Fireplace not drawing properly

We have a two sided fireplace in our house. The house is 18 years old and the fireplace is original to the house. We purchased the house about a year ago. We tried several times last winter to have a fire and most of the time smoke backed up in the house. We have tried having a window partially/fully open and warming the chimney prior to lighting the logs, with no luck.
I measured the chimney height tonight and it is taller than it needs to be. I was told it needs to be 2' taller than the point where it is 10' away from the roof. There is a large rooftop A/C unit 7' feet away from the chimney that is 2' taller than the chimney. Should I raise the chimney above the A/C unit? What else should I look for?
Thanks,
cm
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cm wrote:

Hi, I wonder if you have a damper to open?
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Tony,
Thanks. The damper is wide open when I light the fire. With a flashlight I can see all the way to the top of the chimney.
cm

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"cm" wrote

2 sided? Can you define what you mean there? Is it one that is open to 2 roms at the same time (back and front) as like a center of the house chimney may be?
If so, more often than not, the grate is too low in that configuration causing smoke to go out the sides into one or both rooms. It's also possible a fan or some other air source in one room is pushing the smoke across into the other.

Not bad, but doesnt sound likely just now that the AC unit is at fault. There are other things to check first.

Ok, you may actually have it too far open. Some fireplaces dont draw as well with it all the way open. It sounds illogical, but it can be true. Mine operates best at the 2/3 position for example. Open it too far, and the wind makes the flow reverse into the house.
Here's a list of things to rule out.
- Is the grate too low or are you building the fire right on the base? The fireplace design has to be made for that and most are not. Too much 'top room' before the lintel can cause the smoke to redirect wrong.
- if with a grate, are you trying to build the fire more towards the center or front? (assuming here your '2 sided' isnt the above where it's basically an open hole between 2 rooms). Most fires will smoke and not draw right unless the grate is pushed more towards the back (not flush to the wall, but much nearer to it than the center).
- If a grate, is it too large? Many people get one too large for the fireplace because visually 'it fits' but then the fire is too much for the draw to handle. At a rough guess there should be at least 6 inches on each side clear from the brick work.
- What kind of wood are you burning? Is it really properly cured? If it's any type of pine, or you get lots of 'popping' then it's smoky green wood (which can also be a fire hazard as it makes more creosote which can catch fire in the chimney). If you arent familiar with burning wood, it's real easy to not know the difference. If you have an experienced neighbor with a fireplace, ask if you can have a bit of well cured wood for 1 fire to check out, or perhaps they can come over and see what yours is doing and be able to tell you.
- Is the wood damp? Wood that is damp or literally frozen, tends to be smoky for a bit (and hard to light obviously!).
- Do you have a chimney cap? Such affects the flow of air but is needed, but it may not be positioned right for your needs. It may for example be too low. Such are normally sold for 'standard single sided fireplaces' and if you have something special, may have to be adjusted for it. I have seen ones that are higher and have a sort of 'chicken wire' down to the base of the chimney to keep birds and squirrels etc out, on specialty (larger than average) fireplaces.
- Have you had the chimney professionally cleaned (which comes with a basic inspection as well and the cleaners normally know a fair amount about draft issues and what can affect them, though may not know exact 'how many inches' details for caps and such (hit or miss, some do, some don't).
The only thing there that is a little expensive, is the cleaning and inspection. You dont need the fiber-optic cable inspection level (thats for follow-up on a damaged one) but the basic one (normally about 100-120$ and often you get 1/3 of that back from your house insurance company if you call then bring the recipt in).
Please bear with me if you have a reply with questions and do not get an answer from me. COX cable in my area is having problems with the newsgroup servers the past 6 days and most days, all the messages 'go away'. My email however is not grunged so if you want to also send me a copy of any replies that way if you get no answer in a day or so, I am happy to help.
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Once I get fire started, I have glass doors to keep out smoke let enough air in to support combustion. My fireplace in family room was problem because when furnace came on nearby it created negative pressure in room drawing smoke out of fireplace. Part of solution was keeping doors open to room from other parts of house. You would do well to sweep chimney yourself or have it done, just to check out your system and make sure there is no creosote build up.
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"Frank" wrote

Definately, but I advise having it done professionally, at least this time. There may be damage and it can be assessed at the same time.
Generally I tend to not adviase folks to do this themselves as they ofen don't really know what to do and end up leaving big areas uncleaned (unaware they are missing a center section with a too short cleaning wand etc).
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My parents house, the chimney is on exterior wall. We have to take a piece of news paper, and fold it in a "fan" shape. Light the paper about half way up, and then hold it up into the chimney. When your hand gets warm, take the flaming news paper, and stick it under the wood holder grate. It takes some practice.
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I built a house with a two sided fireplace. I never got it to quit smoking in the house. It was better when I put a glass door on one side of it, and sealed it all around, but there still were small places where air could get through. It's the nature of a double sided fireplace.
Think about it. All there needs to be for smoke to come out one side is a little air going in the other side. About the only thing that helped, and only a little was putting a couple of rows of bricks under the fire grate, and putting the grate on bricks itself. Lucky I had enough height in the hearth to do that. But it still smoked.
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I have to open a nearly window to get no smoke, some newer houses with tyvek and windows that seal tight can have issues. Raise chimney with stove pipe to see if it helps. Maybe its a poor design and a lip is needed to lower hood, raise fire or close down doors.
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wrote:

If this is the same kind of 2 sided fireplace that I had in my previous house, there were two dampers and both of them had to be open in order to start a fire and a window had to be cracked open. A rather hot and relatively smokeless fire had to be started (paper) and kept going several seconds before adding dry kindling and finally wood to the fire.
We had glass doors on both sides and they had to be open when starting and then closed when the fire got started properly. Even taking all precautions to start a fire without getting smoke into the living area, it was a difficult task to accomplish. Once started though, it seemed to work well.
Good luck
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cm wrote:

Fireplaces never vent well. It's because it's like an upside down funnel, large at the bottom and cramming all that smoke into a small flue. My fireplace always smoked. After I put a little wood stove in the fireplace and a stove pipe up to the flue I never had the problem again. The stove had plenty of draft. That's how the stove company installed it.
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Claude Hopper wrote: ...

That's simply not so...some draw very well.
A lot of difficulties w/ newer houses is they're sealed so tight there's an inadequate air source for them to draw. This can be tested by opening a window nearby slightly.
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Thanks for all the advice. With temps heading back into the 90s I will have to wait another week or so to try a few of your suggestions. I will update my findings then.
Thanks again,
cm

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The design of a good working fireplace and chimney is an art form.
When you design a chimney, the first thing is to consider the size of fire that will be used. Next is to design the chimney of the right size to fit the fire, so that as much of it as possible is inside the insulated exterior of your property. A warm chimney will work well. Ensure it has enough fresh air to burn, without the air being pulled through badly fitting doors and windows.
Your set up would appear to be badly designed, or perhaps someone has changed the original setup?
When you light a fire, the first thing that needs to happen is that the kindling produces enough heat to lift the plug of cold air that is inside the chimney, lift it out of the top and push it to one side. If the fire struggles to find fresh air to burn, the process will stall, and smoke will billow into the room. The fire needs a direct supply of fresh air from somewhere. The best solution is a pipe direct from the outside, this will avoid the struggle for air and eliminate drafts in the home. The next thing is for a fire to burn well, it needs to have a warm insulated chimney, the inside needs to warm up quickly to get rid of the smoke. A well insulated chimney is essential, especially when you want it to burn slowly. Having more than the minimum chimney poking through the roof is bad. A cap on the top to stop the rain from entering and cooling the rising air will help.
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