Chimney downdraft question.

[JohnMickish]

I have problems with cold air flowing into one of my wood fireplaces and want some advice/help on what to do.

The house is a 1975 one story rambler and I have two wood burining fireplaces, one on the main floor and one in the basement. Both are in the SW corner of the house, basically on top of each other with separate chimneys. The main floor unit is fine, but the one in the basement has such a rush of cold air running down the chimney when I open the flue I cannot get a fire started and it just pushes the smoke into the house.

I have tried paper up the chimney to start and that will start an updraft but as soon as the paper is out the air reverses direction. The colder it is outside the worse it it.

The chimney is not plugged since the fireplace works fine in the spring/fall, just not when it's very cold outside.

I have tried opening a window but that dosen't help. Both chimneys are right next to each other on the roof and the same hight.

Is there a cap or something I can purchase to help this?

[Finns]

Maybe more paper burning till all the air in the chimney is warmed and rising .

Finns.

[Bigsmitty]

The problem is that the cold air is heavy and it wants to come down the flue. Especially in the basement where often times there is a negitive pressure. One thing that works is a top sealing damper. This is a cap that has a flap inside it that you can shut when your not using it. You keep your existing damper "always open" and control the top sealing damper from a lever - cable inside your firebox. This helps because when its sealed at the top, your flue stays warm all the way to the top. Therefore your fire starts easier. There are a few on the market. Chimalator brand is my favorite. There made in Bloomington. Plan on spending a couple hundred bucks or so. Good luck.

[Pat K]

Sounds like negative pressure in the house. Is there a fresh air duct from outside to the utility room near the furnace?

[IFallsRon]

I presume that your fireplace is vented to the outside to draw in fresh air through the firebox. Check to see that your ashbox isn't too full, restricting air flow.

Can you get the basement fireplace established without the main floor running?

Do you have a normally-vented gas water heater in the basement? Are you running the dryer, stovetop or bathroom vents while your're trying to get a fire going?

[King Canada]

Listen to Bigsmitty

[JohnMickish]

No, I do not have a fresh air duct in the basement, and the furnace and water heater are non power vented. I don't remember if having the upstairs fp makes a difference or not. I do not believe that any of the fans are running when I have tried to establish a fire.

Yes, it is a negative pressure problem, how is that fixed?

[swamptiger]

Do a Google search on "cold backdraft at standby" You will find several sources which discuss the possible reasons for the reverse draft in your chimney.

If you remember your high school science lessons, warm air rises. Cold air is heavier and denser than warm air. So the warmer air rises to the upper floor, while the cold air tends to settle to the lower. The warmer air will naturally try to escape out through the chimney on the upper floor (following the path of least resistance), and since, "for every action, there is an equal and opposite reaction", the air must be replaced somehow, so the path of least resistance for the replacement air is probably down through the chimney on the lower floor.

[HaywardBound]

Make sure you have a couple of carbon monoxide detectors in the house.

[Smokey]

I second what King Canada says.

[Bigsmitty]

If you opened a window and still had the same problem then its not a negative pressure situation. When the window was opened it equalized the pressure in the room. Go buy a top sealing damper. You'll love it. By the way.... its the only solution to keeping bats out of your chimney.