View Full Version : Firplace/Downdraft question
01-01-2003, 11:58 PM
Have a double chimney, one firplace upstairs, one down. Firplace upstairs is a straight shot up to the top of the chimney, it works fine with no downdraft. Downstairs however is a totally diffirent story. It has bend in the flue I assume to get on the other side of the one from upstairs. It has a terrible downdraft at times. So bad that it completely fills the room with smoke if it is windy outside. I try to "pre-heat" the flue with some lit newspapers but that doesnt work too well. The only answer has been to hold something over the fireplace while it is heating up but that only holds out so much smoke. Is there something I can do (in the spring when its warm!) to solve this problem? A cap or deflector of some sort? Would that help?
Any thoughts or comments appreciated!
01-02-2003, 12:57 AM
This is one subject I don't normally post on. chimneys are strange things. The fact that the upstairs works gives me the clue that might be the answer as to why.
I have a very tall chimney and a tall chimney has good points and bad. On a cold day the chimney will cause a reverse draft because of all the cold air that is in the long chimney. The only answer is to preheat it. Once it has hot air in the chimney it should draw like a train. and be very effective. That is how mine works.
make sure you have it checked out by a pro. Chimeny fires are a bad thing and the condition of the chimney is the big cause of them.
01-02-2003, 01:16 AM
Thanks for the response. I'm sorry but I'm not sure I understand what you feel the problem is. The cold air in the upstairs chimney is helping cause the downdraft? Excuse my missing your point! All this holiday food has me dumbed down...:). By the way, how do you pre heat your fireplace? Like I said we have used burning newspaper but generally that just plows back in our faces!
01-02-2003, 03:14 AM
The basic fact that it is a two story chimney, You have about 24 to 30 ft of cold air in the chimney. Cold air drops warm air rises. The cold air in the chimney starts to fall when you open the flue. It draws in the cold air outside and you have a nice draft down the chimney. You need to get the air heated and one way to do that is with burning paper. One thing that helps is to open a window slightly as you are starting the fire. That will allow some air to be drawn to the fire.
What you have is a classic issue and one that there is not a real easy solution you just have to try to get a system that works for you. A gas fire starter system works well, but if you don't have one now much help. You might try lighting paper in the flue area and closing the damper slightly to cut down on the back flow. For me I just light the fire and open the window. I get a short back flow and then it draws well and I can close the window.
Hope this helps
01-04-2003, 09:35 PM
My chimney is 2 stories plus, and I don't have a problem. Mainly because I usually leave the flue open. It is too easy to forget to shut it, and I never shut it until the fire is all the way out.
When I do start a fire, maybe I don't get a down draft because the warm air from the house has been sneaking up the flue anyway. So the air movement is up to begin with.
The air in the chimney is cold and heavier, the air in the house is warm and lighter. So maybe if you open the flue and the doors, and let it be for a minute, the air flow will begin to move up as your house air escapes. Then start the fire and it should be ok.
01-05-2003, 01:01 PM
Thanks folks, I wll try cracking open the door nearby and opening the flue only a little to get it started. The basement is a really cold one so there isnt much warm air in there to begin with. The downdraft is, at times, terrible! Never had one near this bad. Will let you know what happens. Thanks.
01-05-2003, 11:52 PM
Hey, HD? Before you go, I'd like to ask a question or two.
When the downstairs fireplace smokes, is the upstairs one already lit? I suspect that's the case, but I'd like to be sure.
Also - is your basement really airtight? Have you gone around and sealed every little place where a cold draft could get in?
I ask because both could be contributing to the problem.
If the upstairs fireplace is lit, or if a furnace or fueled water heater is operating and drawing combustion air from inside the house, that leaves the house with a net deficit of air - IOW a vacuum. Replacement air's gotta come from someplace, and in this case your downstairs fireplace is a likely candidate. Right down the flue, out the fireplace, up the stairs, and into the other fireplace to feed the fire.
If the basement is awfully airtight and draft-free, that'll make the problem worse. If the house can't suck outside air from anyplace else, it'll sip it through the flue.
Yeah, I think your best bet is to open a window or door to the outdoors when you light the fireplace. That should serve as a vacuum break, at least until you get the fire going.
While you're checking stuff out, peek around to see if you have any floor drains in the basement. Check to see if they're obstructed. Got a rug over one or more to kill a draft? Open it back up & let the draft in. Ya wanna feed a fire, ya gotta feed it plenty of air... and that's GOTTA come from SOMEPLACE. A floor drain, at least, will let in a warmer draft than a window will. Maybe as much as 80 degrees warmer, depending on where you live.
-- Tim --
Learn from the mistakes of others.
You can't possibly live long enough to make them all yourself.
I had the same trouble after I moved in my 40-years old house 4 years ago, possibly not as severe at yours, but I've had my share of house full of smoke and freezing-cold basement floor, believe me.
Anyway, I took to the reading (which I always do before hiring somebody; find it very helpful as far as saving a bundle is concerned), and the explanation turned out to be rather simple. I'll try to put it in simple words.
Imagine your house filled with the air; the colder (heavier) air will stay at the bottom, and the higher you go, the lighter and warmer the air gets. And the air pressure at the bottom of the house will be defined by the mass density of the air in the house, which is a mixture of colder and warmer air.
Now imagine your basement chimney as a vertical pipe running OUTSIDE OF THE HOUSE (I'd bet my hand your fireplace is at an outer wall, and the chimney runs up 'through' this outer wall) and entering the house at its bottom. Now, since the air in this 'pipe' gets the outdoor temperature, or close to that, throughout its height, the air (heavy cold air) pressure at the pipe's bottom from this cold air will be greater than that from the house air (definitely warmer than in the chimney). As a result, the cold air from the chimney pushes into the house, pushing the warmest air out of your house through the attic, windows, etc. And the colder is the air in the chimney is, the stronger is the downdraft, and the more difficult it is to 'warm up' the chimney with the newspapers.
Having understood that, I realized that the only real fix would be to have the air in the chimney at approximately the same temperature as in the house -- which made me feel sad (shall we "thank" the guy(s) who suggested this design of chimney running outside of the house? Just look at the houses where a woodstove is used to heat the house, like in the villages of my home Russia -- the chimney always goes through the attic near the highest point of the roof!). I realized it was unlikey a chimney mason would fix the problem, since it was a conceptual design flaw.
But I was able to figure out a decently effective remedy -- I removed my lower damper, and installed a damper on the top of the chimney (these are available on the market -- see later). The rationale was: if I don't let the outdoor air easily get into the chimney, the air in it will normally stay warmer, and I'll have less trouble warming it up when starting the fire. Also, I'll reduce the intake of the cold air while there is no fire in the fireplace.
Boy, the result exceeded my expectations. Since the top-damper has a rubber gasket (it's OK since the temperature at the top of the chimney does not get too high), it is much more air-tight then my regular cast-iron lower damper was. Hence now I barely feel the cold downdraft when the fireplace is not on. Now, when I start the fire, I get everything ready before I light; then open the damper and light a paper torch without delay -- then it takes only a second or two before the air starts sucking up. Then I light the wood, and, here we go, -- no smoke!
I'm not sure if your case is fixable with this remedy. Whether it fixable or not, depends on how well (or how badly?) the air in your chimney is warmed by your house now. The top-damper cost me about 240 canadian bucks, they are bloody expensive for their simple design, so see for yourself if you want to risk some 150 US$ (although, it will mitigate the cold floor problem anyway).
If you shop for one, consider the following features:
- how airtight it is; the tighter the better; take my advice of seeing the thing 'alive' rather than buying by a picture;
- is it likely to freeze up in winter (mine works like a 'hat' popping up and dropping down on the chimney opening, hence no water/snow gets onto its gasket when not open -- it's Lyemance (?) brand);
- safety device in case of a chimney fire.
Oh, and if you decide to keep it as you have it now, opening windows in the basement when you start the fire should help a bit, but not too much. Given the 'theory' above, opening the windows will reduce the 'power' of the backdraft flow through the chimney, since the cold air will also be sucked in via windows. Hence it should be easier to overcome this chimney donward flow with a torch.
Anyway, good luck, and greetings from Canada,
P.S. I seldom visit this forum lately; feel free to e-mail me at firstname.lastname@example.org should you have questions.
01-10-2003, 09:47 AM
No, the upstairs is never lit when we start downstairs. We use it rarely. As for airtight basement, I wish! I have been on the draft patrol for a few weeks now. Recaulked and added trim around the door to the outside, insulated some unused cabinets that are on the outside walls (floor to ceiling fishing rod closet) etc. It is better now but still gets cold and can feel air moving slightly when you sit for a while. The damper is not air tight and I think the biggest contributor to the draft situation. There is an oversized (or I have been told that its oversized) return vent in the room for three (count 'em - 3!) oil burning furnaces in the unfinished part of the basement next to the finished room. That is a very good point though. I will add trying to start the fire when the furnaces are off to my list of solutions! Thanks for the comments.
01-10-2003, 10:28 PM
Now THAT was well spake - and food for quite a bit of additional thought. Thanks, Yuri! Yuri?
Oh, BTW - if you're around & see this - better think twice about betting a hand on that outside-wall chimney deal. More than half the chimneys I've seen thus far have been well inside the house's "footprint". One of ours is.
-- Tim --
There are two ways to have enough.
One is to get more.
The other is to need less.
01-11-2003, 02:06 PM
Thanks Yuri, everything you said makes sense. This fireplace is placed, you go it right, on an outside wall with the chimney outside the house going up two stories. My latest update..... we had a pretty good downdraft going last night. I stoked the fireplace, opened the back door about a foot, waited for the furnaces to shut down to see if the return vent had any impact and VOILA! Alot better. Still held a blanket over the opening to block the smoke some while it started up just in case. Only a small bit came out. Easiest/smokeless start we've had in months.
My brother in law is a brick mason so I am going to ask him about the top damper and see if he can do something with the install. The original damper has seen better days and should probably be replaced anyway. Thanks again!
Tim, the only thing I wanted to point out saying that I'd bet my hand ... etc ... was that this downdraft thing is unlikely to exist with the chimneys that are within the house's footprint (BTW, my chimney is outside my house's footprint for sure).
Anyway, it's been a pleasure to get a bit useful for you folks,
01-13-2003, 10:29 PM
Well, I'd sure like to say that you offered some great input - and I'd further like to formally welcome you to the forum. I hope you stick around.
-- Tim --
Everything you are is as old as time itself.
That stuff of which you are made has been around forever,
and will be around forever.
You are only the current arrangement of that stuff.