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noname50's avatar

Proper use of 1 fireplace, when you have 2?

Asked by noname50 (154points) December 5th, 2010

I have 2 fireplaces. House is a split level. One fp in the LR on main level and 1 on the lowest level, folks have called, the sub basement. I’m using the LR one but the lower level seems smokey. Does the flu, (sp) need to be open on the lower level when using the upper level fireplace? Can they both be used at the same time? Vise versa on using only one. Thanks.

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11 Answers

Tropical_Willie's avatar

Each fireplace should have it OWN Flue. There should not be a connection between the two.
Make sure the lower level flue is closed. The chimney outside should have separate flues comimg out at the top of the chimney. Is there a furnace / hot water heater connected to this chimney ? ?

CyanoticWasp's avatar

One thing that can happen in homes that have and use fireplaces is that when the house furnace kicks on, either because other heating zones in the house create the demand, or for water heating, the combustion air can be pulled… from the fireplace flue.

Whenever the furnace starts, it pulls in combustion air from inside the dwelling, uses it to burn the fuel in the furnace (whether oil or gas), and sends it up the furnace flue. It used to be that houses weren’t so well-sealed, and outside air would find its way through small window casing openings, under door thresholds, and through imperfect seals in the walls themselves. No more. Now that houses are wrapped in Tyvek and window and door seals are so good, there’s much less air infiltration. But the combustion air is still being used in the furnace and is still going up the flue. So what is happening is that the home has a negative air pressure, and it sucks air from from outside wherever it can. If your chimney flue is open, then it’s the most likely place.

So your furnace is probably pulling some of the smoke down the flue and into the room to equalize the air pressure in the home.

There are a couple of ways to avoid this.

1. Be sure that the furnace won’t turn on while the fireplace is being used by simply turning it off until hours after the fire is out.

2. Isolate the room with the fireplace from the rest of the house (may be difficult in a living room, since most don’t have doors that you can close and seal), or

3. Provide a direct air inlet to the furnace from outside so that it’s not pulling ‘room air’ in. The house will maintain its neutral air pressure and not try to suck any more in from outside to make up for the combustion loss. (This cold air inlet to the furnace will reduce its efficiency somewhat, since you’ll be mixing frigid air with the fuel instead of pre-heated room temperature air, but it’s far safer for you than the situation you have described, which can kill you – as well as potentially suck hot embers down the flue, out of the fireplace and into the room, which is also no good.)

4. It may be possible to install a damper in the fireplace flues that prevents the reverse flow of smoke and air back into the house via that route – and maybe you already have that and my advice above is all wrong – but I’ve lived in houses that don’t have such a device, and I’ve seen it happen.

PS: Welcome to Fluther.

noname50's avatar

Thanks to both resposes.

To clarify: I don’t see alot of smoke, it’s more the smell. Smoke detectors are not going off. Please note, each fireplace has it’s own flue, the flue on the lower level was closed and there is no water heater or furnance connected.

The second fp is in the same finished room as the furnance and water heater. They are closed off with sliding doors. I did think the central heat may have been playing a part in the problem, but not certain. There is a separate “stack” on the roof, from which the heat “smoke” exists. I’m pretty sure there is a damper but will confirm.—Thanks.

CyanoticWasp's avatar

To re-clarify: Any fireplace flue will have a damper that you can manually open and close. What I meant was the type of damper that your furnace likely has on its air inlet, which opens to admit air only… you won’t see any reverse flow from that (absent catastrophic failure of the system) because it closes itself and doesn’t permit a reverse flow. A strictly manual fireplace damper won’t have that feature.

noname50's avatar

Ok, I’m back.

I had the fireplace inspected and cleaned a week ago today, last Friday. I did not have any problems with the the smoke/smell prior to this. I did check the lower level fp this morning and it seems that the damper/flue, whichever you pull open and close, is not closing completely. As soon as i started fire upstairs, i could smell in the lower level. I did turn the heat off, so no conflict there i guess.

My questions/concern is: what if i wanted to use both fireplaces at the same time? Shouldn’t i be able to do that? Does anything on the roof/chimney play a part? Maybe i’m a little paranoid now, that the folks went up on the roof. As indicated, i had been using the fp with no problem, prior to the inspection last week. I don’t see anything noticeable coming from the buring fp, but my lower level is now smokey and it is making its way to the upper level. I can see the smoke going up from the buring fp.

Insight is appreciated.


CyanoticWasp's avatar

My best guess on what is happening is that if the lower level damper (the mechanism that allows or prevents the passage of air and smoke in the flue) was not closing completely, then the slight down-draft of cold air in the lower level fireplace flue (which is normal enough in cold weather when there’s no fire) is carrying some of the smoke from the upper level fireplace after it exits the chimney at the roof top.

You need to have the damper fixed so that it will close, number 1. Even without fires burning, you’ll have a continuous supply of cold outside air coming down the flue otherwise. It would probably help the situation if you can completely open the downstairs damper to start a fire there and have the flue working in the right direction, so that more smoke isn’t drawn downward.

But you need to have that damper fixed ASAP, no doubt about it.

noname50's avatar

Thanks Cyanotic!!! So, I had someone look at the lower fp and they did find that it wasn’t closing due to small glitch. Just have to manuver to ensure it closes properly. It was getting caught. I will wait til later this evening or tomorrow and lite some paper to see if I smell anything downstairs.

So, you’re saying by warming the lower fp, it will aide in the flow of smoking going upwards. Is this something I should do on a regular basis?

Thanks again.

CyanoticWasp's avatar

No. If the dampers close properly for each fireplace then they truly should be independent of each other. But for now, while the improperly closing damper on the lower level won’t close fully, it would help to have some kind of flow going up the chimney, and a fire is one way to do that. (A fan or blower placed where it can blow upward into the flue – while the damper is opened – would have the same effect, if the air flow could be directed well enough.)

noname50's avatar

Ok, great. Thanks for clarifying.

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