoke problems. Do chimneys / flue operate _that_ differently?

Lastly, a quick question about damp logs. Do you ever burn damp wood and, if so, what sort of performance do you get from it?

Cheers, Max

[LazyPup]

From what i can see in the photo that definitely appears to be an auxillary combustion air intake.

You may try using a shop vac to suck the dust and ash out of the opening to see if you can access the damper. The wire you mentioned is most likely the damper control, which is used to close the damper, preventing cold air from coming in when the fireplace is not in use.
(A word of caution when using a shop vac to clean a fireplace or burner-firplaces and burners contain carbon soot whish is almost pure carbon. Under rare circumstances spontaneous combustion can occur when carbon is rapidly oxydized such as being drawn into a shop vac or blown with high pressure air. For safe sake, as soon as you finish take the shop vac outside and empty all the contents to prevent the possibility of a fire inside from concealed spntaneous combustion.)

Contray to the opinion of many, a wood burning fireplace ranks dead last as an efficient source of home heating. Cured hardwood contains approximately 45% carbon. The percentage of carbon by weight of mass drops considerably by moisture content. Wet or green wood is in the order of 16% carbon per pound.

Carbon is the basic fuel source in all fossil fuels. The combustion of carbon requires 2.5lbs of oxygen per pound of carbon. Air at standard atmospheric pressure weighs approximately 1/12 of a pound per cu/ft, thus it requires 12 x 2.5 = 30 cu/ft of air to combust one pound of carbon.

A typical residential wood burning fireplace draws its combustion air from the room air, thus for every pound of carbon burned it requires 30 cu/ft of air from the living space.

In addition to combuston air, there is typically another 100 to 200 cu/ft of air from the living space lost to flue losses during the combustion process.

We could then say that it would require upwards of 230cu/ft of air per pound of carbon, which would be 2lbs of dry wood.

Most studies have concluded that one cord of hardwood has approximately the same BTU content as 100 gal of home heating oil, whereas the extremes of combustion and flue losses reduces the average recoverable heat to approximately 12% to 15% by comparison to an oil burner that may be 85% efficient.

When one then considers the cost of a cord of hardwood delivered, or the cost of transporting, chain saws, wood splitting equipment and your personal labor it is easy to see why wood rates at the bottom of the scale.

While their are many improvements to the fireplace to increase its efficiency, such as the ducted combustion air, in the end, at best fireplace efficiencies can hardly approach 35%.

The question then becomes, is a fireplace practical? As a primary source of home heating the answer is simply NO, on the other hand, if you are like myself, and many others, there is nothing more soothing on a cold winter nite than curling up by the fire, just keep in mind, it is for aestheticts ,not economy. not to mention, it is nice to have at least one source of heat, however innefficient in the case of a power outage.

By the way, you stated you have trouble with smoke in the room when you first light the fire. Try burning tow or three sheets of newspaper to create a rapid rise in temp to preheat the flue and begin the draft.

[Max]

Thanks LP. Lots of good info there. We actually have gas heat. We hang out in our family room for the most part and it has cathedral ceilings. Plus, the room opens directly into the kitchen. What I am trying to say is that we spend a fortune on gas bills and we never even really sit in warm comfort. The house is about 23 years old, perhaps we need a study of the house to see if we are losing heat through the windows or something like that. All of our friend's house are nice and warm but ours is not. Mind you, my wife keeps the thermostat at about 64 so maybe it's not surprising that we are cold all the time.

[LazyPup]

While it certainly would not pass for a professional study, there is a relatively inexpensive method to find your major heat loss areas.

If you have a good 35mm camera go to a PHotography supply store and get a 36 exposure roll of infra-red film. (You may have to special order it).

On a cold day with the heat running, take pictures of the house from the outside. Start with a full view of all four sides, then get close shots of doors, windows and other suspect areas.

Have the film processed and examine the pictures. The pictures will appear grossly out of focus because their is a focal shift in the infra-red spectrum,,(some quality 35mm lenses actually have an infra-red focal index,,you first focus normal, then shift the lense to the IR index before you shoot the picture.)

When you examine the pictures, the brighter the color the greater the heat loss, by example if you see a bright red line around a door of window frame, you know that is a major heat loss area.

Most Infra red film has a very low ASA rating so you should use a tripod to steady the camera.

While it is not a truely professional heat loss study, it is one of the tools that is used to do the studies and it will provide you some very good information to decide where to approach the problems.

In my estimation, if you have the camera available, it would be $20 +/- well spent.

[Max]

We do have the camera so I will give that a shot. We don't have a tripod but I want to get one anyway to go with my new Canon Digital Rebel. My wife as 35mm Canon so the tripod should be interchangeable.

Other rooms in the house are fine, just the open areas. I've heard people using their ceiling fans to keep the room cold in the summer and warm in the winter but we haven't tried that yet. The fan has no heating element (I think some might?) but I understand that heat rises so blowing the air down sounds like a great way of keeping the heat from rising to the high ceiling.

[LazyPup]

Look on the distance scale on the Canon lenses. You will see an index point in the center that is the distance to the focal point when the lense has been flocused. About 1/4" to the left of that index their is another index with an "R" over it. You may have noticed it before but never knew what it was for. That is the Infra-Red focal index.

Once you have your lense focused, note where the distance index is on the distance ring, then slide the distance ring until that point is lined up with the "R" index and your are focused or "INfra Red" spectrum.

[Max]

Any chance you could explain the theory of relativity too? Thanks for your help. I didn't see the R index but I'm still learning SLR photography.

[LazyPup]

I was in the Air Force for 1966 to 1973 and from 68 to 72 i was stationed in Germany. During that period I got extremely interested in photography as a hobby. By the time i left Germany to come back to the states i had aquire 2 Pentax Spotmatic bodies and 19 lenses ranging from a 17mm fish eye to a 1000mm tele. A Minolta twin lense reflex 2 1/4 x 2 1/4 with 4 lenses and a Century Graphic 4 x 5 press camera with two roll film backs, two polaroid backs and a sheet film holder with 18 sheet film packs. a Durst 2 1/4 x 3 1/4 color pack enlarger and numerous roll film developing tanks ranging from a single roll nikor to a 12 roll nikor which i used to home process Kodak slides and B&W. I dabbled a bit at color processing but it was simply too slow and involved to really do much with it.

I didnt like my job field in the Air Force much so once I completed the mandatory training in my field I voluntarily took the Air Force "Still Photographers Specialist Course" in hopes of cross training into the base photo lab.

In the mean time I was the manager of the base photo hobby shop for about a year, where i was involved in teaching basic darkroom processing, enlarging and developing.

My primary area of inerest was shooting landscapes under available light, which meant extemely long exposures. (I once took a picture in a wine cellar in Germany using only one candle for light. The exposure was 8hrs with 400asa film)

While attending college in Massachusetts I needed a sleeper course to fill my course load so I took Photography 101. When we were required to do a landscape scene for our portfolio I used a home made vice grip plier mount to attach my camera to a steel post on the main street in Springfield, Mass. By using 64asa B&W film and stacking neutral density filters I took a daytime picture that required a 4 hour exposure. The end result was a daylight picture of the main street downtown without a single person in the picture, except one drunk who was sleeping on a buss stop bench and ther were no cars in the traffic lanes on the street. (No one was present in the image long enough to register on the film). I never told the instructor how i got the people out of the picture, but it won me an honorable mention at the state photo show.