Downdraft problem, oil into fireplace flue

cwilliams2000

I realized today that I have a lousy problem.  Basically I have 2 flues, one for oil heat ex and one for fireplace.  We dont use the fireplace and I noticed the smell of oil exahust from the fireplace.  This year I installed two small stainless caps on each flue and the edges are touching one another, so I think what is happening is that when the oil heat runs, the warm air goes up and the oher flue which is ice cold here, always has a slight downdraft and when I opened the damper, the exahust smell is very strong coming in.  The temp fix is that I plugged the fireplace flue with insulation and that seemed to have stopped it for now.



Is this common or what have you done to solve it, I think my best choice may be a sealing plate on the top of the fieplace flue or to install an insert with its own liner and cap.  Thank you

steamer7676

be very carefull

this sounds extremely dangerous i really hope you have a good co detector and smoke detectors. any time flue gas can get back in your living space you absolutely have a big problem . if you don't use the fire place seal the opening permanently asap and have a pro come by and check your system. don't mess around with flue gas .

Gordy

Negative pressure

 Your house may be tight construction. What happens is when the boiler starts its using inside air for combustion, the air to replace it has to come from some where. Usually its the path with the least resistance, and that would be the adjacent flue for the fireplace. The wheel is already set in motion with a cold flue sucking the exhaust from the boiler down the chimney.



 I would suggest a top seal damper for the fireplace flue. Lyemance is the brand I bought myself very good product, and easy to install.



 The reverse could also happen if you burn a fire, and the boiler is not running also, but you can not put a top damper on that flue it must always be open.



 You could also add make up air to the boiler room. This could bring air in directly to the boiler when it is on.





 Couple of questions.



 Has this always been an issue?



Added any new exhaust fans to baths or kitchens which did not have them before the problem developed?



Done any weather sealing recently?



These can all contribute to negative pressurization.



 I recently added a couple of the lyemance dampers to two fireplaces in my home. They have adjacent flues, and you light one, and get a smoke odor in the other. The top dampers cured this plus they have an air tight seal which is way better then a metal damper.





Another possible scenereo is that one or both flues have a cracked flue tile, or bad joint allowing flue gas to pass between the two before it even gets out of the chimney. Have a chimney inspection done for piece of mind if anything.



Gordy

Big Ed_4

Fan

Any over powering exhaust fans ?? One of these fancy new kitchens with high volume fans would cause your problem ... They need fresh air vents to equalize the pressure ..

icesailor

Downdrafts:

Your make up air for the boiler is coming from your fireplace flue. If the wind shifts and the wind first blows across the fireplace flue, you won't have a problem. When the wind shifts and first blows across the boiler flue, the air being sucked down the chimney goes down the fireplace flue. Either open a window in the cellar or do something to give the burner free access to make up air or you could die. I'm not kidding. If it was gas, you could easily die. People have died under these conditions. If yo don't understand this, or don't know what you are doing, get someone who does. If you can find someone.

I can not impress upon you the seriousness of this condition. The odor of the oil flue is only a tip off.

I once heard a general rule.

With oil, first you smell it, then you see it (smoke/soot(, then you die.

With gas, first you die, then you smell it, then you see it.

Either way, you are dead.

cwilliams2000

Think I have it

I understand the downdraft issues but I don't think its a matter of not having enough air to draw in. I think the issue is the fact I installed two individual flue caps next to each other and the oil flue isn't able to disperese its pressured exahust straight out, so when it hits the top of the cap it splits and one side of it is right next to the other cap for my fireplace and some id draw down.



I am going to remove the oil cap and see if the problem is gone.

Gordy

Flue cap misunderstanding

 Flue caps, and top sealing dampers are 2 different things. Some come as combination units.



You should have flue caps installed to keep the weather, and critters out of the flue.



Top sealing dampers install directly on the flue top. When closed it creates a positve seal so no smoke or fumes can be sucked in to the chimney. If you still get fumes or smoke with one installed then there is a breach in the flues causing cross contamination. This is not good the flue then needs repair either a tile is cracked or a joint has seperated.





Removing the flue cap may help, but if the wind happens to be blowing in the direction of the adjacent flue it will still suck the gasses in. Now the flue will allow rain, snow, animals ect. in to the flue because it is unprotected causing damage to the clay flue tiles over time.



Gordy

Paul Fredricks_3

WIth or without the caps...

You still shouldn't get oil exhaust coming down the fireplace flue. As stated above, sounds like you need fresh air in the house. Nearly every house act s as a chimney. Crack open your front door and see if you fell cold air coming in. If you do it's because the warm air in the house is getting out somewhere. Many times it's straight up through the roof, but bathroom and kitchen exhausts make the problem worse. So does an oil burner that uses inside air.

cwilliams2000

could be right

I know what you are saying, I will definitely check it out to be sure, it might be simple for me just t install the beckett outside air kit and that will help eliminate the possibility of it now or later.

Gordy

Good choice

 Installing an outside air kit would be the best choice in my opinion. 



  There are a lot of things that can make a home go negative pressure more than it all ready inherantly is. Dryers running, Bath exhaust fans, Kitchen exhaust fans, burning fires in a fireplace. 



  Those are all variables as far as when they are running. May be none of them will be on one time the boiler cycles, and the next time they are all running. An outside air kit is a sure way to have consistent make up air for the boiler no matter what is causing the house to go negative pressure

Paul Pollets

Chimney liner

I suggest you'd want to install a stainless chimney liner for the oil combustion. It will eliminate any crossover into the fireplace flue and make the burner more efficient. You'll still need proper combustion fresh air to the burner and the burner needs to be re-tuned once the liner is installed.

icesailor

Downwind fireplace flues:

It doesn't matter how many flue and chimney liners you install, if the wind is blowing and the boiler flue is exhausting upwind of the fireplace flue, and if an appliance needs make up air, it will suck air down the fireplace.

Flowing air has a lower pressure than static air. The air in the house is higher than the outside. The house is constantly trying to equalize the pressure differential. High pressure air inside the house will equalize through indoor leaks. That's how draft works. If you make a perfectly draft free house, it will not allow a chimney to draw. The higher the wind speed, the lower the pressure. When the wind speed drops, the inside pressure will drop. Slowing the draft.. My iceboat will to 3 to 5 times faster than the wind speed because of this and other factors.

There's nothing abnormal about this. The more you frack with this, the worse you can make it. Give it make up air and you will be done with it.

On many more than one occasion, I have seen masons seal up a perfectly good chimney flue because they didn't understand what what they were dealing with 

Paul Fredricks_3

Just a thought

We have a customer with a 2 story house and a one story addition on one side. At the end of the addition is a fire place. The chimney is to code as it is at least 3' higher than anything within 10' of it (if I remember the code correctly). But it is still shorter than the 2 floor part of the house. Because the house is taller it is acting as a chimney and the warm air tries to exit at the top of the house which results in air being pulled down the fireplace chimney. We had our chimney expert check it out and that was his conclusion, with no real way to fix the problem. 

Gordy

Exterior chimney

Mr. Fredricks in your situation if its an exterior chimney they struggle also do to the fact the flue gets real cold compared to a chimney that is built inside the envelope. It does not matter if its metal or masonary chimney. All though the second story is probably having an effect also. A lot can depend on wind direction ect.



 If the chimney is inherently cold it will take a lot more preheat to get a draft going.



The flue top style dampers are great in that they seal the chimney air tight at the top of the flue allowing the flue to stay a bit warmer then if it is dampend from the fire box.



 I have installed two, and love them. Easy to install set it on top of the flue with silicone, drop the cable down the flue, mount the cable retainer bracket to the side of the fire box, cut cable to length, install handle, done.



Gordy

icesailor

Downdrafts and seemingly poor drafts:

If there is no wind out, and you have some windows or doors cracked so as to equalize the pressure, the chimney will work fine. When the wind comes up, it will not. The higher the outside wind speed, the worse it will work. Then, there's turbulence. For example, if the house has a NW to SE orientation, and the chimney is on the SE end, and the wind is blowing from the NW, when it hits the NW side of the building, the wind will rise up and roll over the house. It will "roll" down the roof and will try to "push" down the chimney. It's why the snow drifts form on the Lee side of the house.

I fly to and from work 5 days a week. When there's a storm, the wind is usually from the SE. From 150 degrees blowing to the NW, 330 degrees. Many times, I come home and the wind is honking at up to 30+ MPH. The ceiling may be 100'. IFR conditions. The ATC controllers vector us up to Plymouth where we start our approach from whatever altitude we have clearance for. Over 1000', the air is relatively calm. When we hit the glide slope over Barnstable Harbor and start down, the turbulence starts to pick up at or under 1000'. The wind has been blowing unobstructed across Nantucket Sound and reaches the Cape Cod shore in Yarmouth, where it meets resistance. It flows across Lewis Bay and hits the land. The land gives the wind sheet resistance on the bottom and the top breaks away and starts to roll. It hits the airport and rolls merrily down the runway, picking up more turbulence. At the NW end of the runway, there is a big sand pit to the south of the runway and a big hill on the North. The wind then really gets to rolling. It's up to over 500' off the ground. There is no visibility. We fly merrily into this carnival ride and the closer we get to the end of the runway, the worse the plane yaws and pitches. Sometimes, there are some real slammers. At 2400' and 100' up, the runway strobe approach lights appear and it is a drop/slam in to the runway. Thank goodness for good pilots.

The same wind that slams us around on the approach is the same wind that blows over the house. You have to understand about the wind to understand draft.

Paul Fredricks_3

Yep

And this is an exterior chimney, and worse than that. Picture the chimney on the end of the addition, sticking up 10' from the roof. And it's still shorter than the main part of the house. to correct the situation they would have to add approximately 10' more to the top of the chimney. I wouldn't want to be near it in a wind storm.





And don't call me Mr Fredricks!  

Gordy

Liners

 I believe Mr. Pollets is refering to the fact that fuel burning appliances, and clay tile flues do not get along very well due to acidic condensation. Also the possibility which  the thread does not know unless there is a chimney inspection done.  If there is a breach ( cracked clay tile or missing  mortar in a tile joint) of each flue then the exhaust will cross contaminated the unused flue before it even exits the chimney. If this were the case which is unknown then a chimney liner would be effective in resolving those issues.





 Gordy

Gordy

Sorry

 Respect thing, Child hood taught won't happen again......Paul